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This document describes an internationalization extension for the Kerberos V5 protocol. The extension allows error messages to be sent in the users' language.
1.
Introduction
2.
Conventions Used in This Document
3.
Negotiating Support for Internationalization
3.1.
PA-I18N
4.
Internationalization of KRB-ERROR
5.
Security Considerations
6.
IANA Considerations
7.
Normative References
Appendix A.
Copying Conditions
§
Author's Address
§
Intellectual Property and Copyright Statements
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The Kerberos V5 (Neuman, C., Yu, T., Hartman, S., and K. Raeburn, “The Kerberos Network Authentication Service (V5),” July 2005.) [RFC4120] 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.
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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 (Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” March 1997.) [RFC2119].
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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.
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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.
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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 (Yergeau, F., “UTF-8, a transformation format of ISO 10646,” November 2003.) [RFC3629].
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.
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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.
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TBA
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| [RFC2119] | Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” BCP 14, RFC 2119, March 1997 (TXT, HTML, XML). |
| [RFC3629] | Yergeau, F., “UTF-8, a transformation format of ISO 10646,” STD 63, RFC 3629, November 2003 (TXT). |
| [RFC4120] | Neuman, C., Yu, T., Hartman, S., and K. Raeburn, “The Kerberos Network Authentication Service (V5),” RFC 4120, July 2005 (TXT). |
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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.
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| Simon Josefsson | |
| SJD | |
| Email: | simon@josefsson.org |
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