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Network Working Group                                            R. MahyRequest for Comments: 5028                                   PlantronicsCategory: Standards Track                                   October 2007A Telephone Number Mapping (ENUM) Service Registration forInstant Messaging (IM) ServicesStatus 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,RFC3986 [3]), such as 'im:user@example.com'.  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 inRFC 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 inRFC 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 inRFC 3861 [4]).  This   document registers an enumservice for advertising IM information   associated with an E.164 number.Mahy                        Standards Track                     [Page 1]

RFC 5028                     IM Enumservice                 October 20072.  ENUM Service Registration - im   As defined inRFC 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 inRFC 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:      Seesection 3.   Intended usage:      COMMON   Author:      Rohan Mahy (rohan@ekabal.com)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 inRFC 3761, and a thorough   analysis of threats to the DNS itself is covered inRFC 3833 [11].   Many of these problems are prevented when the resolver verifies theMahy                        Standards Track                     [Page 2]

RFC 5028                     IM Enumservice                 October 2007   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 inRFC 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 andRFC 3761 [1].5.  References5.1.  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",RFC4035, March 2005.Mahy                        Standards Track                     [Page 3]

RFC 5028                     IM Enumservice                 October 20075.2.  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: rohan@ekabal.comMahy                        Standards Track                     [Page 4]

RFC 5028                     IM Enumservice                 October 2007Full Copyright Statement   Copyright (C) The IETF Trust (2007).   This document is subject to the rights, licenses and restrictions   contained inBCP 78, and except as set forth therein, the authors   retain all their rights.   This document and the information contained herein are provided on an   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND   THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS   OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF   THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.Intellectual Property   The IETF takes no position regarding the validity or scope of any   Intellectual Property Rights or other rights that might be claimed to   pertain to the implementation or use of the technology described in   this document or the extent to which any license under such rights   might or might not be available; nor does it represent that it has   made any independent effort to identify any such rights.  Information   on the procedures with respect to rights in RFC documents can be   found inBCP 78 andBCP 79.   Copies of IPR disclosures made to the IETF Secretariat and any   assurances of licenses to be made available, or the result of an   attempt made to obtain a general license or permission for the use of   such proprietary rights by implementers or users of this   specification can be obtained from the IETF on-line IPR repository athttp://www.ietf.org/ipr.   The IETF invites any interested party to bring to its attention any   copyrights, patents or patent applications, or other proprietary   rights that may cover technology that may be required to implement   this standard.  Please address the information to the IETF at   ietf-ipr@ietf.org.Mahy                        Standards Track                     [Page 5]