Internet DRAFT - draft-ietf-lamps-ocsp-nonce
draft-ietf-lamps-ocsp-nonce
LAMPS M. Sahni, Ed.
Internet-Draft Palo Alto Networks
Updates: 6960 (if approved) September 10, 2020
Intended status: Standards Track
Expires: March 14, 2021
OCSP Nonce Extension
draft-ietf-lamps-ocsp-nonce-05
Abstract
This document specifies the updated format of the Nonce extension in
the Online Certificate Status Protocol (OCSP) request and response
messages. OCSP is used to check the status of a certificate and the
Nonce extension is used to cryptographically bind an OCSP response
message to a particular OCSP request message. This document updates
RFC 6960.
Status of This Memo
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This Internet-Draft will expire on March 14, 2021.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 2
2. OCSP Extensions . . . . . . . . . . . . . . . . . . . . . . . 2
2.1. Nonce Extension . . . . . . . . . . . . . . . . . . . . . 3
3. Security Considerations . . . . . . . . . . . . . . . . . . . 3
3.1. Replay Attack . . . . . . . . . . . . . . . . . . . . . . 4
3.2. Nonce Collision . . . . . . . . . . . . . . . . . . . . . 4
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
5. Changes to Appendix B. of RFC 6960 . . . . . . . . . . . . . 4
5.1. Changes to Appendix B.1. OCSP in ASN.1 - 1998 Syntax . . 4
5.2. Changes to Appendix B.2 OCSP in ASN.1 - 2008 Syntax . . . 5
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
6.1. Normative References . . . . . . . . . . . . . . . . . . 5
6.2. Informative References . . . . . . . . . . . . . . . . . 5
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
This document updates the usage and format of the Nonce extension
used in OCSP request and response messages. This extension was
previously defined in section 4.4.1 of [RFC6960]. [RFC6960] does not
mention any minimum and maximum length of nonce in the Nonce
extension. Lacking limits on the length of nonce in the Nonce
extension, an OCSP responders that follow [RFC6960] may be vulnerable
to various attacks like Denial of Service attacks [RFC4732], chosen
prefix attacks to get a desired signature, and possible evasions
using the Nonce extension data. This document specifies a lower
limit of 1 and an upper limit of 32 to the length of nonce in the
Nonce extension. This document updates [RFC6960].
1.1. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2. OCSP Extensions
The message format for OCSP request and response is defined in
[RFC6960]. [RFC6960] also defines the standard extensions for OCSP
messages based on the extension model employed in X.509 version 3
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certificates (see [RFC5280]). This document only specifies the new
format for Nonce extension and does not change specification of any
of the other standard extensions defined in [RFC6960].
2.1. Nonce Extension
This section replaces the entirety of the Section 4.4.1 of [RFC6960]
which describes the OCSP Nonce extension.
The nonce cryptographically binds a request and a response to prevent
replay attacks. The nonce is included as one of the
requestExtensions in requests, while in responses it would be
included as one of the responseExtensions. In both the request and
the response, the nonce will be identified by the object identifier
id-pkix-ocsp-nonce, while the extnValue is the value of the nonce.
If Nonce extension is present then the length of nonce MUST be at
least 1 octet and can be up to 32 octets.
A server MUST reject any OCSP request having a nonce in the Nonce
extension with length of 0 octets or more than 32 octets with the
malformedRequest OCSPResponseStatus as described in section 4.2.1 of
[RFC6960].
The value of the nonce MUST be generated using a cryptographically
strong pseudorandom number generator (see [RFC4086]). The minimum
nonce length of 1 octet is defined to provide backward compatibility
with older clients that follow [RFC6960]. Newer OCSP clients that
support this document MUST use a length of 32 octets for the nonce in
Nonce extension. OCSP responders MUST accept lengths of at least 16
octets, and MAY choose to ignore the Nonce extension for requests
where the length of the nonce is less than 16 octets
id-pkix-ocsp OBJECT IDENTIFIER ::= { id-ad-ocsp }
id-pkix-ocsp-nonce OBJECT IDENTIFIER ::= { id-pkix-ocsp 2 }
Nonce ::= OCTET STRING(SIZE(1..32))
3. Security Considerations
The security considerations of OCSP, in general, are described in
[RFC6960]. During the interval in which the previous OCSP response
for a certificate is not expired but the responder has a changed
status for that certificate, a copy of that OCSP response can be used
to indicate that the status of the certificate is still valid.
Including client's Nonce value in the OCSP response makes sure that
the response is the latest response from the server and not an old
copy.
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3.1. Replay Attack
The Nonce extension is used to avoid replay attacks. Since the OCSP
responder may choose to not send the Nonce extension in the OCSP
response even if the client has sent the Nonce extension in the
request [RFC5019], an on-path attacker can intercept the OCSP request
and respond with an earlier response from the server without the
Nonce extension. This can be mitigated by configuring the server to
use a short time interval between the thisUpdate and nextUpdate
fields in the OCSP response.
3.2. Nonce Collision
If the value of nonce used by a client in OCSP request is
predictable, then an attacker may prefetch responses with the
predicted nonce and can replay them, thus defeating the purpose of
using nonce. Therefore the value of Nonce extension in the OCSP
request MUST contain cryptographically strong randomness and MUST be
freshly generated at the time of creating the OCSP request. Also if
the length of nonce is too small e.g. 1 octet then an on-path
attacker can prefetch responses with all the possible values of nonce
and replay a matching nonce.
4. IANA Considerations
This document does not call for any IANA actions.
5. Changes to Appendix B. of RFC 6960
This section updates the ASN.1 definitions of the OCSP Nonce
extension in Appendix B.1 and Appendix B.2 of [RFC6960] The
Appendix B.1 defines OCSP using ASN.1 - 1998 Syntax and Appendix B.2
defines OCSP using ASN.1 - 2008 Syntax
5.1. Changes to Appendix B.1. OCSP in ASN.1 - 1998 Syntax
OLD Syntax:
The definition of OCSP Nonce Extension is not provided in
Appendix B.1 of [RFC6960] for the ASN.1 - 1998 Syntax.
NEW Syntax:
Nonce ::= OCTET STRING(SIZE(1..32))
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5.2. Changes to Appendix B.2 OCSP in ASN.1 - 2008 Syntax
OLD Syntax:
re-ocsp-nonce EXTENSION ::= { SYNTAX OCTET STRING IDENTIFIED
BY id-pkix-ocsp-nonce }
NEW Syntax:
re-ocsp-nonce EXTENSION ::= { SYNTAX OCTET STRING(SIZE(1..32))
IDENTIFIED BY id-pkix-ocsp-nonce }
6. References
6.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", DOI 10.17487/RFC8174, RFC 8174, BCP 14,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
<https://www.rfc-editor.org/info/rfc5280>.
[RFC6960] Santesson, S., Myers, M., Ankney, R., Malpani, A.,
Galperin, S., and C. Adams, "X.509 Internet Public Key
Infrastructure Online Certificate Status Protocol - OCSP",
RFC 6960, DOI 10.17487/RFC6960, June 2013,
<https://www.rfc-editor.org/info/rfc6960>.
6.2. Informative References
[RFC4086] Eastlake 3rd, D., Schiller, J., and S. Crocker,
"Randomness Requirements for Security", BCP 106, RFC 4086,
DOI 10.17487/RFC4086, June 2005,
<https://www.rfc-editor.org/info/rfc4086>.
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[RFC4732] Handley, M., Ed., Rescorla, E., Ed., and IAB, "Internet
Denial-of-Service Considerations", RFC 4732,
DOI 10.17487/RFC4732, December 2006,
<https://www.rfc-editor.org/info/rfc4732>.
[RFC5019] Deacon, A. and R. Hurst, "The Lightweight Online
Certificate Status Protocol (OCSP) Profile for High-Volume
Environments", RFC 5019, DOI 10.17487/RFC5019, September
2007, <https://www.rfc-editor.org/info/rfc5019>.
Author's Address
Mohit Sahni (editor)
Palo Alto Networks
3000 Tannery Way
Santa Clara, CA 95054
US
Email: msahni@paloaltonetworks.com
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