[Docs] [txt|pdf|xml|html] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits]

Versions: 00 01 03 04 05 06 07 08 RFC 5924

SIP WG                                                       S. Lawrence
Internet-Draft                                     Nortel Networks, Inc.
Intended status:  Standards Track                             V. Gurbani
Expires:  April 9, 2009                Bell Laboratories, Alcatel-Lucent
                                                        October 06, 2008


  Using Extended Key Usage (EKU) for Session Initiation Protocol (SIP)
                           X.509 Certificates
                         draft-ietf-sip-eku-03

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
   have been or will be disclosed, and any of which he or she becomes
   aware will be disclosed, in accordance with Section 6 of BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt.

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on April 9, 2009.

Copyright Notice

   Copyright (C) The IETF Trust (2008).

Abstract

   This memo documents an extended key usage (EKU) X.509 certificate
   extension for identifying the holder of a certificate as
   authoritative for a Session Initiation Protocol (SIP) service in the
   domain named by the DNS name in the certificate.





Lawrence & Gurbani        Expires April 9, 2009                 [Page 1]


Internet-Draft                   SIP EKU                    October 2008


Table of Contents

   1.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Key Words  . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.2.  Abstract syntax notation . . . . . . . . . . . . . . . . .  3
   2.  Problem statement  . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Restricting usage to SIP . . . . . . . . . . . . . . . . . . .  4
     3.1.  Extended Key Usage values for SIP domains  . . . . . . . .  4
   4.  Using the SIP EKU in a certificate . . . . . . . . . . . . . .  5
   5.  Implications for a Certification Authority . . . . . . . . . .  6
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . .  6
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  6
   8.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . .  6
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . .  7
     9.1.  Normative References . . . . . . . . . . . . . . . . . . .  7
     9.2.  Informative References . . . . . . . . . . . . . . . . . .  7
   Appendix A.  ASN.1 Module  . . . . . . . . . . . . . . . . . . . .  8
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . .  8
   Intellectual Property and Copyright Statements . . . . . . . . . . 10
































Lawrence & Gurbani        Expires April 9, 2009                 [Page 2]


Internet-Draft                   SIP EKU                    October 2008


1.  Terminology

1.1.  Key Words

   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 [1].

1.2.  Abstract syntax notation

   All X.509 certificate X.509 [4] extensions are defined using ASN.1
   X.680 [5],X.690 [6].


2.  Problem statement

   Consider the SIP RFC 3261 [2] trapezoid shown in Figure 1.



     Proxy-A.example.com           Proxy-B.example.net
        +-------+                    +-------+
        | Proxy |--------------------| Proxy |
        +----+--+                    +---+---+
             |                           |
             |                           |
             |                           |
             |                         +---+
           0---0                       |   |
            /-\                        |___|
           +---+                      /    /
                                     +----+
      alice@example.com          bob@example.net


                          Figure 1: SIP Trapezoid

   Assume that alice@example.com creates an INVITE for bob@example.net;
   her user agent routes the request to some proxy in her domain,
   example.com.  Suppose also that example.com is a large organization
   that maintains several SIP proxies, and her INVITE arrived at an
   outbound proxy Proxy-A.example.com.  In order to route the request
   onward, Proxy-A uses RFC 3263 [7] resolution and finds that Proxy-
   B.example.net is a valid proxy for example.net that uses TLS.  Proxy-
   A.example.com requests a TLS connection to Proxy-B.example.net, and
   in the TLS handshake each presents a certificate to authenticate that
   connection.  The validation of these certificates by each proxy to
   determine whether or not their peer is authoritative for the



Lawrence & Gurbani        Expires April 9, 2009                 [Page 3]


Internet-Draft                   SIP EKU                    October 2008


   appropriate SIP domain is defined in Domain Certificates in the
   Session Initiation Protocol (SIP) [8].

   A SIP domain name is frequently textually identical to the same DNS
   name used for other purposes.  For example, the DNS name example.com
   can serve as a SIP domain name, an email domain name, and a web
   service name.  Since these different services within a single
   organization might be administered independently and hosted
   separately, it is desirable that a certificate be able to bind the
   DNS name to its usage as a SIP domain name without creating the
   implication that the entity presenting the certificate is also
   authoritative for some other purpose.  A mechanism is needed to allow
   the certificate issued to a proxy to be restricted such that the
   subject name(s) it contains are valid only for use in SIP.  In our
   example, Proxy-B possesses a certificate making it authoritative as a
   SIP server for the domain example.net; furthermore, it has a policy
   that requires the client's SIP domain be authenticated through a
   similar certificate.  Proxy-A is authoritative as a SIP server for
   the domain example.com; when Proxy-A makes a TLS connection to
   Proxy-B, the latter accepts the connection based on its policy.


3.  Restricting usage to SIP

   This memo defines a certificate profile for restricting the usage of
   a domain name binding to usage as a SIP domain name.  RFC 5280 [3]
   Section 4.2.1.12 defines a mechanism for this purpose:  an "Extended
   Key Usage" (EKU) attribute, where the purpose of the EKU extension is
   described as:

      "If the extension is present, then the certificate MUST only be
      used for one of the purposes indicated.  If multiple purposes are
      indicated the application need not recognize all purposes
      indicated, as long as the intended purpose is present.
      Certificate using applications MAY require that the extended key
      usage extension be present and that a particular purpose be
      indicated in order for the certificate to be acceptable to that
      application."

   A certificate whose purpose is to bind a SIP domain identity without
   binding other non-SIP identities MUST include an id-kp-SIPdomain
   attribute in the Extended Key Usage extension value (see
   Section 3.1).

3.1.  Extended Key Usage values for SIP domains

   RFC 5280 [3] specifies the EKU X.509 certificate Extension for use in
   the Internet.  The extension indicates one or more purposes for which



Lawrence & Gurbani        Expires April 9, 2009                 [Page 4]


Internet-Draft                   SIP EKU                    October 2008


   the certified public key is valid.  The EKU extension can be used in
   conjunction with the key usage extension, which indicates how the
   public key in the certificate may be used, in a more basic
   cryptographic way.

   The EKU extension syntax is repeated here for convenience:

         ExtKeyUsageSyntax  ::=  SEQUENCE SIZE (1..MAX) OF KeyPurposeId

         KeyPurposeId  ::=  OBJECT IDENTIFIER

   This specification defines the KeyPurposeId id-kp-sipDomain.
   Inclusion of this KeyPurposeId in a certificate indicates that the
   use of any Subject names in the certificate is restricted to use by a
   SIP service (along with any usages allowed by other EKU values).

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

         id-kp-sipDomain  OBJECT IDENTIFIER  ::=  { id-kp 20 }


4.  Using the SIP EKU in a certificate

   Section 7.1 of Domain Certificates in the Session Initiation Protocol
   [8] contains the steps for finding an identity (or a set of
   identities) in an X.509 certificate for SIP.  In order to determine
   whether the usage of a certificate is restricted, implementations
   MUST perform the step given below as a part of the certificate
   validation:

   The Extended Key Usage value(s), if any, MUST be examined:

   o  If the certificate does not contain any EKU values (the Extended
      Key Usage extension does not exist), it is a matter of local
      policy whether or not to accept the certificate for use as a SIP
      certificate.

   o  If the certificate contains the id-kp-sipDomain EKU extension,
      then the certificate MUST be accepted as valid for use as a SIP
      certificate.

   o  If the certificate does not contain the id-kp-sipDomain EKU value,
      but does contain the id-kp-anyExtendedKeyUsage EKU value, it is a
      matter of local policy whether or not to accept it for use as a
      SIP certificate.




Lawrence & Gurbani        Expires April 9, 2009                 [Page 5]


Internet-Draft                   SIP EKU                    October 2008


   o  If the certificate does not contain the id-kp-sipDomain EKU value,
      but does contain either the id-kp-serverAuth or id-kp-clientAuth
      EKU values, it is a matter of local policy whether or not to
      accept it for use as a SIP certificate.

         id-kp-serverAuth and id-kp-clientAuth EKU values are defined in
         Section 4.2.1.12 of RFC 5280 [3].

   o  If EKU extension exists but does not contain any of the id-kp-
      sipDomain, id-kp-anyExtendedKeyUsage, id-kp-serverAuth, or id-kp-
      clientAuth EKU values, then the certificate MUST NOT be accepted
      as valid for use as a SIP certificate.


5.  Implications for a Certification Authority

   The procedures and practices employed by a certification authority
   MUST ensure that the correct values for the EKU extension and
   subjectAltName are inserted in each certificate that is issued.  For
   certificates that indicate authority over a SIP domain, but not over
   services other than SIP, certificate authorities MUST include the id-
   kp-sipDomain EKU extension.


6.  Security Considerations

   This memo defines an EKU X.509 certificate extension that restricts
   the the usage of a certificate to a SIP service belonging to an
   autonomous domain.  Relying parties may execute applicable policies
   (such as those related to billing) on receiving a certificate with
   the id-kp-sipDomain EKU value.  An id-kp-sipDomain EKU value does not
   introduce any new security or privacy concerns.


7.  IANA Considerations

   The id-kp-sipDomain purpose requires an object identifier (OID).  The
   objects are defined in an arc delegated by IANA to the PKIX working
   group.  No further action is necessary by IANA.


8.  Acknowledgments

   The following IETF contributors provided substantive input to this
   document:  Jeroen van Bemmel, Michael Hammer, Cullen Jennings, Paul
   Kyzivat, Derek MacDonald, Dave Oran, Jon Peterson, Eric Rescorla,
   Jonathan Rosenberg, Russ Housley, Paul Hoffman, and Stephen Kent.




Lawrence & Gurbani        Expires April 9, 2009                 [Page 6]


Internet-Draft                   SIP EKU                    October 2008


   Sharon Boyen and Trevor Freeman reviewed the document and facilitated
   the discussion on id-kp-anyExtendedKeyUsage, id-kpServerAuth and id-
   kp-ClientAuth purposes in certificates.


9.  References

9.1.  Normative References

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

   [2]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,
        Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP:
        Session Initiation Protocol", RFC 3261, June 2002.

   [3]  Cooper, D., Santesson, S., Farrell, S., Boyen, S., Housley, R.,
        and W. Polk, "Internet X.509 Public Key Infrastructure
        Certificate and Certificate Revocation List (CRL) Profile",
        RFC 5280, May 2008.

   [4]  International International Telephone and Telegraph Consultative
        Committee, "Information Technology - Open Systems
        Interconnection - The Directory: Authentication Framework",
        CCITT Recommendation X.509, November 1988.

   [5]  International International Telephone and Telegraph Consultative
        Committee, "Specification of Abstract Syntax Notation One
        (ASN.1): Specification of Basic Notation", CCITT Recommendation
        X.680, July 1994.

   [6]  International Telecommunications Union, "Information Technology
        - ASN.1 encoding rules: Specification of Basic Encoding Rules
        (BER), Canonical Encoding Rules (CER) and Distinguished Encoding
        Rules (DER)", ITU-T Recommendation X.690, 1994.

   [7]  Rosenberg, J. and H. Schulzrinne, "Session Initiation Protocol
        (SIP): Location SIP Servers", RFC 3263, June 2002.

9.2.  Informative References

   [8]  Gurbani, V., Lawrence, S., and A. Jeffrey, "Domain Certificates
        in the Session Initiation Protocol (SIP)",
        draft-ietf-sip-domain-certs-03.txt (work in progress),
        July 2008.






Lawrence & Gurbani        Expires April 9, 2009                 [Page 7]


Internet-Draft                   SIP EKU                    October 2008


Appendix A.  ASN.1 Module

      SIPDomainCertExtn
        { iso(1) identified-organization(3) dod(6) internet(1)
          security(5) mechanisms(5) pkix(7) id-mod(0)
          id-mod-sip-domain-extns2007(VALUE-TBD) }

      DEFINITIONS IMPLICIT TAGS ::=
      BEGIN

      -- OID Arcs

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

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

      id-aca  OBJECT IDENTIFIER  ::=
         { iso(1) identified-organization(3) dod(6) internet(1)
           security(5) mechanisms(5) pkix(7) 10 }

      -- Extended Key Usage Values

      id-kp-sipDomain  OBJECT IDENTIFIER  ::=  { id-kp 20 }

      END


Authors' Addresses

   Scott Lawrence
   Nortel Networks, Inc.
   600 Technology Park
   Billerica, MA  01821
   USA

   Phone:  +1 978 248 5508
   Email:  scott.lawrence@nortel.com










Lawrence & Gurbani        Expires April 9, 2009                 [Page 8]


Internet-Draft                   SIP EKU                    October 2008


   Vijay K. Gurbani
   Bell Laboratories, Alcatel-Lucent
   1960 Lucent Lane
   Room 9C-533
   Naperville, IL  60566
   USA

   Phone:  +1 630 224-0216
   Email:  vkg@alcatel-lucent.com










































Lawrence & Gurbani        Expires April 9, 2009                 [Page 9]


Internet-Draft                   SIP EKU                    October 2008


Full Copyright Statement

   Copyright (C) The IETF Trust (2008).

   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, THE IETF TRUST AND
   THE INTERNET ENGINEERING TASK FORCE DISCLAIM 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.


Intellectual Property

   The IETF takes no position regarding the validity or scope of any
   Intellectual Property Rights or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights
   might or might not be available; nor does it represent that it has
   made any independent effort to identify any such rights.  Information
   on the procedures with respect to rights in RFC documents can be
   found in BCP 78 and BCP 79.

   Copies of IPR disclosures made to the IETF Secretariat and any
   assurances of licenses to be made available, or the result of an
   attempt made to obtain a general license or permission for the use of
   such proprietary rights by implementers or users of this
   specification can be obtained from the IETF on-line IPR repository at
   http://www.ietf.org/ipr.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights that may cover technology that may be required to implement
   this standard.  Please address the information to the IETF at
   ietf-ipr@ietf.org.


Acknowledgment

   Funding for the RFC Editor function is provided by the IETF
   Administrative Support Activity (IASA).





Lawrence & Gurbani        Expires April 9, 2009                [Page 10]


Html markup produced by rfcmarkup 1.129c, available from https://tools.ietf.org/tools/rfcmarkup/