SIP M. Munakata
Internet-Draft S. Schubert
Intended status: Standards Track T. Ohba
Expires: August 22, 2007 NTT
February 18, 2008
UA-Driven Privacy Mechanism for SIP
draft-ietf-sip-ua-privacy-01
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Copyright (C) The IETF Trust (2007).
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.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Concept of Privacy . . . . . . . . . . . . . . . . . . . . . . 4
4. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 5
5. Treatment of Privacy-Sensitive Information . . . . . . . . . . 5
5.1. Anonymous URI and Display-Name . . . . . . . . . . . . . . 5
5.2. Anonymous IP Address . . . . . . . . . . . . . . . . . . . 6
6. User Agent Behavior . . . . . . . . . . . . . . . . . . . . . 7
6.1. Generating Anonymous Message . . . . . . . . . . . . . . . 7
6.2. Indication to Maintain Privacy . . . . . . . . . . . . . . 7
7. Proxy Behavior . . . . . . . . . . . . . . . . . . . . . . . . 8
8. Security Considerations . . . . . . . . . . . . . . . . . . . 8
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8
10.1. Normative References . . . . . . . . . . . . . . . . . . . 8
10.2. Informative References . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 9
Intellectual Property and Copyright Statements . . . . . . . . . . 10
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1. Introduction
Privacy is defined in [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 an exchange
of SIP (Session Initiation Protocol) [RFC3261] communications.
In SIP, identity is most commonly carried in the form of a SIP URI
and an optional 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.
RFC 3323 defines privacy mechanisms for SIP, based on techniques
available at the time of publication. Some of these mechanisms rely
on the use of a separate privacy service to 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 RFC 3323 was defined.
A number of issues have been identified with the mechanisms defined
in RFC 3323, especially with mechanisms that depend on a privacy
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 must be present in the
signaling path of any subsequent requests that carry that
Call-ID. For requests within the same dialog this can be
achieved using the record-route mechanism. For requests outside
the dialog that carry the 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
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dialog.
To solve the problems, this document proposes a new privacy mechanism
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 Relay
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 the supplementary information that
can be used to guess the user's identity.
3. Concept of Privacy
The concept of privacy in this document 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.
Privacy-sensitive information includes 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's UA, an IP address in an SDP (Session
Description Protocol)[RFC4566] that tells the location of a user's UA
and can be used to establish a connection. A host name in Call-ID is
also regarded as privacy-sensitive information because it may reveal
the user's domain name.
Privacy-sensitive information is divided into two types, information
inserted by the user's UA and information inserted by other SIP
entities (e.g., proxies, B2BUAs). A user agent can maintain privacy
of the UA-inserted information by itself. On the other hand,
regarding the information inserted by other entities, a user agent
can insert a privacy flag and request intermediaries not to add the
privacy-sensitve information.
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4. Requirements
The requirements for the 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
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 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 IP 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.ietf-behave-turn], a user agent can now obtain URI(s) and IP
address(es) for media that are 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 GRUU mechanism. By sending a REGISTER
request requesting GRUU, the UA can obtain an anonymous URI, which
can later be used for Contact 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
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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 user agent. This URI SHOULD be
used for Contact header.
The user agent using the "temp-gruu" as a contact URI is RECOMMENDED
to set "Anonymous" as a display-name in any header where the 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.
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, which allows a STUN server to act as a media relay.
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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 UA-inserted privacy-sensitive information in SIP
requests and responses when user privacy is requested. Section 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 privacy-sensitive information. Section 6.2 describes more
about this.
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 5.1 and 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 will be given in a future version of
this draft.
6.2. Indication to 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 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 6.1, it SHOULD set a flag to request
intermediaries not to add privacy-sensitive information.
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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
9. IANA Considerations
TBD
10. References
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.
[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.
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[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.
[RFC3324] Watson, M., "Short Term Requirements for Network Asserted
Identity", RFC 3324, November 2002.
[RFC4474] Peterson, J. and C. Jennings, "Enhancements for
Authenticated Identity Management in the Session
Initiation Protocol (SIP)", RFC 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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