Internet Draft Mark Watson
Document: draft-ietf-sipping-nai-reqs-01.txt Nortel Networks
Category: Informational
Expires November 2002 May 2002
Short term requirements for Network Asserted Identity
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
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 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.
Abstract
A Network Asserted Identity is an identity initially derived by a SIP
network intermediary as a result of an authentication process. This
draft describes short term requirements for the exchange of Network
Asserted Identities within networks of securely interconnected
trusted nodes and to User Agents securely connected to such networks.
Table of Contents
1. Introduction...................................................2
2. Definitions....................................................2
2.1 Identity...................................................2
2.2 Network Asserted Identity..................................3
2.3 Trust Domains..............................................3
3. Generation of Network Asserted Identity........................5
4. Transport of Network Asserted Identity.........................5
4.1 Sending of Network Asserted Identity within a Trust Domain.5
4.2 Receiving of Network Asserted Identity withing a Trust Domain
...............................................................5
Watson Expires - November 2002 [Page 1]
Network Asserted Identity û short term requirements May 2002
4.3 Sending of Network Asserted Identity to entities outside a
Trust Domain...................................................5
4.4 Receiving of Network Asserted Identity by a node outside the
Trust Domain...................................................5
5. Parties with Network Asserted Identities.......................6
6. Types of Network Asserted Identity.............................6
7. Privacy of Network Asserted Identity...........................6
8. Next steps.....................................................7
9. Security considerations........................................7
10. IANA Considerations...........................................7
11. References....................................................8
12. Acknowledgments...............................................8
13. AuthorsÆ Addresses............................................8
14. Full Copyright Statement......................................8
1. Introduction
SIP [1] allows users to assert their identity in a number of ways
e.g. using the From: header. However, there is no requirement for
these identities to be anything other than the users desired alias.
An authenticated identity of a user can be obtained using SIP Digest
Authentication (or by other means). However, UAs do not always have
the necessary key information to authenticate another UA. .
A Network Asserted Identity is an identity initially derived by a SIP
network intermediary as a result of an authentication process. This
may or may not be based on SIP Digest authentication. This draft
describes short term requirements for the exchange of Network
Asserted Identities within networks of securely interconnected
trusted nodes and also to User Agents with secure connections to such
networks.
Such a network is described in this draft as a Trust Domain and we
present a strict definition of trust and Trust Domain for the
purposes of this draft. These short-term requirements provide only
for the exchange of Network Asserted Identitied within a Trust Domain
and to an entity directly connected to the trust domain.
General requirements for transport of Network Asserted Identities on
the Internet are out of scope of this draft.
2. Definitions
2.1 Identity
Watson Expires - November 2002 [Page 2]
Network Asserted Identity û short term requirements May 2002
An Identity, for the purposes of this draft, is a URI, and optionally
a Display Name. The URI MUST be meaningful to the domain identified
in the URI when used as a SIP Request-URI.
If the URI is a sip: or sips: URI, then depending on the local policy
of the domain identified in the URI, the URI MAY identify some
specific entity, such as a person.
If the URI is a tel: URI, then depending on the local policy of the
owner of the number range within which the telephone number lies, the
number MAY identify some specific entity, such as a telephone line.
However, it should be noted that identifying the owner of the number
range is a less straightforward process than identifying the domain
which owns a sip: or sips: URI.
2.2 Network Asserted Identity
A Network Asserted Identity is an identity derived by a SIP network
entity as a result of an authentication process.
The authentication process used, or at least it's
reliability/strength, is a known feature of the Trust Domain using
the Network Asserted Identity mechanism i.e. in the language of 2.3
below, it is defined in Spec(T).
2.3 Trust Domains
A Trust Domain for the purposes of Network Asserted Identity is a set
of SIP nodes (UAC, UAS, proxies or other network intermediaries) that
are trusted to exchange Network Asserted Identity information in the
sense described below.
A node can be a member of a Trust Domain, T, only if the node is know
to be compliant to a certain set of specifications, Spec(T), which
characterize the handling of Network Asserted Identity within the
Trust Domain, T.
Trust Domains are constructed by human beings who know the properties
of the equipment they are using/deploying. In the simplest case, a
Trust Domain is a set of devices with a single owner/operator who can
accurately know the behaviour of those devices.
Such simple Trust Domains may be joined into larger Trust Domains by
bi-lateral agreements between the owners/operators of the devices.
We say a node is ætrustedÆ (with respect to a given Trust Domain) if
and only if it is a member of that domain.
Watson Expires - November 2002 [Page 3]
Network Asserted Identity û short term requirements May 2002
We say that a node, A, in the domain is ætrusted byÆ a node, B, (or
æB trusts AÆ) if and only if:
(i) there is a secure connection between the nodes, AND
(ii) B has configuration information indicating that A is a member of
the Trust Domain.
Note that B may or may not be a member of the Trust Domain. For
example, B may be a UA which trusts a given network intermediary, A
(e.g. its home proxy).
A æsecure connectionÆ in this context means that messages cannot be
read by third parties, cannot be modified by third parties without
detection and that B can be sure that the message really did come
from A. The level of security required is a feature of the Trust
Domain i.e. it is defined in Spec(T).
Within this context, SIP signaling information received by one node
FROM a node that it trusts is known to have been generated and passed
through the network according to the procedures of the particular
specification set Spec(T), and therefore can be known to be valid, or
at least as valid as specified in the specifications Spec(T).
Equally, a node can be sure that signaling information passed TO a
node that it trusts will be handled according to the procedures of
Spec(T).
For these capabilities to be useful, Spec(T) must contain
requirements as to how the Network Asserted Identity is generated,
how its privacy is protected and how its integrity is maintained as
it is passed around the network. A reader of Spec(T) can then make an
informed judgement about the authenticity and reliability of Network
Asserted Information received from the Trust Domain T.
The term ætrustedÆ (with respect to a given Trust Domain) can be
applied to a given node in an absolute sense û it is just equivalent
to saying the node is a member of the Trust Domain. However, the node
itself does not know whether another arbitrary node is ætrustedÆ,
even within the Trust Domain. It does know about certain nodes with
which it has secure connections as described above.
With the definition above, statements such as æA trusted node SHALL
...Æ are just shorthand for æA node compliant to this specification
SHALL...Æ.
Watson Expires - November 2002 [Page 4]
Network Asserted Identity û short term requirements May 2002
Statements such as æWhen a node receives information from a trusted
node...Æ are NOT valid, because one node does not have complete
knowledge about all the other nodes in the trust domain.
Statements such as æWhen a node receives information from another
node that it trusts...Æ ARE valid, and should be interpreted
according to the criteria (i) and (ii) above.
3. Generation of Network Asserted Identity
A Network Asserted Identity is generated by a network intermediary
following an Authentication process which authenticates the entity
(UA) to be identified.
The Authentication process(es) used are a characteristic feature of
the Trust Domain, and MUST be specified in Spec(T).
It shall be possible for a UA to provide a preferred identity to the
network intermediary, which MAY be used to inform the generation of
the Network Asserted Identity according to the policies of the Trust
Domain.
4. Transport of Network Asserted Identity
4.1 Sending of Network Asserted Identity within a Trust Domain
It shall be possible for one node within a Trust Domain to securely
send a Network Asserted Identity to another node that it trusts.
4.2 Receiving of Network Asserted Identity withing a Trust Domain
It shall be possible for one node within a Trust Domain to receive a
Network Asserted identity from another node that it trusts.
4.3 Sending of Network Asserted Identity to entities outside a Trust
Domain
If a node, A, within the Trust Domain, is trusted by a node, B,
outside the Trust Domain, then it shall be possible for A to securely
send a Network Asserted Identity to B.
This is most often used to pass a Network Asserted Identity directly
to a UA.
4.4 Receiving of Network Asserted Identity by a node outside the Trust
Domain
It shall be possible for a node outside the Trust Domain to receive a
Network Asserted Identity from a node that it trusts.
Watson Expires - November 2002 [Page 5]
Network Asserted Identity û short term requirements May 2002
Network Asserted Identity received in this way may be considered
valid, and used for display to the user, input data for services etc.
Network Asserted Identity information received by one node from a
node which it does not trust carries no guarantee of authenticity or
integrity because it is not known that the procedures of Spec(T) were
followed to generate and transport the information. Such information
MUST NOT be used. i.e. it shall not be displayed to the user, passed
to other nodes, used as input data for services etc.
5. Parties with Network Asserted Identities
A Network Asserted Identity identifies the originator of the message
in which it was received.
For example,
o a Network Asserted Identity received in an initial INVITE
(outside the context of any existing dialog) identifies the
calling party.
o a Network Asserted Identity received in a 180 Ringing response
to such an INVITE identifies the party who is ringing.
o a Network Asserted Identity received in a 200 response to such
an INVITE identifies the party who has answered.
6. Types of Network Asserted Identity
Each party shall have at most one Network Asserted Identity.
It shall be possible for the capability to transport multiple
identities associated with a single party to be introduced in future.
7. Privacy of Network Asserted Identity
The means by which any privacy requirements in respect of the Network
Asserted Identity are determined are outside the scope of this draft.
It shall be possible to indicate that a Network Asserted Identity is
subject to a privacy requirement which prevents it being passed to
other users.
It shall be possible to indicate that the user has requested that the
Network Asserted Identity be not passed to other users.
Watson Expires - November 2002 [Page 6]
Network Asserted Identity û short term requirements May 2002
The mechanism shall support Trust Domain policies where the above two
indications are equivalent, and policies where they are not.
The Network Asserted Identity specification shall require that in the
case that the Network Asserted Identity cannot be passed to other
users, the mechanism of 3.2 SHALL NOT be used i.e. a trusted node
shall not pass the identity to a node it does not trust. However, the
mechanism of 3.1 MAY be used to transfer the identity within the
trusted network.
Note that æanonymityÆ requests from users or subscribers may well
require functionality in addition to the above handling of Network
Asserted Identities. Such additional functionality is out of the
scope of this document.
8. Next steps
It is has been agreed to adopt draft-jennings-sipping-nai-00 [2] as a
working group item to implement the requirements of this draft.
9. Security considerations
The requirements in this draft are NOT intended to result in a
mechanism with general applicability between arbitrary hosts on the
Internet.
Rather, the intention is to state requirements for a mechanism to be
used within a community of devices which are known to obey the
specification of the mechanism (Spec(T)) and between which there are
secure connections. Such a community is known here as a Trust Domain.
The requirements on the mechanisms used for security and to initially
derive the Network Asserted Identity must be part of the
specification Spec(T).
Such devices may be hosts on the Internet.
The requirements also support the transfer of information from a node
within the Trust Domain, via a secure connection to a node outside
the Trust Domain.
Use of this mechanism in any other context has serious security
shortcomings, namely that there is absolutely no guarantee that the
information has not been modified, or was even correct in the first
place.
10. IANA Considerations
This document does not have any implications for IANA.
Watson Expires - November 2002 [Page 7]
Network Asserted Identity û short term requirements May 2002
11. References
[1] J. Rosenberg et al, ôSIP: Session initiation protocol," draft-
ietf-sip-rfc2543bis-09.txt, February 27th, 2002.
[2] C.Jennings, ôNetwork Asserted Identity headerö, draft-jennings-
sipping-nai-00, May 2002, work in progress.
12. Acknowledgments
Thanks are due to Jon Peterson, Cullen Jennings and Allison Mankin
for comments on this draft.
13. AuthorsÆ Addresses
Mark Watson
Nortel Networks (UK)
Maidenhead Office Park (Bray House)
Westacott Way
Maidenhead,
Berkshire Tel: +44 (0)1628-434456
England Email: mwatson@nortelnetworks.com
14. Full Copyright Statement
Copyright (C) The Internet Society (2002). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
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
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English. The limited permissions granted above are perpetual and
will not be revoked by the Internet Society or its successors or
assigns. This document and the information contained
herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND
THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT
Watson Expires - November 2002 [Page 8]
Network Asserted Identity û short term requirements May 2002
THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR
ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A
PARTICULAR PURPOSE."
Watson Expires - November 2002 [Page 9]
