Network Working Group                                            R. Mahy
Request for Comments: 5028                                   Plantronics
Category: Standards Track                                   October 2007


      A Telephone Number Mapping (ENUM) Service Registration for
                   Instant Messaging (IM) Services

Status of This Memo

  This document specifies an Internet standards track protocol for the
  Internet community, and requests discussion and suggestions for
  improvements.  Please refer to the current edition of the "Internet
  Official Protocol Standards" (STD 1) for the standardization state
  and status of this protocol.  Distribution of this memo is unlimited.

Abstract

  This document registers a Telephone Number Mapping (ENUM) service for
  Instant Messaging (IM).  Specifically, this document focuses on
  provisioning 'im:' URIs (Uniform Resource Identifiers) in ENUM.

1.  Introduction

  ENUM (E.164 Number Mapping, RFC 3761 [1]) is a system that uses DNS
  (Domain Name Service, RFC 1034 [2]) to translate telephone numbers,
  such as '+12025550100', into URIs (Uniform Resource Identifiers, RFC
  3986 [3]), such as 'im:[email protected]'.  ENUM exists primarily to
  facilitate the interconnection of systems that rely on telephone
  numbers with those that use URIs to identify resources.

  Instant Messaging (IM) is a service defined in RFC 2778 [6] that
  allows users to send and receive typically short, often textual
  messages in near real-time.  The IETF has defined a generic URI used
  to identify an IM service for a particular resource: the 'im:' URI
  scheme (defined in RFC 3861 [4]).  RFC 3861 [4] also defines rules
  for discovering service running specific protocols, such as SIP (the
  Session Initiation Protocol, RFC 3261 [8]) and XMPP (the eXtensible
  Messaging and Presence Protocol, RFC 3921 [9]) from a specific 'im:'
  URI.

  RFC 3953 [10] already defines an enumservice for presence services,
  which returns 'pres:' URIs (also defined in RFC 3861 [4]).  This
  document registers an enumservice for advertising IM information
  associated with an E.164 number.






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2.  ENUM Service Registration - im

  As defined in RFC 3761 [1], the following is a template covering
  information needed for the registration of the enumservice specified
  in this document:

  Enumservice Name:
     "im"
  Enumservice Type:
     "im"
  Enumservice Subtypes:
     N/A
  URI scheme(s):
     "im:"
  Functional Specification:
     This Enumservice indicates that the resource identified is an
     'im:' URI.  The 'im:' URI scheme does not identify any particular
     protocol that will be used to handle instant messaging receipt or
     delivery, rather the mechanism in RFC 3861 [4] is used to discover
     whether an IM protocol supported by the party querying ENUM is
     also supported by the target resource.
  Security considerations:
     See section 3.
  Intended usage:
     COMMON
  Author:
     Rohan Mahy ([email protected])

3.  Security Considerations

  The Domain Name System (DNS) does not make policy decisions about
  which records it provides to a DNS resolver.  All DNS records must be
  assumed to be available to all inquirers at all times.  The
  information provided within an ENUM record set must therefore be
  considered open to the public -- which is a cause for some privacy
  considerations.

  Revealing an 'im:' URI by itself is unlikely to introduce many
  privacy concerns, although, depending on the structure of the URI, it
  might reveal the full name or employer of the target.  The use of
  anonymous URIs mitigates this risk.

  As ENUM uses DNS, which in its current form is an insecure protocol,
  there is no mechanism for ensuring that the answer returned to a
  query is authentic.  An analysis of threats specific to the
  dependence of ENUM on the DNS is provided in RFC 3761, and a thorough
  analysis of threats to the DNS itself is covered in RFC 3833 [11].
  Many of these problems are prevented when the resolver verifies the



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  authenticity of answers to its ENUM queries via DNSSEC [5] in zones
  where it is available.

  More serious security concerns are associated with potential attacks
  against an underlying Instant Messaging system (for example, message
  forgery and tampering).  For this reason, IM protocols have a number
  of security requirements (detailed in RFC 2779 [7]) that call for
  authentication, integrity and confidentiality properties, and similar
  measures to prevent such attacks.  Any instant messaging protocol
  used in conjunction with the 'im:' URI scheme is required to meet
  these requirements.

  Unlike a traditional telephone number, the resource identified by an
  'im:' URI may require that callers provide cryptographic credentials
  for authentication and authorization before instant messages are
  exchanged.  In concert with instant messaging protocols, ENUM can
  actually provide far greater protection from unwanted callers than
  does the existing PSTN, despite the public availability of ENUM
  records.

4.  IANA Considerations

  This document requests registration of the "im" Enumservice according
  to the definitions in this document and RFC 3761 [1].

5.  References

5.1.  Normative References

  [1]   Faltstrom, P. and M. Mealling, "The E.164 to Uniform Resource
        Identifiers (URI) Dynamic Delegation Discovery System (DDDS)
        Application (ENUM)", RFC 3761, April 2004.

  [2]   Mockapetris, P., "Domain names - concepts and facilities", STD
        13, RFC 1034, November 1987.

  [3]   Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
        Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986,
        January 2005.

  [4]   Peterson, J., "Address Resolution for Instant Messaging and
        Presence", RFC 3861, August 2004.

  [5]   Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose,
        "Protocol Modifications for the DNS Security Extensions", RFC
        4035, March 2005.





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5.2.  Informative References

  [6]   Day, M., Rosenberg, J., and H. Sugano, "A Model for Presence
        and Instant Messaging", RFC 2778, February 2000.

  [7]   Day, M., Aggarwal, S., Mohr, G., and J. Vincent, "Instant
        Messaging / Presence Protocol Requirements", RFC 2779, February
        2000.

  [8]   Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,
        Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP:
        Session Initiation Protocol", RFC 3261, June 2002.

  [9]   Saint-Andre, P., Ed., "Extensible Messaging and Presence
        Protocol (XMPP): Instant Messaging and Presence", RFC 3921,
        October 2004.

  [10]  Peterson, J., "Telephone Number Mapping (ENUM) Service
        Registration for Presence Services", RFC 3953, January 2005.

  [11]  Atkins, D. and R. Austein, "Threat Analysis of the Domain Name
        System (DNS)", RFC 3833, August 2004.

Author's Address

  Rohan Mahy
  Plantronics

  EMail: [email protected]






















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