[Docs] [txt|pdf] [Tracker] [Email] [Diff1] [Diff2] [Nits]

Versions: 00 01 02 03 04 draft-ietf-sipping-certs

SIP                                                          C. Jennings
Internet-Draft                                             Cisco Systems
Expires: January 16, 2005                                    J. Peterson
                                                           NeuStar, Inc.
                                                           July 18, 2004


                 Certificate Management Service for SIP
                    draft-jennings-sipping-certs-04

Status of this Memo

   By submitting this Internet-Draft, I certify that any applicable
   patent or other IPR claims of which I am aware have been disclosed,
   and any of which I become aware will be disclosed, in accordance with
   RFC 3668.

   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 January 16, 2005.

Copyright Notice

   Copyright (C) The Internet Society (2004).  All Rights Reserved.

Abstract

   This draft defines a Credential Service that uses a SIP subscribe/
   notify mechanism to discover other users' certificates and
   credentials and be notified about changes to these certificates.
   Other user agents that want to contact that AOR can retrieve these
   certificates from the server.  The result is that widespread
   deployment of S/MIME in SIP is possible, because no extra expense or
   effort is required of the end user.




Jennings & Peterson     Expires January 16, 2005                [Page 1]


Internet-Draft              SIP Certificates                   July 2004


   This work is being discussed on the sipping@ietf.org mailing list.

Table of Contents

   1.   Introduction . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.   Conventions  . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.   Goals  . . . . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.   UA Discovering Certificates  . . . . . . . . . . . . . . . .   4
   5.   UA Discovering and Publishing Credentials  . . . . . . . . .   5
   6.   Credential Server Behavior . . . . . . . . . . . . . . . . .   5
   7.   Negotiation of Secure Session  . . . . . . . . . . . . . . .   6
   8.   Encrypting Bodies of SIP messages  . . . . . . . . . . . . .   7
   9.   Signing Bodies of SIP message  . . . . . . . . . . . . . . .   8
   10.  Examples . . . . . . . . . . . . . . . . . . . . . . . . . .   8
     10.1   Encrypted Page Mode IM Message . . . . . . . . . . . . .   8
     10.2   SRTP Phone Call  . . . . . . . . . . . . . . . . . . . .   9
     10.3   Setting and Retrieving UA Credentials  . . . . . . . . .  10
   11.  Security Considerations  . . . . . . . . . . . . . . . . . .  11
     11.1   Trusting the Identity of a Certificate . . . . . . . . .  11
     11.2   Conformity to the SACRED Framework . . . . . . . . . . .  12
   12.  IANA . . . . . . . . . . . . . . . . . . . . . . . . . . . .  12
     12.1   Certificate Event Package  . . . . . . . . . . . . . . .  12
     12.2   Credential Event Package . . . . . . . . . . . . . . . .  13
     12.3   PKCS #8  . . . . . . . . . . . . . . . . . . . . . . . .  13
   13.  References . . . . . . . . . . . . . . . . . . . . . . . . .  14
   13.1   Normative References . . . . . . . . . . . . . . . . . . .  14
   13.2   Informational References . . . . . . . . . . . . . . . . .  15
        Authors' Addresses . . . . . . . . . . . . . . . . . . . . .  16
        Intellectual Property and Copyright Statements . . . . . . .  17






















Jennings & Peterson     Expires January 16, 2005                [Page 2]


Internet-Draft              SIP Certificates                   July 2004


1.  Introduction

   SIP provides a mechanism for end to end encryption and integrity
   using S/MIME, and several security properties of SIP depend on S/
   MIME.  S/MIME has not been widely implemented or deployed due to the
   complexity of providing a reasonable key management infrastructure.
   This document proposes a way to address certificate discovery,
   retrieval, and management for SIP deployments.  It follows the Sacred
   Framework RFC 3760 [7] for management of the credentials.  Combined
   with the Identity [2] work, this work allows users to have
   certificates that are not signed by any well known certificate
   authority while still strongly binding the user's identity to the
   certificate.  This mechanism allows UAs such as IP phones to enroll
   and get their credentials without any more configuration information
   than they commonly have today, without any extra effort or key clicks
   by the end user, and without any extra expense for the end user.
   This mechanism also lets the UA discover and retrieve the public
   certificate for any other user and find out about certificate
   revocations.

   The general approach is to provide a new SIP service referred to as a
   Credential Server that allows UAs to subscribe to some other user's
   certificate.  The certificate is delivered in a SIP NOTIFY to the UA
   that subscribes.  The identity of the certificate can be vouched for
   using Identity [2] work.  The Credential Service can manage public
   certificates as well as credentials that include the user's private
   key.  The user can install new credentials to the Credential Server
   using a SIP PUBLISH.  The Credential Server authenticates UAs that
   are changing credentials or requesting private keys using a shared
   secret that both the UA and the Server know.  Typically this will be
   the same shared secret that is used in Register with the Registrar
   for the domain.

   The mechanism described in this document works for both self signed
   certificates and certificates signed by a well known certificate
   authority; however, it is imagined that most UAs using this would
   only use self signed certificates and would use an Authentication
   Service as described in [2] to provide strong identity binding to the
   certificates.

   Previous versions of this draft (00 to 02) used HTTP instead of SIP
   for communicating with the Credential Server.  The key difference
   with using SIP is that a certificate can be revoked by sending a new
   NOTIFY; in the HTTP based scheme, the certificates were cached for a
   predefined period of time, typically one day, so that a revocation
   could only take effect after the cache expired.  The earlier version
   also did not deal with the SACRED problem and allowed several devices
   with the same AOR to all have different private keys.  This resulted



Jennings & Peterson     Expires January 16, 2005                [Page 3]


Internet-Draft              SIP Certificates                   July 2004


   in very large SIP message and was looking fairly unwieldy; so now,
   the UAs for one AOR share private keying material and use the SACRED
   framework to move it between devices.

   This basic approach of this work is independent of the details of
   body modification [13] and identity discussions.  However, the
   choices made there will affect the mechanisms used to implement the
   approach described here.

2.  Conventions

   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 [5].

   Certificate: An X.509 style certificate containing a public key and a
   list of identities in the SubjectAltName that are bound to this key.
   The certificates discussed in this draft are generally self signed
   and use the mechanisms in the Identity work [2] to vouch for their
   validity.

   Credential: For this document, this means the combination of a
   certificate and the associated private key.

3.  Goals

   o  Allow negotiation of E2E encrypted sessions.
   o  Allow end to end encryption and integrity of SIP bodies that may
      be delivered in SIP signaling, such as page mode MESSAGEs or
      NOTIFY bodies in presence.
   o  Work for users with multiple UA devices.
   o  Provide a certificate revocation mechanism.

4.  UA Discovering Certificates

   UAs discover certificates by sending a SUBSCRIBE with an event type
   of pkix-cert to the AOR for which a certificate is desired.  This
   could be a SIP or tel URL.  The resulting NOTIFY will contain an
   application/pkix-cert body which contains the certificates.  The UA
   MUST follow the procedures in Section 11.1 to decide if the received
   certificate can be used.  The UA needs to cache this certificate for
   future use.  The certificate MUST be removed from the cache if it has
   expired, if it is updated by a subsequent NOTIFY, or if the
   subscription has been terminated.  The NOTIFY containing a
   certificate must be signed by an Authentication Service as described
   in Identity.  If the identity asserted by the Authentication Service
   does not match the identity requests, the certificates in the NOTIFY
   are discarded and MUST NOT be used.



Jennings & Peterson     Expires January 16, 2005                [Page 4]


Internet-Draft              SIP Certificates                   July 2004


5.  UA Discovering and Publishing Credentials

   UAs discover credentials by subscribing to their AOR with an event
   type of credential, which will result in a message containing both an
   application/pkix-cert body and an application/pkcs8 body that has the
   associated private key information for the certificate.  The UA can
   change the user's certificate and private key by sending the server a
   PUBLISH[3] with an event type of credential that contains both an
   application/pkix-cert and an application/pkcs8 body.

   The UA needs to authenticate to the Credential Server for these
   operations.  The UA MUST use TLS to connect to the server.  The UA
   may be configured with a specific name for the Credential Server;
   otherwise it defaults to the name of the domain in the User's AOR.
   The TLS connection MUST present a certificate that matches the
   expected name for the credential server, so that the UA knows it is
   talking to the correct server.  If the certificate presented by the
   server does not match the expected server, the UA MUST terminate the
   connection and notify the user.  If the UA does not do so, it may end
   up publishing its private key information to an attacker.  The
   Credential Server will authenticate the UA using the usual SIP Digest
   mechanism, so the UA can expect to receive a SIP challenge to the
   SUBSCRIBE or PUBLISH messages.

   The application/pkix-cert body is a DER encoded X.509 certificate
   [10].  The application/pkcs8 bodies contains a DER encoded PKCS #8
   object that contains the private key.  The PKCS #8 objects MUST be of
   type PrivateKeyInfo.  The integrity and confidentiality of the PKCS
   #8 objects is provided by the TLS transport.  The transport encoding
   of all the MIME bodies is binary.

6.  Credential Server Behavior

   The Credential Server stores credentials for users and can provide
   the credentials or certificates to other user agents.  The
   credentials are indexed by an URI that corresponds to the AOR of the
   user.  When a UA requests a public certificate with a SUBSCRIBE, the
   server sends it in a NOTIFY and sends a subsequent NOTIFY any time it
   changes.  When a credential is requested, the Server digest
   challenges the requesting UA to authenticate it so that the Server
   can verify that the UA is authorized to receive the requested
   credentials.

   When the Credential Server receives a SUBSCRIBE for a certificate, it
   first checks to see if it has credentials for the requested URI.  If
   it does not it returns a response indicating the user was not found.
   Otherwise it sets up a subscription and forms a NOTIFY with the
   certificate in the body and the From header field value set to the



Jennings & Peterson     Expires January 16, 2005                [Page 5]


Internet-Draft              SIP Certificates                   July 2004


   request URI of the SUBSCRIBE.  It MUST send this NOTIFY through an
   Authentication Service (as described in Identity [2]) or implement an
   Authentication Service itself.  The Server is encouraged to keep the
   subscriptions active for AORs that are communicating frequently but
   MAY unsubscribe at any point of time.  Any time the credentials for
   this URI change, the Server MUST send a new NOTIFY to any active
   subscriptions.

   When a Credential Server receives a SUBSCRIBE for a credential, the
   Server has to authenticate and authorize the UA and validate that
   adequate transport security is being used.  The Server MUST digest
   challenge the UA to authenticate the UA and then decide if it is
   authorized to receive the credentials.

   Once the UA has authenticated with the Server, the Server can set up
   a subscription and send a Notify message that MUST contain the
   credentials.  This NOTIFY message is sent thought an Authorization
   Service in the same way as the certificate subscriptions.  If the
   credential changes, the Server MUST terminate any current
   subscriptions and force the UA to re-authenticate.  This is so that
   if a secret for retrieving the credentials gets compromised, the
   rogue UA will not continue to receive credentials after the
   compromised secret has been changed.

   When the Credential Server receives a PUBLISH to update credentials,
   it MUST authenticate and authorize this the same way it does the
   subscriptions for credentials.  If this succeeds, the Server updates
   the credential for this URI and processes all the active
   subscriptions to this URI as described above.

7.  Negotiation of Secure Session

   SIP uses an offer/answer negotiation mechanism[16] that describes
   sessions using SDP that may contain keying material, described in
   [14], for media protocols such as SRTP [15].  This keying material
   needs to be protected, and SIP does this by encrypting the SDP bodies
   using S/MIME.

   If a UA receives both an unencrypted and an encrypted SDP offer in an
   multipart/alternative body, it interprets these as it would a normal
   multipart alternative as defined in RFC 2046 [17], which means it
   picks the last alternative that it can support.  Any bodies that
   cannot be decrypted are treated as unsupportable.  The sending UA
   should generally put encrypted offers after unencrypted ones, since
   encrypted ones are preferred.  The UA constructs the answer to the
   offer as it normally would and may include both encrypted and
   unencrypted versions of the answer using multipart/alternative.  The
   only wrinkle here is that if the UA sent multiple bodies with an



Jennings & Peterson     Expires January 16, 2005                [Page 6]


Internet-Draft              SIP Certificates                   July 2004


   offer, it needs to be able to match the answer (or answeres) to the
   offer that was chosen.

   The UA that made the offer can uniquely identify the various MIME
   bodies using a MIME Content-ID header.  However, the UA sending the
   answers needs to provide the label of the Content-ID in the response.
   Solutions were considered that put the Content-ID identifier in a SIP
   Header, a MIME header, or an SDP attribute.  Since the issue here is
   fundamentally about providing information that is all at the MIME
   level about the relation between one set of multipart/alternatives
   and the other MIME body that is being sent, the best solution seems
   to involve passing this tag at the MIME level.  A new MIME header
   called "Content-Related-To" updates RFC 2045 with:


    rid := "Content-Related-To" ":" msg-id

   and adds "[rid CRLF]" to the entity-headers.

   The identifier supplied in the Content-Related-To header must be a
   valid Content-ID from a previous MIME message that this body is
   related to.

   The UA looks at the multipart/alternatives and selects the best one
   it can use.  It MUST include a Content-Related-To in the MIME for the
   answer that copies the tag from the related Content-ID header of the
   offer body it has chosen to use.

   In a typical call from Alice to Bob, Alice would first subscribe to
   Bob's certificate.  If this worked, then Alice would send an Invite
   to Bob that contained an RTP session in unencrypted SDP and an SRTP
   session in encrypted SDP.  Bob would select the SRTP session and send
   an answer with encrypted SDP selecting the SRTP session.  Both
   Alice's and Bob's UAs would indicate to the user that a secure call
   had been negotiated.  Alice and Bob could note that the call was
   secure and adjust their conversation accordingly.

8.  Encrypting Bodies of SIP messages

   Applications such as presence and 911 location information result in
   information with significant privacy requirements being sent in SIP.
   Particular MIME types may define special meanings when both an
   encrypted and unencrypted body are received, but, unless otherwise
   specified, the UA SHOULD use the encrypted version if it can decrypt
   it, and ignore the unencrypted version.  There is no requirement for
   the two versions to have the same information.  For example, a page
   mode message could have an unencrypted version that said "I'm in the
   Middle East visiting people" while the encrypted version had much



Jennings & Peterson     Expires January 16, 2005                [Page 7]


Internet-Draft              SIP Certificates                   July 2004


   more sensitive information like "I'm over at Osama's house at
   21.25'24"N 39.49'24"E".  Depending whether the receiving device can
   decrypt this or not, a different message gets displayed to the
   receiving user.

9.  Signing Bodies of SIP message

   In general, signing messages with self-signed certificates is not
   that useful unless some other means is used to vouch that the
   certificate has some meaning.  If the Authentication Service is used
   to do this, then the Authentication Service is providing integrity
   across all the bodies and binding them with an identity.  In this
   case, the additional signature becomes redundant.  Because of this,
   it is recommended that signing bodies SHOULD NOT be used if the
   certificate is a self signed certificate.

10.  Examples

   In all these examples, large parts of the message are omitted to
   highlight what is relevant to this draft.  The lines in the examples
   that are prefixed by $ represent encrypted blocks of data.

10.1  Encrypted Page Mode IM Message

   In this example, Alice sends Bob an encrypted page mode instant
   message.  If Alice does not already have Bob's public key from
   previous communications, she fetches Bob's public key from Bob's
   credential server:


    SUBSCRIBE sip:bob@biloxi.example.com SIP/2.0
    ...
    Event: certificate

   The credential server responds with the certificate in a NOTIFY.


    NOTIFY alice@atlanta.example.com  SIP/2.0
    Subscription-State: active; expires=7200
    ....
    From: <sip:bob@biloxi.example.com>;tag=1234
    Identity: "12dsfsdk2389403823cbed"
    Identity-Info: sips:billoxi.example.com
    ....
    Event: certificate
    Content-Type: application/pkix-cert

    < certificate data >



Jennings & Peterson     Expires January 16, 2005                [Page 8]


Internet-Draft              SIP Certificates                   July 2004


   Next Alice sends a SIP MESSAGE message to Bob:


    MESSAGE sip:bob@biloxi.example.com SIP/2.0
    ...
    Content-Type: application/pkcs7-mime

    $ Content-Type: text/plain
    $
    $ < encrypted version of "Hello" >



10.2  SRTP Phone Call

   In this example, Alice calls Bob and offers both an RTP and an SRTP
   session.  The SDP for the SRTP session contains the SRTP keying
   material and is encrypted with S/MIME.  If Alice does not already
   have Bob's public key from previous communications, she fetches Bob's
   public key from Bob's credential server in the same way as shown in
   the previous example.

   Alice sends an INVITE to Bob that offers two alternative SDP bodies,
   one of which is encrypted and contains the SRTP keying information.
   The


    INVITE sip:bob@biloxi.example.com SIP/2.0
    ...
    Content-Type: multipart/alternative;boundary=boundary

    --boundary
    Content-ID: 123
    Content-Type: application/sdp
    Content-Disposition: session

    < SDP offer for ordinary RTP only >
    --boundary
    Content-ID: 456
    Content-Type: application/pkcs7-mime
    Content-Disposition: session

    $ Content-Type: application/sdp
    $
    $ < encrypted SDP with key for SRTP >
    --boundary

   If Bob's UA does not have Alice's public key, Bob's UA would fetch it



Jennings & Peterson     Expires January 16, 2005                [Page 9]


Internet-Draft              SIP Certificates                   July 2004


   as shown in the previous example.  Assuming that Bob's UA supported
   encryption, it would select the second alternative offer and
   construct an appropriate answer.  The 200 includes the MIME
   Content-Related-To header that indicates which alternative MIME body
   was chosen.


    200 OK
    ...
    Content-ID: 789
    Content-Related-To: 456
    Content-Type: application/pkcs7-mime
    Content-Disposition: session

    $ Content-Type: application/sdp
    $
    $ < encrypted SDP with key for SRTP >


10.3  Setting and Retrieving UA Credentials

   When Alice's UA wishes to publish Alice's public and private keys to
   the Credential Server, it sends a PUBLISH message like the one below.
   This must be sent over a TLS connection in which the other end of the
   connection presents a certificate that matches the Credential Server
   for Alice and digest challenges the message to authenticate her.


    PUBLISH sip:alice@atlanta.example.com SIP/2.0
    ...
    Content-Type: multipart/mixed;boundary=boundary

    --boundary
    Content-ID: 123
    Content-Type: application/pkix-cert
    Content-Disposition: session

    < Public certificate for Alice >
    --boundary
    Content-ID: 456
    Content-Type: application/pkcs8
    Content-Disposition: session

    < Private Key for Alice >
    --boundary

   If one of Alice's UAs subscribes to the credential event, the UA will
   be digest challenged, and the NOTIFY will include a body similar to



Jennings & Peterson     Expires January 16, 2005               [Page 10]


Internet-Draft              SIP Certificates                   July 2004


   the one in the PUBLISH section above.

11.  Security Considerations

   This whole scheme is highly dependent on trusting the operators of
   the Credential Server and trusting that the Credential Server will
   not be compromised.  The security of all the users will be completely
   compromised if the Credential Server is compromised.

   This work requires the TLS session to be used for communications to
   the Credential Server.  Failing to use TLS or selecting a poor cipher
   suite (such as NULL encryption) will result in credentials being sent
   unencrypted over the network and will render the whole system
   useless.  Implementation really must use TLS or there is no point in
   implementing any of this.  In addition, the correct checking of
   chained certificates as specified in TLS [11] is critical for the
   client to authenticate the server.

   If a particular credential needs to be revoked, the new credential is
   simply published to the Credential Server.  Every device keeping this
   current in its cache will have a subscription to the credential and
   will rapidly (order of seconds) be notified and replace its cache.
   Clients that are not subscribed will subscribe and get the new
   certificate, so they will not end up using the old invalid
   certificate.

11.1  Trusting the Identity of a Certificate

   When a UA wishes to discover the certificate for
   sip:alice@example.com, the UA subscribes to the certificate for
   alice@example.com and receives a certificate in the body of a SIP
   Notify message.  The term original URI is used to describe the
   original URI that was subscribed to.

   If the certificate is signed by a trusted CA, and one of the names in
   the SubjectAltName matches the original URI, then this certificate
   MAY be used but only for exactly the Original URI and not for other
   identities found in the SubjectAltName.  Otherwise, there are several
   steps the UA MUST perform before using this certificate.
   o  The From header in the NOTIFY message MUST match the original URI.
   o  The UA MUST check the Identity header as described in the Identity
      [2] work to validate that bodies have not been tampered with and
      that an Authentication Service has validated this From header.
   o  The UA MUST check the validity time of the certificate and stop
      using the certificate once it is invalid.
   o  The certificate MAY have several names in the SubjectAltName but
      the UA MUST only use this certificate when it needs the
      certificate for the identity in the Original URI.  This means that



Jennings & Peterson     Expires January 16, 2005               [Page 11]


Internet-Draft              SIP Certificates                   July 2004


      the certificate should only be indexed in the certificate cache by
      the value of the original URI, not by the value of all the
      identities found in the SubjectAltName.
   These steps result in a chain of bindings that result in a trusted
   binding between the original URI and a public key.  The Original URI
   is forced to match the From.  The Authentication Service validates
   that this message did come from the identity claimed in the From and
   that the bodies and From have not been tampered with.  The
   certificate in the body contains the public key for the identity.
   Only the UA that can authenticate as this user can tamper with this
   body, so the owner of the identity can provide a false public key but
   other users cannot.  This chain of assertion from original URI, to
   From, to body, to public key is critical to the security of the
   mechanism described in this document.  If any of the steps above are
   not followed, this chain of security will be broken and the system
   will not work.

11.2  Conformity to the SACRED Framework

   This work uses the security design outlined in the SACRED Framework
   [7].  Specifically, it follows the cTLS architecture described in
   section 4.2.2 of RFC 3760.  The client authenticates the server using
   the server's TLS certificate.  The server authenticates the client
   using a SIP digest transaction inside the TLS session.  The TLS
   sessions form a strong session key that is used to protect the
   credentials being exchanged.

   Credential Servers SHOULD implement the server name indication
   extensions in RFC 3546 [8] and they MUST support a TLS profile of
   TLS_RSA_WITH_AES_128_CBC_SHA as described in RFC 3268 [9] and a
   profile of TLS_RSA_WITH_3DES_CBC_SHA.

12.  IANA

   The MIME Content-Related-To header does not require any IANA actions.

12.1  Certificate Event Package


   To: ietf-sip-events@iana.org
   Subject: Registration of new SIP event package

   Package Name: certificate

   Is this registration for a Template Package: No

   Published Specification(s): draft-jennings-sipping-certs




Jennings & Peterson     Expires January 16, 2005               [Page 12]


Internet-Draft              SIP Certificates                   July 2004


   Person & email address to contact for further information:
     Cullen Jennings <fluffy@cisco.com>


12.2  Credential Event Package


   To: ietf-sip-events@iana.org
   Subject: Registration of new SIP event package

   Package Name: credential

   Is this registration for a Template Package: No

   Published Specification(s): draft-jennings-sipping-certs

   Person & email address to contact for further information:
     Cullen Jennings <fluffy@cisco.com>


12.3  PKCS #8






























Jennings & Peterson     Expires January 16, 2005               [Page 13]


Internet-Draft              SIP Certificates                   July 2004


   To: ietf-types@iana.org
   Subject: Registration of MIME media type application/pkcs8

   MIME media type name: application

   MIME subtype name: pkcs8

   Required parameters: None

   Optional parameters: None

   Encoding considerations: will be binary for 8-bit transports

   Security considerations: Carries a cryptographic private key

   Interoperability considerations: None

   Published specification: draft-jennings-sipping-certs

   Applications which use this media type: Any MIME-complaint transport

   Additional information:
     Magic number(s): None
     File extension(s): .p8
     Macintosh File Type Code(s): none

   Person & email address to contact for further information:
     Cullen Jennings <fluffy@cisco.com>

   Intended usage: COMMON

   Author/Change controller:
     Cullen Jennings <fluffy@cisco.com>


13.  References

13.1  Normative References

   [1]   RSA Laboratories, "Private-Key Information Syntax Standard,
         Version 1.2", PKCS 8, November 1993.

   [2]   Peterson, J. and C. Jennings, "Enhancements for Authenticated
         Identity Management in the Session Initiation Protocol (SIP)",
         draft-ietf-sip-identity-02 (work in progress), May 2004.

   [3]   Niemi, A., "Session Initiation Protocol (SIP) Extension for
         Event State Publication", draft-ietf-sip-publish-04 (work in



Jennings & Peterson     Expires January 16, 2005               [Page 14]


Internet-Draft              SIP Certificates                   July 2004


         progress), May 2004.

   [4]   Roach, A., "Session Initiation Protocol (SIP)-Specific Event
         Notification", RFC 3265, June 2002.

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

   [6]   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.

   [7]   Gustafson, D., Just, M. and M. Nystrom, "Securely Available
         Credentials (SACRED) - Credential Server Framework", RFC 3760,
         April 2004.

   [8]   Blake-Wilson, S., Nystrom, M., Hopwood, D., Mikkelsen, J. and
         T. Wright, "Transport Layer Security (TLS) Extensions", RFC
         3546, June 2003.

   [9]   Chown, P., "Advanced Encryption Standard (AES) Ciphersuites for
         Transport Layer Security (TLS)", RFC 3268, June 2002.

   [10]  Housley, R. and P. Hoffman, "Internet X.509 Public Key
         Infrastructure Operational Protocols: FTP and HTTP", RFC 2585,
         May 1999.

   [11]  Dierks, T. and C. Allen, "The TLS Protocol Version 1.0", RFC
         2246, January 1999.

13.2  Informational References

   [12]  Gutmann, P., "Internet X.509 Public Key Infrastructure
         Operational Protocols: Certificate  Store Access via HTTP",
         draft-ietf-pkix-certstore-http-07 (work in progress), May 2004.

   [13]  Mahy, R., "Pros and Cons of allowing SIP Intermediaries to add
         MIME bodies", draft-mahy-sipping-body-add-00 (work in
         progress), July 2004.

   [14]  Andreasen, F., Baugher, M. and D. Wing, "Session Description
         Protocol Security Descriptions for Media Streams",
         draft-ietf-mmusic-sdescriptions-06 (work in progress), July
         2004.

   [15]  Baugher, M., McGrew, D., Naslund, M., Carrara, E. and K.
         Norrman, "The Secure Real-time Transport Protocol (SRTP)", RFC
         3711, March 2004.



Jennings & Peterson     Expires January 16, 2005               [Page 15]


Internet-Draft              SIP Certificates                   July 2004


   [16]  Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with
         Session Description Protocol (SDP)", RFC 3264, June 2002.

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


Authors' Addresses

   Cullen Jennings
   Cisco Systems
   170 West Tasman Drive
   MS: SJC-21/2
   San Jose, CA  95134
   USA

   Phone: +1 408 902-3341
   EMail: fluffy@cisco.com


   Jon Peterson
   NeuStar, Inc.
   1800 Sutter St
   Suite 570
   Concord, CA  94520
   US

   Phone: +1 925/363-8720
   EMail: jon.peterson@neustar.biz
   URI:   http://www.neustar.biz/




















Jennings & Peterson     Expires January 16, 2005               [Page 16]


Internet-Draft              SIP Certificates                   July 2004


Intellectual Property Statement

   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.


Disclaimer of Validity

   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
   INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.


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.


Acknowledgment

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




Jennings & Peterson     Expires January 16, 2005               [Page 17]


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