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+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).
+
+Abstract
+
+   On 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.
+
+1.  Introduction
+
+   This document defines an anonymous mechanism for the Simple
+   Authentication and Security Layer ([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.
+
+
+
+Zeilenga                    Standards Track                     [Page 1]
+
+RFC 4505                Anonymous SASL Mechanism               June 2006
+
+
+2.  The Anonymous Mechanism
+
+   The mechanism consists of a single message from the client to the
+   server.  The client may include in this message trace information in
+   the form of a string of [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.
+
+
+
+
+
+Zeilenga                    Standards Track                     [Page 2]
+
+RFC 4505                Anonymous SASL Mechanism               June 2006
+
+
+3.  The "trace" Profile of "Stringprep"
+
+   This section defines the "trace" profile of [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].
+
+4.  Example
+
+   Here is a sample ANONYMOUS login between an IMAP client and server.
+   In this example, "C:" and "S:" indicate lines sent by the client and
+   server, respectively.  If such lines are wrapped without a new "C:"
+   or "S:" label, then the wrapping is for editorial clarity and is not
+   part of the command.
+
+   Note that this example uses the IMAP profile [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 "+ ").
+
+
+
+
+Zeilenga                    Standards Track                     [Page 3]
+
+RFC 4505                Anonymous SASL Mechanism               June 2006
+
+
+   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.
+
+5.  Security Considerations
+
+   The ANONYMOUS mechanism grants access to services and/or resources by
+   anyone.  For this reason, it should be disabled by default so that
+   the administrator can make an explicit decision to enable it.
+
+   If the anonymous user has any write privileges, a denial-of-service
+   attack is possible by filling up all available space.  This can be
+   prevented by disabling all write access by anonymous users.
+
+   If anonymous users have read and write access to the same area, the
+   server can be used as a communication mechanism to exchange
+   information anonymously.  Servers that accept anonymous submissions
+   should implement the common "drop box" model, which forbids anonymous
+   read access to the area where anonymous submissions are accepted.
+
+   If the anonymous user can run many expensive operations (e.g., an
+   IMAP SEARCH BODY command), this could enable a denial-of-service
+   attack.  Servers are encouraged to reduce the priority of anonymous
+   users or limit their resource usage.
+
+   While servers may impose a limit on the number of anonymous users,
+   note that such limits enable denial-of-service attacks and should be
+   used with caution.
+
+   The trace information is not authenticated, so it can be falsified.
+   This can be used as an attempt to get someone else in trouble for
+   access to questionable information.  Administrators investigating
+   abuse need to realize that this trace information may be falsified.
+
+   A client that uses the user's correct email address as trace
+   information without explicit permission may violate that user's
+   privacy.  Anyone who accesses an anonymous archive on a sensitive
+   subject (e.g., sexual abuse) likely has strong privacy needs.
+   Clients should not send the email address without the explicit
+   permission of the user and should offer the option of supplying no
+   trace information, thus only exposing the source IP address and time.
+
+
+
+Zeilenga                    Standards Track                     [Page 4]
+
+RFC 4505                Anonymous SASL Mechanism               June 2006
+
+
+   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.
+
+6.  IANA Considerations
+
+   The SASL Mechanism registry [IANA-SASL] entry for the ANONYMOUS
+   mechanism has been updated by the IANA to reflect that this document
+   now provides its technical specification.
+
+      To: iana@iana.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 <iesg@ietf.org>
+      Note: Updates existing entry for ANONYMOUS
+
+
+
+
+
+
+
+Zeilenga                    Standards Track                     [Page 5]
+
+RFC 4505                Anonymous SASL Mechanism               June 2006
+
+
+   The [StringPrep] profile "trace", first defined in this RFC, has been
+   registered:
+
+      To: iana@iana.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 <kurt@openldap.org>
+
+7.  Acknowledgement
+
+   This document is a revision of 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.
+
+8.  Normative References
+
+   [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.
+
+
+
+
+
+
+Zeilenga                    Standards Track                     [Page 6]
+
+RFC 4505                Anonymous SASL Mechanism               June 2006
+
+
+9.  Informative References
+
+   [IMAP4]      Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION
+                4rev1", RFC 3501, March 2003.
+
+   [IANA-SASL]  IANA, "SIMPLE AUTHENTICATION AND SECURITY LAYER (SASL)
+                MECHANISMS", <http://www.iana.org/assignments/sasl-
+                mechanisms>.
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+Zeilenga                    Standards Track                     [Page 7]
+
+RFC 4505                Anonymous SASL Mechanism               June 2006
+
+
+Appendix A.  Changes since RFC 2245
+
+   This appendix is non-normative.
+
+   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.
+
+Editor's Address
+
+   Kurt D. Zeilenga
+   OpenLDAP Foundation
+
+   EMail: Kurt@OpenLDAP.org
+
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+Zeilenga                    Standards Track                     [Page 8]
+
+RFC 4505                Anonymous SASL Mechanism               June 2006
+
+
+Full Copyright Statement
+
+   Copyright (C) The Internet Society (2006).
+
+   This document is subject to the rights, licenses and restrictions
+   contained in BCP 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 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
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+   attempt made to obtain a general license or permission for the use of
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+   specification can be obtained from the IETF on-line IPR repository at
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+
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+
+Acknowledgement
+
+   Funding for the RFC Editor function is provided by the IETF
+   Administrative Support Activity (IASA).
+
+
+
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+Zeilenga                    Standards Track                     [Page 9]
+