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NETWORK WORKING GROUP L. Zhu
Internet-Draft K. Jaganathan
Expires: November 21, 2005 Microsoft Corporation
N. Williams
Sun Microsystems
May 20, 2005
OCSP Support for PKINIT
draft-ietf-krb-wg-ocsp-for-pkinit-05
Status of this Memo
This document is an Internet-Draft and is subject to all provisions
of Section 3 of RFC 3667.
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 November 21, 2005.
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
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Version 5 extension that provides for the use of public key
cryptography.
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
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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 [CLARIFICATIONS],
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 [CLARIFICATIONS] 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.
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.
The KDC that receives a PA-PK-OCSP-RESPONSE then SHOULD send a PA-PK-
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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
aid of a valid PA-PK-OCSP-RESPONSE then it SHOULD fail the AS
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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
[CLARIFICATIONS]
RFC-Editor: To be replaced by RFC number for draft-ietf-
krb-wg-kerberos-clarifications. Work in Progress.
[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.
[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.
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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
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Intellectual Property Statement
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Copyright Statement
Copyright (C) The Internet Society (2005). This document is subject
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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.
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