One document matched: draft-ietf-sip-privacy-01.txt
Differences from draft-ietf-sip-privacy-00.txt
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
SIP Working Group Expiration 8/31/01 1
SIP Extensions for Caller Privacy February 2001
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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SIP Extensions for Caller Privacy February 2001
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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SIP Extensions for Caller Privacy February 2001
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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SIP Extensions for Caller Privacy February 2001
+---------+ +--------+
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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SIP Extensions for Caller Privacy February 2001
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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SIP Extensions for Caller Privacy February 2001
Full Copyright Statement
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Expiration Date This memo is filed as <draft-ietf-sip-privacy-
01.txt>, and expires August 31, 2001.
SIP Working Group Expiration 8/31/01 20
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