Network Working Group K. Zeilenga, Ed. Request for Comments: 4505 OpenLDAP Foundation Obsoletes: 2245 June 2006 Category: Standards Track Anonymous Simple Authentication and Security Layer (SASL) Mechanism 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. Copyright Notice Copyright (C) The Internet Society (2006).
AbstractOn the Internet, it is common practice to permit anonymous access to various services. Traditionally, this has been done with a plain- text password mechanism using "anonymous" as the user name and using optional trace information, such as an email address, as the password. As plain-text login commands are not permitted in new IETF protocols, a new way to provide anonymous login is needed within the context of the Simple Authentication and Security Layer (SASL) framework. SASL]) framework. The name associated with this mechanism is "ANONYMOUS". Unlike many other SASL mechanisms, whose purpose is to authenticate and identify the user to a server, the purpose of this SASL mechanism is to allow the user to gain access to services or resources without requiring the user to establish or otherwise disclose their identity to the server. That is, this mechanism provides an anonymous login method. This mechanism does not provide a security layer. This document replaces RFC 2245. Changes since RFC 2245 are detailed in Appendix A.
UTF-8]-encoded [Unicode] characters prepared in accordance with [StringPrep] and the "trace" stringprep profile defined in Section 3 of this document. The trace information, which has no semantical value, should take one of two forms: an Internet email address, or an opaque string that does not contain the '@' (U+0040) character and that can be interpreted by the system administrator of the client's domain. For privacy reasons, an Internet email address or other information identifying the user should only be used with permission from the user. A server that permits anonymous access will announce support for the ANONYMOUS mechanism and allow anyone to log in using that mechanism, usually with restricted access. A formal grammar for the client message using Augmented BNF [ABNF] is provided below as a tool for understanding this technical specification. message = [ email / token ] ;; to be prepared in accordance with Section 3 UTF1 = %x00-3F / %x41-7F ;; less '@' (U+0040) UTF2 = %xC2-DF UTF0 UTF3 = %xE0 %xA0-BF UTF0 / %xE1-EC 2(UTF0) / %xED %x80-9F UTF0 / %xEE-EF 2(UTF0) UTF4 = %xF0 %x90-BF 2(UTF0) / %xF1-F3 3(UTF0) / %xF4 %x80-8F 2(UTF0) UTF0 = %x80-BF TCHAR = UTF1 / UTF2 / UTF3 / UTF4 ;; any UTF-8 encoded Unicode character ;; except '@' (U+0040) email = addr-spec ;; as defined in [IMAIL] token = 1*255TCHAR Note to implementors: The <token> production is restricted to 255 UTF-8-encoded Unicode characters. As the encoding of a characters uses a sequence of 1 to 4 octets, a token may be as long as 1020 octets.
StringPrep]. This profile is designed for use with the SASL ANONYMOUS Mechanism. Specifically, the client is to prepare the <message> production in accordance with this profile. The character repertoire of this profile is Unicode 3.2 [Unicode]. No mapping is required by this profile. No Unicode normalization is required by this profile. The list of unassigned code points for this profile is that provided in Appendix A of [StringPrep]. Unassigned code points are not prohibited. Characters from the following tables of [StringPrep] are prohibited: - C.2.1 (ASCII control characters) - C.2.2 (Non-ASCII control characters) - C.3 (Private use characters) - C.4 (Non-character code points) - C.5 (Surrogate codes) - C.6 (Inappropriate for plain text) - C.8 (Change display properties are deprecated) - C.9 (Tagging characters) No additional characters are prohibited. This profile requires bidirectional character checking per Section 6 of [StringPrep]. IMAP4] of SASL. The base64 encoding of challenges and responses as well as the "+ " preceding the responses are part of the IMAP4 profile, not part of SASL itself. Additionally, protocols with SASL profiles permitting an initial client response will be able to avoid the extra round trip below (the server response with an empty "+ ").
In this example, the trace information is "sirhc". S: * OK IMAP4 server ready C: A001 CAPABILITY S: * CAPABILITY IMAP4 IMAP4rev1 AUTH=DIGEST-MD5 AUTH=ANONYMOUS S: A001 OK done C: A002 AUTHENTICATE ANONYMOUS S: + C: c2lyaGM= S: A003 OK Welcome, trace information has been logged.
Anonymous proxy servers could enhance this privacy but would have to consider the resulting potential denial-of-service attacks. Anonymous connections are susceptible to man-in-the-middle attacks that view or alter the data transferred. Clients and servers are encouraged to support external data security services. Protocols that fail to require an explicit anonymous login are more susceptible to break-ins given certain common implementation techniques. Specifically, Unix servers that offer user login may initially start up as root and switch to the appropriate user id after an explicit login command. Normally, such servers refuse all data access commands prior to explicit login and may enter a restricted security environment (e.g., the Unix chroot(2) function) for anonymous users. If anonymous access is not explicitly requested, the entire data access machinery is exposed to external security attacks without the chance for explicit protective measures. Protocols that offer restricted data access should not allow anonymous data access without an explicit login step. General [SASL] security considerations apply to this mechanism. [StringPrep] security considerations and [Unicode] security considerations discussed in [StringPrep] apply to this mechanism. [UTF-8] security considerations also apply. IANA-SASL] entry for the ANONYMOUS mechanism has been updated by the IANA to reflect that this document now provides its technical specification. To: firstname.lastname@example.org Subject: Updated Registration of SASL mechanism ANONYMOUS SASL mechanism name: ANONYMOUS Security considerations: See RFC 4505. Published specification (optional, recommended): RFC 4505 Person & email address to contact for further information: Kurt Zeilenga <Kurt@OpenLDAP.org> Chris Newman <Chris.Newman@sun.com> Intended usage: COMMON Author/Change controller: IESG <email@example.com> Note: Updates existing entry for ANONYMOUS
The [StringPrep] profile "trace", first defined in this RFC, has been registered: To: firstname.lastname@example.org Subject: Initial Registration of Stringprep "trace" profile Stringprep profile: trace Published specification: RFC 4505 Person & email address to contact for further information: Kurt Zeilenga <email@example.com> RFC 2245 by Chris Newman. Portions of the grammar defined in Section 1 were borrowed from RFC 3629 by Francois Yergeau. This document is a product of the IETF SASL WG. [ABNF] Crocker, D. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", RFC 4234, October 2005. [IMAIL] Resnick, P., "Internet Message Format", RFC 2822, April 2001. [SASL] Melnikov, A., Ed. and K. Zeilenga, Ed., "Simple Authentication and Security Layer (SASL)", RFC 4422, June 2006. [StringPrep] Hoffman, P. and M. Blanchet, "Preparation of Internationalized Strings ('stringprep')", RFC 3454, December 2002. [Unicode] The Unicode Consortium, "The Unicode Standard, Version 3.2.0" is defined by "The Unicode Standard, Version 3.0" (Reading, MA, Addison-Wesley, 2000. ISBN 0-201-61633-5), as amended by the "Unicode Standard Annex #27: Unicode 3.1" (http://www.unicode.org/reports/tr27/) and by the "Unicode Standard Annex #28: Unicode 3.2" (http://www.unicode.org/reports/tr28/). [UTF-8] Yergeau, F., "UTF-8, a transformation format of ISO 10646", RFC 3629 (also STD 63), November 2003.
RFC 2245 allows the client to include optional trace information in the form of a human readable string. RFC 2245 restricted this string to US-ASCII. As the Internet is international, this document uses a string restricted to UTF-8 encoded Unicode characters. A "stringprep" profile is defined to precisely define which Unicode characters are allowed in this string. While the string remains restricted to 255 characters, the encoded length of each character may now range from 1 to 4 octets. Additionally, a number of editorial changes were made.
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