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Versions: (draft-munakata-sip-privacy-new) 00 01 02 03 04 05 06 07 08 RFC 5767

SIP                                                          M. Munakata
Internet-Draft                                               S. Schubert
Intended status: Informational                                   T. Ohba
Expires: August 13, 2009                                             NTT
                                                        February 9, 2009


                  UA-Driven Privacy Mechanism for SIP
                      draft-ietf-sip-ua-privacy-05

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   This Internet-Draft is submitted to IETF in full conformance with the
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   This Internet-Draft will expire on August 13, 2009.

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   Copyright (c) 2009 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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Abstract

   This document defines a guideline for a user agent to generate an



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   anonymous SIP message by utilizing mechanisms such as GRUU (Globally
   Routable User Agent URIs) and TURN (Traversal Using Relays around
   NAT) without the need for a privacy service defined in RFC 3323.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Concept of Privacy . . . . . . . . . . . . . . . . . . . . . .  3
   4.  Treatment of Privacy-Sensitive Information . . . . . . . . . .  4
     4.1.  Obtaining a Functional Anonymous URI Using the GRUU
           Mechanism  . . . . . . . . . . . . . . . . . . . . . . . .  4
     4.2.  Obtaining a Functional Anonymous IP Address Using the
           TURN Mechanism . . . . . . . . . . . . . . . . . . . . . .  5
   5.  User Agent Behavior  . . . . . . . . . . . . . . . . . . . . .  6
     5.1.  Critical Privacy-Sensitive Information . . . . . . . . . .  6
       5.1.1.  Contact Header Field . . . . . . . . . . . . . . . . .  6
       5.1.2.  From Header Field in requests  . . . . . . . . . . . .  7
       5.1.3.  Via Header Field in requests . . . . . . . . . . . . .  8
       5.1.4.  IP Addresses in SDP  . . . . . . . . . . . . . . . . .  8
     5.2.  Non-Critical Privacy-Sensitive Information . . . . . . . .  8
       5.2.1.  Host Names in Other SIP Header Fields  . . . . . . . .  8
       5.2.2.  Optional SIP Header Fields . . . . . . . . . . . . . .  8
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . .  9
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  9
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . .  9
     8.1.  Normative References . . . . . . . . . . . . . . . . . . .  9
     8.2.  Informative References . . . . . . . . . . . . . . . . . . 10
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10





















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1.  Introduction

   [RFC3323] defines a privacy mechanism for the SIP (Session Initiation
   Protocol)[RFC3261], based on techniques available at the time of its
   publication.  This mechanism relies on the use of a separate privacy
   service to remove privacy-sensitive information from SIP messages
   sent by a user agent before forwarding those messages to the final
   destination.  Since then, numerous SIP extensions have been proposed
   and standardized.  Some of those enable a user agent to withhold its
   user's identity and related information without the need for privacy
   services, which was not possible when RFC 3323 was defined.

   The purpose of this document is not to obsolete RFC 3323, but to
   enhance overall privacy mechanism in SIP by allowing a user agent to
   take control of its privacy, rather than being completely dependent
   on an external privacy service.

   The UA-driven privacy mechanism defined in this document will not
   eliminate the need for the RFC 3323 usage defined in [RFC3325], which
   instructs a privacy service not to forward a P-Asserted-Identity
   header field outside the Trust Domain.  In order to prevent
   forwarding a P-Asserted-Identity header field outside the Trust
   Domain, a user agent needs to include the Privacy header field with
   value 'id' (Privacy:id) in the request, even when the user agent is
   utilizing this specification.

   This document defines a guideline in which a user agent controls all
   the privacy functions on its own utilizing SIP extensions such as
   GRUU (Globally Routable User Agent URIs) [I-D.ietf-sip-gruu] and TURN
   (Traversal Using Relays around NAT) [I-D.ietf-behave-turn].


2.  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 [RFC2119].

   privacy-sensitive information:
               The information that identifies a user who sends the SIP
               message, as well as other information that can be used to
               guess the user's identity.


3.  Concept of Privacy

   The concept of privacy in this document is the act of concealing
   privacy-sensitive information.  The protection of network privacy



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   (e.g., topology hiding) is outside the scope for this document.

   Privacy-sensitive information includes display-name and URI (Uniform
   Resource Identifier) in a From header field that can reveal the
   user's name and affiliation (e.g., company name), and IP addresses or
   host names in a Contact header field, a Via header field, a Call-ID
   header field, or an SDP (Session Description Protocol) [RFC4566] body
   that might reveal the location of a user agent.


4.  Treatment of Privacy-Sensitive Information

   Some fields of a SIP message potentially contain privacy-sensitive
   information but are not essential for achieving the intended purpose
   of the message and can be omitted without any side effects.  Other
   fields are essential for achieving the intended purpose of the
   message and need to contain anonymized values in order to avoid
   disclosing privacy-sensitive information.  Of the privacy-sensitive
   information listed in section 3, URIs, host names, and IP addresses
   in Contact, Via, and SDP must be functional (i.e., suitable for
   purpose) even when they are anonymized.

   With the use of GRUU [I-D.ietf-sip-gruu] and TURN
   [I-D.ietf-behave-turn], a user agent can obtain URIs and IP addresses
   for media and signaling that are functional yet anonymous, and do not
   identify either the user agent or the user.  Instructions on how to
   obtain a functional anonymous URI and IP address are given in Section
   4.1 and 4.2, respectively.

   Host names should be concealed because the user's identity may be
   guessed from them, but they are not always regarded as critical
   privacy-sensitive information.

   In addition, a user agent should be careful not to include any
   information that identifies the user in optional SIP header fields
   such as Subject and User-Agent.

4.1.  Obtaining a Functional Anonymous URI Using the GRUU Mechanism

   A user agent wanting to obtain a functional anonymous URI MUST
   support and utilize the GRUU mechanism unless it is able to obtain a
   functional anonymous URI through other means outside the scope for
   this document.  By sending a REGISTER request requesting GRUU, the
   user agent can obtain an anonymous URI, which can later be used for
   the Contact header field.

   The detailed process on how a user agent obtains a GRUU is described
   in [I-D.ietf-sip-gruu].



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   In order to use the GRUU mechanism to obtain a functional anonymous
   URI, the UA MUST request GRUU in the REGISTER request.  If a "temp-
   gruu" URI parameter and value are present in the REGISTER response,
   the user agent MUST use the value of the "temp-gruu" as an anonymous
   URI representing the user agent.  This means that the user agent MUST
   use this URI as its local target and MUST place this URI in the
   Contact header field of subsequent requests and responses that
   require the local target to be sent.

   If there is no "temp-gruu" URI parameter in the 200 response to the
   REGISTER request, a user agent SHOULD NOT proceed with its
   anonymization process, unless something equivalent to "temp-gruu" is
   provided through some administrative means.

   It is RECOMMENDED that user agent consult the user before sending a
   request without a functional anonymous URI when privacy is requested
   from the user.

   Due to the nature of how GRUU works, the domain name is always
   revealed when GRUU is used.  If revealing the domain name in the
   Contact header field is a concern, usage of a third-party GRUU server
   to obtain a temp-gruu that is irrelevant to users' domain, which is
   outside the scope of this document SHOULD be considered.  Refer to
   the Security Considerations section for details.

4.2.  Obtaining a Functional Anonymous IP Address Using the TURN
      Mechanism

   A user agent that is not provided with a functional anonymous IP
   address through some administrative means MUST obtain a relayed
   address (IP address of a relay) if anonymity is desired for use in
   SDP and in the Via header field.  Such an IP address is to be derived
   from a STUN relay server through the TURN mechanism, which allows a
   STUN server to act as a relay.

   Anonymous IP addresses are needed for two purposes.  The first is for
   use in the Via header field of a SIP request.  By obtaining an IP
   address from a STUN relay server, using that address in the Via
   header field of the SIP request, and sending the SIP request to the
   STUN relay server, the IP address of the user agent will not be
   revealed beyond the relay server.

   The second is for use in SDP as an address for receiving media.  By
   obtaining an IP address from a STUN relay server and using that
   address in SDP, media will be received via the relay server.  Also
   media can be sent via the relay server.  In this way, neither SDP nor
   media packets reveal the IP address of the user agent.




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   It is assumed that a user agent is either manually or automatically
   configured through means such as the configuration framework
   [I-D.ietf-sipping-config-framework] with the address of one or more
   STUN (Session Traversal Utilities for NAT) [I-D.ietf-behave-turn]
   relay servers to obtain anonymous IP address.


5.  User Agent Behavior

   This section describes how to generate an anonymous SIP message at a
   user agent.

   A user agent fully compliant with this document MUST obscure or
   conceal all the critical UA-inserted privacy-sensitive information in
   SIP requests and responses as shown in Section 5.1 when user privacy
   is requested.  In addition, the user agent SHOULD conceal the non-
   critical privacy-sensitive information as shown in Section 5.2.

   Furthermore, when a user agent uses a relay server to conceal its
   identity, the user agent MUST send requests to the relay server to
   ensure request and response follow the same signaling path.

5.1.  Critical Privacy-Sensitive Information

5.1.1.  Contact Header Field

   When using this header field in a dialog-forming request or response
   or in a mid-dialog request or response, this field contains the local
   target, i.e., a URI used to reach the user agent for mid-dialog
   requests and possibly out-of-dialog requests, such as REFER
   [RFC3515].  The Contact header field can also contain a display-name.
   Since the Contact header field is used for routing further requests
   to the user agent, it must include a functional URI even when it is
   anonymized.

   When using this header field in a dialog-forming request or response
   or in a mid-dialog request or response, the user agent MUST anonymize
   the Contact header field using an anonymous URI ("temp-gruu")
   obtained through the GRUU mechanism, unless an equivalent functional
   anonymous URI is provided by some other means.  For out-of-dialog
   request, anonymous URI MAY be set when anonymization is required.

   Refer to Section 4.1 for details on how to obtain an anonymous URI
   through GRUU.

   A display-name in a Contact header MUST be omitted or "Anonymous".





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5.1.2.  From Header Field in requests

   Without privacy considerations, this field contains the identity of
   the user, such as display-name and URI.

   RFCs 3261 and 3323 recommend to set "sip:anonymous@anonymous.invalid"
   as a SIP URI in a From header field when user privacy is requested.
   This raises an issue when the SIP-Identity mechanism [RFC4474] is
   applied to the message, because SIP-Identity requires an actual
   domain name in the From header field.

   A user agent generating an anonymous SIP message supporting this
   specification MUST anonymize the From header field in one of the two
   ways described below.

   Option 1:

   A user agent anonymizes a From header field using an anonymous
   display-name and an anonymous URI following the procedure noted in
   section 4.1.1.3 of RFC 3323.

   The example form of the From header of option 1 is as follows:

      From: "Anonymous" <sip:anonymous@anonymous.invalid>;tag=1928301774

   Option 2:

   A user agent anonymizes a From header field using an anonymous
   display-name and an anonymous URI with user's valid domain name
   instead of "anonymous.invalid".

   The example form of the From header of option 2 is as follows:

      From: "Anonymous" <sip:anonymous@atlanta.com>;tag=1928301774

   A user agent SHOULD go with option 1 to conceal its domain name in
   the From header field.  However, SIP-Identity cannot be used with a
   From header field in accordance with option 1, because the SIP-
   Identity mechanism uses authentication based on the domain name.

   If a user agent expects the SIP-Identity mechanism to be applied to
   the request, it is RECOMMENDED to go with option 2.  However, the
   user's domain name will be revealed from the From header field of
   option 2.

   f the user wants both anonymity and strong identity, a solution would
   be to use a third party anonymization service that issues an Address
   of Record (AoR) for use in the From header field of a request and



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   that also provides a SIP-Identity Authentication Service.Third party
   anonymization service is out of scope for this document.

5.1.3.  Via Header Field in requests

   Without privacy considerations, the bottommost Via header field added
   to a request by a user agent contains the IP address and port or
   hostname that are used to reach the user agent for responses.

   A user agent generating an anonymous SIP request supporting this
   specification MUST anonymize the IP address in the Via header field
   using an anonymous IP address obtained through the TURN mechanism,
   unless an equivalent functional anonymous IP address is provided by
   some other means.

   Via header field SHOULD NOT include a host name.

5.1.4.  IP Addresses in SDP

   A user agent generating an anonymous SIP message supporting this
   specification MUST anonymize IP addresses in SDP, if present, using
   an anonymous IP address obtained through the TURN mechanism, unless
   an equivalent functional anonymous IP address is provided by some
   other means.

   Refer to Section 4.2 for details on how to obtain an IP address
   through TURN.

5.2.  Non-Critical Privacy-Sensitive Information

5.2.1.  Host Names in Other SIP Header Fields

   A user agent generating an anonymous SIP message supporting this
   specification SHOULD conceal host names in any SIP header fields,
   such as Call-ID and Warning header fields, if considered privacy-
   sensitive.

5.2.2.  Optional SIP Header Fields

   Other optional SIP header fields (such as Call-Info, In-Reply-To,
   Organization, Referred-By, Reply-To, Server, Subject, User-Agent, and
   Warning) can contain privacy-sensitive information.

   A user agent generating an anonymous SIP message supporting this
   specification SHOULD NOT include any information that identifies the
   user in such optional header fields.





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6.  Security Considerations

   This specification uses GRUU and TURN and inherits any security
   considerations described in these drafts.

   Furthermore, if the provider of the caller intending to obscure its
   identity consists of a small number of people (e.g. small enterprise,
   SOHO), the domain name alone can reveal the identity of the caller.

   The same can be true when the provider is large but the receiver of
   the call only knows a few people from the source of call.

   There are mainly two places in the message, From header and Contact
   header, where domain name must be functional.

   The domain name in the From header can be obscured as described in
   section 5.1.2, whereas the Contact header field needs to contain a
   valid domain name at all times in order to function properly.

   It is probably important to note that generally a device will not
   show the contact address to the receiver, but this does not mean that
   one can not find the domain name in a message.  In fact as long as
   this specification is used to obscure identity, the message will
   always contain a valid domain name as it inherits key characteristics
   of GRUU.

   If one wants to assure anonymization, it is recommended for the user
   to seek and rely on a third party anonymization service, which is
   outside the scope of this document.

   A third party anonymization service provides registrar and TURN
   service that have no affiliation with the caller's provider, allowing
   caller to completely withhold its identity.


7.  IANA Considerations

   This document requires no action by IANA.


8.  References

8.1.  Normative References

   [I-D.ietf-behave-turn]
              Rosenberg, J., Mahy, R., and P. Matthews, "Traversal Using
              Relays around NAT (TURN): Relay Extensions to Session
              Traversal Utilities for NAT (STUN)",



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              draft-ietf-behave-turn-12 (work in progress),
              November 2008.

   [I-D.ietf-sip-gruu]
              Rosenberg, J., "Obtaining and Using Globally Routable User
              Agent (UA) URIs (GRUU) in the  Session Initiation Protocol
              (SIP)", draft-ietf-sip-gruu-15 (work in progress),
              October 2007.

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

   [RFC3261]  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.

   [RFC4566]  Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
              Description Protocol", RFC 4566, July 2006.

8.2.  Informative References

   [I-D.ietf-sipping-config-framework]
              Channabasappa, S., "A Framework for Session Initiation
              Protocol User Agent Profile Delivery",
              draft-ietf-sipping-config-framework-15 (work in progress),
              February 2008.

   [RFC3323]  Peterson, J., "A Privacy Mechanism for the Session
              Initiation Protocol (SIP)", RFC 3323, November 2002.

   [RFC3325]  Jennings, C., Peterson, J., and M. Watson, "Private
              Extensions to the Session Initiation Protocol (SIP) for
              Asserted Identity within Trusted Networks", RFC 3325,
              November 2002.

   [RFC3515]  Sparks, R., "The Session Initiation Protocol (SIP) Refer
              Method", RFC 3515, April 2003.

   [RFC4474]  Peterson, J. and C. Jennings, "Enhancements for
              Authenticated Identity Management in the Session
              Initiation Protocol (SIP)", RFC 4474, August 2006.









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Authors' Addresses

   Mayumi Munakata
   NTT Corporation

   Email: munakata.mayumi@lab.ntt.co.jp


   Shida Schubert
   NTT Corporation

   Email: shida@ntt-at.com


   Takumi Ohba
   NTT Corporation
   9-11, Midori-cho 3-Chome
   Musashino-shi, Tokyo  180-8585
   Japan

   Phone: +81 422 59 7748
   Email: ohba.takumi@lab.ntt.co.jp
   URI:   http://www.ntt.co.jp




























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