path: root/doc/rfc/rfc3709.txt

Network Working Group                                       S. Santesson
Request for Comments: 3709                                     Microsoft
Category: Standards Track                                     R. Housley
                                                          Vigil Security
                                                              T. Freeman
                                                               Microsoft
                                                           February 2004


               Internet X.509 Public Key Infrastructure:
                    Logotypes in X.509 Certificates

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 (2004).  All Rights Reserved.

Abstract

   This document specifies a certificate extension for including
   logotypes in public key certificates and attribute certificates.























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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  2
       1.1.  Certificate-based Identification . . . . . . . . . . . .  3
       1.2.  Selection of Certificates. . . . . . . . . . . . . . . .  4
       1.3.  Combination of Verification Techniques . . . . . . . . .  5
       1.4.  Terminology. . . . . . . . . . . . . . . . . . . . . . .  6
   2.  Different types of logotypes in Certificates . . . . . . . . .  6
   3.  Logotype Data. . . . . . . . . . . . . . . . . . . . . . . . .  6
   4.  Logotype Extension . . . . . . . . . . . . . . . . . . . . . .  7
       4.1.  Extension Format . . . . . . . . . . . . . . . . . . . .  7
       4.2.  Other Logotypes. . . . . . . . . . . . . . . . . . . . . 11
   5.  Type of Certificates . . . . . . . . . . . . . . . . . . . . . 12
   6.  Use in Clients . . . . . . . . . . . . . . . . . . . . . . . . 12
   7.  Security Considerations. . . . . . . . . . . . . . . . . . . . 13
   8.  IANA Considerations. . . . . . . . . . . . . . . . . . . . . . 15
   9.  Acknowledgments. . . . . . . . . . . . . . . . . . . . . . . . 15
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
       10.1. Normative References . . . . . . . . . . . . . . . . . . 16
       10.2. Informative References . . . . . . . . . . . . . . . . . 16
   A.  ASN.1 Module . . . . . . . . . . . . . . . . . . . . . . . . . 17
   B.  Example Extension. . . . . . . . . . . . . . . . . . . . . . . 19
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 20
   Full Copyright Statement . . . . . . . . . . . . . . . . . . . . . 21

1.  Introduction

   This specification supplements RFC 3280 [PKIX-1], which profiles
   X.509 [X.509] certificates and certificate revocation lists (CRLs)
   for use in the Internet.

   The basic function of a certificate is to bind a public key to the
   identity of an entity (the subject).  From a strictly technical
   viewpoint, this goal could be achieved by signing the identity of the
   subject together with its public key.  However, the art of Public-Key
   Infrastructure (PKI) has developed certificates far beyond this
   functionality in order to meet the needs of modern global networks
   and heterogeneous IT structures.

   Certificate users must be able to determine certificate policies,
   appropriate key usage, assurance level, and name form constraints.
   Before a relying party can make an informed decision whether a
   particular certificate is trustworthy and relevant for its intended
   usage, a certificate may be examined from several different
   perspectives.






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   Systematic processing is necessary to determine whether a particular
   certificate meets the predefined prerequisites for an intended usage.
   Much of the information contained in certificates is appropriate and
   effective for machine processing; however, this information is not
   suitable for a corresponding human trust and recognition process.

   Humans prefer to structure information into categories and symbols.
   Most humans associate complex structures of reality with easily
   recognizable logotypes and marks.  Humans tend to trust things that
   they recognize from previous experiences.  Humans may examine
   information to confirm their initial reaction.  Very few consumers
   actually read all terms and conditions they agree to in accepting a
   service, rather they commonly act on trust derived from previous
   experience and recognition.

   A big part of this process is branding.  Service providers and
   product vendors invest a lot of money and resources into creating a
   strong relation between positive user experiences and easily
   recognizable trademarks, servicemarks, and logotypes.

   Branding is also pervasive in identification instruments, including
   identification cards, passports, driver's licenses, credit cards,
   gasoline cards, and loyalty cards.  Identification instruments are
   intended to identify the holder as a particular person or as a member
   of the community.  The community may represent the subscribers of a
   service or any other group.  Identification instruments, in physical
   form, commonly use logotypes and symbols, solely to enhance human
   recognition and trust in the identification instrument itself.  They
   may also include a registered trademark to allow legal recourse for
   unauthorized duplication.

   Since certificates play an equivalent role in electronic exchanges,
   we examine the inclusion of logotypes in certificates.  We consider
   certificate-based identification and certificate selection.

1.1.  Certificate-based Identification

   The need for human recognition depends on the manner in which
   certificates are used and whether certificates need to be visible to
   human users.  If certificates are to be used in open environments and
   in applications that bring the user in conscious contact with the
   result of a certificate-based identification process, then human
   recognition is highly relevant, and may be a necessity.

   Examples of such applications include:

      -  Web server identification where a user identifies the owner of
         the web site.



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      -  Peer e-mail exchange in B2B, B2C, and private communications.

      -  Exchange of medical records, and system for medical
         prescriptions.

      -  Unstructured e-business applications (i.e., non-EDI
         applications).

      -  Wireless client authenticating to a service provider.

   Most applications provide the human user with an opportunity to view
   the results of a successful certificate-based identification process.
   When the user takes the steps necessary to view these results, the
   user is presented with a view of a certificate.  This solution has
   two major problems.  First, the function to view a certificate is
   often rather hard to find for a non-technical user.  Second, the
   presentation of the certificate is too technical and is not user
   friendly.  It contains no graphic symbols or logotypes to enhance
   human recognition.

   Many investigations have shown that users of today's applications do
   not take the steps necessary to view certificates.  This could be due
   to poor user interfaces.  Further, many applications are structured
   to hide certificates from users.  The application designers do not
   want to expose certificates to users at all.

1.2.  Selection of Certificates

   One situation where software applications must expose human users to
   certificates is when the user must select a single certificate from a
   portfolio of certificates.  In some cases, the software application
   can use information within the certificates to filter the list for
   suitability; however, the user must be queried if more than one
   certificate is suitable.  The human user must select one of them.

   This situation is comparable to a person selecting a suitable plastic
   card from his wallet.  In this situation, substantial assistance is
   provided by card color, location, and branding.

   In order to provide similar support for certificate selection, the
   users need tools to easily recognize and distinguish certificates.
   Introduction of logotypes into certificates provides the necessary
   graphic.








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1.3.  Combination of Verification Techniques

   The use of logotypes will, in many cases, affect the users decision
   to trust and use a certificate.  It is therefore important that there
   be a distinct and clear architectural and functional distinction
   between the processes and objectives of the automated certificate
   verification and human recognition.

   Since logotypes are only aimed for human interpretation and contain
   data that is inappropriate for computer based verification schemes,
   the logotype extension MUST NOT be an active component in automated
   certification path validation.

   Automated certification path verification determines whether the
   end-entity certificate can be verified according to defined policy.
   The algorithm for this verification is specified in RFC 3280
   [PKIX-1].

   The automated processing provides assurance that the certificate is
   valid.  It does not indicate whether the subject is entitled to any
   particular information, or whether the subject ought to be trusted to
   perform a particular service.  These are access control decisions.
   Automatic processing will make some access control decisions, but
   others, depending on the application context, involve the human user.

   In some situations, where automated procedures have failed to
   establish the suitability of the certificate to the task, the human
   user is the final arbitrator of the post certificate verification
   access control decisions.  In the end, the human will decide whether
   or not to accept an executable email attachment, to release personal
   information, or follow the instructions displayed by a web browser.
   This decision will often be based on recognition and previous
   experience.

   The distinction between systematic processing and human processing is
   rather straightforward.  They can be complementary.  While the
   systematic process is focused on certification path construction and
   verification, the human acceptance process is focused on recognition
   and related previous experience.

   There are some situations where systematic processing and human
   processing interfere with each other.  These issues are discussed in
   the Security Considerations section.








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1.4.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in BCP 14, RFC 2119
   [STDWORDS].

2.  Different Types of Logotypes in Certificates

   This specification defines the inclusion of three standard logotype
   types.

     1) Community logotype
     2) Issuer organization logotype
     3) Subject organization logotype

   The community logotype - is the general mark for a community.  It
   identifies a service concept for entity identification and
   certificate issuance.  Many issuers may use a community logotype to
   co-brand with a global community in order to gain global recognition
   of its local service provision.  This type of community branding is
   very common in the credit card business, where local independent card
   issuers include a globally recognized brand (such as VISA and
   MasterCard).

   Issuer organization logotype - is a logotype representing the
   organization identified as part of the issuer name in the
   certificate.

   Subject organization logotype - is a logotype representing the
   organization identified in the subject name in the certificate.

   In addition to the standard logotype types, this specification
   accommodates inclusion of other logotype types where each class of
   logotype is defined by an object identifier.  The object identifier
   can be either locally defined or an identifier defined in section 4.2
   of this document.

3.  Logotype Data

   This specification defines two types of logotype data: image data and
   audio data.  Implementations MUST support image data; however,
   support for audio data is OPTIONAL.

   There is no need to significantly increase the size of the
   certificate by including image and audio data of logotypes.  Rather,
   a URI identifying the location to the logotype data and a one-way
   hash of the referenced data is included in the certificate.



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   Several image files, representing the same image in different
   formats, sizes, and color palates, may represent each logotype image.
   At least one of the image files representing a logotype SHOULD
   contain an image within the size range of 60 pixels wide by 45 pixels
   high, and 200 pixels wide by 150 pixels high.

   Several audio files may further represent the same audio sequence in
   different formats and resolutions.  At least one of the audio files
   representing a logotype SHOULD have a play time between 1 and 30
   seconds.

   If a logotype of a certain type (as defined in section 2) is
   represented by more than one image file, then the image files MUST
   contain variants of roughly the same image.  Likewise, if a logotype
   of a certain type is represented by more than one audio file, then
   the audio files MUST contain variants of the same audio information.
   A spoken message in different languages is considered a variation of
   the same audio information.  Compliant applications MUST NOT display
   more than one of the images and MUST NOT play more than one of the
   audio sequences for any logotype type at the same time.

   A client MAY simultaneously display multiple logotypes of different
   logotype types.  For example, it may display one subject organization
   logotype while also displaying a community logotype, but it MUST NOT
   display multiple image variants of the same community logotype.

   Each logotype present in a certificate MUST be represented by at
   least one image data file.

   Applications SHOULD enhance processing and off-line functionality by
   caching logotype data.

4.  Logotype Extension

   This section specifies the syntax and semantics of the logotype
   extension.

4.1.  Extension Format

   The logotype extension MAY be included in public key certificates
   [PKIX-1] or attribute certificates [PKIX-AC].  The logotype extension
   MUST be identified by the following object identifier:

      id-pe-logotype  OBJECT IDENTIFIER  ::=
         { iso(1) identified-organization(3) dod(6) internet(1)
           security(5) mechanisms(5) pkix(7) id-pe(1) 12 }

   This extension MUST NOT be marked critical.



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   Logotype data may be referenced through either direct or indirect
   addressing.  Clients MUST support both direct and indirect
   addressing.  Certificate issuing applications MUST support direct
   addressing, and certificate issuing applications SHOULD support
   indirect addressing.

   The direct addressing includes information about each logotype in the
   certificate, and URIs point to the image and audio data files.
   Direct addressing supports cases where just one or a few alternative
   images and audio files are referenced.

   The indirect addressing includes one reference to an external hashed
   data structure that contains information on the type, content, and
   location of each image and audio file.  Indirect addressing supports
   cases where each logotype is represented by many alternative audio or
   image files.

   Both direct and indirect addressing accommodate alternative URIs to
   obtain exactly the same item.  This opportunity for replication is
   intended to improve availability.  Therefore, if a client is unable
   to fetch the item from one URI, the client SHOULD try another URI in
   the sequence.  All URIs MUST use either the  HTTP scheme (http://...)
   or the FTP scheme (ftp://...) [URI].  At least one URI in each
   sequence MUST use the HTTP scheme.  Clients MUST support retrieval of
   referenced LogoTypeData with HTTP/1.1 [HTTP/1.1].  Clients MAY
   support retrieval using FTP [FTP].

   The logotype extension MUST have the following syntax:

LogotypeExtn ::= SEQUENCE {
   communityLogos  [0] EXPLICIT SEQUENCE OF LogotypeInfo OPTIONAL,
   issuerLogo      [1] EXPLICIT LogotypeInfo OPTIONAL,
   subjectLogo     [2] EXPLICIT LogotypeInfo OPTIONAL,
   otherLogos      [3] EXPLICIT SEQUENCE OF OtherLogotypeInfo OPTIONAL }

LogotypeInfo ::= CHOICE {
   direct          [0] LogotypeData,
   indirect        [1] LogotypeReference }

LogotypeData ::= SEQUENCE {
   image           SEQUENCE OF LogotypeImage OPTIONAL,
   audio           [1] SEQUENCE OF LogotypeAudio OPTIONAL }

LogotypeImage ::= SEQUENCE {
   imageDetails    LogotypeDetails,
   imageInfo       LogotypeImageInfo OPTIONAL }





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LogotypeAudio ::= SEQUENCE {
   audioDetails    LogotypeDetails,
   audioInfo       LogotypeAudioInfo OPTIONAL }

LogotypeDetails ::= SEQUENCE {
   mediaType       IA5String, -- MIME media type name and optional
                              -- parameters
   logotypeHash    SEQUENCE SIZE (1..MAX) OF HashAlgAndValue,
   logotypeURI     SEQUENCE SIZE (1..MAX) OF IA5String }

LogotypeImageInfo ::= SEQUENCE {
   type            [0] LogotypeImageType DEFAULT color,
   fileSize        INTEGER,  -- In octets
   xSize           INTEGER,  -- Horizontal size in pixels
   ySize           INTEGER,  -- Vertical size in pixels
   resolution      LogotypeImageResolution OPTIONAL,
   language        [4] IA5String OPTIONAL }  -- RFC 3066 Language Tag

LogotypeImageType ::= INTEGER { grayScale(0), color(1) }

LogotypeImageResolution ::= CHOICE {
   numBits         [1] INTEGER,   -- Resolution in bits
   tableSize       [2] INTEGER }  -- Number of colors or grey tones

LogotypeAudioInfo ::= SEQUENCE {
   fileSize        INTEGER,  -- In octets
   playTime        INTEGER,  -- In milliseconds
   channels        INTEGER,  -- 1=mono, 2=stereo, 4=quad
   sampleRate      [3] INTEGER OPTIONAL,  -- Samples per second
   language        [4] IA5String OPTIONAL }  -- RFC 3066 Language Tag

OtherLogotypeInfo ::= SEQUENCE {
   logotypeType    OBJECT IDENTIFIER,
   info            LogotypeInfo }

LogotypeReference ::= SEQUENCE {
   refStructHash   SEQUENCE SIZE (1..MAX) OF HashAlgAndValue,
   refStructURI    SEQUENCE SIZE (1..MAX) OF IA5String }
                    -- Places to get the same "LTD" file

HashAlgAndValue ::= SEQUENCE {
   hashAlg         AlgorithmIdentifier,
   hashValue       OCTET STRING }

   When using indirect addressing, the URI (refStructURI) pointing to
   the external data structure MUST point to a binary file containing
   the DER encoded data with the syntax LogotypeData.  The referenced
   file name SHOULD include a file extension of "LTD".



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   At least one of the optional elements in the LogotypeExtn structure
   MUST be present.  Avoid the use of otherLogos whenever possible.

   The LogotypeReference and LogotypeDetails structures explicitly
   identify one or more one-way hash functions employed to authenticate
   referenced data files.  Clients MUST support the SHA-1 [SHS] one-way
   hash function, and clients MAY support other one-way hash functions.
   CAs MUST include a SHA-1 hash value for each referenced file,
   calculated on the whole file, and CAs MAY include other one-way hash
   values.  Clients MUST compute a one-way hash value using one of the
   identified functions, and clients MUST discard the logotype data if
   the computed one-way hash function value does not match the one-way
   hash function value in the certificate extension.

   A MIME type is used to specify the format of the file containing the
   logotype data.  Implementations MUST support both the JPEG and GIF
   image formats (with MIME types of "image/jpeg" and "image/gif"
   [MEDIA], respectively).  Animated images SHOULD NOT be used.
   Implementations that support audio MUST support the MP3 audio format
   (with a MIME type of "audio/mpeg" [AUDIO/MPEG]).  MIME types MAY
   include parameters.

   When language is specified, the language tag MUST use the RFC 3066
   [LANGCODES] syntax.

   Logotype types defined in this specification are:

      Community Logotype:  If communityLogos is present, the logotypes
      MUST represent one or more communities with which the certificate
      issuer is affiliated.  The communityLogos MAY be present in an end
      entity certificate, a CA certificate, or an attribute certificate.
      The communityLogos contains a sequence of Community Logotypes,
      each representing a different community.  If more than one
      Community logotype is present, they MUST be placed in order of
      preferred appearance.  Some clients MAY choose to display a subset
      of the present community logos; therefore the placement within the
      sequence aids the client selection.  The most preferred logotype
      MUST be first in the sequence, and the least preferred logotype
      MUST be last in the sequence.

      Issuer Organization Logotype:  If issuerLogo is present, the
      logotype MUST represent the issuer's organization.  The logotype
      MUST be consistent with, and require the presence of, an
      organization name stored in the organization attribute in the
      issuer field (for either a public key certificate or attribute
      certificate).  The issuerLogo MAY be present in an end entity
      certificate, a CA certificate, or an attribute certificate.




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      Subject Organization Logotype:  If subjectLogo is present, the
      logotype MUST represent the subject's organization.  The logotype
      MUST be consistent with, and require the presence of, an
      organization name stored in the organization attribute in the
      subject field (for either a public key certificate or attribute
      certificate).  The subjectLogo MAY be present in an end entity
      certificate, a CA certificate, or an attribute certificate.

   The relationship between the subject organization and the subject
   organization logotype, and the relationship between the issuer and
   either the issuer organization logotype or the community logotype,
   are relationships asserted by the issuer.  The policies and practices
   employed by the issuer to check subject organization logotypes or
   claims its issuer and community logotypes is outside the scope of
   this document.

4.2.  Other Logotypes

   Logotypes identified by otherLogos (as defined in 4.1) can be used to
   enhance the display of logotypes and marks that represent partners,
   products, services, or any other characteristic associated with the
   certificate or its intended application environment when the standard
   logotype types are insufficient.

   The conditions and contexts of the intended use of these logotypes
   are defined at the discretion of the local client application.

   The following other logotype types are defined in this document:

         -  Loyalty logotype
         -  Certificate Background logotype

   OID Definitions:

         id-logo OBJECT IDENTIFIER ::= { id-pkix 20 }

         id-logo-loyalty    OBJECT IDENTIFIER ::= { id-logo 1 }

         id-logo-background OBJECT IDENTIFIER ::= { id-logo 2 }

   A loyalty logotype, if present, MUST contain a logotype associated
   with a loyalty program related to the certificate or its use.  The
   relation between the certificate and the identified loyalty program
   is beyond the scope of this document.  The logotype extension MAY
   contain more than one Loyalty logotype.






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   The certificate background logotype, if present, MUST contain a
   graphical image intended as a background image for the certificate,
   and/or a general audio sequence for the certificate.  The background
   image MUST allow black text to be clearly read when placed on top of
   the background image.  The logotype extension MUST NOT contain more
   than one certificate background logotype.

5.  Type of Certificates

   Logotypes MAY be included in public key certificates and attribute
   certificates at the discretion of the certificate issuer; however,
   logotypes MUST NOT be part of certification path validation or any
   type of automated processing.  The sole purpose of logotypes is to
   enhance the display of a particular certificate, regardless of its
   position in a certification path.

6.  Use in Clients

   All PKI implementations require relying party software to have some
   mechanism to determine whether a trusted CA issues a particular
   certificate.  This is an issue for certification path validation,
   including consistent policy and name checking.

   After a certification path is successfully validated, the replying
   party trusts the information that the CA includes in the certificate,
   including any certificate extensions.  The client software can choose
   to make use of such information, or the client software can ignore
   it.  If the client is unable to support a provided logotype, the
   client MUST NOT report an error, rather the client MUST behave as
   though no logotype extension was included in the certificate.
   Current standards do not provide any mechanism for cross-certifying
   CAs to constrain subordinate CAs from including private extensions
   (see the security considerations section).

   Consequently, if relying party software accepts a CA, then it should
   be prepared to (unquestioningly) display the associated logotypes to
   its human user, given that it is configured to do so.  Information
   about the logotypes is provided so that the replying party software
   can select the one that will best meet the needs of the human user.
   This choice depends on the abilities of the human user, as well as
   the capabilities of the platform on which the replaying party
   software is running.  If none of the provided logotypes meets the
   needs of the human user or matches the capabilities of the platform,
   then the logotypes can be ignored.

   A client MAY, subject to local policy, choose to display none, one,
   or any number of the logotypes in the logotype extension.




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   In many cases, a client will be used in an environment with a good
   network connection and also used in an environment with little or no
   network connectivity.  For example, a laptop computer can be docked
   with a high-speed LAN connection, or it can be disconnected from the
   network altogether.  In recognition of this situation, the client
   MUST include the ability to disable the fetching of logotypes.
   However, locally cached logotypes can still be displayed when the
   user disables the fetching of additional logotypes.

   A client MAY, subject to local policy, choose any combination of
   audio and image presentation for each logotype.  That is, the client
   MAY display an image with or without playing a sound, and it MAY play
   a sound with or without displaying an image.  A client MUST NOT play
   more than one logotype audio sequence at the same time.

   The logotype is to be displayed in conjunction with other identity
   information contained in the certificate.  The logotype is not a
   replacement for this identity information.

   Care is needed when designing replying party software to ensure that
   an appropriate context of logotype information is provided.  This is
   especially difficult with audio logotypes.  It is important that the
   human user be able to recognize the context of the logotype, even if
   other audio streams are being played.

   If the relying party software is unable to successfully validate a
   particular certificate, then it MUST NOT display any logotype data
   associated with that certificate.

7.  Security Considerations

   Implementations that simultaneously display multiple logotype types
   (subject organization, issuer, community or other), MUST ensure that
   there is no ambiguity as to the binding between the image and the
   type of logotype that the image represents.  "Logotype type" is
   defined in section 2, and it refers to the type of entity or
   affiliation represented by the logotype, not the type of binary
   format.

   Logotypes are very difficult to securely and accurately define.
   Names are also difficult in this regard, but logotypes are even
   worse.  It is quite difficult to specify what is, and what is not, a
   legitimate logotype of an organization.  There is an entire legal
   structure around this issue, and it will not be repeated here.
   However, issuers should be aware of the implications of including
   images associated with a trademark or servicemark before doing so.





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   As logotypes can be difficult (and sometimes expensive) to verify,
   the possibility of errors related to assigning wrong logotypes to
   organizations is increased.

   This is not a new issue for electronic identification instruments.
   It is already dealt with in a number of similar situations in the
   physical world, including physical employee identification cards.
   Secondly, there are situations where identification of logotypes is
   rather simple and straightforward, such as logotypes for well-known
   industries and institutes.  These issues should not stop those
   service providers who want to issue logotypes from doing so, where
   relevant.

   It is impossible to prevent fraudulent creation of certificates by
   dishonest or badly performing issuers, containing names and logotypes
   that the issuer has no claim to or has failed to check correctly.
   Such certificates could be created in an attempt to socially engineer
   a user into accepting a certificate.  The premise used for the
   logotype work is thus that logotype graphics in a certificate are
   trusted only if the certificate is successfully validated within a
   valid path.  It is thus imperative that the representation of any
   certificate that fails to validate is not enhanced in any way by
   using the logotype graphic.

   Logotype data is fetched from a server when it is needed.  By
   watching activity on the network, an observer can determine which
   clients are making use of certificates that contain particular
   logotype data.  This observation can potentially introduce privacy
   issues.  Since clients are expected to locally cache logotype data,
   network traffic to the server containing the logotype data will not
   be generated every time the certificate is used.  In cases where
   logotype data is not cashed, monitoring would reveal usage frequency.
   In cases where logotype data is cached, monitoring would reveal when
   a certain logotype image or audio sequence is used for the first
   time.

   Certification paths may also impose name constraints that are
   systematically checked during certification path processing, which,
   in theory, may be circumvented by logotypes.

   Certificate path processing as defined in RFC 3280 [PKIX-1] does not
   constrain the inclusion of logotype data in certificates.  A parent
   CA can constrain certification path validation such that subordinate
   CAs cannot issue valid certificates to end-entities outside a limited
   name space or outside specific certificate polices.  A malicious CA
   can comply with these name and policy requirements and still include
   inappropriate logotypes in the certificates that it issues.  These
   certificates will pass the certification path validation algorithm,



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   which means the client will trust the logotypes in the certificates.
   Since there is no technical mechanism to prevent or control
   subordinate CAs from including the logotype extension or its
   contents, where appropriate, a parent CA could employ a legal
   agreement to impose a suitable restriction on the subordinate CA.
   This situation is not unique to the logotype extension.

   The controls available to a parent CA to protect itself from rogue
   subordinate CAs are non-technical.  They include:

      -  Contractual agreements of suitable behavior, including terms of
         liability in case of material breach.

      -  Control mechanisms and procedures to monitor and follow-up
         behavior of subordinate CAs.

      -  Use of certificate policies to declare an assurance level of
         logotype data, as well as to guide applications on how to treat
         and display logotypes.

      -  Use of revocation functions to revoke any misbehaving CA.

   There is not a simple, straightforward, and absolute technical
   solution.  Rather, involved parties must settle some aspects of PKI
   outside the scope of technical controls.  As such, issuers need to
   clearly identify and communicate the associated risks.

8.  IANA Considerations

   Certificate extensions and attribute certificate extensions are
   identified by object identifiers (OIDs).  The OID for the extension
   defined in this document was assigned from an arc delegated by the
   IANA to the PKIX Working Group.  No further action by the IANA is
   necessary for this document or any anticipated updates.

9.  Acknowledgments

   This document is the result of contributions from many professionals.
   The authors appreciate contributions from all members of the IETF
   PKIX Working Group.  We extend a special thanks to Al Arsenault,
   David Cross, Tim Polk, Russel Weiser, Terry Hayes, Alex Deacon,
   Andrew Hoag, Randy Sabett, Denis Pinkas, Magnus Nystrom, Ryan Hurst,
   and Phil Griffin for their efforts and support.

   Russ Housley thanks the management at RSA Laboratories, especially
   Burt Kaliski, who supported the development of this specification.
   The vast majority of the work on this specification was done while
   Russ was employed at RSA Laboratories.



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10.  References

10.1.  Normative References

   [LANGCODES]  Alvestrand, H., "Tags for Identification of Languages",
                BCP 47, RFC 3066, January 2001.

   [PKIX-1]     Housley, R., Polk, W., Ford, W. and D. Solo, "Internet
                X.509 Public Key Infrastructure: Certificate and
                Certificate Revocation List (CRL) Profile", RFC 3280,
                April 2002.

   [PKIX-AC]    Farrell, S. and R. Housley, "An Internet Attribute
                Certificate Profile for Authorization", RFC 3281, April
                2002.

   [SHS]        Federal Information Processing Standards Publication
                (FIPS PUB) 180-1, Secure Hash Standard, 17 April 1995.
                [Supersedes FIPS PUB 180 dated 11 May 1993.]

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

   [HTTP/1.1]   Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
                Masinter, L., Leach P. and T. Berners-Lee, "Hypertext
                Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.

   [FTP]        Postel, J. and J. Reynolds, "File Transfer Protocol",
                STD 9, RFC 959, October 1985.

   [URI]        Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform
                Resource Identifiers (URI): Generic Syntax", RFC 2396,
                August 1998.

   [MEDIA]      Freed, N. and N. Borenstein, "Multipurpose Internet Mail
                Extensions (MIME) Part Two: Media Types", RFC 2046,
                November 1996.

   [AUDIO/MPEG] Nilsson, M., "The audio/mpeg Media Type", RFC 3003,
                November 2000.

10.2.  Informative References

   [X.509]      ITU-T Recommendation X.509 (2000) | ISO/IEC 9594-8:2001,
                Information technology - Open Systems Interconnection -
                The Directory: Public-key and attribute certificate
                frameworks




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APPENDIX A.  ASN.1 Module

LogotypeCertExtn
  { iso(1) identified-organization(3) dod(6) internet(1)
    security(5) mechanisms(5) pkix(7) id-mod(0)
    id-mod-logotype(22) }

DEFINITIONS IMPLICIT TAGS ::=
BEGIN

IMPORTS
   AlgorithmIdentifier FROM PKIX1Explicit88 -- RFC 3280
     { iso(1) identified-organization(3) dod(6) internet(1)
       security(5) mechanisms(5) pkix(7) id-mod(0)
       id-pkix1-explicit(18) };


-- Logotype Extension OID

id-pe-logotype  OBJECT IDENTIFIER  ::=
   { iso(1) identified-organization(3) dod(6) internet(1)
     security(5) mechanisms(5) pkix(7) id-pe(1) 12 }


-- Logotype Extension Syntax

LogotypeExtn ::= SEQUENCE {
   communityLogos  [0] EXPLICIT SEQUENCE OF LogotypeInfo OPTIONAL,
   issuerLogo      [1] EXPLICIT LogotypeInfo OPTIONAL,
   subjectLogo     [2] EXPLICIT LogotypeInfo OPTIONAL,
   otherLogos      [3] EXPLICIT SEQUENCE OF OtherLogotypeInfo OPTIONAL }

LogotypeInfo ::= CHOICE {
   direct          [0] LogotypeData,
   indirect        [1] LogotypeReference }

LogotypeData ::= SEQUENCE {
   image           SEQUENCE OF LogotypeImage OPTIONAL,
   audio           [1] SEQUENCE OF LogotypeAudio OPTIONAL }

LogotypeImage ::= SEQUENCE {
   imageDetails    LogotypeDetails,
   imageInfo       LogotypeImageInfo OPTIONAL }

LogotypeAudio ::= SEQUENCE {
   audioDetails    LogotypeDetails,
   audioInfo       LogotypeAudioInfo OPTIONAL }




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LogotypeDetails ::= SEQUENCE {
   mediaType       IA5String, -- MIME media type name and optional
                              -- parameters
   logotypeHash    SEQUENCE SIZE (1..MAX) OF HashAlgAndValue,
   logotypeURI     SEQUENCE SIZE (1..MAX) OF IA5String }

LogotypeImageInfo ::= SEQUENCE {
   type            [0] LogotypeImageType DEFAULT color,
   fileSize        INTEGER,  -- In octets
   xSize           INTEGER,  -- Horizontal size in pixels
   ySize           INTEGER,  -- Vertical size in pixels
   resolution      LogotypeImageResolution OPTIONAL,
   language        [4] IA5String OPTIONAL }  -- RFC 3066 Language Tag

LogotypeImageType ::= INTEGER { grayScale(0), color(1) }

LogotypeImageResolution ::= CHOICE {
   numBits         [1] INTEGER,   -- Resolution in bits
   tableSize       [2] INTEGER }  -- Number of colors or grey tones

LogotypeAudioInfo ::= SEQUENCE {
   fileSize        INTEGER,  -- In octets
   playTime        INTEGER,  -- In milliseconds
   channels        INTEGER,  -- 1=mono, 2=stereo, 4=quad
   sampleRate      [3] INTEGER OPTIONAL,  -- Samples per second
   language        [4] IA5String OPTIONAL }  -- RFC 3066 Language Tag

OtherLogotypeInfo ::= SEQUENCE {
   logotypeType    OBJECT IDENTIFIER,
   info            LogotypeInfo }

LogotypeReference ::= SEQUENCE {
   refStructHash   SEQUENCE SIZE (1..MAX) OF HashAlgAndValue,
   refStructURI    SEQUENCE SIZE (1..MAX) OF IA5String }
                      -- Places to get the same "LTD" file

-- Note: The content of referenced "LTD" files is defined by the
--       LogotypeData type

HashAlgAndValue ::= SEQUENCE {
   hashAlg         AlgorithmIdentifier,
   hashValue       OCTET STRING }

-- Other logotype type OIDs

id-logo OBJECT IDENTIFIER ::= { iso(1) identified-organization(3)
   dod(6) internet(1) security(5) mechanisms(5) pkix(7) 20 }




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id-logo-loyalty    OBJECT IDENTIFIER ::= { id-logo 1 }

id-logo-background OBJECT IDENTIFIER ::= { id-logo 2 }


END

APPENDIX B.  Example Extension

   The following example displays a logotype extension containing one
   Issuer logotype using direct addressing.  The issuer logotype image
   is of the type image/gif.  The logotype image file is referenced
   through 1 URI and the image is hashed by one sha1 hash value.

   The values on the left are the ASN.1 tag and length, in hexadecimal.

30  106: SEQUENCE {
06    8:   OBJECT IDENTIFIER '1 3 6 1 5 5 7 1 12'
04   94:   OCTET STRING, encapsulates {
30   92:     SEQUENCE {
A1   90:       [1] {
A0   88:         [0] {
30   86:           SEQUENCE {
30   84:             SEQUENCE {
30   82:               SEQUENCE {
16    9:                 IA5String 'image/gif'
30   33:                 SEQUENCE {
30   31:                   SEQUENCE {
30    7:                     SEQUENCE {
06    5:                       OBJECT IDENTIFIER sha1 (1 3 14 3 2 26)
       :                       }
04   20:                     OCTET STRING
       :           8F E5 D3 1A 86 AC 8D 8E 6B C3 CF 80 6A D4 48 18
       :           2C 7B 19 2E
       :                     }
       :                   }
30   34:                 SEQUENCE {
16   32:                   IA5String 'http://logo.example.com/logo.gif'
       :                   }
       :                 }
       :               }
       :             }
       :           }
       :         }
       :       }
       :     }
       :   }




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Authors' Addresses

   Stefan Santesson
   Microsoft Denmark
   Tuborg Boulevard 12
   DK-2900 Hellerup
   Denmark

   EMail: stefans@microsoft.com


   Russell Housley
   Vigil Security, LLC
   918 Spring Knoll Drive
   Herndon, VA 20170
   USA

   EMail: housley@vigilsec.com


   Trevor Freeman
   Microsoft Corporation
   One Microsoft Way
   Redmond WA 98052
   USA

   EMail: trevorf@microsoft.com
























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Full Copyright Statement

   Copyright (C) The Internet Society (2004).  This document is subject
   to the rights, licenses and restrictions contained in BCP 78 and
   except as set forth therein, the authors retain all their rights.

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Acknowledgement

   Funding for the RFC Editor function is currently provided by the
   Internet Society.









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