Network Working Group S. Josefsson Internet-Draft SJD Updates: 4120 (if approved) January 9, 2008 Intended status: Standards Track Expires: July 12, 2008 Kerberos V5 Internationalization of Error Messages draft-josefsson-kerberos5-i18n-00 Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. 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. This Internet-Draft will expire on July 12, 2008. Copyright Notice Copyright (C) The IETF Trust (2008). Abstract This document describes an internationalization extension for the Kerberos V5 protocol. The extension allows error messages to be sent in the users' language. Josefsson Expires July 12, 2008 [Page 1] Internet-Draft KRB-ERROR i18n January 2008 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Conventions Used in This Document . . . . . . . . . . . . . . . 3 3. Negotiating Support for Internationalization . . . . . . . . . 3 3.1. PA-I18N . . . . . . . . . . . . . . . . . . . . . . . . . . 3 4. Internationalization of KRB-ERROR . . . . . . . . . . . . . . . 4 5. Security Considerations . . . . . . . . . . . . . . . . . . . . 5 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5 7. Normative References . . . . . . . . . . . . . . . . . . . . . 5 Appendix A. Copying Conditions . . . . . . . . . . . . . . . . . . 5 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 5 Intellectual Property and Copyright Statements . . . . . . . . . . 6 Josefsson Expires July 12, 2008 [Page 2] Internet-Draft KRB-ERROR i18n January 2008 1. Introduction The Kerberos V5 [3] specification uses the KRB-ERROR packet to signal error conditions. The KRB-ERROR packet contains a field "e-text" which holds additional text to explain the error code. The "e-text" type is KerberosString, which may only contain US-ASCII characters. Traditionally the field has only been used to send english help texts. There is a desire to provide error messages in a users' own language. This document specifies how clients and KDC negotiate support for a internationalization extension. When the extension is negotiated, this document goes on to describe how the KRB-ERROR packet is modified in order to support translated error messages. 2. Conventions Used in This Document The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [1]. 3. Negotiating Support for Internationalization The client can request support for internationalization by including a PA-DATA element with padata-type of PA-I18N in the KDC-REQ. The PA-DATA carry a list in preference order to indicate the languages the client needs error messages in. 3.1. PA-I18N Language-Tag ::= IA5String -- RFC 4646 Language-Tag PA-I18N ::= SEQUENCE OF Language-Tag An empty list can be used to signal support of this extension without requesting any particular languages. The KDC MAY include a PA-DATA element with a padata-type of PA-I18N in the KDC-REP message, containing a list of languages supported by the KDC. This can be useful if the languages preferred by the client is not supported by the KDC, to allow clients to more easily select another language tag. Josefsson Expires July 12, 2008 [Page 3] Internet-Draft KRB-ERROR i18n January 2008 4. Internationalization of KRB-ERROR When the PA-I18N extension is negotiated the server MAY send the following structure wherever a KRB-ERROR packet can be sent. KRB-I18N-ERROR ::= [APPLICATION 4] SEQUENCE { pvno [0] INTEGER (5), msg-type [1] INTEGER (30), ctime [2] KerberosTime OPTIONAL, cusec [3] Microseconds OPTIONAL, stime [4] KerberosTime, susec [5] Microseconds, error-code [6] Int32, crealm [7] Realm OPTIONAL, cname [8] PrincipalName OPTIONAL, realm [9] Realm -- service realm --, sname [10] PrincipalName -- service name --, e-text [11] SEQUENCE OF ErrorMessage, e-data [12] OCTET STRING OPTIONAL } ErrorMessage ::= SEQUENCE { langtag [0] IA5String -- RFC 4646 Language-Tag --, msg [1] UTF8String } Compared to KRB-ERROR, this changes the type of the "e-text" field from KerberosString to ErrorMessage. The APPLICATION tag is changed from 30 to 4 to help automatic decoding of KRB-ERROR and KRB-I18N- ERROR. The "ErrorMessage" type holds one error message in a specific language. The "langtag" field follows the Language-Tag format. The "msg" field holds the text message, encoded in UTF-8 [2]. The "e-text" field holds a list of "ErrorMessage" structures. Each member of the list will contain the error message in a particular language. The languages of messages returned will be in a sub-set of languages requested by the client. The server MAY return strings in other languages as well. It is RECOMMENDED that KDC always return the error message in the "en" (English) language. This improves debugging and logging. Josefsson Expires July 12, 2008 [Page 4] Internet-Draft KRB-ERROR i18n January 2008 5. Security Considerations If a client requests a large number of languages, it can consume a significant amount of resources on the KDC and will also increase the packet size. This can be used as a denial of service attack. KDCs can chose to temporarily disable translations for a particular client, or require that clients pre-authenticates themselves. 6. IANA Considerations TBA 7. Normative References [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [2] Yergeau, F., "UTF-8, a transformation format of ISO 10646", STD 63, RFC 3629, November 2003. [3] Neuman, C., Yu, T., Hartman, S., and K. Raeburn, "The Kerberos Network Authentication Service (V5)", RFC 4120, July 2005. Appendix A. Copying Conditions Regarding this entire document or any portion of it, the author makes no guarantees and is not responsible for any damage resulting from its use. The author grants irrevocable permission to anyone to use, modify, and distribute it in any way that does not diminish the rights of anyone else to use, modify, and distribute it, provided that redistributed derivative works do not contain misleading author or version information. Derivative works need not be licensed under similar terms. Author's Address Simon Josefsson SJD Email: simon@josefsson.org Josefsson Expires July 12, 2008 [Page 5] Internet-Draft KRB-ERROR i18n January 2008 Full Copyright Statement Copyright (C) The IETF Trust (2008). 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, 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. 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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. Acknowledgment Funding for the RFC Editor function is provided by the IETF Administrative Support Activity (IASA). Josefsson Expires July 12, 2008 [Page 6]