wdiff draft-ietf-sip-ua-privacy-00.txt draft-ietf-sip-ua-privacy-01.txt

SIP M. Munakata
Internet-Draft S. Schubert
Intended status: Standards Track T. Ohba
Expires: May 15, 2008 NTT
November 12, August 22, 2007 NTT
February 18, 2008

UA-Driven Privacy Mechanism for SIP
draft-ietf-sip-ua-privacy-00
draft-ietf-sip-ua-privacy-01

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Abstract

To withhold a user's identity and related information, RFC 3323
defines a Privacy mechanism for SIP, which requires the use of an
privacy service. This document proposes a new privacy mechanism that
a user agent can facilitate to conceal privacy-sensitive information
without the need for aid from a privacy service.

Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Concept of Privacy . . . . . . . . . . . . . . . . . . . . . . 4
4. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 5
5. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 5
6.
5. Treatment of User Privacy Related Privacy-Sensitive Information . . . . . . . . . . 5
6.1.
5.1. Anonymous URI and Display-Name . . . . . . . . . . . . . . . . . . . . . . 6
6.2. 5
5.2. Anonymous IP Address . . . . . . . . . . . . . . . . . . . 6
7.
6. User Agent Behavior . . . . . . . . . . . . . . . . . . . . . 7
7.1.
6.1. Generating Anonymous Message . . . . . . . . . . . . . . . 7
7.2.
6.2. Indication to maintain Maintain Privacy . . . . . . . . . . . . . . 7
8.
7. Proxy Behavior . . . . . . . . . . . . . . . . . . . . . . . . 8
9.
8. Security Considerations . . . . . . . . . . . . . . . . . . . 8
10.
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
11.
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8
11.1.
10.1. Normative References . . . . . . . . . . . . . . . . . . . 8
11.2.
10.2. Informative References . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 9
Intellectual Property and Copyright Statements . . . . . . . . . . 10

1. Introduction

Privacy is defined in this document [RFC3323] as the withholding of the identity of
a person (and related personal information) from destination(s) of
messages and/or intermediaries handling these messages in a an exchange
of SIP (Session Initiation Protocol) [RFC3261] dialog. communications.

In SIP, identity is most commonly carried in the form of a SIP URI
and an optional display name, display-name, which commonly appear in the To, From
and other header fields of SIP requests and responses.

There are numerous other places in SIP messages in which identity-
related information can be revealed. For example, the Contact header
field contains a SIP URI. Moreover, information in the Record-Route
and Via headers could inadvertently reveal something about the
originator of a message.

To provide privacy, [RFC3323]

RFC 3323 defines a privacy mechanism mechanisms for SIP,
which was then based on techniques
available at the best current practice time of publication. Some of these mechanisms rely
on the use of a separate privacy service to maintain privacy. remove sensitive
information from 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 seem
to enable a user agent to withhold its user's identity and related
information without dependency on privacy services, which was not
possible when RFC3323 RFC 3323 was defined.

Some aspect

A number of issues have been identified with the mechanisms defined
in RFC 3323, especially its dependency with mechanisms that depend on a privacy
service to provide privacy, seems to cause some issues, which we hope
that we can resolve with this specification.

Some of the issues identified with the RFC 3323 are shown below.
service.

1. There is no assurance that a privacy service exists in the
signaling path.

2. There is no way that the user requesting the privacy can figure
out that the privacy function was properly executed.

3. A privacy service that modifies a Call-ID in the establishment of
the original dialog must be present in the
signaling path of the
subsequent request such as REFER. If a privacy service
anonymizes a Call-ID and the anonymized Call-ID is referenced in
a any subsequent SIP message for the purpose of a call-back or a call
replacement, requests that carry that
Call-ID. For requests within the privacy service needs to same dialog this can be in a signaling path
to replace
achieved using the anonymized Call-ID with record-route mechanism. For requests outside
the original Call-ID
appropriately, regardless of being inside/outside dialog that carry the dialog. Call-ID in a Replaces, Join or Target-
Dialog header field, for example, there is no defined mechanism.

4. To map the referenced dialog to a dialog attempt invoked by
REFER, for example, the privacy service needs to retain the
correspondence relation between original information and modified
information beyond the actual dialog duration of the referenced
dialog.

To solve the problems, this document proposes a new privacy mechanism
in which a user agent executes 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 Relay
NAT)[I-D.rosenberg-midcom-turn].
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].

3. Concept of Privacy

privacy-sensitive information:
The concept of privacy in this document means the concealing of information that relates to a user, identifies a user, and belongs to
a user, user who sends the SIP
message, as well as the supplementary information that
can be used to guess the user's identity.

3. Concept of Privacy

The scope concept of privacy in this document is to withhold means the concealing of the
identity of a user and supplementary information. The scope of this
document is to withhold the privacy-sensitive information of the user
who sends the SIP message from other users and intermediaries
handling the message. The protection of network privacy (e.g.,
topology hiding) is outside the scope of this document.

User-privacy-related

Privacy-sensitive information includes display name display-name and URI in a From
header that can reveal the user's name and affiliation (e.g., company
name), contact information in a Contact header that is used to
communicate with the user, user's UA, an IP address in an SDP (Session
Description Protocol)[RFC4566] that tells the location of a user's
terminal UA
and can be used to establish a connection. A host name in Call-ID is
also regarded as user-privacy-related privacy-sensitive information because it may reveal
the user's domain name.

Privacy-sensitive information is divided into two types, user-
inserted information
inserted by the user's UA and network-inserted information. information inserted by other SIP
entities (e.g., proxies, B2BUAs). A user agent can maintain privacy
of the user-inserted UA-inserted information by itself. On the other hand,
regarding the network-inserted information, information inserted by other entities, a user agent
can insert a privacy flag and request intermediaries not to add the user-privacy-related
privacy-sensitve information.

4. Use Cases

The following are the use cases from the viewpoint of privacy.

Case 1: User privacy is required and a user agent can anonymize all
of the user-inserted privacy-related information by itself.

Case 2: User privacy is required but a user agent cannot anonymize
the user-inserted privacy-related information all by itself.

Case 3: User privacy is not required. The user does not want
privacy at all and would like to reveal his/her identity.

Note that Case 2 is based on the premise that the user agent has
limited capabilities and it cannot find a GRUU or TURN server. Case
2 is outside the scope of this document.

5. Requirements

The following are requirements to cover the use cases in for the previous
section. UA-driven privacy mechanism are as follows:

Req 1: A user agent MUST be able to send a SIP request that is fully
anonymized. This is, any headers and body inserted by the UA
user agent does not jeopardize user privacy.

Req 2: It MUST be possible for a user agent to indicate to
downstream entities that a user is requesting privacy.

Req 3: When privacy is requested, a proxy SHOULD honor the request
and only add information necessary to route the call while
withholding any sensitive information that may reveal
anything about the user if possible.

Req 4: Mechanism defined here MUST be backward compatible with the
pre-existing privacy mechanism already in place.

5. Treatment of User Privacy Related Privacy-Sensitive Information

Except by means of a privacy service, RFC 3323 does not provide means
to obscure two important pieces of information about the user agent,
which are a URI used to exchange signaling (Contact, From, for
example), and an IP address address(es) used to exchange media.

RFC 3323 recommends to set sip:anonymous@anonymous.invalid as a SIP
URI in a From header when user privacy is required. Although, the
From header field URI may need to be an anonymous but functional URI.
For example, a mechanism of SIP-Identity [RFC4474] requires a
functional From header even if it is anonymous.

With the use of GRUU [I-D.ietf-sip-gruu] and TURN
[I-D.rosenberg-midcom-turn], UA
[I-D.ietf-behave-turn], a user agent can now obtain URI URI(s) and IP address
address(es) for media that are functional, which are usable to exchange either signaling or
media while providing privacy.

6.1. functional yet anonymous, in that they
do not identify the user agent.

5.1. Anonymous URI and Display-Name

A user agent wanting to obtain functional anonymous URI SHOULD
support and SHOULD utilize the Global Routable User Agent URI (GRUU) GRUU mechanism. By sending a REGISTER
request requesting GRUU, the UA can obtain an anonymous URI, which
can later be used for From, Contact
and other headers where the URI of the originator is needed. header.

The detailed process on how a user agent obtains a GRUU is described
in [I-D.ietf-sip-gruu]. If the Registrar supports GRUU and returns a
REGISTER response, the user agent SHOULD search within the REGISTER
response for a "temp-gruu" URI parameter, which provides the desired
privacy property.

If the "temp-gruu" URI parameter and value exist within the REGISTER
response, the user agent SHOULD use the value of the "temp-gruu" as
an anonymous URI representing the originator. user agent. This URI SHOULD be
used for Contact and From, for example, wherever the originator of
the URI is required. header.

The user agent setting using the "temp-gruu" as a GRUU SHOULD contact URI is RECOMMENDED
to set "Anonymous" as a display name display-name in any header where the display display-
name of the originator is set. That indicates the anonymity of the
request to intermediaries that may invoke some services based on the
anonymity of the call. The temp-gruu alone is not sufficient to
invoke such service because GRUU is merely a URI that is a sequence
of strings and digits with no explicit semantics to indicate that it
is an anonymous URI.

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.

Note: How to obtain an anonymous URI for From and any headers other
than the Contact is FFS.

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

6.2.

5.2. Anonymous IP Address

It is assumed that a user agent is either manually or automatically
configured through means such as a configuration framework
[I-D.ietf-sipping-config-framework] with the address of one or more
STUN relay servers.

Two IP addresses are needed to maintain privacy, one to be used in
signaling such as in a Via header, another to be used in SDP for
media.

A user agent that is not provided with a functional anonymous IP
address through some administrative means, SHOULD obtain a relayed
address (IP address of the media relay) for use in SDP, derived from
a STUN [I-D.ietf-behave-turn] relay server using the STUN Relay
Usage[I-D.rosenberg-midcom-turn], relay
usage, which allows a STUN server to act as a media relay.

Note: A relayed IP address may be used for a Via header, but some
commented that is not an appropriate to be used for signaling.
There was a comment about the IP address in Via being stripped
by the proxy, but that would require that a proxy compliant to
this specification is in the signaling path.

6. User Agent Behavior

A user agent fully compliant with this document SHOULD obscure or
conceal all the user-inserted privacy-related UA-inserted privacy-sensitive information in SIP
requests and responses when user privacy is requested. Section 7.1 6.1
describes how to generate an anonymous message at a user agent.

When a user agent generates an anonymous message based on this
specification, it SHOULD set an indication to tell intermediaries not
to add or modify user-privacy-related privacy-sensitive information. Section 7.2 6.2 describes more
about this.

7.1.

6.1. Generating Anonymous Message

The two pieces of information that a user agent needs to obscure
while sustaining its purpose and functionality are the URI and IP
address used for establishing a media/signaling session.
Instructions on how to obtain an functional anonymous URI and IP
address are given in Section 6.1 5.1 and 6.2, 5.2, respectively.

For anonymizing any headers and information in a SIP message, the
user agent SHOULD follow the instructions in this document.

Note: Instructions to treat each SIP header/parameter in generating
an anonymous SIP message SIP message will be given in a future.

7.2. future version of
this draft.

6.2. Indication to maintain Maintain Privacy

This document defines a privacy flag, which indicates that the user
requires privacy for the SIP message. Without a privacy flag,
intermediaries might add some user-privacy-related privacy-sensitive information in the
message, even if a user agent had anonymized the message as perfectly
as possible.

When a user agent generates an anonymous message by itself according
to the guidelines in Section 7.1, 6.1, it SHOULD set a flag to request
intermediaries not to add user-privacy-related privacy-sensitive information.

Note: The mechanism of the flag is FFS.

7. Proxy Behavior

When a proxy receives a SIP message containing a privacy flag, the
proxy compliant with this specification MUST NOT add any information
that may reveal something about the sender that is irrelevant to
routing unless the proxy knows that such information will be deleted
before it leaves the boundary of the Trust Domain[RFC3324].

A proxy MUST NOT modify the privacy flag, if present.

8. Security Considerations

TBD

10.

9. IANA Considerations

TBD

11.

10. References

11.1.

10.1. 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)",
draft-ietf-behave-turn-06 (work in progress),
January 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.

[I-D.rosenberg-midcom-turn]
Rosenberg, J., "Traversal Using Relay NAT (TURN)",
draft-rosenberg-midcom-turn-08 (work in progress),
September 2005.

[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.

10.2. 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.

11.2. Informative References

[RFC3324] Watson, M., "Short Term Requirements for Network Asserted
Identity", RFC 3324, November 2002.

[RFC4566] Handley, M., Jacobson, V.,

[RFC4474] Peterson, J. and C. Perkins, "SDP: Jennings, "Enhancements for
Authenticated Identity Management in the Session
Description Protocol",
Initiation Protocol (SIP)", RFC 4566, July 4474, August 2006.

Authors' Addresses

Mayumi Munakata
NTT Corporation

Phone: +81 422 36 7565
Email: munakata.mayumi@lab.ntt.co.jp

Shida Schubert
NTT Corporation

Phone: +1 604 762 5606
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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