LAMPS M. Sahni, Ed.
Internet-Draft Palo Alto Networks
Intended status: Standards Track April 26, 2020
Expires: October 28, 2020
OCSP Nonce Extension
draft-ietf-lamps-ocsp-nonce-01
Abstract
This document specifies the updated format of the Nonce extension in
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 in the OCSP request and response messages to
avoid replay attacks. This document updates the RFC 6960
Status of This Memo
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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
6.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 6
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 4.1.1 of [RFC6960]. The [RFC6960] does
not mention any minimum and maximum length of the nonce extension.
Due to not having an upper or lower limit of the length of the Nonce
extension, the 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 from the
OCSP responder and possible evasions that can use the Nonce extension
data for evasion. This document specifies a lower limit of 1 and an
upper limit of 32 to the length of the Nonce extension. This
document updates the [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 the OCSP request and response is defined in
the [RFC6960]. It also defines the standard extensions for OCSP
messages based on the extension model employed in X.509 version 3
certificates (see [RFC5280]). Following is the list of standard
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extensions that can be used in the OCSP messages by the OCSP
responder and OCSP client.
* Nonce
* CRL References
* Acceptable Response Types
* Archive Cutoff
* CRL Entry Extensions
* Service Locator
* Preferred Signature Algorithms
* Extended Response Definition
This document only specifies the new format for Nonce extension and
does not change the specification of any of the other standard
extensions.
2.1. Nonce Extension
This section updates the Section 4.4.1 [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 extension with
length of more than 32 octets with the malformedRequest
OCSPResponseStatus as described in section 4.2.1 of [RFC6960]
The minimum nonce length of 1 octet is defined to provide the
backward compatibility with clients following [RFC6960]. However the
newer OCSP clients MUST use length of at least 16 octets for Nonce
extension and the value of the nonce MUST be generated using a
cryptographically strong pseudorandom number generator.
Nonce ::= OCTET STRING(SIZE(1..32))
3. Security Considerations
The security considerations of OCSP, in general, are described in the
[RFC6960]. The Nonce extension is used to avoid replay attacks
during the interval in which the previous OCSP response for a
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certificate is not expired but the responder has a changed status for
that certificate. 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.
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], a man in the middle (MITM) entity can intercept
the OCSP request and respond with an earlier response from the server
without the Nonce extension. This can be mitigated by the server
using a closer nextUpdate value in the OCSP response.
3.2. Nonce Collision
If the value of the nonce used by a client is not random enough, then
an attacker may prefetch responses with the predicted nonce and can
replay them, thus defeating the purpose of using nonce. Therefore
the client MUST use a nonce value that contains cryptographically
strong randomness and is freshly generated. Also if the length of
the nonce is very small e.g. 1 octet then an attacker can prefetch
responses with all the possible values of the nonce and replay a
matching nonce. A client SHOULD use 32 octets for the nonce length.
4. IANA Considerations
This document does not include any new media type registrations
for OCSP.
5. Changes to Appendix B. of RFC 6960
This section updates the ASN.1 definitions of the OCSP Nonce
extension in the Appendix B.1 and Appendix B.2 of the [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 the
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
[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>.
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[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>.
6.3. URIs
[1] https://tools.ietf.org/html/rfc6960#section-4.4.1
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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