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Versions: 00                                                            
               Internet Draft                                             Mark Watson
               Document: draft-watson-sipping-nai-reqs-00.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
               
                  There is no requirement for identities identities asserted by a UA in
                  a SIP message to be anything other than the userÆs desired alias. An
                  authenticated identity of a user can be obtained using SIP
                  authentication, however it is unlikely that the necessary Public Key
                  Infrastructure to facilitate this for UAs will be available soon.
               
                  A Network Asserted Identity is an identity obtained 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.
               
                  General requirements for transport of Network Asserted Identities on
                  the Internet are out of scope of this draft.
               
                  Table of Contents
               
               
               1. Introduction
               
               
               
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                  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
                  Authentication (or by other means). However, it is unlikely that the
                  necessary Public Key Infrastructure to globally facilitate this for
                  users will be available soon.
               
                  A Network Asserted Identity is an identity obtained by a SIP network
                  intermediary as a result of an authentication process. This may or
                  may not be based on SIP 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. These
                  short-term requirements provide only for the exchange of Network
                  Asserted Identitied within a Trust Domain.
               
                  General requirements for transport of Network Asserted Identities on
                  the Internet are out of scope of this draft.
               
               2. Trust Domains
               
                  A Trust Domain for the purposes of Network Asserted Identity is a set
                  of SIP nodes (UAC, UAS, proxiesor other network intermediaries) that
                  are known to be compliant to SIP specifications for Network Asserted
                  Identity.
               
                  This document presents requirements for such specifications.
               
                  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
                  it is a member of that domain.
               
                  We say that one node in the domain is ætrusted byÆ another if:
               
                  (i) there is a secure connection between the nodes, AND
                  (ii) they have configuration information to indicate that they are
                  members of the same Trust Domain.
               
               
               
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                  This most often applies to network intermediaries such as proxies in
                  the Trust Domain.
               
                  A æsecure connectionÆ in this context means that messages cannot be
                  read by third parties and cannot be modified or inserted by third
                  parties without detection (e.g. IPSEC, TLS etc.).
               
                  We say that a node, A, in the domain is ætrusted byÆ a node, B,
                  outside the domain 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.
               
                  This most often applies to a UA which trusts a given network
                  intermediary (e.g. its home proxy).
               
                  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.
               
                  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.
               
                  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, and therefore can be known to be valid, or at
                  least as valid as specified in the specifications.
               
               3. Transport of Network Asserted Identity
               
               3.1 Passing of Network Asserted Identity within a Trust Domain
               
                  It shall be possible for one node within a Trust Domain to securely
                  pass a Network Asserted Identity to another node that it trusts.
               
               
               
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               3.2 Passing of Network Asserted Identity to entities outside a Trust
                   Domain
               
                  It shall be possible for a node within the Trust Domain to securely
                  pass a Network Asserted Identity to a node outside the trust domain.
               
                  This is most often used to pass a Network Asserted Identity directly
                  to a UA.
               
                  A node SHOULD disregard Network Asserted Identity received from a
                  node it does not trust.
                  Note that a node outside the Trust Domain receiving this information
                  MAY pass it on to other nodes. However, such information SHOULD NOT
                  be treated as valid, since nodes outside the Trust Domain are not
                  guaranteed to operate according to the Network Asserted Identity
                  specification, and so may have modified the Network Asserted
                  Identity.
               
               4. Parties with Network Asserted Identities
               
               4.1 Calling user
               
                  A Network Asserted Identity of the calling user shall be supported.
               
               4.2 Called user
               
                  A Network Asserted Identity of the called user shall be supported.
               
               4.3 Extensibility
               
                  It shall be possible to define further parties to whom Network
                  Asserted Identities may relate in future.
               
               5. 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.
               
               6. 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.
               
               
               
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                  In this case, the Network Asserted Identity specification shall
                  require that 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.
               
                  It shall be possible to indicate whether the Network Asserted
                  Identity is private due to a request from the user/subscriber or for
                  another reason.
               
                  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.
               
               7. Next steps
               
                  It is proposed to rapidly specify a mechanism to meet the
                  requirements of this draft.
               
                  It should be noted that the mechanisms of [2] meet all the above
                  requirements (and some others).
               
               8. 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 and between which there are secure
                  connections. Such a community is known as a Trust Domain.
               
                  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.
               
               9. IANA Considerations
               
                  This document does not have any implications for IANA.
               
               
               
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               10. References
               
                  [1] J. Rosenberg et al, ôSIP: Session initiation protocol," draft-
                  ietf-sip-rfc2543bis-09.txt, February 27th, 2002.
               
                  [2] W. Marshall et al, "SIP Extensions for Caller Identity and                                                                       th                  Privacy", draft-ietf-sip-privacy-04.txt, February 27 , 2002.
               
               
               11. Acknowledgments
               
               
               
               
               
               12. 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
               
               
               13. Full Copyright Statement
               
                  Copyright (C) The Internet Society (2002).  All Rights Reserved.
               
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                  ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A
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