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heimdal/doc/standardisation/draft-lha-krb-wg-ticket-extensions-00.txt
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Network Working Group L. Hornquist Astrand
Internet-Draft Apple, Inc
Intended status: Standards Track August 13, 2008
Expires: February 14, 2009
Kerberos ticket extensions
draft-lha-krb-wg-ticket-extensions-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
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This Internet-Draft will expire on February 14, 2009.
Copyright Notice
Copyright (C) The IETF Trust (2008).
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Abstract
The Kerberos protocol does not allow ticket extensions. This make it
harder to deploy features like referrals and PKCROSS.
Since the Kerberos protocol did not specified extensibility for the
Ticket structure and the current implementations are aware of the
contents of tickets, the extension protocol cannot simply extend the
Ticket ASN.1 structure. Instead, the extension data needs to be
hidden inside the ticket.
Table of Contents
1. Requirements Notation . . . . . . . . . . . . . . . . . . . . 3
2. Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. How to request a new assignment for a ticket extension . . . . 6
4. Security Considerations . . . . . . . . . . . . . . . . . . . 7
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 8
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
7. Normative References . . . . . . . . . . . . . . . . . . . . . 10
Appendix A. Ticket-extensions ASN.1 Module . . . . . . . . . . . 11
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 12
Intellectual Property and Copyright Statements . . . . . . . . . . 13
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1. Requirements Notation
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 [RFC2119].
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2. Protocol
The ticket and enc-part as defined by [RFC4120] is defined as follow:
Ticket ::= [APPLICATION 1] SEQUENCE {
tkt-vno [0] INTEGER (5),
realm [1] Realm,
sname [2] PrincipalName,
enc-part [3] EncryptedData -- EncTicketPart
}
EncryptedData ::= SEQUENCE {
etype [0] Int32 -- EncryptionType --,
kvno [1] UInt32 OPTIONAL,
cipher [2] OCTET STRING -- ciphertext
}
This document uses the special encryption type etype-TBETicket to
signal that enc-part.cipher contains the DER-encoded TBETicket
structure, instead of an encrypted EncTicketPart.
etype-TBETicket INTEGER ::= 4711 -- TBA XXX --
krb5int32 ::= INTEGER (-2147483648..2147483647)
TBETicket ::= SEQUENCE {
etype [0] krb5int32 -- EncryptionType --,
cipher [1] OCTET STRING
extensions [2] SEQUENCE OF TicketExtension OPTIONAL
}
TicketExtension ::= SEQUENCE {
te-type [0] krb5int32,
te-data [1] OCTET STRING
te-csum [2] Checksum OPTIONAL
}
The content of cipher data and encryption type fields is moved inside
TBETicket.
Negative ticket extensions types (te-type) is private extensions and
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MUST only be used for experimentation.
The te-type field is specificing the type of the content in te-data.
Unknown te-types MUST be ignored both by the client and the server.
The te-csum field is optional for the type, when in use by type type
specifed in te-type, the key have to be specifed (usually the session
key of the ticket) and the key usage number.
The KDC MUST only return this extension in the AS-REQ if all other
KDCs for the same realm also supports this extension.
The KDC MUST only return this extension in the TGS-REQ to server the
KDC knows supports these extension. This includes both cross realm
tickets and service tickets.
The KDC MAY return extended tickets to servers supporting ticket
extensions even if the extended ticket does not contain any
extensions.
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3. How to request a new assignment for a ticket extension
When anyone is writing a internet-draft for which a new assignment
for te-type is needed/wanted under the ticket extension, then the
proper way to do so is as follows:
EXAMPLE-MODULE DEFINITIONS ::= BEGIN
krb5-ticket-extension-Name ::= INTEGER nnn
-- IANA: please assign nnn
-- RFC-Editor: replace nnn with IANA-assigned
-- number and remove this note
END
IANA: Don't do note above, its an example, remove this note RFC-
Editor: Don't do note above, its an example, remove this note IANA
will assign the number as part of the RFC publication process.
When reviewing the document, the reviewer should take sure to check
that if te-csum is used, the siging key and key usage is specifed.
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4. Security Considerations
This document describes how to extend Kerberos tickets to include
additional data in the ticket. This does have a security
implications since the extension data in the TBETicket is only
optionally signed, not encrypted and is not replay protected. It is
up to the consumers of this interface to make sure its used safely.
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5. Acknowledgements
Thanks to Leif Johansson, and Kamada Ken'ichi for reviewing the
document and provided suggestions for improvements.
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6. IANA Considerations
There are currently no ticket extensions. Future ticket extensions
will be published at:
http://www.iana.org/assignments/NNNNNNNN
-- IANA: please name registry, proposal: krb5-ticket-extensions
IANA is requested to maintain this registry for future assignments.
New assignments can only be made via Specification Required as
described in [RFC2434].
IANA will assign the number as part of the RFC publication process.
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7. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 2434,
October 1998.
[RFC4120] Neuman, C., Yu, T., Hartman, S., and K. Raeburn, "The
Kerberos Network Authentication Service (V5)", RFC 4120,
July 2005.
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Appendix A. Ticket-extensions ASN.1 Module
KerberosV5-TicketExtensions {
iso(1) identified-organization(3) dod(6) internet(1)
security(5) kerberosV5(2) modules(4) ticket-extensions(TBA)
--- XXX who is the registerar for this number ?
} DEFINITIONS EXPLICIT TAGS ::= BEGIN
IMPORTS
-- as defined in RFC 4120
Int32, Checksum
FROM KerberosV5Spec2 { iso(1) identified-organization(3)
dod(6) internet(1) security(5) kerberosV5(2)
modules(4) krb5spec2(2) }
etype-TBETicket INTEGER ::= 4711 -- XXX TBA --
TBETicket ::= SEQUENCE {
etype [0] Int32 -- EncryptionType --,
cipher [1] OCTET STRING
extensions [2] SEQUENCE OF TicketExtension OPTIONAL
}
TicketExtension ::= SEQUENCE {
te-type [0] krb5int32,
te-data [1] OCTET STRING
te-csum [2] Checksum
}
END
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Author's Address
Love Hornquist Astrand
Apple, Inc
Cupertino
USA
Email: lha@apple.com
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Copyright (C) The IETF Trust (2008).
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Hornquist Astrand Expires February 14, 2009 [Page 13]
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