draft-ietf-lamps-ocsp-nonce-02.txt   draft-ietf-lamps-ocsp-nonce-03.txt 
LAMPS M. Sahni, Ed. LAMPS M. Sahni, Ed.
Internet-Draft Palo Alto Networks Internet-Draft Palo Alto Networks
Updates: 6960 (if approved) May 15, 2020 Updates: 6960 (if approved) August 14, 2020
Intended status: Standards Track Intended status: Standards Track
Expires: November 16, 2020 Expires: February 15, 2021
OCSP Nonce Extension OCSP Nonce Extension
draft-ietf-lamps-ocsp-nonce-02 draft-ietf-lamps-ocsp-nonce-03
Abstract Abstract
This document specifies the updated format of the Nonce extension in This document specifies the updated format of the Nonce extension in
Online Certificate Status Protocol (OCSP) request and response Online Certificate Status Protocol (OCSP) request and response
messages. OCSP is used to check the status of a certificate and the 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 Nonce extension is used in the OCSP request and response messages to
avoid replay attacks. This document updates the RFC 6960 avoid replay attacks. This document updates the RFC 6960
Status of This Memo Status of This Memo
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on November 16, 2020. This Internet-Draft will expire on February 15, 2021.
Copyright Notice Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of (https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 2 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 2
2. OCSP Extensions . . . . . . . . . . . . . . . . . . . . . . . 3 2. OCSP Extensions . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Nonce Extension . . . . . . . . . . . . . . . . . . . . . 3 2.1. Nonce Extension . . . . . . . . . . . . . . . . . . . . . 3
3. Security Considerations . . . . . . . . . . . . . . . . . . . 4 3. Security Considerations . . . . . . . . . . . . . . . . . . . 4
3.1. Replay Attack . . . . . . . . . . . . . . . . . . . . . . 4 3.1. Replay Attack . . . . . . . . . . . . . . . . . . . . . . 4
3.2. Nonce Collision . . . . . . . . . . . . . . . . . . . . . 4 3.2. Nonce Collision . . . . . . . . . . . . . . . . . . . . . 4
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
5. Changes to Appendix B. of RFC 6960 . . . . . . . . . . . . . 4 5. Changes to Appendix B. of RFC 6960 . . . . . . . . . . . . . 4
5.1. Changes to Appendix B.1. OCSP in ASN.1 - 1998 Syntax . . 4 5.1. 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 5.2. Changes to Appendix B.2 OCSP in ASN.1 - 2008 Syntax . . . 5
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 5 6. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
6.1. Normative References . . . . . . . . . . . . . . . . . . 5 6.1. Normative References . . . . . . . . . . . . . . . . . . 5
6.2. Informative References . . . . . . . . . . . . . . . . . 5 6.2. Informative References . . . . . . . . . . . . . . . . . 6
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 6 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction 1. Introduction
This document updates the usage and format of the Nonce extension This document updates the usage and format of the Nonce extension
used in OCSP request and response messages. This extension was used in OCSP request and response messages. This extension was
previously defined in section 4.1.1 of [RFC6960]. The [RFC6960] does previously defined in section 4.1.1 of [RFC6960]. The [RFC6960] does
not mention any minimum and maximum length of the nonce extension. 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 Due to not having an upper or lower limit of the length of the Nonce
extension, the OCSP responders that follow [RFC6960] may be extension, the OCSP responders that follow [RFC6960] may be
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"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP "OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
2. OCSP Extensions 2. OCSP Extensions
The message format for the OCSP request and response is defined in The message format for the OCSP request and response is defined in
the [RFC6960]. It also defines the standard extensions for OCSP the [RFC6960]. It also defines the standard extensions for OCSP
messages based on the extension model employed in X.509 version 3 messages based on the extension model employed in X.509 version 3
certificates (see [RFC5280]). Following is the list of standard certificates (see [RFC5280]). The following is a list of standard
extensions that can be used in the OCSP messages by the OCSP extensions that can be used in the OCSP messages by the OCSP
responder and OCSP client. responder and OCSP client.
* Nonce * Nonce
* CRL References * CRL References
* Acceptable Response Types * Acceptable Response Types
* Archive Cutoff * Archive Cutoff
* CRL Entry Extensions * CRL Entry Extensions
* Service Locator * Service Locator
* Preferred Signature Algorithms * Preferred Signature Algorithms
* Extended Response Definition * Extended Response Definition
This document only specifies the new format for Nonce extension and This document only specifies the new format for Nonce extension and
does not change the specification of any of the other standard does not change the specification of any of the other standard
extensions. extensions.
2.1. Nonce Extension 2.1. Nonce Extension
This section updates the Section 4.4.1 of [RFC6960] which describes This section replaces the entirety of the Section 4.4.1 of [RFC6960]
the OCSP Nonce extension. which describes the OCSP Nonce extension.
The nonce cryptographically binds a request and a response to prevent The nonce cryptographically binds a request and a response to prevent
replay attacks. The nonce is included as one of the replay attacks. The nonce is included as one of the
requestExtensions in requests, while in responses it would be requestExtensions in requests, while in responses it would be
included as one of the responseExtensions. In both the request and included as one of the responseExtensions. In both the request and
the response, the nonce will be identified by the object identifier the response, the nonce will be identified by the object identifier
id-pkix-ocsp-nonce, while the extnValue is the value of the nonce. 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 If Nonce extension is present then the length of nonce MUST be at
least 1 octet and can be up to 32 octets. least 1 octet and can be up to 32 octets.
A server MUST reject any OCSP request having a Nonce extension with A server MUST reject any OCSP request having a Nonce extension with
length of more than 32 octets with the malformedRequest length of more than 32 octets with the malformedRequest
OCSPResponseStatus as described in section 4.2.1 of [RFC6960] OCSPResponseStatus as described in section 4.2.1 of [RFC6960]
The minimum nonce length of 1 octet is defined to provide the The value of the nonce MUST be generated using a cryptographically
backward compatibility with clients following [RFC6960]. However the strong pseudorandom number generator. The OCSP clients SHOULD use a
newer OCSP clients MUST use length of at least 16 octets for Nonce length of 32 octets for the Nonce extension. The minimum nonce
extension and the value of the nonce MUST be generated using a length of 1 octet is defined to provide the backward compatibility
cryptographically strong pseudorandom number generator. 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.
id-pkix-ocsp OBJECT IDENTIFIER ::= { id-ad-ocsp }
id-pkix-ocsp-nonce OBJECT IDENTIFIER ::= { id-pkix-ocsp 2 }
Nonce ::= OCTET STRING(SIZE(1..32)) Nonce ::= OCTET STRING(SIZE(1..32))
3. Security Considerations 3. Security Considerations
The security considerations of OCSP, in general, are described in the The security considerations of OCSP, in general, are described in the
[RFC6960]. The Nonce extension is used to avoid replay attacks [RFC6960]. The Nonce extension is used to avoid replay attacks
during the interval in which the previous OCSP response for a during the interval in which the previous OCSP response for a
certificate is not expired but the responder has a changed status for certificate is not expired but the responder has a changed status for
that certificate. Including client's Nonce value in the OCSP that certificate. Including client's Nonce value in the OCSP
response makes sure that the response is the latest response from the response makes sure that the response is the latest response from the
server and not an old copy. server and not an old copy.
3.1. Replay Attack 3.1. Replay Attack
The Nonce extension is used to avoid replay attacks. Since the OCSP The Nonce extension is used to avoid replay attacks. Since the OCSP
responder may choose to not send the Nonce extension in 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 response even if the client has sent the Nonce extension in the
request [RFC5019], a man in the middle (MITM) entity can intercept request [RFC5019], an on-path attacker can intercept the OCSP request
the OCSP request and respond with an earlier response from the server and respond with an earlier response from the server without the
without the Nonce extension. This can be mitigated by the server Nonce extension. This can be mitigated by configuring the server to
using a closer nextUpdate value in the OCSP response. use a short time interval between thisUpdate and nextUpdate fields in
the OCSP response.
3.2. Nonce Collision 3.2. Nonce Collision
If the value of the nonce used by a client is not random enough, then If the value of the nonce used by a client in OCSP request is not
an attacker may prefetch responses with the predicted nonce and can random enough, then an attacker may prefetch responses with the
replay them, thus defeating the purpose of using nonce. Therefore predicted nonce and can replay them, thus defeating the purpose of
the client MUST use a nonce value that contains cryptographically using nonce. Therefore the value of Nonce extension in the OCSP
strong randomness and is freshly generated. Also if the length of request MUST contain cryptographically strong randomness and MUST be
the nonce is very small e.g. 1 octet then an attacker can prefetch freshly generated at the time of creating the OCSP request. Also if
responses with all the possible values of the nonce and replay a the length of the nonce extension is too small e.g. 1 octet then an
matching nonce. A client SHOULD use 32 octets for the nonce length. on-path attacker can prefetch responses with all the possible values
of the nonce and replay a matching nonce.
4. IANA Considerations 4. IANA Considerations
This document does not call for any IANA actions. This document does not call for any IANA actions.
5. Changes to Appendix B. of RFC 6960 5. Changes to Appendix B. of RFC 6960
This section updates the ASN.1 definitions of the OCSP Nonce 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 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 Appendix B.1 defines OCSP using ASN.1 - 1998 Syntax and Appendix B.2
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