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+Network Working Group                                       S. Santesson
+Request for Comments: 4681                                  A. Medvinsky
+Updates: 4346                                                    J. Ball
+Category: Standards Track                                      Microsoft
+                                                            October 2006
+
+
+                       TLS User Mapping Extension
+
+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 (2006).
+
+Abstract
+
+   This document specifies a TLS extension that enables clients to send
+   generic user mapping hints in a supplemental data handshake message
+   defined in RFC 4680.  One such mapping hint is defined in an
+   informative section, the UpnDomainHint, which may be used by a server
+   to locate a user in a directory database.  Other mapping hints may be
+   defined in other documents in the future.
+
+Table of Contents
+
+   1. Introduction ....................................................2
+      1.1. Terminology ................................................2
+      1.2. Design Considerations ......................................2
+   2. User Mapping Extension ..........................................3
+   3. User Mapping Handshake Exchange .................................3
+   4. Message Flow ....................................................5
+   5. Security Considerations .........................................6
+   6. UPN Domain Hint (Informative) ...................................7
+   7. IANA Considerations .............................................8
+   8. Normative References ............................................9
+   9. Acknowledgements ................................................9
+
+
+
+
+
+
+
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+Santesson, et al.           Standards Track                     [Page 1]
+
+RFC 4681               TLS User Mapping Extension           October 2006
+
+
+1.  Introduction
+
+   This document has a normative part and an informative part.  Sections
+   2-5 are normative.  Section 6 is informative.
+
+   This specification defines a TLS extension and a payload for the
+   SupplementalData handshake message, defined in RFC 4680 [N6], to
+   accommodate mapping of users to their user accounts when using TLS
+   client authentication as the authentication method.
+
+   The new TLS extension (user_mapping) is sent in the client hello
+   message.  Per convention defined in RFC 4366 [N4], the server places
+   the same extension (user_mapping) in the server hello message, to
+   inform the client that the server understands this extension.  If the
+   server does not understand the extension, it will respond with a
+   server hello omitting this extension, and the client will proceed as
+   normal, ignoring the extension, and not include the
+   UserMappingDataList data in the TLS handshake.
+
+   If the new extension is understood, the client will inject
+   UserMappingDataList data in the SupplementalData handshake message
+   prior to the Client's Certificate message.  The server will then
+   parse this message, extracting the client's domain, and store it in
+   the context for use when mapping the certificate to the user's
+   directory account.
+
+   No other modifications to the protocol are required.  The messages
+   are detailed in the following sections.
+
+1.1.  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 RFC 2119 [N1].
+
+   The syntax for the TLS User Mapping extension is defined using the
+   TLS Presentation Language, which is specified in Section 4 of [N2].
+
+1.2.  Design Considerations
+
+   The reason the mapping data itself is not placed in the extension
+   portion of the client hello is to prevent broadcasting this
+   information to servers that don't understand the extension.
+
+
+
+
+
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+Santesson, et al.           Standards Track                     [Page 2]
+
+RFC 4681               TLS User Mapping Extension           October 2006
+
+
+2.  User Mapping Extension
+
+   A new extension type (user_mapping(6)) is added to the Extension used
+   in both the client hello and server hello messages.  The extension
+   type is specified as follows.
+
+      enum {
+           user_mapping(6), (65535)
+      } ExtensionType;
+
+   The "extension_data" field of this extension SHALL contain
+   "UserMappingTypeList" with a list of supported hint types where:
+
+      struct {
+            UserMappingType user_mapping_types<1..2^8-1>;
+      } UserMappingTypeList;
+
+   Enumeration of hint types (user_mapping_types) defined in this
+   document is provided in Section 3.
+
+   The list of user_mapping_types included in a client hello SHALL
+   signal the hint types supported by the client.  The list of
+   user_mapping_types included in the server hello SHALL signal the hint
+   types preferred by the server.
+
+   If none of the hint types listed by the client is supported by the
+   server, the server SHALL omit the user_mapping extension in the
+   server hello.
+
+   When the user_mapping extension is included in the server hello, the
+   list of hint types in "UserMappingTypeList" SHALL be either equal to,
+   or a subset of, the list provided by the client.
+
+3.  User Mapping Handshake Exchange
+
+   The underlying structure of the SupplementalData handshake message,
+   used to carry information defined in this section, is defined in RFC
+   4680 [N6].
+
+   A new SupplementalDataType [N6] is defined to accommodate
+   communication of generic user mapping data.  See RFC 2246 (TLS 1.0)
+   [N2] and RFC 4346 (TLS 1.1) [N3] for other handshake types.
+
+   The information in this data type carries one or more unauthenticated
+   hints, UserMappingDataList, inserted by the client side.  Upon
+   receipt and successful completion of the TLS handshake, the server
+
+
+
+
+
+Santesson, et al.           Standards Track                     [Page 3]
+
+RFC 4681               TLS User Mapping Extension           October 2006
+
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+   MAY use this hint to locate the user's account from which user
+   information and credentials MAY be retrieved to support
+   authentication based on the client certificate.
+
+      struct {
+            SupplementalDataType supp_data_type;
+            uint16 supp_data_length;
+            select(SupplementalDataType) {
+               case user_mapping_data: UserMappingDataList;
+               }
+      } SupplementalDataEntry;
+
+      enum {
+            user_mapping_data(0), (65535)
+      } SupplementalDataType;
+
+   The user_mapping_data(0) enumeration results in a new supplemental
+   data type UserMappingDataList with the following structure:
+
+      enum {
+            (255)
+      } UserMappingType;
+
+      struct {
+             UserMappingType user_mapping_version;
+             uint16 user_mapping_length;
+             select(UserMappingType) { }
+      } UserMappingData;
+
+      struct{
+         UserMappingData user_mapping_data_list<1..2^16-1>;
+      }UserMappingDataList;
+
+   user_mapping_length
+      This field is the length (in bytes) of the data selected by
+      UserMappingType.
+
+   The UserMappingData structure contains a single mapping of type
+   UserMappingType.  This structure can be leveraged to define new types
+   of user mapping hints in the future.  The UserMappingDataList MAY
+   carry multiple hints; it is defined as a vector of UserMappingData
+   structures.
+
+   No preference is given to the order in which hints are specified in
+   this vector.  If the client sends more than one hint, then the Server
+   SHOULD use the applicable mapping supported by the server.
+
+
+
+
+
+Santesson, et al.           Standards Track                     [Page 4]
+
+RFC 4681               TLS User Mapping Extension           October 2006
+
+
+   Implementations MAY support the UPN domain hint as specified in
+   Section 6 of this document.  Implementations MAY also support other
+   user mapping types as they are defined.  Definitions of standards-
+   track user mapping types must include a discussion of
+   internationalization considerations.
+
+4.  Message Flow
+
+   In order to negotiate sending user mapping data to a server in
+   accordance with this specification, clients MUST include an extension
+   of type "user_mapping" in the (extended) client hello, which SHALL
+   contain a list of supported hint types.
+
+   Servers that receive an extended client hello containing a
+   "user_mapping" extension MAY indicate that they are willing to accept
+   user mapping data by including an extension of type "user_mapping" in
+   the (extended) server hello, which SHALL contain a list of preferred
+   hint types.
+
+   After negotiation of the use of user mapping has been successfully
+   completed (by exchanging hello messages including "user_mapping"
+   extensions), clients MAY send a "SupplementalData" message containing
+   the "UserMappingDataList" before the "Certificate" message.  The
+   message flow is illustrated in Figure 1 below.
+
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+Santesson, et al.           Standards Track                     [Page 5]
+
+RFC 4681               TLS User Mapping Extension           October 2006
+
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+      Client                                               Server
+
+      ClientHello
+       /* with user_mapping ext */ -------->
+                                                      ServerHello
+                                      /* with user-mapping ext */
+                                                     Certificate*
+                                               ServerKeyExchange*
+                                              CertificateRequest*
+                                   <--------      ServerHelloDone
+
+      SupplementalData
+       /* with UserMappingDataList */
+      Certificate*
+      ClientKeyExchange
+      CertificateVerify*
+      [ChangeCipherSpec]
+      Finished                     -------->
+                                               [ChangeCipherSpec]
+                                   <--------             Finished
+      Application Data             <------->     Application Data
+
+   * Indicates optional or situation-dependent messages that are not
+     always sent according to RFC 2246 [N2] and RFC 4346 [N3].
+
+              Figure 1.  Message Flow with User Mapping Data
+
+   The server MUST expect and gracefully handle the case where the
+   client chooses not to send any supplementalData handshake message
+   even after successful negotiation of extensions.  The client MAY at
+   its own discretion decide that the user mapping hint it initially
+   intended to send no longer is relevant for this session.  One such
+   reason could be that the server certificate fails to meet certain
+   requirements.
+
+5.  Security Considerations
+
+   The user mapping hint sent in the UserMappingDataList is
+   unauthenticated data that MUST NOT be treated as a trusted
+   identifier.  Authentication of the user represented by that user
+   mapping hint MUST rely solely on validation of the client
+   certificate.  One way to do this is to use the user mapping hint to
+   locate and extract a certificate of the claimed user from the trusted
+   directory and subsequently match this certificate against the
+   validated client certificate from the TLS handshake.
+
+
+
+
+
+
+Santesson, et al.           Standards Track                     [Page 6]
+
+RFC 4681               TLS User Mapping Extension           October 2006
+
+
+   As the client is the initiator of this TLS extension, it needs to
+   determine when it is appropriate to send the User Mapping
+   Information.  It may not be prudent to broadcast a user mapping hint
+   to just any server at any time.
+
+   To avoid superfluously sending user mapping hints, clients SHOULD
+   only send this information if it recognizes the server as a
+   legitimate recipient.  Recognition of the server can be done in many
+   ways.  One way to do this could be to recognize the name and address
+   of the server.
+
+   In some cases, the user mapping hint may itself be regarded as
+   sensitive.  In such cases, the double handshake technique described
+   in [N6] can be used to provide protection for the user mapping hint
+   information.
+
+6.  UPN Domain Hint (Informative)
+
+   This specification provides an informative description of one user
+   mapping hint type for Domain Name hints and User Principal Name
+   hints.  Other hint types may be defined in other documents in the
+   future.
+
+   The User Principal Name (UPN) in this hint type represents a name
+   that specifies a user's entry in a directory in the form
+   userName@domainName.  Traditionally, Microsoft has relied on the
+   presence of such a name form to be present in the client certificate
+   when logging on to a domain account.  However, this has several
+   drawbacks since it prevents the use of certificates with an absent
+   UPN and also requires re-issuance of certificates or issuance of
+   multiple certificates to reflect account changes or creation of new
+   accounts.  The TLS extension, in combination with the defined hint
+   type, provides a significant improvement to this situation as it
+   allows a single certificate to be mapped to one or more accounts of
+   the user and does not require the certificate to contain a
+   proprietary UPN.
+
+   The domain_name field MAY be used when only domain information is
+   needed, e.g., where a user have accounts in multiple domains using
+   the same username name, where that user name is known from another
+   source (e.g., from the client certificate).  When the user name is
+   also needed, the user_principal_name field MAY be used to indicate
+   both username and domain name.  If both fields are present, then the
+   server can make use of whichever one it chooses.
+
+      enum {
+             upn_domain_hint(64), (255)
+      } UserMappingType;
+
+
+
+Santesson, et al.           Standards Track                     [Page 7]
+
+RFC 4681               TLS User Mapping Extension           October 2006
+
+
+      struct {
+             opaque user_principal_name<0..2^16-1>;
+             opaque domain_name<0..2^16-1>;
+      } UpnDomainHint;
+
+      struct {
+             UserMappingType user_mapping_version;
+             uint16 user_mapping_length;
+             select(UserMappingType) {
+                   case upn_domain_hint: UpnDomainHint;
+             }
+      } UserMappingData;
+
+   The user_principal_name field, when specified, SHALL be of the form
+   "user@domain", where "user" is a UTF-8 encoded Unicode string that
+   does not contain the "@" character, and "domain" is a domain name
+   meeting the requirements in the following paragraph.
+
+   The domain_name field, when specified, SHALL contain a domain name
+   [N5] in the usual text form; in other words, a sequence of one or
+   more domain labels separated by ".", each domain label starting and
+   ending with an alphanumeric character and possibly also containing
+   "-" characters.  This field is an "IDN-unaware domain name slot" as
+   defined in RFC 3490 [N7], and therefore, domain names containing
+   non-ASCII characters have to be processed as described in RFC 3490
+   before being stored in this field.
+
+   The UpnDomainHint MUST at least contain a non-empty
+   user_principal_name or a non-empty domain_name.  The UpnDomainHint
+   MAY contain both user_principal_name and domain_name.
+
+7.  IANA Considerations
+
+   IANA has taken the following actions:
+
+   1) Created an entry, user_mapping(6), in the existing registry for
+      ExtensionType (defined in RFC 4366 [N4]).
+
+   2) Created an entry, user_mapping_data(0), in the new registry for
+      SupplementalDataType (defined in RFC 4680).
+
+   3) Established a registry for TLS UserMappingType values.  The first
+      entry in the registry is upn_domain_hint(64).  TLS UserMappingType
+      values in the inclusive range 0-63 (decimal) are assigned via RFC
+      2434 [N8] Standards Action.  Values from the inclusive range
+      64-223 (decimal) are assigned via RFC 2434 Specification Required.
+      Values from the inclusive range 224-255 (decimal) are reserved for
+      RFC 2434 Private Use.
+
+
+
+Santesson, et al.           Standards Track                     [Page 8]
+
+RFC 4681               TLS User Mapping Extension           October 2006
+
+
+8.  Normative References
+
+   [N1]   Bradner, S., "Key words for use in RFCs to Indicate
+          Requirement Levels", BCP 14, RFC 2119, March 1997.
+
+   [N2]   Dierks, T. and C. Allen, "The TLS Protocol Version 1.0", RFC
+          2246, January 1999.
+
+   [N3]   Dierks, T. and E. Rescorla, "The Transport Layer Security
+          (TLS) Protocol Version 1.1", RFC 4346, April 2006.
+
+   [N4]   Blake-Wilson, S., Nystrom, M., Hopwood, D., Mikkelsen, J., and
+          T. Wright, "Transport Layer Security (TLS) Extensions", RFC
+          4366, April 2006.
+
+   [N5]   Mockapetris, P., "Domain names - concepts and facilities", STD
+          13, RFC 1034, November 1987.
+
+   [N6]   Santesson, S., "TLS Handshake Message for Supplemental Data",
+          RFC 4680, October 2006.
+
+   [N7]   Faltstrom, P., Hoffman, P., and A. Costello,
+          "Internationalizing Domain Names in Applications (IDNA)", RFC
+          3490, March 2003.
+
+   [N8]   Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
+          Considerations Section in RFCs", BCP 26, RFC 2434, October
+          1998.
+
+9.  Acknowledgements
+
+   The authors extend a special thanks to Russ Housley, Eric Resocorla,
+   and Paul Leach for their substantial contributions.
+
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+Santesson, et al.           Standards Track                     [Page 9]
+
+RFC 4681               TLS User Mapping Extension           October 2006
+
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+Authors' Addresses
+
+   Stefan Santesson
+   Microsoft
+   Finlandsgatan 30
+   164 93 KISTA
+   Sweden
+
+   EMail: stefans@microsoft.com
+
+
+   Ari Medvinsky
+   Microsoft
+   One Microsoft Way
+   Redmond, WA 98052-6399
+   USA
+
+   EMail: arimed@microsoft.com
+
+
+   Joshua Ball
+   Microsoft
+   One Microsoft Way
+   Redmond, WA 98052-6399
+   USA
+
+   EMail: joshball@microsoft.com
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+Santesson, et al.           Standards Track                    [Page 10]
+
+RFC 4681               TLS User Mapping Extension           October 2006
+
+
+Full Copyright Statement
+
+   Copyright (C) The Internet Society (2006).
+
+   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.
+
+   This document and the information contained herein are provided on an
+   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
+   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
+   ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
+   INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
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+
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+
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+Acknowledgement
+
+   Funding for the RFC Editor function is provided by the IETF
+   Administrative Support Activity (IASA).
+
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+Santesson, et al.           Standards Track                    [Page 11]
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