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Versions: (draft-dcsgroup-sip-privacy) 00 01 02 03 04

SIP Working Group                                           W. Marshall
Internet Draft                                                     AT&T
Document: <draft-ietf-sip-privacy-01.txt>
                                                        K. Ramakrishnan
                                                     TeraOptic Networks

                                                              E. Miller
                                                             G. Russell
                                                              CableLabs

                                                               B. Beser
                                                      Pacific Broadband

                                                            M. Mannette
                                                        K. Steinbrenner
                                                                   3Com

                                                                D. Oran
                                                           F. Andreasen
                                                                  Cisco

                                                             J. Pickens
                                                                  Com21

                                                            P. Lalwaney
                                                                  Nokia

                                                             J. Fellows
                                                               Motorola

                                                               D. Evans
                                                 D. R. Evans Consulting

                                                               K. Kelly
                                                               NetSpeak

                                                              M. Watson
                                                        Nortel Networks

                                                         February, 2001


             SIP Extensions for Caller Identity and Privacy


Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026 [1].

   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
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   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.

   The distribution of this memo is unlimited.  It is filed as <draft-
   ietf-sip-privacy-01.txt>, and expires August 31, 2001. Please send
   comments to the authors.



1. Abstract

   This document describes extensions to the Session Initiation
   Protocol (SIP) that allow parties in a SIP session to be identified
   by different types of party information such as calling and called
   party. For each type of party information, different types of
   identity information, e.g. subscriber, or terminal, can be provided.
   The extensions can furthermore be used in an environment where one
   or more proxies serve as intermediaries which can provide and verify
   the identity of the parties either directly or indirectly, while
   still respecting desired privacy. Each party can specify the level
   of privacy that should be afforded them, from simple suppression of
   party information to full IP address privacy.


2. Conventions used in this document

   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 [2].


3. Introduction

   In order for SIP [4] to be a viable alternative to the current PSTN,
   SIP must support certain popular telephony services as well as some
   regulatory and public safety requirements. These include Calling
   Identity Delivery services, Calling Identity Delivery Blocking, as
   well as the ability to trace the originator of a call. While SIP can
   support each of these services independently, certain combinations
   cannot be supported. For example, a caller that wants to maintain
   privacy and consequently provides unintelligible information in the
   From header field will not be identifiable. However, since the
   contents of the From header cannot be modified this will prevent
   certain services, e.g. return call or call trace, to be preformed by
   entities more than a single hop away. We note that this problem is
   not telephony specific but applies to other forms of session
   initiation as well. Furthermore, the issue of privacy in an IP
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   environment is more complicated than in the PSTN, as the caller and
   callee will normally exchange IP traffic directly, and IP address
   information itself may reveal some privacy. The issue of IP address
   privacy for both the caller and callee consequently needs to be
   addressed as well.

   In order to solve the above we assume an architecture where a SIP
   User Agent is associated with a trusted proxy, and proxies in turn
   communicate with other proxies and user agents which may or may not
   be trusted. Calls utilizing the services of this architecture must
   both be placed and received through the trusted proxy.

   This document defines two extensions to SIP that allow the parties
   to be identified by a trusted intermediary while still being able to
   maintain their privacy. A new general header, Remote-Party-ID,
   identifies each party. Different types of party information can be
   provided, e.g. calling, or called party, and for each type of party,
   different types of identity information, e.g. subscriber, or
   terminal, can be provided. Since a party may not wish to reveal some
   or all of this information to an untrusted entity, the party can
   request a specific level of privacy for each. The intermediary also
   has the ability to specify a specific level of privacy. We also
   define another new general header, Anonymity, which defines other
   types of privacy requested by the party. Currently, the only such
   type is IP address privacy.

   The trusted intermediary verifies the Remote-Party-ID information
   supplied and ensures the privacy requested, including IP address
   privacy, is provided when forwarding a message across an untrusted
   boundary. Remote-Party-ID information that was not successfully
   verified, is tagged with an indication of this, so the receiver
   knows whether it should trust the information or not.

   This document defines a set of party types and identity information.
   New types of party and identity information may be introduced,
   thereby allowing new services to make use of the generic party
   information, privacy and authenticity handling defined here.


4. Protocol Overview

   UACs that wish to use the extensions defined here MUST include a
   Proxy-Require header in the initial INVITE request containing the
   option tag "privacy". When such a UAC initiates a call, it SHOULD
   include a calling subscriber Remote-Party-ID header field in the
   initial INVITE request in order to identify the originator of the
   call. This Remote-Party-ID MUST contain a SIP-URL identifying the
   UAC and MAY contain a "display-name" for the UAC as well. The party
   type SHOULD be set to "calling" and the identity type SHOULD be set
   to "subscriber", however other types of party and identity
   information may be included as well. If Remote-Party-ID privacy is
   desired, the UAC MUST include a privacy token set to one or more of
   "uri", "name" or "full". If IP address privacy is desired, the UAC
   MUST include an Anonymity header set to "ipaddr".
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   When a proxy supporting this extension receives an INVITE from an
   untrusted entity, it looks for the presence of a Remote-Party-ID
   header with calling subscriber information. If one is found, the
   proxy determines if the previous hop was a UA the proxy serves. If
   so, the calling subscriber Remote-Party-ID information is verified
   and modified if needed. If the request instead came from another
   untrusted entity, the proxy either removes the calling subscriber
   Remote-Party-ID information or marks it as being untrusted.
   Alternatively, the proxy MAY reject the request, e.g. with a 403 or
   407. Other types of Remote-Party-ID information may be present as
   well. For each of these, the proxy MUST mark the information as
   being untrusted, if the request was received from an untrusted
   entity. Additional procedures may be defined as well.

   Prior to forwarding the request to an untrusted entity, the proxy
   MUST look for the presence of a privacy request indication in each
   Remote-Party-ID header field. If one is found, the privacy requested
   MUST be provided for that Remote-Party-ID header field prior to
   forwarding the request. For uri and name privacy, this typically
   involves encrypting and possibly removing information provided in
   the Remote-Party-ID. The proxy MUST also look for the presence of an
   Anonymity header requesting IP address privacy. If IP Address
   privacy is requested, the proxy MUST ensure that IP address privacy
   is provided through a level of indirection for signaling and media.
   We refer to the function that provides this level of indirection as
   an Anonymizer. The Anonymity header MUST be removed as well.

   Once a UAS supporting this extension receives the INVITE, it can use
   the calling subscriber Remote-Party-ID information provided to
   identify the originator of the call, unless the originator had
   requested privacy. If the INVITE contained a Proxy-Require with an
   option tag of "privacy", the UAS SHOULD include a called subscriber
   Remote-Party-ID identifying itself in the first non-100 response.
   The party information SHOULD be set to "called" and the identity
   information SHOULD be set to "subscriber". Additional Remote-Party-
   ID header fields may be provided as well. If the UAS desires privacy
   for a Remote-Party-ID, it MUST include a privacy request indication
   in that Remote-Party-ID header. If the UAS desires IP address
   privacy, the UAS MUST include an Anonymity header indicating this.

   The UAS MAY also include Remote-Party-ID headers in subsequent
   provisional and final responses to the INVITE. The UAS SHOULD
   include a called party Remote-Party-ID header if the contents are
   different than sent in a previous response. The party information
   SHOULD be set to "called" and the identity information SHOULD be set
   to "subscriber". Additional Remote-Party-ID header fields may be
   provided as well.

   When a proxy supporting this extension receives a non-100 response
   to the initial INVITE, it looks for a Remote-Party-ID header field
   and applies similar processing as for the initial INVITE with one
   difference. If the INVITE did not contain a Proxy-Require with an
   option tag of "privacy", the proxy MUST ensure that any privacy
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   requested in the response is provided prior to forwarding it,
   irrespective of whether the previous hop is trusted or not.

   Finally, when the UAC receives the first non-100 response from the
   UAS, it can use the called subscriber Remote-Party-ID information
   provided to identify the called party, unless the terminator had
   requested privacy. Subsequent non-100 responses MAY contain Remote-
   Party-ID information as well. When the UAC receives the final 200
   response, it MAY contain a called subscriber Remote-Party-ID header
   identifying the party the UAC was connected to.


5. Header Field Definitions

   Table 1 below is an extension of tables 4 and 5 in [4] for the new
   headers defined here:


                      where  enc.  e-e  ACK  BYE  CAN  INV  OPT  REG
     Anonymity          g     n     h    -    -    -    o    -    -
     Remote-Party-ID    g     n     h    -    -    -    o    -    -

   Table 1: Summary of header fields.


   The headers can be used in an INVITE as well as any response to an
   INVITE.

5.1 Remote-Party-ID Header Field Definitions

   The Remote-Party-ID header field provides information about the
   remote party. Different types of party information can be provided,
   e.g. calling and called, and for each, different types of identity
   information can be provided as well. A request or response MAY
   contain more than one Remote-Party-ID header field with privacy
   requested independently for each. Remote-Party-ID is defined by the
   following ABNF [3]:

     Remote-Party-ID    = "Remote-Party-ID" ":" [display-name]
                                "<" addr-spec ">" *(";" rpi-token)

     rpi-token          = rpi-screen | rpi-pty-type |
                           rpi-id-type | rpi-privacy | other-rpi-token

     rpi-screen         = "screen" "=" ("no" | "yes" )

     rpi-pty-type       = "party" "=" ( "calling" | "called"  | token )

     rpi-id-type        = "id-type" "=" ( "subscriber" | "user" |
                                "alias" | "return" | "term"  | token )

     rpi-privacy        = "privacy" "=" 1#(
                            ("full" | "name" | "uri" | "off" | token )
                            [ "-" ( "network" | token ) ]  )
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     other-rpi-token    = token ["=" (token | quoted-string)]

   Furthermore, we define the value "private" for "other-user" in an
   "addr-spec", to indicate that the user part of an "addr-spec" is in
   a non-intelligible form. The syntax for "other-user" is therefore
   refined to:

     other-user         = token  | "private"

   Comparisons follow the case-sensitivity rules defined by SIP [4].

   The "display-name" in Remote-Party-ID is a text string that
   identifies the name of the party. The "addr-spec" contains
   information identifying the party either in clear-text or encrypted
   form. In the latter case, the "user" part of the "addr-spec"
   typically contains the encrypted party information, whereas the
   "hostport" identifies the entity that can decrypt the information.
   Furthermore, an "other-user" value of "private" will then be present
   to indicate that the "addr-spec" is non-intelligible. Depending on
   the rpi-pty-type, the "addr-spec" can be used as the Request-URI by
   the UA to initiate certain call control functions or subsequent
   calls that are required to reference the party.

   The rpi-screen parameter describes what verification the Remote-
   Party-ID information has undergone. The value "yes" indicates the
   Remote-Party-ID was verified successfully by the proxy itself or the
   proxy received the message from a trusted proxy with this
   indication. The value "no" (assumed by default) indicates the
   Remote-Party-ID was either not verified successfully by the proxy or
   the proxy received the message from an untrusted entity. Multiple
   rpi-screen parameters MAY be present in a Remote-Party-ID -  if both
   "yes" and "no" are present, "no" will take precedence.

   The rpi-pty-type describes the type of party to which this header
   refers. There MUST NOT be more than one rpi-pty-type present in a
   Remote-Party-ID. If absent, the parameter describes the party from
   which it was received, i.e. "calling" party in the case of INVITE,
   and "called" in the case of responses. Additional values may be
   defined as extensions.

   The rpi-id-type describes the nature of the identity provided.
   Several types of identity may be provided for each party, however
   there MUST NOT be more than one rpi-id-type present in a given
   Remote-Party-ID. If the rpi-id-type parameter is absent, the Remote-
   Party-ID contains the subscriber identity.

   This document defines five identity types - additional values may be
   defined as extensions. The types are defined based on the nature of
   the information they represent, as opposed to a particular
   application. Individual applications requiring identity information
   will specify which identities should be used for that application:

   Subscriber identity (rpi-id-type="subscriber"):
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     This identifies the owner of the subscription which is being used
     for the session.

   User identity (rpi-id-type="user"):

     This identifies the individual participating in the session. For
     example when multiple individuals are able to originate sessions
     under the same subscription. If absent, this is assumed to be the
     same as the subscriber identity.

   Alias identity (rpi-id-type="alias"):

     This is an identity which the party has asked to be identified by.
     For example a user may have a 'business' and a 'personal' address,
     and may ask to be identified by one of these when initiating a
     session using the other subscription. If absent, this is assumed
     to be the same as the subscriber identity.

   Return session identity (rpi-id-type="return")

     This identifies the point to which the party wishes return
     sessions to be addressed. For example a business may wish to
     provide a 'freephone' identity to encourage return calls. If
     absent, this is assumed to be the same as the subscriber identity.

   Terminal identity (rpi-id-type="term")

     This identifies the terminal being used for the session. For
     example several users may be able to 'log in' to a single
     terminal, in which case the identity of the terminal will differ
     from that of the user, subscriber, etc. If absent, this is assumed
     to be the same as the subscriber identity.

   UAs SHOULD NOT include multiple Remote-Party-ID headers containing
   the same identity information marked with different rpi-id-types.

   The rpi-privacy parameter describes whether the identity information
   must be hidden from untrusted entities. There MAY be multiple rpi-
   privacy parameters in a Remote-Party-ID. If privacy is requested, it
   MUST be one or more of "full", "uri", or "name". The value "full"
   requests that both the "display-name" and the "addr-spec" must be
   hidden. The values "name" and "uri" request that the "display-name"
   or the "addr-spec" must be hidden respectively. The value "off"
   indicates that lack of privacy is explicitly requested, and MUST be
   the only value if present. The values may be postfixed with a string
   indicating that the privacy request was made by an entity other than
   the party itself. Postfixing with the value "-network" indicates
   that the network proxies have requested that the information be
   hidden. Additional values may be defined as extensions.

   It should be noted, that an entity requesting only Remote-Party-ID
   privacy will not receive complete privacy. The values "uri" and
   "name" merely affect information that may be displayed as opposed to
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   truly hiding the identity of the requesting entity since the
   identity of the host, e.g. IP address, is not hidden. For full
   privacy, the entity should request IP address privacy as well - see
   Section 5.2.

   Finally, the "other-rpi-token" parameter allows Remote-Party-ID to
   be extended with other types of parameters.

5.2 Anonymity Header Field Definition

   The Anonymity header field allows a SIP user agent to indicate the
   degree of other privacy that should be provided to its session. The
   only type of other privacy defined here is IP address privacy.

   The ABNF for the header field follows:

     Anonymity          = "Anonymity" ":"  1#privacy-tag
     privacy-tag        = "ipaddr" | "off" | token

   Comparisons follow the case-sensitivity rules defined by SIP [4].

   If privacy is requested, it MUST currently be "ipaddr" (extensions
   may change this). The value "off" indicates that no privacy is
   requested, and MUST be the only value if present. Additional values
   may be defined as extensions.

   The value "ipaddr" requests IP privacy such that the other party
   does not learn the IP address of this party.

   It should be noted, that an entity requesting only IP address
   privacy merely hides its IP address without suppressing its
   identity. For full privacy, the entity should thus also request
   privacy for its Remote-Party-ID information. Note however, that the
   use of extensions that do not consider privacy impacts, may in turn
   violate privacy.

   The value "off" indicates no privacy is requested, and MUST be the
   only value if present.

   Absence of the Anonymity header in a request or response is
   identical to the value "off", unless provisioned otherwise.

   It should be noted, that the Anonymity header field allows both the
   originating and terminating UA to indicate its desire for IP address
   privacy.


6. Protocol Semantics

   Below, we provide the protocol semantics for a UAC, a UAS, and a
   proxy.



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6.1 UAC Behavior

   When a UAC supporting this extension initiates a call through its
   trusted proxy, it SHOULD include a calling subscriber Remote-Party-
   ID header in the initial INVITE request in order to identify the
   originator of the call. The Remote-Party-ID header MUST at a minimum
   contain an "addr-spec" to uniquely identify the calling subscriber.
   The "addr-spec" SHOULD be the same string as appears in the Request-
   URI for incoming call attempts. The Remote-Party-ID SHOULD include
   an rpi-pty-type set to "calling" and an rpi-id-type set to
   "subscriber" - we refer to this as a calling subscriber Remote-
   Party-ID. The rpi-screen parameter SHOULD NOT be included. The
   Remote-Party-ID MAY optionally include a "display-name" which SHOULD
   be set to a name that the proxy has associated with the calling
   subscriber, e.g. the subscribers full name. The UAC MAY include
   other Remote-Party-ID information as well.

   If the UAC desires Remote-Party-ID privacy for the call, it MUST
   include an rpi-privacy parameter for each relevant Remote-Party-ID.
   The rpi-privacy parameter MUST specify the desired level of privacy,
   e.g. "uri", to maintain privacy of the "addr-spec". As honoring the
   privacy requested depends on the proxy, the UAC MUST furthermore
   include a Proxy-Require header with an option-tag of "privacy".

   If the UAC desires "name" or "full" privacy, the UAC MUST NOT reveal
   the originating subscriber's name in the "display-name" portion of
   any other header than Remote-Party-ID. This can be achieved by
   either not providing a "display-name" or setting the "display-name"
   to "anonymous" in such fields, e.g. From and Contact.

   If the UAC desires "uri" or "full" privacy, the UAC MUST NOT reveal
   the subscriber's identity in any other header field than Remote-
   Party-ID. In particular, the contents of header fields needs to be
   considered as described below:
   * From:      The UAC SHOULD supply a cryptographically random
   identifier for the userinfo, and a non-identifying hostname, e.g.
   "localhost", in the host name.
   * To:        If a telephone number is used in the addr-spec, the
   telephone number SHOULD be a full E.164 number including the country
   code that is different from the From: header. If a host name is
   included, it SHOULD be the non-identifying name "localhost".
   * Contact:   The same cryptographically random identifier used in
   the From header field SHOULD be supplied for the userinfo, and an
   IP-address SHOULD be used in the host name.
   * All other headers that may contain either an IP address or a
   domain name, e.g. Call-ID, and Via, SHOULD use the IP-address form.
   It should however be noted, that this simple privacy step may be
   overcome fairly easily in many cases.

   The UAC may also explicitly request that privacy is not to be
   provided for a Remote-Party-ID by setting the rpi-privacy parameter
   to "off". This is also the default value, unless provisioned
   otherwise.

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   If the UAC desires IP address privacy, it MUST include an Anonymity
   header field set to "ipaddr". The value "off", which is the default
   unless provisioned otherwise, may be provided if IP address privacy
   is explicitly not requested.

   If the UAC desires "ipaddr" privacy, then the following header field
   requirements apply:
   * From:      The UAC MUST use the non-identifying host name
   "localhost".
   * Call-ID:   The UAC MUST NOT base the Call-ID on the originator's
   IP address.

   The first non-100 response received by the UAC MAY contain Remote-
   Party-ID header fields. A Remote-Party-ID with party type "called"
   will identify the called party. If such a Remote-Party-ID header
   field either does not contain an rpi-screen parameter, or it
   contains an rpi-screen parameter with the value "no" (this includes
   the case where both "yes" and "no" is provided), the UAC SHOULD NOT
   trust the validity of the information provided.

   Subsequent responses received by the UAC MAY also contain Remote-
   Party-ID header fields. New Remote-Party-Ids with party type
   "called" identify other parties to which the session has been
   directed, for whatever reason.

   Remote-Party-ID headers contained in the final response, with rpi-
   pty-type set to "called" identify the party which has answered the
   session.

6.2 UAS Behavior

   A UAS supporting this extension and receiving an INVITE from its
   trusted proxy looks for a Remote-Party-ID header field with rpi-pty-
   type "calling" and rpi-id-type "subscriber", i.e. a calling
   subscriber Remote-Party-ID, to identify the originator of the
   request. If rpi-pty-type is omitted from a Remote-Party-ID in the
   INVITE, "calling" is assumed, and if rpi-id-type is omitted,
   "subscriber" is assumed. If a calling subscriber Remote-Party-ID
   either does not contain an rpi-screen parameter or it contains an
   rpi-screen parameter with a value of "no" (this includes the case
   where both "yes" and "no" is provided), the UAS SHOULD NOT trust the
   validity of the information provided. Otherwise, the UAS SHOULD use
   the information provided to identify the calling party rather than
   any information provided in the From or any other header field. Note
   that the INVITE MAY contain other Remote-Party-ID header fields.

   If the initial INVITE contained a Proxy-Require header field with an
   option tag of "privacy", the UAS SHOULD insert a called subscriber
   Remote-Party-ID header field identifying itself into the first non-
   100 response it sends. The called subscriber Remote-Party-ID SHOULD
   contain an rpi-pty-type of "called" and an rpi-id-type of
   "subscriber. Otherwise, the rules for the Remote-Party-ID are
   similar to those for the initial INVITE sent by a UAC. In addition,
   the UAS MAY insert Remote-Party-ID headers in any further responses.
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   The UAS SHOULD insert a new called subscriber Remote-Party-ID header
   if the called party information changed from the called party
   information sent in the previous response. Note that the UAS may
   request privacy for the Remote-Party-ID information as well.

   The UAS MAY request IP-address privacy by including an Anonymity
   header set to "ipaddr" in the first non-100 response it sends. It
   should be noted though, that the UAS can not depend on this privacy
   being honored, if the original INVITE did not contain a Proxy-
   Require with an option tag of "privacy".

6.3 Proxy Behavior

   When a proxy supporting this extension receives an INVITE from an
   untrusted entity, the proxy first determines if the request came
   from a UAC that it serves. If so, it examines the INVITE for the
   presence of calling subscriber Remote-Party-ID header fields. If a
   calling subscriber Remote-Party-ID header field is present, the
   information supplied is verified and, if needed, rewritten. The
   proxy MUST verify that the "addr-spec" provided in a calling
   subscriber Remote-Party-ID is a valid "addr-spec" for that UAC; if
   not, the proxy MUST rewrite the "addr-spec" with a valid "addr-spec"
   for that UAC. If "display-name" is provided in a calling subscriber
   Remote-Party-ID, the proxy MUST verify that the "display-name" is a
   valid string for the UAC; if not or if the "display-name" is
   omitted, the proxy MUST rewrite the "display-name" with a valid
   string for the UAC or remove the "display-name". The proxy MUST also
   add an rpi-screen parameter with a value of "yes". If an rpi-screen
   parameter was already present in the calling subscriber Remote-
   Party-ID, it MUST be discarded.

   If a Remote-Party-ID header was not present in the INVITE, but the
   proxy is able to identify the originating UAC anyway, the proxy
   inserts a Remote-Party-ID header with the correct information.

   If the request instead came from an untrusted entity, and it was not
   a UAC the proxy serves or the proxy is unable to identify the
   entity, the proxy MUST either remove any calling subscriber Remote-
   Party-ID header or add "screen=no" before the request is forwarded.
   In the latter case, the proxy SHOULD furthermore ensure this is the
   only rpi-screen parameter. Alternatively, the proxy MAY reject the
   request, e.g. with a 403 or 407.

   The INVITE MAY contain additional Remote-Party-ID header fields.
   When the request was received from an untrusted entity, each of
   these MUST be verified by the proxy. If the proxy is able to
   successfully verify the information in a Remote-Party-ID header
   field, the proxy MUST add an rpi-screen parameter set to "yes" for
   that Remote-Party-ID. Furthermore, this MUST be the only rpi-screen
   parameter for that Remote-Party-ID. If verification fails however,
   further processing depends on the reason for the failure. Two
   different failure reasons are defined here:
   * The information provided could not be verified because the proxy
     does not support this particular Remote-Party-ID.
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   * The information provided is incorrect and the proxy detected that.
   In the first case, the proxy MUST add an rpi-screen parameter set to
   "no". The proxy SHOULD furthermore ensure this is the only rpi-
   screen parameter. In the second case, the proxy MUST by default add
   an rpi-screen parameter set to "no" and ensure this is the only rpi-
   screen parameter, however individual extensions and local procedures
   MAY specify a different behavior, for example rewrite or removal of
   the offending Remote-Party-ID header field.

   Note, that the proxy does not check a "display-name" provided in the
   From header field.

   The proxy furthermore looks for the presence of a privacy request in
   any of the Remote-Party-ID headers as well as an Anonymity header.
   If privacy was requested, and the next hop is trusted, the proxy
   MUST ensure that a Proxy-Require header with an option-tag of
   "privacy" is present.

   If the proxy forwards the request to an untrusted entity, and
   privacy was requested, the proxy MUST ensure the privacy requested
   will be honored.

   For each Remote-Party-ID requesting privacy, the proxy MUST do the
   following:
   * If rpi-privacy contains the value "full" or "uri", the proxy MUST
     replace the "addr-spec" in that Remote-Party-ID header field with
     a private "addr-spec". The private "addr-spec" MUST list the proxy
     itself in the hostport and include a "user=private" user
     parameter.
   * If rpi-privacy contains the value "full" or "name", the proxy MUST
     delete the "display-name" in that Remote-Party-ID header field.

   Generation of the user part of a private "addr-spec" is a proxy
   internal issue as long as the requested privacy is honored. However,
   it is RECOMMENDED to construct the user part by including:
   1) the initial "addr-spec",
   2) the value of rpi-privacy, and
   3) sufficient checksum information to prevent tampering by the
      untrusted party.
   All of this information MUST then be encoded or encrypted such that
   the next hop is unable to discern the original Remote-Party-ID. It
   is RECOMMENDED that the string be encrypted with a symmetric private
   key, and converted to a printable string using Base64 encoding. The
   proxy MAY include other information in the user part as well.

   For IP-address privacy, the proxy MUST ensure that the request is
   rewritten in a way that ensures that the IP-address of the
   originating UAC will not be revealed. This implies that neither SIP
   signaling nor IP media streams are exchanged directly between the
   UAC and UAS. A level of indirection which we call an Anonymizer MUST
   be provided.

   Prior to forwarding the request to an untrusted entity, the proxy
   MAY remove any "privacy" option tag present in a Proxy-Require
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   header field to prevent unnecessary failure of the request if
   downstream proxies do not support this extension. Note that this
   will unfortunately also prevent downstream proxies and UASs from
   determining if their previous hop supports the extension.

   When receiving the first non-100 response to the initial INVITE from
   an untrusted entity, the proxy first determines if the response came
   from a UAS that it serves.

   If it did, the proxy examines the response for the presence of a
   called subscriber Remote-Party-ID and privacy requests (incl. IP
   address privacy) and applies similar processing as for an INVITE
   received from a UAC served by the proxy. Furthermore, if the
   original INVITE did not contain a Proxy-Require header field with an
   option tag of "privacy", the proxy can not determine if the previous
   hop supports the privacy extension or not. Consequently, if the
   response contains a request for privacy, the privacy MUST be applied
   by this proxy, irrespective of whether the upstream hop is trusted
   or not.

   If the response came from an untrusted entity, and it was not a UAS
   the proxy serves, the proxy MUST either remove any called subscriber
   Remote-Party-ID header fields provided or set "screen=no" before the
   response is forwarded upstream. The same action MUST be taken when
   the initial INVITE did not contain a Proxy-Require with an option
   tag of "privacy", irrespective of whether the downstream hop was
   trusted or not. The reason for this is, that without the proxy-
   require in the initial INVITE, the proxy does not know if the
   downstream proxies performed proper privacy handling.

   Finally, the response MAY contain additional Remote-Party-ID header
   fields. The proxy MUST apply similar processing as for an INVITE
   received from a UAC served by the proxy. In particular, the proxy
   MUST ensure it provides the proper screening indication of any
   Remote-Party-ID information received and performs the correct
   privacy handling as well.


6.4 Additional proxy behavior

   A proxy supporting this extension SHOULD be prepared to receive a
   request containing a SIP-URL with a user parameter of "private". If
   the "hostport" part of the SIP-URL identifies the proxy handling the
   request, the proxy MUST recover the private information. For proxies
   that use the encryption recommendation provided earlier, this
   implies decrypting the "user" portion of the SIP-URL and replacing
   it with the decrypted SIP-URL that was contained in the "user"
   portion as well as any other SIP information included. Note that the
   decrypted SIP-URL may itself contain a "private" SIP-URL.

   If the proxy is unable to recover a "private" SIP-URL, it MUST fail
   the request with a 4xx error code.


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7 Example of Use

   In this Section, we illustrate how the request for privacy may work
   in practice. It should be noted that the privacy service described
   can be implemented in a number of ways; we merely describe one
   possible solution in this section.

7.1 Basic Privacy Example

   The Figure below illustrates a basic privacy example scenario


                +---------+             +--------+
     1: INVITE  | Proxy-o | 2: INVITE   | Proxy-t| 3: INVITE
       +------->|         |------------>|        |---------+
       |        +---------+             +--------+         |
       |                                                   |
       |                 trust boundary                    |
   . . |. . . . . . . . . . . . . . . . . . . . . . .. . . | . . .
       |                                                   |
       |                                                   \/
   +------+                  RTP/RTCP                   +------+
   | UA-o |<------------------------------------------->| UA-t |
   +------+                                             +------+

                Figure 1 - Basic Privacy Example


   The originating user agent (UA-o) sends an INVITE (1) to Proxy-o
   where it identifies itself and requests uri and name, i.e. full,
   privacy. Since the From header field contains calling identity
   information, UA-o supplies a cryptographically random identifier for
   the user info, and the non-identifying hostname "localhost" rather
   than its true identity:

        INVITE
        From:            sip:xyz@localhost
        Remote-Party-ID: "John Doe" <sip:jdoe@foo.com>;party=calling;
                                id-type=subscriber;privacy=full
        Proxy-Require:   privacy



   Proxy-o verifies the calling subscriber information before it sends
   INVITE (2) to Proxy-t, which in this case is trusted. Since the
   calling subscriber Remote-Party-ID was verified successfully,
   Proxy-o adds an rpi-screen parameter set to "yes". When Proxy-t
   receives the INVITE, it examines the privacy request included in the
   INVITE and sees that uri and name privacy is requested. Proxy-t
   therefore removes the "display-name" from the calling subscriber
   Remote-Party-ID, encrypts the "addr-spec" and rpi-privacy, puts the
   result in the "user" part, inserts itself as the "hostport" and adds
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   a "user=private" user parameter. Also, Proxy-t removes the
   Proxy-Require "privacy":

        INVITE
        From:            sip:xyz@localhost
        Remote-Party-ID: <sip:e(<sip:jdoe@foo.com>;privacy=full
                                )@proxy-t.foo.com;user=private
                         >;party=calling;id-type=subscriber;
                                        privacy=full;screen=yes

   UA-t notes the presence of the Remote-Party-ID, but since it
   indicates full privacy, UA-t can only identify the calling
   subscriber as private, however it knows that the subscribers
   identity has been verified since the rpi-screen parameter is set to
   "yes". UA-t decides to accept the call setup, and responds with a
   180 Ringing. In this case, there is no request for privacy, so only
   the called subscriber Remote-Party-ID of the called party is added:

        180
        Remote-Party-ID: <sip:mdoe@foo.com>;party=called;
                                                id-type=subscriber

   Proxy-t verifies the information provided, adds the omitted
   "display-name" to the Remote-Party-ID as well as an rpi-screen
   parameter set to "yes". Since no privacy was requested, proxy-t can
   provide the Remote-Party-ID information to proxy-o in clear:

        180
        Remote-Party-ID: "Mary Doe" <sip:mdoe@foo.com>;party=called;
                                        id-type=subscriber;screen=yes

   Proxy-o forwards the response to UA-o as is.


   While this illustrates the basic operation of the service, there are
   additional issues that need to be considered. In SIP, there are
   several fields that can reveal the identity of the calling party,
   either in part or completely. Other protocols used, e.g. SDP and RTP
   may reveal identity information as well. A user agent wishing to not
   reveal its identity should consider each of these. The next example
   looks more closely at this.

7.2 Full Privacy Example

   The second example we look at is one where IP-address privacy is
   requested. The Figure below illustrates how IP address privacy can
   be achieved by inserting a trusted intermediary, an anonymizer, for
   the media streams between UA-o and UA-t. The interface between the
   proxies and the media anonymizer is purposely not defined here:





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                +---------+             +--------+
     1: INVITE  | Proxy-o | 2: INVITE   | Proxy-t| 3: INVITE
       +------->|         |------------>|        |----------+
       |        +---------+             +--------+          |
       |                  \           /                     |
       |                   \         /                      |
       |      SIP           +--------+           SIP        |
       | +----------------->| anony- |-------------------+  |
       | |          +------>|  mizer |--------+          |  |
       | |          |       +--------+        |          |  |
       | |          |                         |          |  |
       | |          |                         |          |  |
       | |          |     trust boundary      |          |  |
   . . |.|. . . . . | . . . . . . . . . . . . | . . .. . |..| . . .
       | |          |                         |          |  |
       | |          |                         |         \/ \/
   +------+ RTP/RTCP|                         |RTP/RTCP +------+
   | UA-o |<--------+                         +-------->| UA-t |
   +------+                                             +------+

                Figure 2 - Full Privacy Example


   For all signaling and media exchange purposes, the anonymizer adds a
   level of indirection thereby hiding the IP address(es) of UA-o from
   UA-t. This indirection is used both for the media streams and SIP
   signaling, beyond the initial INVITE, exchanged directly between
   UA-o and UA-t.

   In addition to the requirements listed earlier, the following
   commonly used header fields may reveal privacy information as well,
   which can be remedied as described:

   * A Contact header field must be set to point to the anonymizer to
     prevent any direct signaling between UA-o and UA-t
   * Via, Recourd-Route, Route, and any other header fields identifying
     either UA-o or Proxy-o must be hidden, e.g. by encryption or
     simple stateful removal and re-insertion by Proxy-t.

   An alternative to the media anonymizer function shown above is to
   implement the anonymizer as a back to back User Agent thereby
   trivially hiding IP address information in the SIP signaling itself.

   Furthermore, when SDP is used to describe the media in the session,
   the session descriptions exchanged by the user agents need to be
   modified to direct the media streams to the anonymizer. The use of
   SDP fields revealing calling identity information needs to be
   considered as well. Similar concerns apply to the use of RTCP.





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8. Security Considerations

   A user requesting complete privacy must still authenticate himself
   to the proxy, and therefore the SIP messages between the UA and the
   proxy MUST be protected. Likewise, it is necessary that the proxies
   take precautions to protect the user identification information from
   eavesdropping and interception. Use of IPSec between the UA and
   proxy as well as between proxies is recommended.


9. Notice Regarding Intellectual Property Rights

   AT&T may seek patent or other intellectual property protection for
   some or all of the technologies disclosed in the document. If any
   standards arising from this disclosure are or become protected by
   one or more patents assigned to AT&T, AT&T intends to disclose those
   patents and license them on reasonable and non-discriminatory terms.
   Future revisions of this draft may contain additional information
   regarding specific intellectual property protection sought or
   received.

   3COM may seek patent or other intellectual property protection for
   some or all of the technologies disclosed in the document. If any
   standards arising from this disclosure are or become protected by
   one or more patents assigned to 3COM, 3COM intends to disclose those
   patents and license them on reasonable and non-discriminatory terms.
   Future revisions of this draft may contain additional information
   regarding specific intellectual property protection sought or
   received.

10. References


   1. Bradner, S., "The Internet Standards Process -- Revision 3", BCP
      9, RFC 2026, October 1996.

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

   3  Crocker, D. and Overell, P.(Editors), "Augmented BNF for Syntax
      Specifications: ABNF", RFC 2234, Internet Mail Consortium and
      Demon Internet Ltd., November 1997

   4  M. Handley, H. Schulzrinne, E. Schooler, and J. Rosenberg, "SIP:
      session initiation protocol," Request for Comments (Proposed
      Standard) 2543, Internet Engineering Task Force, Mar. 1999.









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11. Acknowledgments

   The Distributed Call Signaling work in the PacketCable project is
   the work of a large number of people, representing many different
   companies.  The authors would like to recognize and thank the
   following for their assistance: John Wheeler, Motorola; David
   Boardman, Daniel Paul, Arris Interactive; Bill Blum, Jon Fellows,
   Jay Strater, Jeff Ollis, Clive Holborow, Motorola; Doug Newlin,
   Guido Schuster, Ikhlaq Sidhu, 3Com; Jiri Matousek, Bay Networks;
   Farzi Khazai, Nortel; John Chapman, Bill Guckel, Michael Ramalho,
   Cisco; Chuck Kalmanek, Doug Nortz, John Lawser, James Cheng, Tung-
   Hai Hsiao, Partho Mishra, AT&T; Telcordia Technologies; and Lucent
   Cable Communications.


12. Author's Addresses

   Bill Marshall
   AT&T
   Florham Park, NJ  07932
   Email: wtm@research.att.com

   K. K. Ramakrishnan
   TeraOptic Networks
   Sunnyvale, CA
   Email: kk@teraoptic.com

   Ed Miller
   CableLabs
   Louisville, CO  80027
   Email: E.Miller@Cablelabs.com

   Glenn Russell
   CableLabs
   Louisville, CO  80027
   Email: G.Russell@Cablelabs.com

   Burcak Beser
   Pacific Broadband Communications
   San Jose, CA
   Email: Burcak@pacband.com

   Mike Mannette
   3Com
   Rolling Meadows, IL  60008
   Email: Michael-Mannette@3com.com

   Kurt Steinbrenner
   3Com
   Rolling Meadows, IL  60008
   Email: Kurt-Steinbrenner@3com.com



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   Dave Oran
   Cisco
   Acton, MA  01720
   Email: oran@cisco.com

   Flemming Andreasen
   Cisco
   Edison, NJ
   Email: fandreas@cisco.com

   John Pickens
   Com21
   San Jose, CA
   Email: jpickens@com21.com

   Poornima Lalwaney
   Nokia
   San Diego, CA  92121
   Email: poornima.lalwaney@nokia.com

   Jon Fellows
   Motorola
   San Diego, CA  92121
   Email: jfellows@gi.com

   Doc Evans
   D. R. Evans Consulting
   Boulder, CO  80303
   Email: n7dr@arrl.net

   Keith Kelly
   NetSpeak
   Boca Raton, FL  33587
   Email: keith@netspeak.com

   Mark Watson
   Nortel Networks
   Maidenhead, UK
   Email: mwatson@nortelnetworks.com















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Full Copyright Statement

   "Copyright (C) The Internet Society (2001). All Rights Reserved.
   This document and translations of it may be copied and furnished to
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   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph
   are included on all such copies and derivative works. However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
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   INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR
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   Expiration Date This memo is filed as <draft-ietf-sip-privacy-
   01.txt>, and expires August 31, 2001.




























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