LAMPS M. Sahni, Ed.
Internet-Draft Palo Alto Networks
Updates: 6960 (if approved) August 14, 2020
Intended status: Standards Track
Expires: February 15, 2021
OCSP Nonce Extension
draft-ietf-lamps-ocsp-nonce-03
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 . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Nonce Extension . . . . . . . . . . . . . . . . . . . . . 3
3. Security Considerations . . . . . . . . . . . . . . . . . . . 4
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 . . 5
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 . . . . . . . . . . . . . . . . . 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.
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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]). The following is a list of standard
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 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 extension with
length of 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. The OCSP clients SHOULD use a
length of 32 octets for the Nonce extension. The minimum nonce
length of 1 octet is defined to provide the backward compatibility
with older clients following [RFC6960] however, the newer OCSP
clients MUST use a length of at least 16 octets for Nonce extension.
The OCSP responder MAY choose to ignore Nonce extension for the
requests where length of the Nonce extension is less than 16 octets.
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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 the
[RFC6960]. The Nonce extension is used to avoid replay attacks
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. 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], 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 thisUpdate and nextUpdate fields in
the OCSP response.
3.2. Nonce Collision
If the value of the nonce used by a client in OCSP request 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 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 the nonce extension is too small e.g. 1 octet then an
on-path attacker can prefetch responses with all the possible values
of the nonce and replay a matching nonce.
4. IANA Considerations
This document does not call for any IANA actions.
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
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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))
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>.
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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>.
[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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