path: root/doc/rfc/rfc2510.txt

Network Working Group                                            C. Adams
Request for Comments: 2510                           Entrust Technologies
Category: Standards Track                                      S. Farrell
                                                                      SSE
                                                               March 1999


                Internet X.509 Public Key Infrastructure
                    Certificate Management Protocols

Status of this Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (1999).  All Rights Reserved.

Abstract

   This document describes the Internet X.509 Public Key Infrastructure
   (PKI) Certificate Management Protocols. Protocol messages are defined
   for all relevant aspects of certificate creation and management.
   Note that "certificate" in this document refers to an X.509v3
   Certificate as defined in [COR95, X509-AM].

   The key words "MUST", "MUST NOT", "REQUIRED", "SHOULD", "SHOULD NOT",
   "RECOMMENDED", "MAY", and "OPTIONAL" in this document (in uppercase,
   as shown) are to be interpreted as described in [RFC2119].

Introduction

   The layout of this document is as follows:

   - Section 1 contains an overview of PKI management;
   - Section 2 contains discussion of assumptions and restrictions;
   - Section 3 contains data structures used for PKI management messages;
   - Section 4 defines the functions that are to be carried out in PKI
     management by conforming implementations;
   - Section 5 describes a simple protocol for transporting PKI messages;
   - the Appendices specify profiles for conforming implementations and
     provide an ASN.1 module containing the syntax for all messages
     defined in this specification.




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1 PKI Management Overview

   The PKI must be structured to be consistent with the types of
   individuals who must administer it.  Providing such administrators
   with unbounded choices not only complicates the software required but
   also increases the chances that a subtle mistake by an administrator
   or software developer will result in broader compromise. Similarly,
   restricting administrators with cumbersome mechanisms will cause them
   not to use the PKI.

   Management protocols are REQUIRED to support on-line interactions
   between Public Key Infrastructure (PKI) components.  For example, a
   management protocol might be used between a Certification Authority
   (CA) and a client system with which a key pair is associated, or
   between two CAs that issue cross-certificates for each other.

1.1 PKI Management Model

   Before specifying particular message formats and procedures we first
   define the entities involved in PKI management and their interactions
   (in terms of the PKI management functions required).  We then group
   these functions in order to accommodate different identifiable types
   of end entities.

1.2 Definitions of PKI Entities

   The entities involved in PKI management include the end entity (i.e.,
   the entity to be named in the subject field of a certificate) and the
   certification authority (i.e., the entity named in the issuer field
   of a certificate). A registration authority MAY also be involved in
   PKI management.

1.2.1 Subjects and End Entities

   The term "subject" is used here to refer to the entity named in the
   subject field of a certificate; when we wish to distinguish the tools
   and/or software used by the subject (e.g., a local certificate
   management module) we will use the term "subject equipment". In
   general, the term "end entity" (EE) rather than subject is preferred
   in order to avoid confusion with the field name.

   It is important to note that the end entities here will include not
   only human users of applications, but also applications themselves
   (e.g., for IP security). This factor influences the protocols which
   the PKI management operations use; for example, application software
   is far more likely to know exactly which certificate extensions are
   required than are human users. PKI management entities are also end
   entities in the sense that they are sometimes named in the subject



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   field of a certificate or cross-certificate. Where appropriate, the
   term "end-entity" will be used to refer to end entities who are not
   PKI management entities.

   All end entities require secure local access to some information --
   at a minimum, their own name and private key, the name of a CA which
   is directly trusted by this entity and that CA's public key (or a
   fingerprint of the public key where a self-certified version is
   available elsewhere). Implementations MAY use secure local storage
   for more than this minimum (e.g., the end entity's own certificate or
   application-specific information). The form of storage will also vary
   -- from files to tamper-resistant cryptographic tokens.  Such local
   trusted storage is referred to here as the end entity's Personal
   Security Environment (PSE).

   Though PSE formats are beyond the scope of this document (they are
   very dependent on equipment, et cetera), a generic interchange format
   for PSEs is defined here - a certification response message MAY be
   used.

1.2.2 Certification Authority

   The certification authority (CA) may or may not actually be a real
   "third party" from the end entity's point of view. Quite often, the
   CA will actually belong to the same organization as the end entities
   it supports.

   Again, we use the term CA to refer to the entity named in the issuer
   field of a certificate; when it is necessary to distinguish the
   software or hardware tools used by the CA we use the term "CA
   equipment".

   The CA equipment will often include both an "off-line" component and
   an "on-line" component, with the CA private key only available to the
   "off-line" component. This is, however, a matter for implementers
   (though it is also relevant as a policy issue).

   We use the term "root CA" to indicate a CA that is directly trusted
   by an end entity; that is, securely acquiring the value of a root CA
   public key requires some out-of-band step(s). This term is not meant
   to imply that a root CA is necessarily at the top of any hierarchy,
   simply that the CA in question is trusted directly.

   A "subordinate CA" is one that is not a root CA for the end entity in
   question. Often, a subordinate CA will not be a root CA for any
   entity but this is not mandatory.





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1.2.3 Registration Authority

   In addition to end-entities and CAs, many environments call for the
   existence of a Registration Authority (RA) separate from the
   Certification Authority. The functions which the registration
   authority may carry out will vary from case to case but MAY include
   personal authentication, token distribution, revocation reporting,
   name assignment, key generation, archival of key pairs, et cetera.

   This document views the RA as an OPTIONAL component - when it is not
   present the CA is assumed to be able to carry out the RA's functions
   so that the PKI management protocols are the same from the end-
   entity's point of view.

   Again, we distinguish, where necessary, between the RA and the tools
   used (the "RA equipment").

   Note that an RA is itself an end entity. We further assume that all
   RAs are in fact certified end entities and that RAs have private keys
   that are usable for signing. How a particular CA equipment identifies
   some end entities as RAs is an implementation issue (i.e., this
   document specifies no special RA certification operation). We do not
   mandate that the RA is certified by the CA with which it is
   interacting at the moment (so one RA may work with more than one CA
   whilst only being certified once).

   In some circumstances end entities will communicate directly with a
   CA even where an RA is present. For example, for initial registration
   and/or certification the subject may use its RA, but communicate
   directly with the CA in order to refresh its certificate.

1.3 PKI Management Requirements

   The protocols given here meet the following requirements on PKI
   management.

      1. PKI management must conform to the ISO 9594-8 standard and the
         associated amendments (certificate extensions)

      2. PKI management must conform to the other parts of this series.

      3. It must be possible to regularly update any key pair without
         affecting any other key pair.

      4. The use of confidentiality in PKI management protocols must be
         kept to a minimum in order to ease regulatory problems.





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      5. PKI management protocols must allow the use of different
         industry-standard cryptographic algorithms, (specifically
         including RSA, DSA, MD5, SHA-1) -- this means that any given
         CA, RA, or end entity may, in principle, use whichever
         algorithms suit it for its own key pair(s).

      6. PKI management protocols must not preclude the generation of
         key pairs by the end-entity concerned, by an RA, or by a CA --
         key generation may also occur elsewhere, but for the purposes
         of PKI management we can regard key generation as occurring
         wherever the key is first present at an end entity, RA, or CA.

      7. PKI management protocols must support the publication of
         certificates by the end-entity concerned, by an RA, or by a CA.
         Different implementations and different environments may choose
         any of the above approaches.

      8. PKI management protocols must support the production of
         Certificate Revocation Lists (CRLs) by allowing certified end
         entities to make requests for the revocation of certificates -
         this must be done in such a way that the denial-of-service
         attacks which are possible are not made simpler.

      9. PKI management protocols must be usable over a variety of
         "transport" mechanisms, specifically including mail, http,
         TCP/IP and ftp.

      10. Final authority for certification creation rests with the CA;
          no RA or end-entity equipment can assume that any certificate
          issued by a CA will contain what was requested -- a CA may
          alter certificate field values or may add, delete or alter
          extensions according to its operating policy. In other words,
          all PKI entities (end-entities, RAs, and CAs) must be capable
          of handling responses to requests for certificates in which
          the actual certificate issued is different from that requested
          (for example, a CA may shorten the validity period requested).
          Note that policy may dictate that the CA must not publish or
          otherwise distribute the certificate until the requesting
          entity has reviewed and accepted the newly-created certificate
          (typically through use of the PKIConfirm message).

      11. A graceful, scheduled change-over from one non-compromised CA
          key pair to the next (CA key update) must be supported (note
          that if the CA key is compromised, re-initialization must be
          performed for all entities in the domain of that CA). An end
          entity whose PSE contains the new CA public key (following a
          CA key update) must also be able to verify certificates
          verifiable using the old public key. End entities who directly



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          trust the old CA key pair must also be able to verify
          certificates signed using the new CA private key.  (Required
          for situations where the old CA public key is "hardwired" into
          the end entity's cryptographic equipment).

      12. The Functions of an RA may, in some implementations or
          environments, be carried out by the CA itself. The protocols
          must be designed so that end entities will use the same
          protocol (but, of course, not the same key!) regardless of
          whether the communication is with an RA or CA.

      13. Where an end entity requests a certificate containing a given
          public key value, the end entity must be ready to demonstrate
          possession of the corresponding private key value. This may be
          accomplished in various ways, depending on the type of
          certification request. See Section 2.3, "Proof of Possession
          of Private Key", for details of the in-band methods defined
          for the PKIX-CMP (i.e., Certificate Management Protocol)
          messages.

PKI Management Operations

   The following diagram shows the relationship between the entities
   defined above in terms of the PKI management operations. The letters
   in the diagram indicate "protocols" in the sense that a defined set
   of PKI management messages can be sent along each of the lettered
   lines.
























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      +---+     cert. publish        +------------+      j
      |   |  <---------------------  | End Entity | <-------
      | C |             g            +------------+      "out-of-band"
      |   |                            | ^                loading
      | e |                            | |      initial
      | r |                          a | | b     registration/
      | t |                            | |       certification
      |   |                            | |      key pair recovery
      | / |                            | |      key pair update
      |   |                            | |      certificate update
      | C |  PKI "USERS"               V |      revocation request
      | R | -------------------+-+-----+-+------+-+-------------------
      | L |  PKI MANAGEMENT    | ^              | ^
      |   |    ENTITIES      a | | b          a | | b
      |   |                    V |              | |
      | R |             g   +------+    d       | |
      | e |   <------------ | RA   | <-----+    | |
      | p |      cert.      |      | ----+ |    | |
      | o |       publish   +------+   c | |    | |
      | s |                              | |    | |
      | i |                              V |    V |
      | t |          g                 +------------+   i
      | o |   <------------------------|     CA     |------->
      | r |          h                 +------------+  "out-of-band"
      | y |      cert. publish              | ^         publication
      |   |      CRL publish                | |
      +---+                                 | |    cross-certification
                                          e | | f  cross-certificate
                                            | |       update
                                            | |
                                            V |
                                          +------+
                                          | CA-2 |
                                          +------+

                           Figure 1 - PKI Entities

   At a high level the set of operations for which management messages
   are defined can be grouped as follows.

      1 CA establishment: When establishing a new CA, certain steps are
        required (e.g., production of initial CRLs, export of CA public
        key).

      2 End entity initialization: this includes importing a root CA
        public key and requesting information about the options
        supported by a PKI management entity.




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      3 Certification: various operations result in the creation of new
        certificates:

        3.1 initial registration/certification: This is the process
            whereby  an end entity first makes itself known to a CA or
            RA, prior to the CA issuing a certificate or certificates
            for that end entity. The end result of this process (when it
            is successful) is that a CA issues a certificate for an end
            entity's public key, and returns that certificate to the end
            entity and/or posts that certificate in a public repository.
            This process may, and typically will, involve multiple
            "steps", possibly including an initialization of the end
            entity's equipment. For example, the end entity's equipment
            must be securely initialized with the public key of a CA, to
            be used in validating certificate paths.  Furthermore, an
            end entity typically needs to be initialized with its own
            key pair(s).

        3.2 key pair update:  Every key pair needs to be updated
            regularly (i.e., replaced with a new key pair), and a new
            certificate needs to be issued.

        3.3 certificate update: As certificates expire they may be
            "refreshed" if nothing relevant in the environment has
            changed.

        3.4 CA key pair update: As with end entities, CA key pairs need
            to be updated regularly; however, different mechanisms are
            required.

        3.5 cross-certification request:  One CA requests issuance of a
            cross-certificate from another CA.  For the purposes of this
            standard, the following terms are defined.  A "cross-
            certificate" is a certificate in which the subject CA and
            the issuer CA are distinct and SubjectPublicKeyInfo contains
            a verification key (i.e., the certificate has been issued
            for the subject CA's signing key pair).  When it is
            necessary to distinguish more finely, the following terms
            may be used: a cross-certificate is called an "inter-domain
            cross-certificate" if the subject and issuer CAs belong to
            different administrative domains; it is called an "intra-
            domain cross-certificate" otherwise.









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   Notes:

   Note 1. The above definition of "cross-certificate" aligns with the
   defined term "CA-certificate" in X.509.  Note that this term is not
   to be confused with the X.500 "cACertificate" attribute type, which
   is unrelated.

   Note 2. In many environments the term "cross-certificate", unless
   further qualified, will be understood to be synonymous with "inter-
   domain cross-certificate" as defined above.

   Note 3. Issuance of cross-certificates may be, but is not
   necessarily, mutual; that is, two CAs may issue cross-certificates
   for each other.

        3.6 cross-certificate update: Similar to a normal certificate
            update but involving a cross-certificate.

      4 Certificate/CRL discovery operations: some PKI management
        operations result in the publication of certificates or CRLs:

        4.1 certificate publication: Having gone to the trouble of
            producing a certificate, some means for publishing it is
            needed.  The "means" defined in PKIX MAY involve the
            messages specified in Sections 3.3.13 - 3.3.16, or MAY
            involve other methods (LDAP, for example) as described in
            the "Operational Protocols" documents of the PKIX series of
            specifications.

        4.2 CRL publication: As for certificate publication.

      5 Recovery operations: some PKI management operations are used
        when an end entity has "lost" its PSE:

        5.1 key pair recovery:  As an option, user client key materials
            (e.g., a user's private key used for decryption purposes)
            MAY be backed up by a CA, an RA, or a key backup system
            associated with a CA or RA. If an entity needs to recover
            these backed up key materials (e.g., as a result of a
            forgotten password or a lost key chain file), a  protocol
            exchange may be needed to support such recovery.

      6 Revocation operations: some PKI operations result in the
        creation of new CRL entries and/or new CRLs:

        6.1 revocation request:  An authorized person advises a CA of an
            abnormal situation requiring certificate revocation.




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      7 PSE operations: whilst the definition of PSE operations (e.g.,
        moving a PSE, changing a PIN, etc.) are beyond the scope of this
        specification, we do define a PKIMessage (CertRepMessage) which
        can form the basis of such operations.

   Note that on-line protocols are not the only way of implementing the
   above operations.  For all operations there are off-line methods of
   achieving the same result, and this specification does not mandate
   use of on-line protocols.  For example, when hardware tokens are
   used, many of the operations MAY be achieved as part of the physical
   token delivery.

   Later sections define a set of standard messages supporting the above
   operations.  The protocols for conveying these exchanges in different
   environments (file based, on-line, E-mail, and WWW) is also
   specified.

2. Assumptions and restrictions

2.1 End entity initialization

   The first step for an end entity in dealing with PKI management
   entities is to request information about the PKI functions supported
   and to securely acquire a copy of the relevant root CA public key(s).

2.2 Initial registration/certification

   There are many schemes that can be used to achieve initial
   registration and certification of end entities. No one method is
   suitable for all situations due to the range of policies which a CA
   may implement and the variation in the types of end entity which can
   occur.

   We can however, classify the initial registration / certification
   schemes that are supported by this specification. Note that the word
   "initial", above, is crucial - we are dealing with the situation
   where the end entity in question has had no previous contact with the
   PKI. Where the end entity already possesses certified keys then some
   simplifications/alternatives are possible.

   Having classified the schemes that are supported by this
   specification we can then specify some as mandatory and some as
   optional. The goal is that the mandatory schemes cover a sufficient
   number of the cases which will arise in real use, whilst the optional
   schemes are available for special cases which arise less frequently.
   In this way we achieve a balance between flexibility and ease of
   implementation.




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   We will now describe the classification of initial registration /
   certification schemes.

2.2.1 Criteria used

2.2.1.1 Initiation of registration / certification

   In terms of the PKI messages which are produced we can regard the
   initiation of the initial registration / certification exchanges as
   occurring wherever the first PKI message relating to the end entity
   is produced. Note that the real-world initiation of the registration
   / certification procedure may occur elsewhere (e.g., a personnel
   department may telephone an RA operator).

   The possible locations are at the end entity, an RA, or a CA.

2.2.1.2 End entity message origin authentication

   The on-line messages produced by the end entity that requires a
   certificate may be authenticated or not. The requirement here is to
   authenticate the origin of any messages from the end entity to the
   PKI (CA/RA).

   In this specification, such authentication is achieved by the PKI
   (CA/RA) issuing the end entity with a secret value (initial
   authentication key) and reference value (used to identify the
   transaction) via some out-of-band means. The initial authentication
   key can then be used to protect relevant PKI messages.

   We can thus classify the initial registration/certification scheme
   according to whether or not the on-line end entity -> PKI messages
   are authenticated or not.

   Note 1: We do not discuss the authentication of the PKI -> end entity
   messages here as this is always REQUIRED. In any case, it can be
   achieved simply once the root-CA public key has been installed at the
   end entity's equipment or it can be based on the initial
   authentication key.

   Note 2: An initial registration / certification procedure can be
   secure where the messages from the end entity are authenticated via
   some out- of-band means (e.g., a subsequent visit).

2.2.1.3 Location of key generation

   In this specification, "key generation" is regarded as occurring
   wherever either the public or private component of a key pair first
   occurs in a PKIMessage. Note that this does not preclude a



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   centralized key generation service - the actual key pair MAY have
   been generated elsewhere and transported to the end entity, RA, or CA
   using a (proprietary or standardized) key generation request/response
   protocol (outside the scope of this specification).

   There are thus three possibilities for the location of "key
   generation":  the end entity, an RA, or a CA.

2.2.1.4 Confirmation of successful certification

   Following the creation of an initial certificate for an end entity,
   additional assurance can be gained by having the end entity
   explicitly confirm successful receipt of the message containing (or
   indicating the creation of) the certificate. Naturally, this
   confirmation message must be protected (based on the initial
   authentication key or other means).

   This gives two further possibilities: confirmed or not.

2.2.2 Mandatory schemes

   The criteria above allow for a large number of initial registration /
   certification schemes. This specification mandates that conforming CA
   equipment, RA equipment, and EE equipment MUST support the second
   scheme listed below. Any entity MAY additionally support other
   schemes, if desired.

2.2.2.1 Centralized scheme

   In terms of the classification above, this scheme is, in some ways,
   the simplest possible, where:

   - initiation occurs at the certifying CA;
   - no on-line message authentication is required;
   - "key generation" occurs at the certifying CA (see Section 2.2.1.3);
   - no confirmation message is required.

   In terms of message flow, this scheme means that the only message
   required is sent from the CA to the end entity. The message must
   contain the entire PSE for the end entity. Some out-of-band means
   must be provided to allow the end entity to authenticate the message
   received and decrypt any encrypted values.









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2.2.2.2 Basic authenticated scheme

   In terms of the classification above, this scheme is where:

   - initiation occurs at the end entity;
   - message authentication is REQUIRED;
   - "key generation" occurs at the end entity (see Section 2.2.1.3);
   - a confirmation message is REQUIRED.

   In terms of message flow, the basic authenticated scheme is as
   follows:

      End entity                                          RA/CA
      ==========                                      =============
           out-of-band distribution of Initial Authentication
           Key (IAK) and reference value (RA/CA -> EE)
      Key generation
      Creation of certification request
      Protect request with IAK
                    -->>--certification request-->>--
                                                     verify request
                                                     process request
                                                     create response
                    --<<--certification response--<<--
      handle response
      create confirmation
                    -->>--confirmation message-->>--
                                                     verify confirmation

   (Where verification of the confirmation message fails, the RA/CA MUST
   revoke the newly issued certificate if it has been published or
   otherwise made available.)

2.3 Proof of Possession (POP) of Private Key

   In order to prevent certain attacks and to allow a CA/RA to properly
   check the validity of the binding between an end entity and a key
   pair, the PKI management operations specified here make it possible
   for an end entity to prove that it has possession of (i.e., is able
   to use) the private key corresponding to the public key for which a
   certificate is requested.  A given CA/RA is free to choose how to
   enforce POP (e.g., out-of-band procedural means versus PKIX-CMP in-
   band messages) in its certification exchanges (i.e., this may be a
   policy issue).  However, it is REQUIRED that CAs/RAs MUST enforce POP
   by some means because there are currently many non-PKIX operational
   protocols in use (various electronic mail protocols are one example)
   that do not explicitly check the binding between the end entity and
   the private key.  Until operational protocols that do verify the



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   binding (for signature, encryption, and key agreement key pairs)
   exist, and are ubiquitous, this binding can only be assumed to have
   been verified by the CA/RA. Therefore, if the binding is not verified
   by the CA/RA, certificates in the Internet Public-Key Infrastructure
   end up being somewhat less meaningful.

   POP is accomplished in different ways depending upon the type of key
   for which a certificate is requested. If a key can be used for
   multiple purposes (e.g., an RSA key) then any appropriate method MAY
   be used (e.g., a key which may be used for signing, as well as other
   purposes, SHOULD NOT be sent to the CA/RA in order to prove
   possession).

   This specification explicitly allows for cases where an end entity
   supplies the relevant proof to an RA and the RA subsequently attests
   to the CA that the required proof has been received (and validated!).
   For example, an end entity wishing to have a signing key certified
   could send the appropriate signature to the RA which then simply
   notifies the relevant CA that the end entity has supplied the
   required proof. Of course, such a situation may be disallowed by some
   policies (e.g., CAs may be the only entities permitted to verify POP
   during certification).

2.3.1 Signature Keys

   For signature keys, the end entity can sign a value to prove
   possession of the private key.

2.3.2 Encryption Keys

   For encryption keys, the end entity can provide the private key to
   the CA/RA, or can be required to decrypt a value in order to prove
   possession of the private key (see Section 3.2.8). Decrypting a value
   can be achieved either directly or indirectly.

   The direct method is for the RA/CA to issue a random challenge to
   which an immediate response by the EE is required.

   The indirect method is to issue a certificate which is encrypted for
   the end entity (and have the end entity demonstrate its ability to
   decrypt this certificate in the confirmation message). This allows a
   CA to issue a certificate in a form which can only be used by the
   intended end entity.

   This specification encourages use of the indirect method because this
   requires no extra messages to be sent (i.e., the proof can be
   demonstrated using the {request, response, confirmation} triple of
   messages).



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2.3.3 Key Agreement Keys

   For key agreement keys, the end entity and the PKI management entity
   (i.e., CA or RA) must establish a shared secret key in order to prove
   that the end entity has possession of the private key.

   Note that this need not impose any restrictions on the keys that can
   be certified by a given CA -- in particular, for Diffie-Hellman keys
   the end entity may freely choose its algorithm parameters -- provided
   that the CA can generate a short-term (or one-time) key pair with the
   appropriate parameters when necessary.

2.4 Root CA key update

   This discussion only applies to CAs that are a root CA for some end
   entity.

   The basis of the procedure described here is that the CA protects its
   new public key using its previous private key and vice versa. Thus
   when a CA updates its key pair it must generate two extra
   cACertificate attribute values if certificates are made available
   using an X.500 directory (for a total of four:  OldWithOld;
   OldWithNew; NewWithOld; and NewWithNew).

   When a CA changes its key pair those entities who have acquired the
   old CA public key via "out-of-band" means are most affected. It is
   these end entities who will need access to the new CA public key
   protected with the old CA private key. However, they will only
   require this for a limited period (until they have acquired the new
   CA public key via the "out-of-band" mechanism). This will typically
   be easily achieved when these end entities' certificates expire.

   The data structure used to protect the new and old CA public keys is
   a standard certificate (which may also contain extensions). There are
   no new data structures required.

   Note 1. This scheme does not make use of any of the X.509 v3
   extensions as it must be able to work even for version 1
   certificates. The presence of the KeyIdentifier extension would make
   for efficiency improvements.

   Note 2. While the scheme could be generalized to cover cases where
   the CA updates its key pair more than once during the validity period
   of one of its end entities' certificates, this generalization seems
   of dubious value. Not having this generalization simply means that
   the validity period of a CA key pair must be greater than the
   validity period of any certificate issued by that CA using that key
   pair.



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   Note 3.This scheme forces end entities to acquire the new CA public
   key on the expiry of the last certificate they owned that was signed
   with the old CA private key (via the "out-of-band" means).
   Certificate and/or key update operations occurring at other times do
   not necessarily require this (depending on the end entity's
   equipment).

2.4.1 CA Operator actions

   To change the key of the CA, the CA operator does the following:

      1. Generate a new key pair;

      2. Create a certificate containing the old CA public key signed
         with the new private key (the "old with new" certificate);

      3. Create a certificate containing the new CA public key signed
         with the old private key (the "new with old" certificate);

      4. Create a certificate containing the new CA public key signed
         with the new private key (the "new with new" certificate);

      5. Publish these new certificates via the directory and/or other
         means (perhaps using a CAKeyUpdAnn message);

      6. Export the new CA public key so that end entities may acquire
         it using the "out-of-band" mechanism (if required).

   The old CA private key is then no longer required. The old CA public
   key will however remain in use for some time. The time when the old
   CA public key is no longer required (other than for non-repudiation)
   will be when all end entities of this CA have securely acquired the
   new CA public key.

   The "old with new" certificate must have a validity period starting
   at the generation time of the old key pair and ending at the expiry
   date of the old public key.

   The "new with old" certificate must have a validity period starting
   at the generation time of the new key pair and ending at the time by
   which all end entities of this CA will securely possess the new CA
   public key (at the latest, the expiry date of the old public key).

   The "new with new" certificate must have a validity period starting
   at the generation time of the new key pair and ending at the time by
   which the CA will next update its key pair.





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2.4.2 Verifying Certificates.

   Normally when verifying a signature, the verifier verifies (among
   other things) the certificate containing the public key of the
   signer. However, once a CA is allowed to update its key there are a
   range of new possibilities. These are shown in the table below.

               Repository contains NEW     Repository contains only OLD
                 and OLD public keys        public key (due to, e.g.,
                                             delay in publication)

                  PSE      PSE Contains  PSE Contains    PSE Contains
               Contains     OLD public    NEW public      OLD public
              NEW public       key            key            key
                  key

   Signer's   Case 1:      Case 3:       Case 5:        Case 7:
   certifi-   This is      In this case  Although the   In this case
   cate is    the          the verifier  CA operator    the CA
   protected  standard     must access   has not        operator  has
   using NEW  case where   the           updated the    not updated
   public     the          directory in  directory the  the directory
   key        verifier     order to get  verifier can   and so the
              can          the value of  verify the     verification
              directly     the NEW       certificate    will FAIL
              verify the   public key    directly -
              certificate                this is thus
              without                    the same as
              using the                  case 1.
              directory

   Signer's   Case 2:      Case 4:       Case 6:        Case 8:
   certifi-   In this      In this case  The verifier   Although the
   cate is    case the     the verifier  thinks this    CA operator
   protected  verifier     can directly  is the         has not
   using OLD  must         verify the    situation of   updated the
   public     access the   certificate   case 2 and     directory the
   key        directory    without       will access    verifier can
              in order     using the     the            verify the
              to get the   directory     directory;     certificate
              value of                   however, the   directly -
              the OLD                    verification   this is thus
              public key                 will FAIL      the same as
                                                        case 4.







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2.4.2.1 Verification in cases 1, 4, 5 and 8.

   In these cases the verifier has a local copy of the CA public key
   which can be used to verify the certificate directly. This is the
   same as the situation where no key change has occurred.

   Note that case 8 may arise between the time when the CA operator has
   generated the new key pair and the time when the CA operator stores
   the updated attributes in the directory. Case 5 can only arise if the
   CA operator has issued both the signer's and verifier's certificates
   during this "gap" (the CA operator SHOULD avoid this as it leads to
   the failure cases described below).

2.4.2.2 Verification in case 2.

   In case 2 the verifier must get access to the old public key of the
   CA. The verifier does the following:

      1. Look up the caCertificate attribute in the directory and pick
         the OldWithNew certificate (determined based on validity
         periods);
      2. Verify that this is correct using the new CA key (which the
         verifier has locally);
      3. If correct, check the signer's certificate using the old CA
         key.

   Case 2 will arise when the CA operator has issued the signer's
   certificate, then changed key and then issued the verifier's
   certificate, so it is quite a typical case.

2.4.2.3 Verification in case 3.

   In case 3 the verifier must get access to the new public key of the
   CA. The verifier does the following:

      1. Look up the CACertificate attribute in the directory and pick
         the NewWithOld certificate (determined based on validity
         periods);
      2. Verify that this is correct using the old CA key (which the
         verifier has stored locally);
      3. If correct, check the signer's certificate using the new CA
         key.

   Case 3 will arise when the CA operator has issued the verifier's
   certificate, then changed key and then issued the signer's
   certificate, so it is also quite a typical case.





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2.4.2.4 Failure of verification in case 6.

   In this case the CA has issued the verifier's PSE containing the new
   key without updating the directory attributes. This means that the
   verifier has no means to get a trustworthy version of the CA's old
   key and so verification fails.

   Note that the failure is the CA operator's fault.

2.4.2.5 Failure of verification in case 7.

   In this case the CA has issued the signer's certificate protected
   with the new key without updating the directory attributes. This
   means that the verifier has no means to get a trustworthy version of
   the CA's new key and so verification fails.

   Note that the failure is again the CA operator's fault.

2.4.3 Revocation - Change of CA key

   As we saw above the verification of a certificate becomes more
   complex once the CA is allowed to change its key. This is also true
   for revocation checks as the CA may have signed the CRL using a newer
   private key than the one that is within the user's PSE.

   The analysis of the alternatives is as for certificate verification.

3. Data Structures

   This section contains descriptions of the data structures required
   for PKI management messages. Section 4 describes constraints on their
   values and the sequence of events for each of the various PKI
   management operations. Section 5 describes how these may be
   encapsulated in various transport mechanisms.

3.1 Overall PKI Message

   All of the messages used in this specification for the purposes of
   PKI management use the following structure:

     PKIMessage ::= SEQUENCE {
         header           PKIHeader,
         body             PKIBody,
         protection   [0] PKIProtection OPTIONAL,
         extraCerts   [1] SEQUENCE SIZE (1..MAX) OF Certificate OPTIONAL
     }





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   The PKIHeader contains information which is common to many PKI
   messages.

   The PKIBody contains message-specific information.

   The PKIProtection, when used, contains bits that protect the PKI
   message.

   The extraCerts field can contain certificates that may be useful to
   the recipient. For example, this can be used by a CA or RA to present
   an end entity with certificates that it needs to verify its own new
   certificate (if, for example, the CA that issued the end entity's
   certificate is not a root CA for the end entity).  Note that this
   field does not necessarily contain a certification path - the
   recipient may have to sort, select from, or otherwise process the
   extra certificates in order to use them.

3.1.1 PKI Message Header

   All PKI messages require some header information for addressing and
   transaction identification. Some of this information will also be
   present in a transport-specific envelope; however, if the PKI message
   is protected then this information is also protected (i.e., we make
   no assumption about secure transport).

   The following data structure is used to contain this information:

     PKIHeader ::= SEQUENCE {
         pvno                INTEGER     { ietf-version2 (1) },
         sender              GeneralName,
         -- identifies the sender
         recipient           GeneralName,
         -- identifies the intended recipient
         messageTime     [0] GeneralizedTime         OPTIONAL,
         -- time of production of this message (used when sender
         -- believes that the transport will be "suitable"; i.e.,
         -- that the time will still be meaningful upon receipt)
         protectionAlg   [1] AlgorithmIdentifier     OPTIONAL,
         -- algorithm used for calculation of protection bits
         senderKID       [2] KeyIdentifier           OPTIONAL,
         recipKID        [3] KeyIdentifier           OPTIONAL,
         -- to identify specific keys used for protection
         transactionID   [4] OCTET STRING            OPTIONAL,
         -- identifies the transaction; i.e., this will be the same in
         -- corresponding request, response and confirmation messages
         senderNonce     [5] OCTET STRING            OPTIONAL,
         recipNonce      [6] OCTET STRING            OPTIONAL,
         -- nonces used to provide replay protection, senderNonce



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         -- is inserted by the creator of this message; recipNonce
         -- is a nonce previously inserted in a related message by
         -- the intended recipient of this message
         freeText        [7] PKIFreeText             OPTIONAL,
         -- this may be used to indicate context-specific instructions
         -- (this field is intended for human consumption)
         generalInfo     [8] SEQUENCE SIZE (1..MAX) OF
                                InfoTypeAndValue     OPTIONAL
         -- this may be used to convey context-specific information
         -- (this field not primarily intended for human consumption)
     }

     PKIFreeText ::= SEQUENCE SIZE (1..MAX) OF UTF8String
         -- text encoded as UTF-8 String (note:  each UTF8String SHOULD
         -- include an RFC 1766 language tag to indicate the language
         -- of the contained text)

   The pvno field is fixed (at one) for this version of this
   specification.

   The sender field contains the name of the sender of the PKIMessage.
   This name (in conjunction with senderKID, if supplied) should be
   usable to verify the protection on the message.  If nothing about the
   sender is known to the sending entity (e.g., in the init. req.
   message, where the end entity may not know its own Distinguished Name
   (DN), e-mail name, IP address, etc.), then the "sender" field MUST
   contain a "NULL" value; that is, the SEQUENCE OF relative
   distinguished names is of zero length. In such a case the senderKID
   field MUST hold an identifier (i.e., a reference number) which
   indicates to the receiver the appropriate shared secret information
   to use to verify the message.

   The recipient field contains the name of the recipient of the
   PKIMessage. This name (in conjunction with recipKID, if supplied)
   should be usable to verify the protection on the message.

   The protectionAlg field specifies the algorithm used to protect the
   message. If no protection bits are supplied (note that PKIProtection
   is OPTIONAL) then this field MUST be omitted; if protection bits are
   supplied then this field MUST be supplied.

   senderKID and recipKID are usable to indicate which keys have been
   used to protect the message (recipKID will normally only be required
   where protection of the message uses Diffie-Hellman (DH) keys).







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   The transactionID field within the message header MAY be used to
   allow the recipient of a response message to correlate this with a
   previously issued request. For example, in the case of an RA there
   may be many requests "outstanding" at a given moment.

   The senderNonce and recipNonce fields protect the PKIMessage against
   replay attacks.

   The messageTime field contains the time at which the sender created
   the message. This may be useful to allow end entities to correct
   their local time to be consistent with the time on a central system.

   The freeText field may be used to send a human-readable message to
   the recipient (in any number of languages).  The first language used
   in this sequence indicates the desired language for replies.

   The generalInfo field may be used to send machine-processable
   additional data to the recipient.

3.1.2 PKI Message Body

     PKIBody ::= CHOICE {       -- message-specific body elements
         ir      [0]  CertReqMessages,        --Initialization Request
         ip      [1]  CertRepMessage,         --Initialization Response
         cr      [2]  CertReqMessages,        --Certification Request
         cp      [3]  CertRepMessage,         --Certification Response
         p10cr   [4]  CertificationRequest,   --PKCS #10 Cert. Req.
           -- the PKCS #10 certification request (see [PKCS10])
         popdecc [5]  POPODecKeyChallContent, --pop Challenge
         popdecr [6]  POPODecKeyRespContent,  --pop Response
         kur     [7]  CertReqMessages,        --Key Update Request
         kup     [8]  CertRepMessage,         --Key Update Response
         krr     [9]  CertReqMessages,        --Key Recovery Request
         krp     [10] KeyRecRepContent,       --Key Recovery Response
         rr      [11] RevReqContent,          --Revocation Request
         rp      [12] RevRepContent,          --Revocation Response
         ccr     [13] CertReqMessages,        --Cross-Cert. Request
         ccp     [14] CertRepMessage,         --Cross-Cert. Response
         ckuann  [15] CAKeyUpdAnnContent,     --CA Key Update Ann.
         cann    [16] CertAnnContent,         --Certificate Ann.
         rann    [17] RevAnnContent,          --Revocation Ann.
         crlann  [18] CRLAnnContent,          --CRL Announcement
         conf    [19] PKIConfirmContent,      --Confirmation
         nested  [20] NestedMessageContent,   --Nested Message
         genm    [21] GenMsgContent,          --General Message
         genp    [22] GenRepContent,          --General Response
         error   [23] ErrorMsgContent         --Error Message
     }



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   The specific types are described in Section 3.3 below.

3.1.3 PKI Message Protection

   Some PKI messages will be protected for integrity. (Note that if an
   asymmetric algorithm is used to protect a message and the relevant
   public component has been certified already, then the origin of
   message can also be authenticated.  On the other hand, if the public
   component is uncertified then the message origin cannot be
   automatically authenticated, but may be authenticated via out-of-band
   means.)

   When protection is applied the following structure is used:

     PKIProtection ::= BIT STRING

   The input to the calculation of PKIProtection is the DER encoding of
   the following data structure:

     ProtectedPart ::= SEQUENCE {
         header    PKIHeader,
         body      PKIBody
     }

   There MAY be cases in which the PKIProtection BIT STRING is
   deliberately not used to protect a message (i.e., this OPTIONAL field
   is omitted) because other protection, external to PKIX, will instead
   be applied. Such a choice is explicitly allowed in this
   specification.  Examples of such external protection include PKCS #7
   [PKCS7] and Security Multiparts [RFC1847] encapsulation of the
   PKIMessage (or simply the PKIBody (omitting the CHOICE tag), if the
   relevant PKIHeader information is securely carried in the external
   mechanism); specification of external protection using PKCS #7 will
   be provided in a separate document.  It is noted, however, that many
   such external mechanisms require that the end entity already
   possesses a public-key certificate, and/or a unique Distinguished
   Name, and/or other such infrastructure-related information. Thus,
   they may not be appropriate for initial registration, key-recovery,
   or any other process with "boot-strapping" characteristics.  For
   those cases it may be necessary that the PKIProtection parameter be
   used.  In the future, if/when external mechanisms are modified to
   accommodate boot-strapping scenarios, the use of PKIProtection may
   become rare or non-existent.

   Depending on the circumstances the PKIProtection bits may contain a
   Message Authentication Code (MAC) or signature. Only the following
   cases can occur:




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   - shared secret information

   In this case the sender and recipient share secret information
   (established via out-of-band means or from a previous PKI management
   operation).  PKIProtection will contain a MAC value and the
   protectionAlg will be the following:

     PasswordBasedMac ::= OBJECT IDENTIFIER --{1 2 840 113533 7 66 13}
     PBMParameter ::= SEQUENCE {
         salt                OCTET STRING,
         owf                 AlgorithmIdentifier,
         -- AlgId for a One-Way Function (SHA-1 recommended)
         iterationCount      INTEGER,
         -- number of times the OWF is applied
         mac                 AlgorithmIdentifier
         -- the MAC AlgId (e.g., DES-MAC, Triple-DES-MAC [PKCS11],
     }   -- or HMAC [RFC2104, RFC2202])

   In the above protectionAlg the salt value is appended to the shared
   secret input. The OWF is then applied iterationCount times, where the
   salted secret is the input to the first iteration and, for each
   successive iteration, the input is set to be the output of the
   previous iteration. The output of the final iteration (called
   "BASEKEY" for ease of reference, with a size of "H") is what is used
   to form the symmetric key. If the MAC algorithm requires a K-bit key
   and K <= H, then the most significant K bits of BASEKEY are used. If
   K > H, then all of BASEKEY is used for the most significant H bits of
   the key, OWF("1" || BASEKEY) is used for the next most significant H
   bits of the key, OWF("2" || BASEKEY) is used for the next most
   significant H bits of the key, and so on, until all K bits have been
   derived. [Here "N" is the ASCII byte encoding the number N and "||"
   represents concatenation.]

   - DH key pairs

   Where the sender and receiver possess Diffie-Hellman certificates
   with compatible DH parameters, then in order to protect the message
   the end entity must generate a symmetric key based on its private DH
   key value and the DH public key of the recipient of the PKI message.
   PKIProtection will contain a MAC value keyed with this derived
   symmetric key and the protectionAlg will be the following:










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     DHBasedMac ::= OBJECT IDENTIFIER --{1 2 840 113533 7 66 30}

     DHBMParameter ::= SEQUENCE {
         owf                 AlgorithmIdentifier,
         -- AlgId for a One-Way Function (SHA-1 recommended)
         mac                 AlgorithmIdentifier
         -- the MAC AlgId (e.g., DES-MAC, Triple-DES-MAC [PKCS11],
     }   -- or HMAC [RFC2104, RFC2202])

   In the above protectionAlg OWF is applied to the result of the
   Diffie-Hellman computation. The OWF output (called "BASEKEY" for ease
   of reference, with a size of "H") is what is used to form the
   symmetric key. If the MAC algorithm requires a K-bit key and K <= H,
   then the most significant K bits of BASEKEY are used. If K > H, then
   all of BASEKEY is used for the most significant H bits of the key,
   OWF("1" || BASEKEY) is used for the next most significant H bits of
   the key, OWF("2" || BASEKEY) is used for the next most significant H
   bits of the key, and so on, until all K bits have been derived. [Here
   "N" is the ASCII byte encoding the number N and "||" represents
   concatenation.]

   - signature

   Where the sender possesses a signature key pair it may simply sign
   the PKI message. PKIProtection will contain the signature value and
   the protectionAlg will be an AlgorithmIdentifier for a digital
   signature (e.g., md5WithRSAEncryption or dsaWithSha-1).

   - multiple protection

   In cases where an end entity sends a protected PKI message to an RA,
   the RA MAY forward that message to a CA, attaching its own protection
   (which MAY be a MAC or a signature, depending on the information and
   certificates shared between the RA and the CA). This is accomplished
   by nesting the entire message sent by the end entity within a new PKI
   message. The structure used is as follows.

     NestedMessageContent ::= PKIMessage

3.2 Common Data Structures

   Before specifying the specific types that may be placed in a PKIBody
   we define some data structures that are used in more than one case.








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3.2.1 Requested Certificate Contents

   Various PKI management messages require that the originator of the
   message indicate some of the fields that are required to be present
   in a certificate. The CertTemplate structure allows an end entity or
   RA to specify as much as it wishes about the certificate it requires.
   CertTemplate is identical to a Certificate but with all fields
   optional.

   Note that even if the originator completely specifies the contents of
   a certificate it requires, a CA is free to modify fields within the
   certificate actually issued.  If the modified certificate is
   unacceptable to the requester, the Confirmation message may be
   withheld, or an Error Message may be sent (with a PKIStatus of
   "rejection").

   See [CRMF] for CertTemplate syntax.

3.2.2 Encrypted Values

   Where encrypted values (restricted, in this specification, to be
   either private keys or certificates) are sent in PKI messages the
   EncryptedValue data structure is used.

   See [CRMF] for EncryptedValue syntax.

   Use of this data structure requires that the creator and intended
   recipient respectively be able to encrypt and decrypt. Typically,
   this will mean that the sender and recipient have, or are able to
   generate, a shared secret key.

   If the recipient of the PKIMessage already possesses a private key
   usable for decryption, then the encSymmKey field MAY contain a
   session key encrypted using the recipient's public key.

3.2.3 Status codes and Failure Information for PKI messages

   All response messages will include some status information. The
   following values are defined.

     PKIStatus ::= INTEGER {
         granted                (0),
         -- you got exactly what you asked for
         grantedWithMods        (1),
         -- you got something like what you asked for; the
         -- requester is responsible for ascertaining the differences
         rejection              (2),
         -- you don't get it, more information elsewhere in the message



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         waiting                (3),
         -- the request body part has not yet been processed,
         -- expect to hear more later
         revocationWarning      (4),
         -- this message contains a warning that a revocation is
         -- imminent
         revocationNotification (5),
         -- notification that a revocation has occurred
         keyUpdateWarning       (6)
         -- update already done for the oldCertId specified in
         -- the key update request message
     }

   Responders may use the following syntax to provide more information
   about failure cases.

     PKIFailureInfo ::= BIT STRING {
     -- since we can fail in more than one way!
     -- More codes may be added in the future if/when required.
         badAlg           (0),
         -- unrecognized or unsupported Algorithm Identifier
         badMessageCheck  (1),
         -- integrity check failed (e.g., signature did not verify)
         badRequest       (2),
         -- transaction not permitted or supported
         badTime          (3),
         -- messageTime was not sufficiently close to the system time,
         -- as defined by local policy
         badCertId        (4),
         -- no certificate could be found matching the provided criteria
         badDataFormat    (5),
         -- the data submitted has the wrong format
         wrongAuthority   (6),
         -- the authority indicated in the request is different from the
         -- one creating the response token
         incorrectData    (7),
         -- the requester's data is incorrect (used for notary services)
         missingTimeStamp (8),
         -- when the timestamp is missing but should be there (by policy)
         badPOP           (9)
         -- the proof-of-possession failed
     }
     PKIStatusInfo ::= SEQUENCE {
         status        PKIStatus,
         statusString  PKIFreeText     OPTIONAL,
         failInfo      PKIFailureInfo  OPTIONAL
     }




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3.2.4 Certificate Identification

   In order to identify particular certificates the CertId data
   structure is used.

   See [CRMF] for CertId syntax.

3.2.5 "Out-of-band" root CA public key

   Each root CA must be able to publish its current public key via some
   "out-of-band" means. While such mechanisms are beyond the scope of
   this document, we define data structures which can support such
   mechanisms.

   There are generally two methods available: either the CA directly
   publishes its self-signed certificate; or this information is
   available via the Directory (or equivalent) and the CA publishes a
   hash of this value to allow verification of its integrity before use.

     OOBCert ::= Certificate

   The fields within this certificate are restricted as follows:

   - The certificate MUST be self-signed  (i.e., the signature must be
     verifiable using the SubjectPublicKeyInfo field);
   - The subject and issuer fields MUST be identical;
   - If the subject field is NULL then both subjectAltNames and
     issuerAltNames extensions MUST be present and have exactly the same
     value;
   - The values of all other extensions must be suitable for a self-
     signed certificate (e.g., key identifiers for subject and issuer
     must be the same).

     OOBCertHash ::= SEQUENCE {
         hashAlg     [0] AlgorithmIdentifier     OPTIONAL,
         certId      [1] CertId                  OPTIONAL,
         hashVal         BIT STRING
         -- hashVal is calculated over the self-signed
         -- certificate with the identifier certID.
     }

   The intention of the hash value is that anyone who has securely
   received the hash value (via the out-of-band means) can verify a
   self- signed certificate for that CA.







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3.2.6 Archive Options

   Requesters may indicate that they wish the PKI to archive a private
   key value using the PKIArchiveOptions structure

   See [CRMF] for PKIArchiveOptions syntax.

3.2.7 Publication Information

   Requesters may indicate that they wish the PKI to publish a
   certificate using the PKIPublicationInfo structure.

   See [CRMF] for PKIPublicationInfo syntax.

3.2.8  Proof-of-Possession Structures

   If the certification request is for a signing key pair (i.e., a
   request for a verification certificate), then the proof of possession
   of the private signing key is demonstrated through use of the
   POPOSigningKey structure.

   See [CRMF] for POPOSigningKey syntax, but note that
   POPOSigningKeyInput has the following semantic stipulations in this
   specification.

     POPOSigningKeyInput ::= SEQUENCE {
         authInfo            CHOICE {
             sender              [0] GeneralName,
             -- from PKIHeader (used only if an authenticated identity
             -- has been established for the sender (e.g., a DN from a
             -- previously-issued and currently-valid certificate))
             publicKeyMAC        [1] PKMACValue
             -- used if no authenticated GeneralName currently exists for
             -- the sender; publicKeyMAC contains a password-based MAC
             -- (using the protectionAlg AlgId from PKIHeader) on the
             -- DER-encoded value of publicKey
         },
         publicKey           SubjectPublicKeyInfo    -- from CertTemplate
     }

   On the other hand, if the certification request is for an encryption
   key pair (i.e., a request for an encryption certificate), then the
   proof of possession of the private decryption key may be demonstrated
   in one of three ways.

      1) By the inclusion of the private key (encrypted) in the
         CertRequest (in the PKIArchiveOptions control structure).




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      2) By having the CA return not the certificate, but an encrypted
         certificate (i.e., the certificate encrypted under a randomly-
         generated symmetric key, and the symmetric key encrypted under
         the public key for which the certification request is being
         made) -- this is the "indirect" method mentioned previously in
         Section 2.3.2.  The end entity proves knowledge of the private
         decryption key to the CA by MACing the PKIConfirm message using
         a key derived from this symmetric key.  [Note that if more than
         one CertReqMsg is included in the PKIMessage, then the CA uses
         a different symmetric key for each CertReqMsg and the MAC uses
         a key derived from the concatenation of all these keys.]  The
         MACing procedure uses the PasswordBasedMac AlgId defined in
         Section 3.1.

      3) By having the end entity engage in a challenge-response
         protocol (using the messages POPODecKeyChall and
         POPODecKeyResp; see below) between CertReqMessages and
         CertRepMessage -- this is the "direct" method mentioned
         previously in Section 2.3.2.  [This method would typically be
         used in an environment in which an RA verifies POP and then
         makes a certification request to the CA on behalf of the end
         entity.  In such a scenario, the CA trusts the RA to have done
         POP correctly before the RA requests a certificate for the end
         entity.]  The complete protocol then looks as follows (note
         that req' does not necessarily encapsulate req as a nested
         message):

                        EE            RA            CA
                         ---- req ---->
                         <--- chall ---
                         ---- resp --->
                                       ---- req' --->
                                       <--- rep -----
                                       ---- conf --->
                         <--- rep -----
                         ---- conf --->

   This protocol is obviously much longer than the 3-way exchange given
   in choice (2) above, but allows a local Registration Authority to be
   involved and has the property that the certificate itself is not
   actually created until the proof of possession is complete.

   If the cert. request is for a key agreement key (KAK) pair, then the
   POP can use any of the 3 ways described above for enc. key pairs,
   with the following changes:  (1) the parenthetical text of bullet 2)
   is replaced with "(i.e., the certificate encrypted under the
   symmetric key derived from the CA's private KAK and the public key
   for which the certification request is being made)"; (2) the first



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   parenthetical text of the challenge field of "Challenge" below is
   replaced with "(using PreferredSymmAlg (see Appendix B6) and a
   symmetric key derived from the CA's private KAK and the public key
   for which the certification request is being made)".  Alternatively,
   the POP can use the POPOSigningKey structure given in [CRMF] (where
   the alg field is DHBasedMAC and the signature field is the MAC) as a
   fourth alternative for demonstrating POP if the CA already has a D-H
   certificate that is known to the EE.

   The challenge-response messages for proof of possession of a private
   decryption key are specified as follows (see [MvOV97, p.404] for
   details).  Note that this challenge-response exchange is associated
   with the preceding cert. request message (and subsequent cert.
   response and confirmation messages) by the nonces used in the
   PKIHeader and by the protection (MACing or signing) applied to the
   PKIMessage.

     POPODecKeyChallContent ::= SEQUENCE OF Challenge
     -- One Challenge per encryption key certification request (in the
     -- same order as these requests appear in CertReqMessages).

     Challenge ::= SEQUENCE {
         owf                 AlgorithmIdentifier  OPTIONAL,
         -- MUST be present in the first Challenge; MAY be omitted in any
         -- subsequent Challenge in POPODecKeyChallContent (if omitted,
         -- then the owf used in the immediately preceding Challenge is
         -- to be used).
         witness             OCTET STRING,
         -- the result of applying the one-way function (owf) to a
         -- randomly-generated INTEGER, A.  [Note that a different
         -- INTEGER MUST be used for each Challenge.]
         challenge           OCTET STRING
         -- the encryption (under the public key for which the cert.
         -- request is being made) of Rand, where Rand is specified as
         --   Rand ::= SEQUENCE {
         --      int      INTEGER,
         --       - the randomly-generated INTEGER A (above)
         --      sender   GeneralName
         --       - the sender's name (as included in PKIHeader)
         --   }
     }

     POPODecKeyRespContent ::= SEQUENCE OF INTEGER
     -- One INTEGER per encryption key certification request (in the
     -- same order as these requests appear in CertReqMessages).  The
     -- retrieved INTEGER A (above) is returned to the sender of the
     -- corresponding Challenge.




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3.3 Operation-Specific Data Structures

3.3.1 Initialization Request

   An Initialization request message contains as the PKIBody an
   CertReqMessages data structure which specifies the requested
   certificate(s).  Typically, SubjectPublicKeyInfo, KeyId, and Validity
   are the template fields which may be supplied for each certificate
   requested (see Appendix B profiles for further information).  This
   message is intended to be used for entities first initializing into
   the PKI.

   See [CRMF] for CertReqMessages syntax.

3.3.2 Initialization Response

   An Initialization response message contains as the PKIBody an
   CertRepMessage data structure which has for each certificate
   requested a PKIStatusInfo field, a subject certificate, and possibly
   a private key (normally encrypted with a session key, which is itself
   encrypted with the protocolEncKey).

   See Section 3.3.4 for CertRepMessage syntax.  Note that if the PKI
   Message Protection is "shared secret information" (see Section
   3.1.3), then any certificate transported in the caPubs field may be
   directly trusted as a root CA certificate by the initiator.

3.3.3 Registration/Certification Request

   A Registration/Certification request message contains as the PKIBody
   a CertReqMessages data structure which specifies the requested
   certificates.  This message is intended to be used for existing PKI
   entities who wish to obtain additional certificates.

   See [CRMF] for CertReqMessages syntax.

   Alternatively, the PKIBody MAY be a CertificationRequest (this
   structure is fully specified by the ASN.1 structure
   CertificationRequest given in [PKCS10]).  This structure may be
   required for certificate requests for signing key pairs when
   interoperation with legacy systems is desired, but its use is
   strongly discouraged whenever not absolutely necessary.









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3.3.4 Registration/Certification Response

   A registration response message contains as the PKIBody a
   CertRepMessage data structure which has a status value for each
   certificate requested, and optionally has a CA public key, failure
   information, a subject certificate, and an encrypted private key.

  CertRepMessage ::= SEQUENCE {
      caPubs          [1] SEQUENCE SIZE (1..MAX) OF Certificate OPTIONAL,
      response            SEQUENCE OF CertResponse
  }

  CertResponse ::= SEQUENCE {
      certReqId           INTEGER,
      -- to match this response with corresponding request (a value
      -- of -1 is to be used if certReqId is not specified in the
      -- corresponding request)
      status              PKIStatusInfo,
      certifiedKeyPair    CertifiedKeyPair    OPTIONAL,
      rspInfo             OCTET STRING        OPTIONAL
      -- analogous to the id-regInfo-asciiPairs OCTET STRING defined
      -- for regInfo in CertReqMsg [CRMF]
  }

  CertifiedKeyPair ::= SEQUENCE {
      certOrEncCert       CertOrEncCert,
      privateKey      [0] EncryptedValue      OPTIONAL,
      publicationInfo [1] PKIPublicationInfo  OPTIONAL
  }

  CertOrEncCert ::= CHOICE {
      certificate     [0] Certificate,
      encryptedCert   [1] EncryptedValue
  }

   Only one of the failInfo (in PKIStatusInfo) and certificate (in
   CertifiedKeyPair) fields can be present in each CertResponse
   (depending on the status). For some status values (e.g., waiting)
   neither of the optional fields will be present.

   Given an EncryptedCert and the relevant decryption key the
   certificate may be obtained. The purpose of this is to allow a CA to
   return the value of a certificate, but with the constraint that only
   the intended recipient can obtain the actual certificate. The benefit
   of this approach is that a CA may reply with a certificate even in
   the absence of a proof that the requester is the end entity which can
   use the relevant private key (note that the proof is not obtained




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   until the PKIConfirm message is received by the CA). Thus the CA will
   not have to revoke that certificate in the event that something goes
   wrong with the proof of possession.

3.3.5 Key update request content

   For key update requests the CertReqMessages syntax is used.
   Typically, SubjectPublicKeyInfo, KeyId, and Validity are the template
   fields which may be supplied for each key to be updated.  This
   message is intended to be used to request updates to existing (non-
   revoked and non-expired) certificates.

   See [CRMF] for CertReqMessages syntax.

3.3.6 Key Update response content

   For key update responses the CertRepMessage syntax is used.  The
   response is identical to the initialization response.

   See Section 3.3.4 for CertRepMessage syntax.

3.3.7 Key Recovery Request content

   For key recovery requests the syntax used is identical to the
   initialization request CertReqMessages.  Typically,
   SubjectPublicKeyInfo and KeyId are the template fields which may be
   used to supply a signature public key for which a certificate is
   required (see Appendix B profiles for further information).

   See [CRMF] for CertReqMessages syntax.  Note that if a key history is
   required, the requester must supply a Protocol Encryption Key control
   in the request message.

3.3.8 Key recovery response content

   For key recovery responses the following syntax is used.  For some
   status values (e.g., waiting) none of the optional fields will be
   present.

     KeyRecRepContent ::= SEQUENCE {
         status          PKIStatusInfo,
         newSigCert  [0] Certificate                   OPTIONAL,
         caCerts     [1] SEQUENCE SIZE (1..MAX) OF
                                      Certificate      OPTIONAL,
         keyPairHist [2] SEQUENCE SIZE (1..MAX) OF
                                      CertifiedKeyPair OPTIONAL
     }




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3.3.9 Revocation Request Content

   When requesting revocation of a certificate (or several certificates)
   the following data structure is used. The name of the requester is
   present in the PKIHeader structure.

     RevReqContent ::= SEQUENCE OF RevDetails

     RevDetails ::= SEQUENCE {
         certDetails         CertTemplate,
         -- allows requester to specify as much as they can about
         -- the cert. for which revocation is requested
         -- (e.g., for cases in which serialNumber is not available)
         revocationReason    ReasonFlags      OPTIONAL,
         -- the reason that revocation is requested
         badSinceDate        GeneralizedTime  OPTIONAL,
         -- indicates best knowledge of sender
         crlEntryDetails     Extensions       OPTIONAL
         -- requested crlEntryExtensions
     }

3.3.10 Revocation Response Content

   The response to the above message. If produced, this is sent to the
   requester of the revocation. (A separate revocation announcement
   message MAY be sent to the subject of the certificate for which
   revocation was requested.)

  RevRepContent ::= SEQUENCE {
      status        SEQUENCE SIZE (1..MAX) OF PKIStatusInfo,
      -- in same order as was sent in RevReqContent
      revCerts  [0] SEQUENCE SIZE (1..MAX) OF CertId OPTIONAL,
      -- IDs for which revocation was requested (same order as status)
      crls      [1] SEQUENCE SIZE (1..MAX) OF CertificateList  OPTIONAL
      -- the resulting CRLs (there may be more than one)
  }

3.3.11 Cross certification request content

   Cross certification requests use the same syntax (CertReqMessages) as
   for normal certification requests with the restriction that the key
   pair MUST have been generated by the requesting CA and the private
   key MUST NOT be sent to the responding CA.

   See [CRMF] for CertReqMessages syntax.






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3.3.12 Cross certification response content

   Cross certification responses use the same syntax (CertRepMessage) as
   for normal certification responses with the restriction that no
   encrypted private key can be sent.

   See Section 3.3.4 for CertRepMessage syntax.

3.3.13 CA Key Update Announcement content

   When a CA updates its own key pair the following data structure MAY
   be used to announce this event.

  CAKeyUpdAnnContent ::= SEQUENCE {
      oldWithNew          Certificate, -- old pub signed with new priv
      newWithOld          Certificate, -- new pub signed with old priv
      newWithNew          Certificate  -- new pub signed with new priv
  }

3.3.14 Certificate Announcement

   This structure MAY be used to announce the existence of certificates.

   Note that this message is intended to be used for those cases (if
   any) where there is no pre-existing method for publication of
   certificates; it is not intended to be used where, for example, X.500
   is the method for publication of certificates.

     CertAnnContent ::= Certificate

3.3.15 Revocation Announcement

   When a CA has revoked, or is about to revoke, a particular
   certificate it MAY issue an announcement of this (possibly upcoming)
   event.

     RevAnnContent ::= SEQUENCE {
         status              PKIStatus,
         certId              CertId,
         willBeRevokedAt     GeneralizedTime,
         badSinceDate        GeneralizedTime,
         crlDetails          Extensions  OPTIONAL
         -- extra CRL details(e.g., crl number, reason, location, etc.)
     }







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   A CA MAY use such an announcement to warn (or notify) a subject that
   its certificate is about to be (or has been) revoked. This would
   typically be used where the request for revocation did not come from
   the subject concerned.

   The willBeRevokedAt field contains the time at which a new entry will
   be added to the relevant CRLs.

3.3.16 CRL Announcement

   When a CA issues a new CRL (or set of CRLs) the following data
   structure MAY be used to announce this event.

     CRLAnnContent ::= SEQUENCE OF CertificateList

3.3.17 PKI Confirmation content

   This data structure is used in three-way protocols as the final
   PKIMessage. Its content is the same in all cases - actually there is
   no content since the PKIHeader carries all the required information.

     PKIConfirmContent ::= NULL

3.3.18 PKI General Message content

  InfoTypeAndValue ::= SEQUENCE {
      infoType               OBJECT IDENTIFIER,
      infoValue              ANY DEFINED BY infoType  OPTIONAL
  }
  -- Example InfoTypeAndValue contents include, but are not limited to:
  --  { CAProtEncCert    = {id-it 1}, Certificate                     }
  --  { SignKeyPairTypes = {id-it 2}, SEQUENCE OF AlgorithmIdentifier }
  --  { EncKeyPairTypes  = {id-it 3}, SEQUENCE OF AlgorithmIdentifier }
  --  { PreferredSymmAlg = {id-it 4}, AlgorithmIdentifier             }
  --  { CAKeyUpdateInfo  = {id-it 5}, CAKeyUpdAnnContent              }
  --  { CurrentCRL       = {id-it 6}, CertificateList                 }
  -- where {id-it} = {id-pkix 4} = {1 3 6 1 5 5 7 4}
  -- This construct MAY also be used to define new PKIX Certificate
  -- Management Protocol request and response messages, or general-
  -- purpose (e.g., announcement) messages for future needs or for
  -- specific environments.

  GenMsgContent ::= SEQUENCE OF InfoTypeAndValue
  -- May be sent by EE, RA, or CA (depending on message content).
  -- The OPTIONAL infoValue parameter of InfoTypeAndValue will typically
  -- be omitted for some of the examples given above.  The receiver is





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  -- free to ignore any contained OBJ. IDs that it does not recognize.
  -- If sent from EE to CA, the empty set indicates that the CA may send
  -- any/all information that it wishes.

3.3.19 PKI General Response content

  GenRepContent ::= SEQUENCE OF InfoTypeAndValue
  -- The receiver is free to ignore any contained OBJ. IDs that it does
  -- not recognize.

3.3.20 Error Message content

     ErrorMsgContent ::= SEQUENCE {
         pKIStatusInfo          PKIStatusInfo,
         errorCode              INTEGER           OPTIONAL,
         -- implementation-specific error codes
         errorDetails           PKIFreeText       OPTIONAL
         -- implementation-specific error details
     }

4. Mandatory PKI Management functions

   The PKI management functions outlined in Section 1 above are
   described in this section.

   This section deals with functions that are "mandatory" in the sense
   that all end entity and CA/RA implementations MUST be able to provide
   the functionality described (perhaps via one of the transport
   mechanisms defined in Section 5). This part is effectively the
   profile of the PKI management functionality that MUST be supported.

   Note that not all PKI management functions result in the creation of
   a PKI message.

4.1 Root CA initialization

   [See Section 1.2.2 for this document's definition of "root CA".]

   A newly created root CA must produce a "self-certificate" which is a
   Certificate structure with the profile defined for the "newWithNew"
   certificate issued following a root CA key update.

   In  order to make the CA's self certificate useful to end entities
   that do not acquire the self certificate via "out-of-band" means, the
   CA must also produce a fingerprint for its public key.  End entities
   that acquire this fingerprint securely via some "out-of-band" means
   can then verify the CA's self-certificate and hence the other
   attributes contained therein.



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   The data structure used to carry the fingerprint is the OOBCertHash.

4.2 Root CA key update

   CA keys (as all other keys) have a finite lifetime and will have to
   be updated on a periodic basis.  The certificates NewWithNew,
   NewWithOld, and OldWithNew (see Section 2.4.1) are issued by the CA
   to aid existing end entities who hold the current self-signed CA
   certificate (OldWithOld) to transition securely to the new self-
   signed CA certificate (NewWithNew), and to aid new end entities who
   will hold NewWithNew to acquire OldWithOld securely for verification
   of existing data.

4.3 Subordinate CA initialization

   [See Section 1.2.2 for this document's definition of "subordinate
   CA".]

   From the perspective of PKI management protocols the initialization
   of a subordinate CA is the same as the initialization of an end
   entity. The only difference is that the subordinate CA must also
   produce an initial revocation list.

4.4 CRL production

   Before issuing any certificates a newly established CA (which issues
   CRLs) must produce "empty" versions of each CRL which is to be
   periodically produced.

4.5 PKI information request

   When a PKI entity (CA, RA, or EE) wishes to acquire information about
   the current status of a CA it MAY send that CA a request for such
   information.

   The CA must respond to the request by providing (at least) all of the
   information requested by the requester.  If some of the information
   cannot be provided then an error must be conveyed to the requester.

   If PKIMessages are used to request and supply this PKI information,
   then the request must be the GenMsg message, the response must be the
   GenRep message, and the error must be the Error message.  These
   messages are protected using a MAC based on shared secret information
   (i.e., PasswordBasedMAC) or any other authenticated means (if the end
   entity has an existing certificate).






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4.6 Cross certification

   The requester CA is the CA that will become the subject of the
   cross-certificate; the responder CA will become the issuer of the
   cross-certificate.

   The requester CA must be "up and running" before initiating the
   cross-certification operation.

4.6.1 One-way request-response scheme:

   The cross-certification scheme is essentially a one way operation;
   that is, when successful, this operation results in the creation of
   one new cross-certificate. If the requirement is that cross-
   certificates be created in "both directions" then each CA in turn
   must initiate a cross-certification operation (or use another
   scheme).

   This scheme is suitable where the two CAs in question can already
   verify each other's signatures (they have some common points of
   trust) or where there is an out-of-band verification of the origin of
   the certification request.

   Detailed Description:

   Cross certification is initiated at one CA known as the responder.
   The CA administrator for the responder identifies the CA it wants to
   cross certify and the responder CA equipment generates an
   authorization code.  The responder CA administrator passes this
   authorization code by out-of-band means to the requester CA
   administrator. The requester CA administrator enters the
   authorization code at the requester CA in order to initiate the on-
   line exchange.

   The authorization code is used for authentication and integrity
   purposes. This is done by generating a symmetric key based on the
   authorization code and using the symmetric key for generating Message
   Authentication Codes (MACs) on all messages exchanged.

   The requester CA initiates the exchange by generating a random number
   (requester random number). The requester CA then sends to the
   responder CA the cross certification request (ccr) message. The
   fields in this message are protected from modification with a MAC
   based on the authorization code.

   Upon receipt of the ccr message, the responder CA checks the protocol
   version, saves the requester random number, generates its own random
   number (responder random number) and validates the MAC. It then



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   generates (and archives, if desired) a new requester certificate that
   contains the requester CA public key and is signed with the responder
   CA signature private key. The responder CA responds with the cross
   certification response (ccp) message. The fields in this message are
   protected from modification with a MAC based on the authorization
   code.

   Upon receipt of the ccp message, the requester CA checks that its own
   system time is close to the responder CA system time, checks the
   received random numbers and validates the MAC.  The requester CA
   responds with the PKIConfirm message. The fields in this message are
   protected from modification with a MAC based on the authorization
   code.  The requester CA writes the requester certificate to the
   Repository.

   Upon receipt of the PKIConfirm message, the responder CA checks the
   random numbers and validates the MAC.

   Notes:

   1. The ccr message must contain a "complete" certification request,
      that is, all fields (including, e.g., a BasicConstraints
      extension) must be specified by the requester CA.
   2. The ccp message SHOULD contain the verification certificate of the
      responder CA - if present, the requester CA must then verify this
      certificate (for example, via the "out-of-band" mechanism).

4.7 End entity initialization

   As with CAs, end entities must be initialized. Initialization of end
   entities requires at least two steps:

      - acquisition of PKI information
      - out-of-band verification of one root-CA public key

   (other possible steps include the retrieval of trust condition
   information and/or out-of-band verification of other CA public keys).

4.7.1 Acquisition of PKI information

   The information REQUIRED is:

      - the current root-CA public key
      - (if the certifying CA is not a root-CA) the certification path
        from  the root CA to the certifying CA together with appropriate
        revocation lists
      - the algorithms and algorithm parameters which the certifying CA
        supports for each relevant usage



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   Additional information could be required (e.g., supported extensions
   or CA policy information) in order to produce a certification request
   which will be successful. However, for simplicity we do not mandate
   that the end entity acquires this information via the PKI messages.
   The end result is simply that some certification requests may fail
   (e.g., if the end entity wants to generate its own encryption key but
   the CA doesn't allow that).

   The required information MAY be acquired as described in Section 4.5.

4.7.2 Out-of-Band Verification of Root-CA Key

   An end entity must securely possess the public key of its root CA.
   One method to achieve this is to provide the end entity with the CA's
   self-certificate fingerprint via some secure "out-of-band" means. The
   end entity can then securely use the CA's self-certificate.

   See Section 4.1 for further details.

4.8 Certificate Request

   An initialized end entity MAY request a certificate at any time (as
   part of an update procedure, or for any other purpose).  This request
   will be made using the certification request (cr) message.  If the
   end entity already possesses a signing key pair (with a corresponding
   verification certificate), then this cr message will typically be
   protected by the entity's digital signature.  The CA returns the new
   certificate (if the request is successful) in a CertRepMessage.

4.9 Key Update

   When a key pair is due to expire the relevant end entity MAY request
   a key update - that is, it MAY request that the CA issue a new
   certificate for a new key pair.  The request is made using a key
   update request (kur) message.  If the end entity already possesses a
   signing key pair (with a corresponding verification certificate),
   then this message will typically be protected by the entity's digital
   signature. The CA returns the new certificate (if the request is
   successful) in a key update response (kup) message, which is
   syntactically identical to a CertRepMessage.

5. Transports

   The transport protocols specified below allow end entities, RAs and
   CAs to pass PKI messages between them. There is no requirement for
   specific security mechanisms to be applied at this level if the PKI
   messages are suitably protected (that is, if the OPTIONAL
   PKIProtection parameter is used as specified for each message).



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5.1 File based protocol

   A file containing a PKI message MUST contain only the DER encoding of
   one PKI message, i.e., there MUST be no extraneous header or trailer
   information in the file.

   Such files can be used to transport PKI messages using, e.g., FTP.

5.2 Direct TCP-Based Management Protocol

   The following simple TCP-based protocol is to be used for transport
   of PKI messages. This protocol is suitable for cases where an end
   entity (or an RA) initiates a transaction and can poll to pick up the
   results.

   If a transaction is initiated by a PKI entity (RA or CA) then an end
   entity must either supply a listener process or be supplied with a
   polling reference (see below) in order to allow it to pick up the PKI
   message from the PKI management component.

   The protocol basically assumes a listener process on an RA or CA
   which can accept PKI messages on a well-defined port (port number
   829). Typically an initiator binds to this port and submits the
   initial PKI message for a given transaction ID. The responder replies
   with a PKI message and/or with a reference number to be used later
   when polling for the actual PKI message response.

   If a number of PKI response messages are to be produced for a given
   request (say if some part of the request is handled more quickly than
   another) then a new polling reference is also returned.

   When the final PKI response message has been picked up by the
   initiator then no new polling reference is supplied.

   The initiator of a transaction sends a "direct TCP-based PKI message"
   to the recipient. The recipient responds with a similar message.

   A "direct TCP-based PKI message" consists of:

         length (32-bits), flag (8-bits), value (defined below)

   The length field contains the number of octets of the remainder of
   the message (i.e., number of octets of "value" plus one).  All 32-bit
   values in this protocol are specified to be in network byte order.

    Message name   flag     value

    pkiMsg         '00'H    DER-encoded PKI message



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      -- PKI message
    pollRep        '01'H    polling reference (32 bits),
                            time-to-check-back (32 bits)
      -- poll response where no PKI message response ready; use polling
      -- reference value (and estimated time value) for later polling
    pollReq        '02'H    polling reference (32 bits)
      -- request for a PKI message response to initial message
    negPollRep     '03'H    '00'H
      -- no further polling responses (i.e., transaction complete)
    partialMsgRep  '04'H    next polling reference (32 bits),
                            time-to-check-back (32 bits),
                            DER-encoded PKI message
      -- partial response to initial message plus new polling reference
      -- (and estimated time value) to use to get next part of response
    finalMsgRep    '05'H    DER-encoded PKI message
      -- final (and possibly sole) response to initial message
    errorMsgRep    '06'H    human readable error message
      -- produced when an error is detected (e.g., a polling reference is
      -- received which doesn't exist or is finished with)

   Where a PKIConfirm message is to be transported (always from the
   initiator to the responder) then a pkiMsg message is sent and a
   negPollRep is returned.

   The sequence of messages which can occur is then:

   a) end entity sends pkiMsg and receives one of pollRep, negPollRep,
   partialMsgRep or finalMsgRep in response.  b) end entity sends
   pollReq message and receives one of negPollRep, partialMsgRep,
   finalMsgRep or errorMsgRep in response.

   The "time-to-check-back" parameter is a 32-bit integer, defined to be
   the number of seconds which have elapsed since midnight, January 1,
   1970, coordinated universal time.  It provides an estimate of the
   time that the end entity should send its next pollReq.

5.3 Management Protocol via E-mail

   This subsection specifies a means for conveying ASN.1-encoded
   messages for the protocol exchanges described in Section 4 via
   Internet mail.

   A simple MIME object is specified as follows.

      Content-Type: application/pkixcmp
      Content-Transfer-Encoding: base64

      <<the ASN.1 DER-encoded PKIX-CMP message, base64-encoded>>



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   This MIME object can be sent and received using common MIME
   processing engines and provides a simple Internet mail transport for
   PKIX-CMP messages.  Implementations MAY wish to also recognize and
   use the "application/x-pkixcmp" MIME type (specified in earlier
   versions of this document) in order to support backward compatibility
   wherever applicable.

5.4 Management Protocol via HTTP

   This subsection specifies a means for conveying ASN.1-encoded
   messages for the protocol exchanges described in Section 4 via the
   HyperText Transfer Protocol.

   A simple MIME object is specified as follows.

      Content-Type: application/pkixcmp

      <<the ASN.1 DER-encoded PKIX-CMP message>>

   This MIME object can be sent and received using common HTTP
   processing engines over WWW links and provides a simple browser-
   server transport for PKIX-CMP messages.  Implementations MAY wish to
   also recognize and use the "application/x-pkixcmp" MIME type
   (specified in earlier versions of this document) in order to support
   backward compatibility wherever applicable.

SECURITY CONSIDERATIONS

   This entire memo is about security mechanisms.

   One cryptographic consideration is worth explicitly spelling out. In
   the protocols specified above, when an end entity is required to
   prove possession of a decryption key, it is effectively challenged to
   decrypt something (its own certificate). This scheme (and many
   others!) could be vulnerable to an attack if the possessor of the
   decryption key in question could be fooled into decrypting an
   arbitrary challenge and returning the cleartext to an attacker.
   Although in this specification a number of other failures in security
   are required in order for this attack to succeed, it is conceivable
   that some future services (e.g., notary, trusted time) could
   potentially be vulnerable to such attacks. For this reason we re-
   iterate the general rule that implementations should be very careful
   about decrypting arbitrary "ciphertext" and revealing recovered
   "plaintext" since such a practice can lead to serious security
   vulnerabilities.






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   Note also that exposing a private key to the CA/RA as a proof-of-
   possession technique can carry some security risks (depending upon
   whether or not the CA/RA can be trusted to handle such material
   appropriately).  Implementers are advised to exercise caution in
   selecting and using this particular POP mechanism.

References

   [COR95]   ISO/IEC JTC 1/SC 21, Technical Corrigendum 2 to ISO/IEC
             9594-8: 1990 & 1993 (1995:E), July 1995.

   [CRMF]    Myers, M., Adams, C., Solo, D. and D. Kemp, "Certificate
             Request Message Format", RFC 2511, March 1999.

   [MvOV97]  A. Menezes, P. van Oorschot, S. Vanstone, "Handbook of
             Applied Cryptography", CRC Press, 1997.

   [PKCS7]   RSA Laboratories, "The Public-Key Cryptography Standards
             (PKCS)", RSA Data Security Inc., Redwood City, California,
             November 1993 Release.

   [PKCS10]  RSA Laboratories, "The Public-Key Cryptography Standards
             (PKCS)", RSA Data Security Inc., Redwood City, California,
             November 1993 Release.

   [PKCS11]  RSA Laboratories, "The Public-Key Cryptography Standards -
             PKCS #11:  Cryptographic token interface standard", RSA
             Data Security Inc., Redwood City, California, April 28,
             1995.

   [RFC1847] Galvin, J., Murphy, S. Crocker, S. and N. Freed, "Security
             Multiparts for MIME:  Multipart/Signed and Multipart/
             Encrypted", RFC 1847, October 1995.

   [RFC2104] Krawczyk, H., Bellare, M. and R. Canetti, "HMAC:  Keyed
             Hashing for Message Authentication", RFC 2104, February
             1997.

   [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
             Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2202] Cheng, P. and R. Glenn, "Test Cases for HMAC-MD5 and HMAC-
             SHA-1", RFC 2202, September 1997.

   [X509-AM] ISO/IEC JTC1/SC 21, Draft Amendments DAM 4 to ISO/IEC
             9594-2, DAM 2 to ISO/IEC 9594-6, DAM 1 to ISO/IEC 9594-7,
             and DAM 1 to ISO/IEC 9594-8 on Certificate Extensions, 1
             December, 1996.



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Acknowledgements

   The authors gratefully acknowledge the contributions of various
   members of the PKIX Working Group.  Many of these contributions
   significantly clarified and improved the utility of this
   specification.

Authors' Addresses

   Carlisle Adams
   Entrust Technologies
   750 Heron Road, Suite E08,
   Ottawa, Ontario
   Canada K1V 1A7

   EMail: cadams@entrust.com


   Stephen Farrell
   Software and Systems Engineering Ltd.
   Fitzwilliam Court
   Leeson Close
   Dublin 2
   IRELAND

   EMail: stephen.farrell@sse.ie

























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APPENDIX A: Reasons for the presence of RAs

   The reasons which justify the presence of an RA can be split into
   those which are due to technical factors and those which are
   organizational in nature. Technical reasons include the following.

     -If hardware tokens are in use, then not all end entities will have
      the equipment needed to initialize these; the RA equipment can
      include the necessary functionality (this may also be a matter of
      policy).

     -Some end entities may not have the capability to publish
      certificates; again, the RA may be suitably placed for this.

     -The RA will be able to issue signed revocation requests on behalf
      of end entities associated with it, whereas the end entity may not
      be able to do this (if the key pair is completely lost).

   Some of the organizational reasons which argue for the presence of an
   RA are the following.

     -It may be more cost effective to concentrate functionality in the
      RA equipment than to supply functionality to all end entities
      (especially if special token initialization equipment is to be
      used).

     -Establishing RAs within an organization can reduce the number of
      CAs required, which is sometimes desirable.

     -RAs may be better placed to identify people with their
      "electronic" names, especially if the CA is physically remote from
      the end entity.

     -For many applications there will already be in place some
      administrative structure so that candidates for the role of RA are
      easy to find (which may not be true of the CA).















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Appendix B. PKI Management Message Profiles.

   This appendix contains detailed profiles for those PKIMessages which
   MUST be supported by conforming implementations (see Section 4).

   Profiles for the PKIMessages used in the following PKI management
   operations are provided:

   - root CA key update
   - information request/response
   - cross-certification request/response (1-way)
   - initial registration/certification
        - basic authenticated scheme
   - certificate request
   - key update

   <<Later versions of this document may extend the above to include
   profiles for the operations listed below (along with other
   operations, if desired).>>

   - revocation request
   - certificate publication
   - CRL publication

B1. General Rules for interpretation of these profiles.

   1. Where OPTIONAL or DEFAULT fields are not mentioned in individual
      profiles, they SHOULD be absent from the relevant message (i.e., a
      receiver can validly reject a message containing such fields as
      being syntactically incorrect).
      Mandatory fields are not mentioned if they have an obvious value
      (e.g., pvno).
   2. Where structures occur in more than one message, they are
      separately profiled as appropriate.
   3. The algorithmIdentifiers from PKIMessage structures are profiled
      separately.
   4. A "special" X.500 DN is called the "NULL-DN"; this means a DN
      containing a zero-length SEQUENCE OF RelativeDistinguishedNames
      (its DER encoding is then '3000'H).
   5. Where a GeneralName is required for a field but no suitable
      value is available (e.g., an end entity produces a request before
      knowing its name) then the GeneralName is to be an X.500 NULL-DN
      (i.e., the Name field of the CHOICE is to contain a NULL-DN).
      This special value can be called a "NULL-GeneralName".
   6. Where a profile omits to specify the value for a GeneralName
      then the NULL-GeneralName value is to be present in the relevant
      PKIMessage field. This occurs with the sender field of the
      PKIHeader for some messages.



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   7. Where any ambiguity arises due to naming of fields, the profile
      names these using a "dot" notation (e.g., "certTemplate.subject"
      means the subject field within a field called certTemplate).
   8. Where a "SEQUENCE OF types" is part of a message, a zero-based
      array notation is used to describe fields within the SEQUENCE OF
      (e.g., crm[0].certReq.certTemplate.subject refers to a
      subfield of the first CertReqMsg contained in a request message).
   9. All PKI message exchanges in Sections B7-B10 require a PKIConfirm
      message to be sent by the initiating entity.  This message is not
      included in some of the profiles given since its body is NULL and
      its header contents are clear from the context.  Any authenticated
      means can be used for the protectionAlg (e.g., password-based MAC,
      if shared secret information is known, or signature).

B2. Algorithm Use Profile

   The following table contains definitions of algorithm uses within PKI
   management protocols.

   The columns in the table are:

Name:      an identifier used for message profiles
Use:       description of where and for what the algorithm is used
Mandatory: an AlgorithmIdentifier which MUST be supported by
           conforming implementations
Others:    alternatives to the mandatory AlgorithmIdentifier

 Name           Use                        Mandatory        Others

 MSG_SIG_ALG    Protection of PKI          DSA/SHA-1        RSA/MD5...
                messages using signature
 MSG_MAC_ALG    protection of PKI          PasswordBasedMac HMAC,
                messages using MACing                       X9.9...
 SYM_PENC_ALG   symmetric encryption of    3-DES (3-key-    RC5,
                an end entity's private    EDE, CBC mode)   CAST-128...
                key where symmetric
                key is distributed
                out-of-band
 PROT_ENC_ALG   asymmetric algorithm       D-H              RSA
                used for encryption of
                (symmetric keys for
                encryption of) private
                keys transported in
                PKIMessages
 PROT_SYM_ALG   symmetric encryption       3-DES (3-key-    RC5,
                algorithm used for         EDE, CBC mode)   CAST-128...
                encryption of private
                key bits (a key of this



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                type is encrypted using
                PROT_ENC_ALG)

Mandatory AlgorithmIdentifiers and Specifications:

DSA/SHA-1:
  AlgId:  {1 2 840 10040 4 3};
  NIST, FIPS PUB 186: Digital Signature Standard, 1994;
  Public Modulus size:  1024 bits.

PasswordBasedMac:
  {1 2 840 113533 7 66 13}, with SHA-1 {1 3 14 3 2 26} as the owf
    parameter and HMAC-SHA1 {1 3 6 1 5 5 8 1 2} as the mac parameter;
  (this specification), along with
  NIST, FIPS PUB 180-1: Secure Hash Standard, April 1995;
  H. Krawczyk, M. Bellare, R. Canetti, "HMAC:  Keyed-Hashing for Message
    Authentication", Internet Request for Comments 2104, February 1997.

3-DES:
  {1 2 840 113549 3 7};
  (used in RSA's BSAFE and in S/MIME).

D-H:
  AlgId:  {1 2 840 10046 2 1};
  ANSI X9.42;
  Public Modulus Size:  1024 bits.
  DHParameter ::= SEQUENCE {
    prime INTEGER, -- p
    base  INTEGER  -- g
  }

B3. "Self-signed" certificates

   Profile of how a Certificate structure may be "self-signed". These
   structures are used for distribution of "root" CA public keys. This
   can occur in one of three ways (see Section 2.4 above for a
   description of the use of these structures):

 Type          Function

 newWithNew    a true "self-signed" certificate; the contained public
               key MUST be usable to verify the signature (though this
               provides only integrity and no authentication whatsoever)
 oldWithNew    previous root CA public key signed with new private key
 newWithOld    new root CA public key signed with previous private key






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   <<Such certificates (including relevant extensions) must contain
   "sensible" values for all fields.  For example, when present
   subjectAltName MUST be identical to issuerAltName, and when present
   keyIdentifiers must contain appropriate values, et cetera.>>

B4. Proof of Possession Profile

   POP fields for use (in signature field of pop field of
   ProofOfPossession structure) when proving possession of a private
   signing key which corresponds to a public verification key for which
   a certificate has been requested.

    Field               Value         Comment

    algorithmIdentifier MSG_SIG_ALG   only signature protection is
                                      allowed for this proof
    signature           present       bits calculated using MSG_SIG_ALG


   <<Proof of possession of a private decryption key which corresponds
   to a public encryption key for which a certificate has been requested
   does not use this profile; instead the method given in protectionAlg
   for PKIConfirm in Section B8 is used.>>

   Not every CA/RA will do Proof-of-Possession (of signing key,
   decryption key, or key agreement key) in the PKIX-CMP in-band
   certification request protocol (how POP is done MAY ultimately be a
   policy issue which is made explicit for any given CA in its
   publicized Policy OID and Certification Practice Statement).
   However, this specification MANDATES that CA/RA entities MUST do POP
   (by some means) as part of the certification process.  All end
   entities MUST be prepared to provide POP (i.e., these components of
   the PKIX-CMP protocol MUST be supported).

B5. Root CA Key Update

   A root CA updates its key pair. It then produces a CA key update
   announcement message which can be made available (via one of the
   transport mechanisms) to the relevant end entities.  A PKIConfirm
   message is NOT REQUIRED from the end entities.

   ckuann message:

    Field        Value                        Comment

    sender       CA name                      responding CA name
    body         ckuann(CAKeyUpdAnnContent)
    oldWithNew   present                      see Section B3 above



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    newWithOld   present                      see Section B3 above
    newWithNew   present                      see Section B3 above
    extraCerts   optionally present           can be used to "publish"
                                              certificates (e.g.,
                                              certificates signed using
                                              the new private key)

B6. PKI Information request/response

   The end entity sends general message to the PKI requesting details
   which will be required for later PKI management operations.  RA/CA
   responds with general response. If an RA generates the response then
   it will simply forward the equivalent message which it previously
   received from the CA, with the possible addition of the certificates
   to the extraCerts fields of the PKIMessage.  A PKIConfirm message is
   NOT REQUIRED from the end entity.

Message Flows:

Step#   End entity                                    PKI

  1     format genm
  2                      ->      genm      ->
  3                                                   handle genm
  4                                                   produce genp
  5                      <-      genp      <-
  6     handle genp


genm:

Field               Value

recipient           CA name
  -- the name of the CA as contained in issuerAltName extensions or
  -- issuer fields within certificates
protectionAlg       MSG_MAC_ALG or MSG_SIG_ALG
  -- any authenticated protection alg.
SenderKID           present if required
  -- must be present if required for verification of message protection
freeText            any valid value
body                genr (GenReqContent)
GenMsgContent       empty SEQUENCE
  -- all relevant information requested
protection          present
  -- bits calculated using MSG_MAC_ALG or MSG_SIG_ALG





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genp:

Field                Value

sender               CA name
  -- name of the CA which produced the message
protectionAlg        MSG_MAC_ALG or MSG_SIG_ALG
  -- any authenticated protection alg.
senderKID            present if required
  -- must be present if required for verification of message protection
body                 genp (GenRepContent)
CAProtEncCert        present (object identifier one
                     of PROT_ENC_ALG), with relevant
                     value
  -- to be used if end entity needs to encrypt information for the CA
  -- (e.g., private key for recovery purposes)
SignKeyPairTypes     present, with relevant value
  -- the set of signature algorithm identifiers which this CA will
  -- certify for subject public keys
EncKeyPairTypes      present, with relevant value
  -- the set of encryption/key agreement algorithm identifiers which
  -- this CA will certify for subject public keys
PreferredSymmAlg     present (object identifier one
                     of PROT_SYM_ALG) , with relevant
                     value
  -- the symmetric algorithm which this CA expects to be used in later
  -- PKI messages (for encryption)
CAKeyUpdateInfo      optionally present, with
                     relevant value
  -- the CA MAY provide information about a relevant root CA key pair
  -- using this field (note that this does not imply that the responding
  -- CA is the root CA in question)
CurrentCRL           optionally present, with relevant value
  -- the CA MAY provide a copy of a complete CRL (i.e., fullest possible
  -- one)
protection           present
  -- bits calculated using MSG_MAC_ALG or MSG_SIG_ALG
extraCerts           optionally present
  -- can be used to send some certificates to the end entity. An RA MAY
  -- add its certificate here.

B7. Cross certification request/response (1-way)

   Creation of a single cross-certificate (i.e., not two at once). The
   requesting CA MAY choose who is responsible for publication of the
   cross-certificate created by the responding CA through use of the
   PKIPublicationInfo control.




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   Preconditions:

   1. Responding CA can verify the origin of the request (possibly
      requiring out-of-band means) before processing the request.
   2. Requesting CA can authenticate the authenticity of the origin of
      the response (possibly requiring out-of-band means) before
      processing the response

Message Flows:

Step#   Requesting CA                                  Responding CA
  1     format ccr
  2                        ->       ccr       ->
  3                                                     handle ccr
  4                                                     produce ccp
  5                        <-       ccp       <-
  6     handle ccp
  7     format conf
  8                        ->       conf      ->
  9                                                     handle conf


ccr:
Field                 Value

sender                Requesting CA name
  -- the name of the CA who produced the message
recipient             Responding CA name
  -- the name of the CA who is being asked to produce a certificate
messageTime           time of production of message
  -- current time at requesting CA
protectionAlg         MSG_SIG_ALG
  -- only signature protection is allowed for this request
senderKID             present if required
  -- must be present if required for verification of message protection
transactionID         present
  -- implementation-specific value, meaningful to requesting CA.
  -- [If already in use at responding CA then a rejection message
  -- MUST be produced by responding CA]
senderNonce           present
  -- 128 (pseudo-)random bits
freeText              any valid value
body                  ccr (CertReqMessages)
                      only one CertReqMsg
                      allowed
  -- if multiple cross certificates are required they MUST be packaged
  -- in separate PKIMessages
certTemplate          present



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  -- details follow
version               v1 or v3
  -- <<v3 STRONGLY RECOMMENDED>>
signingAlg            present
  -- the requesting CA must know in advance with which algorithm it
  -- wishes the certificate to be signed
subject               present
  -- may be NULL-DN only if subjectAltNames extension value proposed
validity              present
  -- MUST be completely specified (i.e., both fields present)
issuer                present
  -- may be NULL-DN only if issuerAltNames extension value proposed
publicKey             present
  -- the key to be certified (which must be for a signing algorithm)
extensions            optionally present
  -- a requesting CA must propose values for all extensions which it
  -- requires to be in the cross-certificate

POPOSigningKey        present
  -- see "Proof of possession profile" (Section B4)

protection            present
  -- bits calculated using MSG_SIG_ALG
extraCerts            optionally present
  -- MAY contain any additional certificates that requester wishes
  -- to include


ccp:
Field                 Value

sender                Responding CA name
  -- the name of the CA who produced the message
recipient             Requesting CA name
  -- the name of the CA who asked for production of a certificate
messageTime           time of production of message
  -- current time at responding CA
protectionAlg         MSG_SIG_ALG
  -- only signature protection is allowed for this message
senderKID             present if required
  -- must be present if required for verification of message
  -- protection
recipKID              present if required
transactionID         present
  -- value from corresponding ccr message
senderNonce           present
  -- 128 (pseudo-)random bits
recipNonce            present



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  -- senderNonce from corresponding ccr message
freeText              any valid value
body                  ccp (CertRepMessage)
                      only one CertResponse allowed
  -- if multiple cross certificates are required they MUST be packaged
  -- in separate PKIMessages
response              present
status                present
PKIStatusInfo.status  present
  -- if PKIStatusInfo.status is one of:
  --   granted, or
  --   grantedWithMods,
  -- then certifiedKeyPair MUST be present and failInfo MUST be absent
failInfo              present depending on
                      PKIStatusInfo.status
  -- if PKIStatusInfo.status is:
  --   rejection
  -- then certifiedKeyPair MUST be absent and failInfo MUST be present
  -- and contain appropriate bit settings


certifiedKeyPair      present depending on
                      PKIStatusInfo.status
certificate           present depending on
                      certifiedKeyPair
  -- content of actual certificate must be examined by requesting CA
  -- before publication

protection            present
  -- bits calculated using MSG_SIG_ALG
extraCerts            optionally present
  -- MAY contain any additional certificates that responder wishes
  -- to include

B8. Initial Registration/Certification (Basic Authenticated Scheme)

   An (uninitialized) end entity requests a (first) certificate from a
   CA. When the CA responds with a message containing a certificate, the
   end entity replies with a confirmation. All messages are
   authenticated.

   This scheme allows the end entity to request certification of a
   locally-generated public key (typically a signature key). The end
   entity MAY also choose to request the centralized generation and
   certification of another key pair (typically an encryption key pair).

   Certification may only be requested for one locally generated public
   key (for more, use separate PKIMessages).



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   The end entity MUST support proof-of-possession of the private key
   associated with the locally-generated public key.

   Preconditions:

   1. The end entity can authenticate the CA's signature based on
      out-of-band means
   2. The end entity and the CA share a symmetric MACing key

   Message flow:

   Step#    End entity                                    PKI
     1      format ir
     2                         ->      ir       ->
     3                                                    handle ir
     4                                                    format ip
     5                         <-      ip       <-
     6      handle ip
     7      format conf
     8                         ->      conf     ->
     9                                                    handle conf

   For this profile, we mandate that the end entity MUST include all
   (i.e., one or two) CertReqMsg in a single PKIMessage and that the PKI
   (CA) MUST produce a single response PKIMessage which contains the
   complete response (i.e., including the OPTIONAL second key pair, if
   it was requested and if centralized key generation is supported). For
   simplicity, we also mandate that this message MUST be the final one
   (i.e., no use of "waiting" status value).

ir:
Field                Value

recipient            CA name
  -- the name of the CA who is being asked to produce a certificate
protectionAlg        MSG_MAC_ALG
  -- only MAC protection is allowed for this request, based on
  -- initial authentication key
senderKID            referenceNum
  -- the reference number which the CA has previously issued to
  -- the end entity (together with the MACing key)
transactionID        present
  -- implementation-specific value, meaningful to end entity.
  -- [If already in use at the CA then a rejection message MUST be
  -- produced by the CA]
senderNonce          present
  -- 128 (pseudo-)random bits
freeText             any valid value



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body                 ir (CertReqMessages)
                     only one or two CertReqMsg
                     are allowed
  -- if more certificates are required requests MUST be packaged in
  -- separate PKIMessages
CertReqMsg           one or two present
  -- see below for details, note: crm[0] means the first (which MUST
  -- be present), crm[1] means the second (which is OPTIONAL, and used
  -- to ask for a centrally-generated key)

crm[0].certReq.      fixed value of zero
   certReqId
  -- this is the index of the template within the message
crm[0].certReq       present
   certTemplate
  -- MUST include subject public key value, otherwise unconstrained
crm[0].pop...        optionally present if public key
   POPOSigningKey    from crm[0].certReq.certTemplate is
                     a signing key
  -- proof of possession MAY be required in this exchange (see Section
  -- B4 for details)
crm[0].certReq.      optionally present
   controls.archiveOptions
  -- the end entity MAY request that the locally-generated private key
  -- be archived
crm[0].certReq.      optionally present
   controls.publicationInfo
  -- the end entity MAY ask for publication of resulting cert.

crm[1].certReq       fixed value of one
   certReqId
  -- the index of the template within the message
crm[1].certReq       present
   certTemplate
  -- MUST NOT include actual public key bits, otherwise unconstrained
  -- (e.g., the names need not be the same as in crm[0])
crm[0].certReq.      present [object identifier MUST be PROT_ENC_ALG]
   controls.protocolEncKey
  -- if centralized key generation is supported by this CA, this
  -- short-term asymmetric encryption key (generated by the end entity)
  -- will be used by the CA to encrypt (a symmetric key used to encrypt)
  -- a private key generated by the CA on behalf of the end entity
crm[1].certReq.      optionally present
   controls.archiveOptions
crm[1].certReq.      optionally present
   controls.publicationInfo
protection           present
  -- bits calculated using MSG_MAC_ALG



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ip:
Field                Value

sender               CA name
  -- the name of the CA who produced the message
messageTime          present
  -- time at which CA produced message
protectionAlg        MS_MAC_ALG
  -- only MAC protection is allowed for this response
recipKID             referenceNum
  -- the reference number which the CA has previously issued to the
  -- end entity (together with the MACing key)
transactionID        present
  -- value from corresponding ir message
senderNonce          present
  -- 128 (pseudo-)random bits
recipNonce           present
  -- value from senderNonce in corresponding ir message
freeText             any valid value
body                 ir (CertRepMessage)
                     contains exactly one response
                     for each request
  -- The PKI (CA) responds to either one or two requests as appropriate.
  -- crc[0] denotes the first (always present); crc[1] denotes the
  -- second (only present if the ir message contained two requests and
  -- if the CA supports centralized key generation).
crc[0].              fixed value of zero
   certReqId
  -- MUST contain the response to the first request in the corresponding
  -- ir message
crc[0].status.       present, positive values allowed:
   status               "granted", "grantedWithMods"
                     negative values allowed:
                        "rejection"
crc[0].status.       present if and only if
   failInfo          crc[0].status.status is "rejection"
crc[0].              present if and only if
   certifiedKeyPair  crc[0].status.status is
                        "granted" or "grantedWithMods"
certificate          present unless end entity's public
                     key is an encryption key and POP
                     is done in this in-band exchange
encryptedCert        present if and only if end entity's
                     public key is an encryption key and
                     POP done in this in-band exchange
publicationInfo      optionally present
  -- indicates where certificate has been published (present at
  -- discretion of CA)



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crc[1].              fixed value of one
   certReqId
  -- MUST contain the response to the second request in the
  -- corresponding ir message
crc[1].status.       present, positive values allowed:
   status               "granted", "grantedWithMods"
                     negative values allowed:
                        "rejection"
crc[1].status.       present if and only if
   failInfo          crc[0].status.status is "rejection"
crc[1].              present if and only if
   certifiedKeyPair  crc[0].status.status is "granted"
                     or "grantedWithMods"
certificate          present
privateKey           present
publicationInfo      optionally present
  -- indicates where certificate has been published (present at
  -- discretion of CA)
protection           present
  -- bits calculated using MSG_MAC_ALG
extraCerts           optionally present
  -- the CA MAY provide additional certificates to the end entity

conf:
Field                Value

recipient            CA name
  -- the name of the CA who was asked to produce a certificate
transactionID        present
  -- value from corresponding ir and ip messages
senderNonce          present
  -- value from recipNonce in corresponding ip message
recipNonce           present
  -- value from senderNonce in corresponding ip message
protectionAlg        MSG_MAC_ALG
  -- only MAC protection is allowed for this message.  The MAC is
  -- based on the initial authentication key if only a signing key
  -- pair has been sent in ir for certification, or if POP is not
  -- done in this in-band exchange.  Otherwise, the MAC is based on
  -- a key derived from the symmetric key used to decrypt the
  -- returned encryptedCert.
senderKID            referenceNum
  -- the reference number which the CA has previously issued to the
  -- end entity (together with the MACing key)
body                 conf (PKIConfirmContent)
  -- this is an ASN.1 NULL
protection           present
  -- bits calculated using MSG_MAC_ALG



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B9. Certificate Request

   An (initialized) end entity requests a certificate from a CA (for any
   reason). When the CA responds with a message containing a
   certificate, the end entity replies with a confirmation. All messages
   are authenticated.

   The profile for this exchange is identical to that given in Section
   B8 with the following exceptions:

     - protectionAlg may be MSG_MAC_ALG or MSG_SIG_ALG in request,
       response, and confirm messages (the determination in the confirm
       message being dependent upon POP considerations for key-
       encipherment and key- agreement certificate requests);
     - senderKID and recipKID are only present if required for message
       verification;
     - body is cr or cp;
       - protocolEncKey is not present;
     - protection bits are calculated according to the protectionAlg
       field.

B10. Key Update Request

   An (initialized) end entity requests a certificate from a CA (to
   update the key pair and corresponding certificate that it already
   possesses). When the CA responds with a message containing a
   certificate, the end entity replies with a confirmation. All messages
   are authenticated.

   The profile for this exchange is identical to that given in Section
   B8 with the following exceptions:

     - protectionAlg may be MSG_MAC_ALG or MSG_SIG_ALG in request,
       response, and confirm messages (the determination in the confirm
       message being dependent upon POP considerations for key-
       encipherment and key- agreement certificate requests);
     - senderKID and recipKID are only present if required for message
       verification;
     - body is kur or kup;
     - protection bits are calculated according to the protectionAlg
       field.










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Appendix C: "Compilable" ASN.1 Module using 1988 Syntax

  PKIXCMP {iso(1) identified-organization(3) dod(6) internet(1)
     security(5) mechanisms(5) pkix(7) id-mod(0) id-mod-cmp(9)}

  DEFINITIONS EXPLICIT TAGS ::=

  BEGIN

  -- EXPORTS ALL --

  IMPORTS

      Certificate, CertificateList, Extensions, AlgorithmIdentifier
             FROM PKIX1Explicit88 {iso(1) identified-organization(3)
             dod(6) internet(1) security(5) mechanisms(5) pkix(7)
             id-mod(0) id-pkix1-explicit-88(1)}}

      GeneralName, KeyIdentifier, ReasonFlags
             FROM PKIX1Implicit88 {iso(1) identified-organization(3)
             dod(6) internet(1) security(5) mechanisms(5) pkix(7)
             id-mod(0) id-pkix1-implicit-88(2)}

      CertTemplate, PKIPublicationInfo, EncryptedValue, CertId,
      CertReqMessages
             FROM PKIXCRMF {iso(1) identified-organization(3)
             dod(6) internet(1) security(5) mechanisms(5) pkix(7)
             id-mod(0) id-mod-crmf(5)}}

      -- CertificationRequest
      --     FROM PKCS10 {no standard ASN.1 module defined;
      --     implementers need to create their own module to import
      --     from, or directly include the PKCS10 syntax in this module}

                       --  Locally defined OIDs  --

  PKIMessage ::= SEQUENCE {
      header           PKIHeader,
      body             PKIBody,
      protection   [0] PKIProtection OPTIONAL,
      extraCerts   [1] SEQUENCE SIZE (1..MAX) OF Certificate OPTIONAL
  }

  PKIHeader ::= SEQUENCE {
      pvno                INTEGER     { ietf-version2 (1) },
      sender              GeneralName,
      -- identifies the sender
      recipient           GeneralName,



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      -- identifies the intended recipient
      messageTime     [0] GeneralizedTime         OPTIONAL,
      -- time of production of this message (used when sender
      -- believes that the transport will be "suitable"; i.e.,
      -- that the time will still be meaningful upon receipt)
      protectionAlg   [1] AlgorithmIdentifier     OPTIONAL,
      -- algorithm used for calculation of protection bits
      senderKID       [2] KeyIdentifier           OPTIONAL,
      recipKID        [3] KeyIdentifier           OPTIONAL,
      -- to identify specific keys used for protection
      transactionID   [4] OCTET STRING            OPTIONAL,
      -- identifies the transaction; i.e., this will be the same in
      -- corresponding request, response and confirmation messages
      senderNonce     [5] OCTET STRING            OPTIONAL,
      recipNonce      [6] OCTET STRING            OPTIONAL,
      -- nonces used to provide replay protection, senderNonce
      -- is inserted by the creator of this message; recipNonce
      -- is a nonce previously inserted in a related message by
      -- the intended recipient of this message
      freeText        [7] PKIFreeText             OPTIONAL,
      -- this may be used to indicate context-specific instructions
      -- (this field is intended for human consumption)
      generalInfo     [8] SEQUENCE SIZE (1..MAX) OF
                             InfoTypeAndValue     OPTIONAL
      -- this may be used to convey context-specific information
      -- (this field not primarily intended for human consumption)
  }

  PKIFreeText ::= SEQUENCE SIZE (1..MAX) OF UTF8String
      -- text encoded as UTF-8 String (note:  each UTF8String SHOULD
      -- include an RFC 1766 language tag to indicate the language
      -- of the contained text)


  PKIBody ::= CHOICE {       -- message-specific body elements
      ir      [0]  CertReqMessages,        --Initialization Request
      ip      [1]  CertRepMessage,         --Initialization Response
      cr      [2]  CertReqMessages,        --Certification Request
      cp      [3]  CertRepMessage,         --Certification Response
      p10cr   [4]  CertificationRequest,   --imported from [PKCS10]
      popdecc [5]  POPODecKeyChallContent, --pop Challenge
      popdecr [6]  POPODecKeyRespContent,  --pop Response
      kur     [7]  CertReqMessages,        --Key Update Request
      kup     [8]  CertRepMessage,         --Key Update Response
      krr     [9]  CertReqMessages,        --Key Recovery Request
      krp     [10] KeyRecRepContent,       --Key Recovery Response
      rr      [11] RevReqContent,          --Revocation Request
      rp      [12] RevRepContent,          --Revocation Response



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      ccr     [13] CertReqMessages,        --Cross-Cert. Request
      ccp     [14] CertRepMessage,         --Cross-Cert. Response
      ckuann  [15] CAKeyUpdAnnContent,     --CA Key Update Ann.
      cann    [16] CertAnnContent,         --Certificate Ann.
      rann    [17] RevAnnContent,          --Revocation Ann.
      crlann  [18] CRLAnnContent,          --CRL Announcement
      conf    [19] PKIConfirmContent,      --Confirmation
      nested  [20] NestedMessageContent,   --Nested Message
      genm    [21] GenMsgContent,          --General Message
      genp    [22] GenRepContent,          --General Response
      error   [23] ErrorMsgContent         --Error Message
  }

  PKIProtection ::= BIT STRING

  ProtectedPart ::= SEQUENCE {
      header    PKIHeader,
      body      PKIBody
  }

  PasswordBasedMac ::= OBJECT IDENTIFIER --{1 2 840 113533 7 66 13}

  PBMParameter ::= SEQUENCE {
      salt                OCTET STRING,
      owf                 AlgorithmIdentifier,
      -- AlgId for a One-Way Function (SHA-1 recommended)
      iterationCount      INTEGER,
      -- number of times the OWF is applied
      mac                 AlgorithmIdentifier
      -- the MAC AlgId (e.g., DES-MAC, Triple-DES-MAC [PKCS11],
  }   -- or HMAC [RFC2104, RFC2202])

  DHBasedMac ::= OBJECT IDENTIFIER --{1 2 840 113533 7 66 30}

  DHBMParameter ::= SEQUENCE {
      owf                 AlgorithmIdentifier,
      -- AlgId for a One-Way Function (SHA-1 recommended)
      mac                 AlgorithmIdentifier
      -- the MAC AlgId (e.g., DES-MAC, Triple-DES-MAC [PKCS11],
  }   -- or HMAC [RFC2104, RFC2202])


  NestedMessageContent ::= PKIMessage

  PKIStatus ::= INTEGER {
      granted                (0),
      -- you got exactly what you asked for
      grantedWithMods        (1),



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      -- you got something like what you asked for; the
      -- requester is responsible for ascertaining the differences
      rejection              (2),
      -- you don't get it, more information elsewhere in the message
      waiting                (3),
      -- the request body part has not yet been processed,
      -- expect to hear more later
      revocationWarning      (4),
      -- this message contains a warning that a revocation is
      -- imminent
      revocationNotification (5),
      -- notification that a revocation has occurred
      keyUpdateWarning       (6)
      -- update already done for the oldCertId specified in
      -- CertReqMsg
  }

  PKIFailureInfo ::= BIT STRING {
  -- since we can fail in more than one way!
  -- More codes may be added in the future if/when required.
      badAlg           (0),
      -- unrecognized or unsupported Algorithm Identifier
      badMessageCheck  (1),
      -- integrity check failed (e.g., signature did not verify)
      badRequest       (2),
      -- transaction not permitted or supported
      badTime          (3),
      -- messageTime was not sufficiently close to the system time,
      -- as defined by local policy
      badCertId        (4),
      -- no certificate could be found matching the provided criteria
      badDataFormat    (5),
      -- the data submitted has the wrong format
      wrongAuthority   (6),
      -- the authority indicated in the request is different from the
      -- one creating the response token
      incorrectData    (7),
      -- the requester's data is incorrect (for notary services)
      missingTimeStamp (8),
      -- when the timestamp is missing but should be there (by policy)
      badPOP           (9)
      -- the proof-of-possession failed
  }

  PKIStatusInfo ::= SEQUENCE {
      status        PKIStatus,
      statusString  PKIFreeText     OPTIONAL,
      failInfo      PKIFailureInfo  OPTIONAL



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  }

  OOBCert ::= Certificate

  OOBCertHash ::= SEQUENCE {
      hashAlg     [0] AlgorithmIdentifier     OPTIONAL,
      certId      [1] CertId                  OPTIONAL,
      hashVal         BIT STRING
      -- hashVal is calculated over DER encoding of the
      -- subjectPublicKey field of the corresponding cert.
  }

  POPODecKeyChallContent ::= SEQUENCE OF Challenge
  -- One Challenge per encryption key certification request (in the
  -- same order as these requests appear in CertReqMessages).

  Challenge ::= SEQUENCE {
      owf                 AlgorithmIdentifier  OPTIONAL,
      -- MUST be present in the first Challenge; MAY be omitted in any
      -- subsequent Challenge in POPODecKeyChallContent (if omitted,
      -- then the owf used in the immediately preceding Challenge is
      -- to be used).
      witness             OCTET STRING,
      -- the result of applying the one-way function (owf) to a
      -- randomly-generated INTEGER, A.  [Note that a different
      -- INTEGER MUST be used for each Challenge.]
      challenge           OCTET STRING
      -- the encryption (under the public key for which the cert.
      -- request is being made) of Rand, where Rand is specified as
      --   Rand ::= SEQUENCE {
      --      int      INTEGER,
      --       - the randomly-generated INTEGER A (above)
      --      sender   GeneralName
      --       - the sender's name (as included in PKIHeader)
      --   }
  }

  POPODecKeyRespContent ::= SEQUENCE OF INTEGER
  -- One INTEGER per encryption key certification request (in the
  -- same order as these requests appear in CertReqMessages).  The
  -- retrieved INTEGER A (above) is returned to the sender of the
  -- corresponding Challenge.


  CertRepMessage ::= SEQUENCE {
      caPubs       [1] SEQUENCE SIZE (1..MAX) OF Certificate OPTIONAL,
      response         SEQUENCE OF CertResponse
  }



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  CertResponse ::= SEQUENCE {
      certReqId           INTEGER,
      -- to match this response with corresponding request (a value
      -- of -1 is to be used if certReqId is not specified in the
      -- corresponding request)
      status              PKIStatusInfo,
      certifiedKeyPair    CertifiedKeyPair    OPTIONAL,
      rspInfo             OCTET STRING        OPTIONAL
      -- analogous to the id-regInfo-asciiPairs OCTET STRING defined
      -- for regInfo in CertReqMsg [CRMF]
  }

  CertifiedKeyPair ::= SEQUENCE {
      certOrEncCert       CertOrEncCert,
      privateKey      [0] EncryptedValue      OPTIONAL,
      publicationInfo [1] PKIPublicationInfo  OPTIONAL
  }

  CertOrEncCert ::= CHOICE {
      certificate     [0] Certificate,
      encryptedCert   [1] EncryptedValue
  }

  KeyRecRepContent ::= SEQUENCE {
      status                  PKIStatusInfo,
      newSigCert          [0] Certificate                   OPTIONAL,
      caCerts             [1] SEQUENCE SIZE (1..MAX) OF
                                          Certificate       OPTIONAL,
      keyPairHist         [2] SEQUENCE SIZE (1..MAX) OF
                                          CertifiedKeyPair  OPTIONAL
  }

  RevReqContent ::= SEQUENCE OF RevDetails

  RevDetails ::= SEQUENCE {
      certDetails         CertTemplate,
      -- allows requester to specify as much as they can about
      -- the cert. for which revocation is requested
      -- (e.g., for cases in which serialNumber is not available)
      revocationReason    ReasonFlags      OPTIONAL,
      -- the reason that revocation is requested
      badSinceDate        GeneralizedTime  OPTIONAL,
      -- indicates best knowledge of sender
      crlEntryDetails     Extensions       OPTIONAL
      -- requested crlEntryExtensions
  }

  RevRepContent ::= SEQUENCE {



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      status       SEQUENCE SIZE (1..MAX) OF PKIStatusInfo,
      -- in same order as was sent in RevReqContent
      revCerts [0] SEQUENCE SIZE (1..MAX) OF CertId OPTIONAL,
      -- IDs for which revocation was requested (same order as status)
      crls     [1] SEQUENCE SIZE (1..MAX) OF CertificateList  OPTIONAL
      -- the resulting CRLs (there may be more than one)
  }


  CAKeyUpdAnnContent ::= SEQUENCE {
      oldWithNew          Certificate, -- old pub signed with new priv
      newWithOld          Certificate, -- new pub signed with old priv
      newWithNew          Certificate  -- new pub signed with new priv
  }

  CertAnnContent ::= Certificate

  RevAnnContent ::= SEQUENCE {
      status              PKIStatus,
      certId              CertId,
      willBeRevokedAt     GeneralizedTime,
      badSinceDate        GeneralizedTime,
      crlDetails          Extensions  OPTIONAL
      -- extra CRL details(e.g., crl number, reason, location, etc.)
}

  CRLAnnContent ::= SEQUENCE OF CertificateList

  PKIConfirmContent ::= NULL

  InfoTypeAndValue ::= SEQUENCE {
      infoType               OBJECT IDENTIFIER,
      infoValue              ANY DEFINED BY infoType  OPTIONAL
  }
  -- Example InfoTypeAndValue contents include, but are not limited to:
  --  { CAProtEncCert    = {id-it 1}, Certificate                     }
  --  { SignKeyPairTypes = {id-it 2}, SEQUENCE OF AlgorithmIdentifier }
  --  { EncKeyPairTypes  = {id-it 3}, SEQUENCE OF AlgorithmIdentifier }
  --  { PreferredSymmAlg = {id-it 4}, AlgorithmIdentifier             }
  --  { CAKeyUpdateInfo  = {id-it 5}, CAKeyUpdAnnContent              }
  --  { CurrentCRL       = {id-it 6}, CertificateList                 }
  -- where {id-it} = {id-pkix 4} = {1 3 6 1 5 5 7 4}
  -- This construct MAY also be used to define new PKIX Certificate
  -- Management Protocol request and response messages, or general-
  -- purpose (e.g., announcement) messages for future needs or for
  -- specific environments.

  GenMsgContent ::= SEQUENCE OF InfoTypeAndValue



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  -- May be sent by EE, RA, or CA (depending on message content).
  -- The OPTIONAL infoValue parameter of InfoTypeAndValue will typically
  -- be omitted for some of the examples given above.  The receiver is
  -- free to ignore any contained OBJ. IDs that it does not recognize.
  -- If sent from EE to CA, the empty set indicates that the CA may send
  -- any/all information that it wishes.

  GenRepContent ::= SEQUENCE OF InfoTypeAndValue
  -- The receiver is free to ignore any contained OBJ. IDs that it does
  -- not recognize.

  ErrorMsgContent ::= SEQUENCE {
      pKIStatusInfo          PKIStatusInfo,
      errorCode              INTEGER           OPTIONAL,
      -- implementation-specific error codes
      errorDetails           PKIFreeText       OPTIONAL
      -- implementation-specific error details
  }



-- The following definition is provided for compatibility reasons with
-- 1988 and 1993 ASN.1 compilers which allow the use of UNIVERSAL class
-- tags (not a part of formal ASN.1); 1997 and subsequent compilers
-- SHOULD comment out this line.

UTF8String ::= [UNIVERSAL 12] IMPLICIT OCTET STRING

END






















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Appendix D: Registration of MIME Type for Section 5

   To: ietf-types@iana.org
   Subject: Registration of MIME media type application/pkixcmp

   MIME media type name: application

   MIME subtype name: pkixcmp

   Required parameters: -

   Optional parameters: -

   Encoding considerations:
   Content may contain arbitrary octet values (the ASN.1 DER encoding of
   a PKI message, as defined in the IETF PKIX Working Group
   specifications).  base64 encoding is required for MIME e-mail; no
   encoding is necessary for HTTP.

   Security considerations:
   This MIME type may be used to transport Public-Key Infrastructure
   (PKI) messages between PKI entities.  These messages are defined by
   the IETF PKIX Working Group and are used to establish and maintain an
   Internet X.509 PKI.  There is no requirement for specific security
   mechanisms to be applied at this level if the PKI messages themselves
   are protected as defined in the PKIX specifications.

   Interoperability considerations: -

   Published specification: this document

   Applications which use this media type:
   Applications using certificate management, operational, or ancillary
   protocols (as defined by the IETF PKIX Working Group) to send PKI
   messages via E-Mail or HTTP.

   Additional information:

     Magic number (s): -
     File extension (s): ".PKI"
     Macintosh File Type Code (s): -

   Person and email address to contact for further information:
   Carlisle Adams, cadams@entrust.com

   Intended usage: COMMON

   Author/Change controller: Carlisle Adams



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Full Copyright Statement

   Copyright (C) The Internet Society (1999).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works.  However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than
   English.

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
























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