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NETWORK WORKING GROUP L. Zhu
Internet-Draft K. Jaganathan
Expires: January 20, 2006 Microsoft Corporation
N. Williams
Sun Microsystems
July 19, 2005
OCSP Support for PKINIT
draft-ietf-krb-wg-ocsp-for-pkinit-06
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 January 20, 2006.
Copyright Notice
Copyright (C) The Internet Society (2005).
Abstract
This document defines a mechanism to enable in-band transmission of
Online Certificate Status Protocol (OCSP) responses in the Kerberos
network authentication protocol. These responses are used to verify
the validity of the certificates used in PKINIT - the Kerberos
Version 5 extension that provides for the use of public key
cryptography.
Zhu, et al. Expires January 20, 2006 [Page 1]
Internet-Draft OCSP Support for PKINIT July 2005
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions Used in This Document . . . . . . . . . . . . . . 3
3. Message Definition . . . . . . . . . . . . . . . . . . . . . . 3
4. Security Considerations . . . . . . . . . . . . . . . . . . . 4
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 5
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 5
7.1 Normative References . . . . . . . . . . . . . . . . . . . 5
7.2 Informative References . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 5
Intellectual Property and Copyright Statements . . . . . . . . 7
Zhu, et al. Expires January 20, 2006 [Page 2]
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1. Introduction
Online Certificate Status Protocol (OCSP) [RFC2560] enables
applications to obtain timely information regarding the revocation
status of a certificate. Because OCSP responses are well-bounded and
small in size, constrained clients may wish to use OCSP to check the
validity of the certificates for Kerberos Key Distribution Center
(KDC) in order to avoid transmission of large Certificate Revocation
Lists (CRLs) and therefore save bandwidth on constrained networks
[OCSP-PROFILE].
This document defines a pre-authentication type [RFC4120], where the
client and the KDC MAY piggyback OCSP responses for certificates used
in authentication exchanges, as defined in [PKINIT].
By using this OPTIONAL extension, PKINIT clients and the KDC can
maximize the reuse of cached OCSP responses.
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 [RFC2119].
3. Message Definition
A pre-authentication type identifier is defined for this mechanism:
PA-PK-OCSP-RESPONSE 18
The corresponding padata-value field [RFC4120] contains the DER [X60]
encoding of the following ASN.1 type:
PKOcspData ::= SEQUENCE OF OcspResponse
-- If more than one OcspResponse is
-- included, the first OcspResponse
-- MUST contain the OCSP response
-- for the signer's certificate.
-- The signer refers to the client for
-- AS-REQ, and the KDC for the AS-REP,
-- respectively.
OcspResponse ::= OCTET STRING
-- Contains a complete OCSP response,
-- as defined in [RFC2560].
The client MAY send OCSP responses for certificates used in PA-PK-AS-
REQ [PKINIT] via a PA-PK-OCSP-RESPONSE.
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The KDC that receives a PA-PK-OCSP-RESPONSE then SHOULD send a PA-PK-
OCSP-RESPONSE containing OCSP responses for certificates used in the
KDC's PA-PK-AS-REP. The client can request a PA-PK-OCSP-RESPONSE by
using a PKOcspData containing an empty sequence.
The KDC MAY send a PA-PK-OCSP-RESPONSE when it does not receive a PA-
PK-OCSP-RESPONSE from the client.
The PA-PK-OCSP-RESPONSE sent by the KDC contains OCSP responses for
certificates used in PA-PK-AS-REP [PKINIT].
Note the lack of integrity protection for the empty or missing OCSP
response; lack of an expected OCSP response from the KDC for the
KDC's certificates SHOULD be treated as an error by the client,
unless it is configured otherwise.
When using OCSP, the response is signed by the OCSP server, which is
trusted by the receiver. Depending on local policy, further
verification of the validity of the OCSP servers may be needed
The client and the KDC SHOULD ignore invalid OCSP responses received
via this mechanism, and they MAY implement CRL processing logic as a
fall-back position, if the OCSP responses received via this mechanism
alone are not sufficient for the verification of certificate
validity. The client and/or the KDC MAY ignore a valid OCSP response
and perform their own revocation status verification independently.
4. Security Considerations
The pre-authentication data in this document do not actually
authenticate any principals, but is designed to be used in
conjunction with PKINIT.
There is no binding between PA-PK-OCSP-RESPONSE pre-authentication
data and PKINIT pre-authentication data other than a given OCSP
response corresponding to a certificate used in a PKINIT pre-
authentication data element. Attacks involving removal or
replacement of PA-PK-OCSP-RESPONSE pre-authentication data elements
are, at worst, downgrade attacks, where a PKINIT client or KDC would
proceed without use of CRLs or OCSP for certificate validation, or
denial of service attacks, where a PKINIT client or KDC that cannot
validate the other's certificate without an accompanying OCSP
response might reject the AS exchange or where they might have to
download very large CRLs in order to continue. Kerberos V does not
protect against denial-of-service attacks, therefore the denial-of-
service aspect of these attacks are acceptable.
If a PKINIT client or KDC cannot validate certificates without the
Zhu, et al. Expires January 20, 2006 [Page 4]
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aid of a valid PA-PK-OCSP-RESPONSE then it SHOULD fail the AS
exchange, possibly according to local configuration.
5. IANA Considerations
No IANA actions are required for this document.
6. Acknowledgements
This document was based on conversations among the authors, Jeffrey
Altman, Sam Hartman, Martin Rex and other members of the Kerberos
working group.
7. References
7.1 Normative References
[PKINIT] RFC-Editor: To be replaced by RFC number for draft-ietf-
cat-kerberos-pk-init. Work in Progress.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2560] Myers, M., Ankney, R., Malpani, A., Galperin, S., and C.
Adams, "X.509 Internet Public Key Infrastructure Online
Certificate Status Protocol - OCSP", RFC 2560, June 1999.
[RFC4120] Neuman, C., Yu, T., Hartman, S., and K. Raeburn, "The
Kerberos Network Authentication Service (V5)", RFC 4120,
July 2005.
[X690] ASN.1 encoding rules: Specification of Basic Encoding
Rules (BER), Canonical Encoding Rules (CER) and
Distinguished Encoding Rules (DER), ITU-T Recommendation
X.690 (1997) | ISO/IEC International Standard 8825-1:1998.
7.2 Informative References
[OCSP-PROFILE]
RFC-Editor: To be replaced by RFC number for draft-deacon-
lightweight-ocsp-profile. Work in Progress.
Zhu, et al. Expires January 20, 2006 [Page 5]
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Authors' Addresses
Larry Zhu
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052
US
Email: lzhu@microsoft.com
Karthik Jaganathan
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052
US
Email: karthikj@microsoft.com
Nicolas Williams
Sun Microsystems
5300 Riata Trace Ct
Austin, TX 78727
US
Email: Nicolas.Williams@sun.com
Zhu, et al. Expires January 20, 2006 [Page 6]
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Intellectual Property Statement
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
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
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.
Disclaimer of Validity
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.
Copyright Statement
Copyright (C) The Internet Society (2005). 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.
Acknowledgment
Funding for the RFC Editor function is currently provided by the
Internet Society.
Zhu, et al. Expires January 20, 2006 [Page 7]

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NETWORK WORKING GROUP L. Zhu
Internet-Draft P. Leach
Updates: 4120 (if approved) K. Jaganathan
Expires: January 20, 2006 Microsoft Corporation
July 19, 2005
Kerberos Cryptosystem Negotiation Extension
draft-zhu-kerb-enctype-nego-03
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 January 20, 2006.
Copyright Notice
Copyright (C) The Internet Society (2005).
Abstract
This document specifies an extension to the Kerberos protocol where
the client can send a list of supported encryption types in
decreasing preference order, and the server then selects an
encryption type that is supported by both the client and the server.
Zhu, et al. Expires January 20, 2006 [Page 1]
Internet-Draft Enctype Negotiation July 2005
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions Used in This Document . . . . . . . . . . . . . . 3
3. Negotiation Extension . . . . . . . . . . . . . . . . . . . . 3
4. Security Considerations . . . . . . . . . . . . . . . . . . . 4
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 4
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
7. Normative References . . . . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 5
Intellectual Property and Copyright Statements . . . . . . . . 7
Zhu, et al. Expires January 20, 2006 [Page 2]
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1. Introduction
Under the current mechanism [RFC4120], the KDC must limit the ticket
session key encryption type (enctype) chosen for a given server to
one it believes is supported by both the client and the server. If
both the client and server understand a stronger enctype than the one
selected by the KDC, they can not negotiate it. As the result, the
protection of application traffic is often weaker than necessary when
the server can support different sets of enctypes depending on the
server application software being used.
This document specifies an extension to the Kerberos protocol to
allow clients and servers to negotiate a different and possible
stronger cryptosystem to be used in subsequent communication.
This extension utilizes an authorization data element in the
authenticator of the AP-REQ message [RFC4120]. The client sends the
list of enctypes that it supports to the server, the server then
informs the client its choice. The negotiated subkey is sent in the
AP-REP message [RFC4120].
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 [RFC2119].
3. Negotiation Extension
If the client prefers an enctype over that of the service ticket
session key, then it sends the list of enctypes it supports
(including the one selected by the KDC) in decreasing preference
order.
The client sends the enctype list via the authorization-data of the
authenticator in the AP-REQ [RFC4120]. A new authorization data
element type AD-ETYPE-NEGOTIATION is defined.
AD-ETYPE-NEGOTIATION 129
This authorization data element itself is enclosed in the AD-IF-
RELEVANT container, thus a correctly implemented server that does not
understand this element should ignore it [RFC4120]. The value of
this authorization element contains the DER [X690] encoding of the
following ASN.1 type:
Zhu, et al. Expires January 20, 2006 [Page 3]
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EtypeList ::= SEQUENCE OF Int32
-- Specifies the enctypes supported by the client.
-- This enctype list is in decreasing preference order
-- (favorite choice first).
-- Int32 is defined in [RFC4120].
If the EtypeList is present and the server prefers an enctype from
the client's enctype list over that of the AP-REQ authenticator
subkey (if that is present) or the service ticket session key, the
server MUST create a subkey using that enctype. This negotiated
subkey is sent in the subkey field of AP-REP message and it is then
used as the protocol key or base key [RFC3961] for subsequent
communication.
This negotiation extension SHOULD NOT be used when the client does
not expect the subkey in the AP-REP message from the server.
A note on key generation: The KDC has a strong Pseudo-Random Number
Generator (PRNG), as such the client can take advantage of the
randomness provided by the KDC by reusing the KDC key data when
generating keys. Implementations SHOULD use the service ticket
session key value as a source of additional entropy when generating
the negotiated subkey. If the AP-REQ authenticator subkey is
present, it MAY also be used as a source of entropy.
The server MAY ignore the preference order indicated by the client.
The policy by which the client or the server chooses an enctype
(i.e., how the preference order for the supported enctypes is
selected) is a local matter.
4. Security Considerations
The client's enctype list and the server's reply enctype are part of
encrypted data, thus the security considerations are the same as
those of the Kerberos encrypted data.
Both the EtypeList and the server's sub-session key are protected by
the session key or sub-session key used for the AP-REQ, and as a
result, if a key for a stronger enctype is negotiated underneath a
key for a weaker enctype, an attacker capable of breaking the weaker
enctype can also discover the key for the stronger enctype. The
advantage of this extension is to minimize the amount of cipher text
encrypted under a weak enctype to which an attacker has access.
5. Acknowledgements
The authors would like to thank the following individuals for their
comments and suggestions: Luke Howard, Tom Yu, Love Hornquist
Zhu, et al. Expires January 20, 2006 [Page 4]
Internet-Draft Enctype Negotiation July 2005
Astrand, Sam Harman, Ken Raeburn and Martin Rex.
6. IANA Considerations
No IANA actions are required for this document.
7. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2743] Linn, J., "Generic Security Service Application Program
Interface Version 2, Update 1", RFC 2743, January 2000.
[RFC3961] Raeburn, K., "Encryption and Checksum Specifications for
Kerberos 5", RFC 3961, February 2005.
[RFC4120] Neuman, C., Yu, T., Hartman, S., and K. Raeburn, "The
Kerberos Network Authentication Service (V5)", RFC 4120,
July 2005.
[X690] ASN.1 encoding rules: Specification of Basic Encoding Rules
(BER), Canonical Encoding Rules (CER) and Distinguished
Encoding Rules (DER), ITU-T Recommendation X.690 (1997) |
ISO/IEC International Standard 8825-1:1998.
Authors' Addresses
Larry Zhu
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052
US
Email: lzhu@microsoft.com
Paul Leach
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052
US
Email: paulle@microsoft.com
Zhu, et al. Expires January 20, 2006 [Page 5]
Internet-Draft Enctype Negotiation July 2005
Karthik Jaganathan
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052
US
Email: karthikj@microsoft.com
Zhu, et al. Expires January 20, 2006 [Page 6]
Internet-Draft Enctype Negotiation July 2005
Intellectual Property Statement
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
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
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.
Disclaimer of Validity
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.
Copyright Statement
Copyright (C) The Internet Society (2005). 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.
Acknowledgment
Funding for the RFC Editor function is currently provided by the
Internet Society.
Zhu, et al. Expires January 20, 2006 [Page 7]