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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) No issues found here. Summary: 0 errors (**), 0 flaws (~~), 1 warning (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 LAMPS M. Sahni, Ed. 3 Internet-Draft Palo Alto Networks 4 Updates: 6960 (if approved) September 10, 2020 5 Intended status: Standards Track 6 Expires: March 14, 2021 8 OCSP Nonce Extension 9 draft-ietf-lamps-ocsp-nonce-05 11 Abstract 13 This document specifies the updated format of the Nonce extension in 14 the Online Certificate Status Protocol (OCSP) request and response 15 messages. OCSP is used to check the status of a certificate and the 16 Nonce extension is used to cryptographically bind an OCSP response 17 message to a particular OCSP request message. This document updates 18 RFC 6960. 20 Status of This Memo 22 This Internet-Draft is submitted in full conformance with the 23 provisions of BCP 78 and BCP 79. 25 Internet-Drafts are working documents of the Internet Engineering 26 Task Force (IETF). Note that other groups may also distribute 27 working documents as Internet-Drafts. The list of current Internet- 28 Drafts is at https://datatracker.ietf.org/drafts/current/. 30 Internet-Drafts are draft documents valid for a maximum of six months 31 and may be updated, replaced, or obsoleted by other documents at any 32 time. It is inappropriate to use Internet-Drafts as reference 33 material or to cite them other than as "work in progress." 35 This Internet-Draft will expire on March 14, 2021. 37 Copyright Notice 39 Copyright (c) 2020 IETF Trust and the persons identified as the 40 document authors. All rights reserved. 42 This document is subject to BCP 78 and the IETF Trust's Legal 43 Provisions Relating to IETF Documents 44 (https://trustee.ietf.org/license-info) in effect on the date of 45 publication of this document. Please review these documents 46 carefully, as they describe your rights and restrictions with respect 47 to this document. Code Components extracted from this document must 48 include Simplified BSD License text as described in Section 4.e of 49 the Trust Legal Provisions and are provided without warranty as 50 described in the Simplified BSD License. 52 Table of Contents 54 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 55 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 2 56 2. OCSP Extensions . . . . . . . . . . . . . . . . . . . . . . . 2 57 2.1. Nonce Extension . . . . . . . . . . . . . . . . . . . . . 3 58 3. Security Considerations . . . . . . . . . . . . . . . . . . . 3 59 3.1. Replay Attack . . . . . . . . . . . . . . . . . . . . . . 4 60 3.2. Nonce Collision . . . . . . . . . . . . . . . . . . . . . 4 61 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4 62 5. Changes to Appendix B. of RFC 6960 . . . . . . . . . . . . . 4 63 5.1. Changes to Appendix B.1. OCSP in ASN.1 - 1998 Syntax . . 4 64 5.2. Changes to Appendix B.2 OCSP in ASN.1 - 2008 Syntax . . . 5 65 6. References . . . . . . . . . . . . . . . . . . . . . . . . . 5 66 6.1. Normative References . . . . . . . . . . . . . . . . . . 5 67 6.2. Informative References . . . . . . . . . . . . . . . . . 5 68 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 6 70 1. Introduction 72 This document updates the usage and format of the Nonce extension 73 used in OCSP request and response messages. This extension was 74 previously defined in section 4.4.1 of [RFC6960]. [RFC6960] does not 75 mention any minimum and maximum length of nonce in the Nonce 76 extension. Lacking limits on the length of nonce in the Nonce 77 extension, an OCSP responders that follow [RFC6960] may be vulnerable 78 to various attacks like Denial of Service attacks [RFC4732], chosen 79 prefix attacks to get a desired signature, and possible evasions 80 using the Nonce extension data. This document specifies a lower 81 limit of 1 and an upper limit of 32 to the length of nonce in the 82 Nonce extension. This document updates [RFC6960]. 84 1.1. Terminology 86 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 87 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 88 "OPTIONAL" in this document are to be interpreted as described in BCP 89 14 [RFC2119] [RFC8174] when, and only when, they appear in all 90 capitals, as shown here. 92 2. OCSP Extensions 94 The message format for OCSP request and response is defined in 95 [RFC6960]. [RFC6960] also defines the standard extensions for OCSP 96 messages based on the extension model employed in X.509 version 3 97 certificates (see [RFC5280]). This document only specifies the new 98 format for Nonce extension and does not change specification of any 99 of the other standard extensions defined in [RFC6960]. 101 2.1. Nonce Extension 103 This section replaces the entirety of the Section 4.4.1 of [RFC6960] 104 which describes the OCSP Nonce extension. 106 The nonce cryptographically binds a request and a response to prevent 107 replay attacks. The nonce is included as one of the 108 requestExtensions in requests, while in responses it would be 109 included as one of the responseExtensions. In both the request and 110 the response, the nonce will be identified by the object identifier 111 id-pkix-ocsp-nonce, while the extnValue is the value of the nonce. 112 If Nonce extension is present then the length of nonce MUST be at 113 least 1 octet and can be up to 32 octets. 115 A server MUST reject any OCSP request having a nonce in the Nonce 116 extension with length of 0 octets or more than 32 octets with the 117 malformedRequest OCSPResponseStatus as described in section 4.2.1 of 118 [RFC6960]. 120 The value of the nonce MUST be generated using a cryptographically 121 strong pseudorandom number generator (see [RFC4086]). The minimum 122 nonce length of 1 octet is defined to provide backward compatibility 123 with older clients that follow [RFC6960]. Newer OCSP clients that 124 support this document MUST use a length of 32 octets for the nonce in 125 Nonce extension. OCSP responders MUST accept lengths of at least 16 126 octets, and MAY choose to ignore the Nonce extension for requests 127 where the length of the nonce is less than 16 octets 129 id-pkix-ocsp OBJECT IDENTIFIER ::= { id-ad-ocsp } 130 id-pkix-ocsp-nonce OBJECT IDENTIFIER ::= { id-pkix-ocsp 2 } 132 Nonce ::= OCTET STRING(SIZE(1..32)) 134 3. Security Considerations 136 The security considerations of OCSP, in general, are described in 137 [RFC6960]. During the interval in which the previous OCSP response 138 for a certificate is not expired but the responder has a changed 139 status for that certificate, a copy of that OCSP response can be used 140 to indicate that the status of the certificate is still valid. 141 Including client's Nonce value in the OCSP response makes sure that 142 the response is the latest response from the server and not an old 143 copy. 145 3.1. Replay Attack 147 The Nonce extension is used to avoid replay attacks. Since the OCSP 148 responder may choose to not send the Nonce extension in the OCSP 149 response even if the client has sent the Nonce extension in the 150 request [RFC5019], an on-path attacker can intercept the OCSP request 151 and respond with an earlier response from the server without the 152 Nonce extension. This can be mitigated by configuring the server to 153 use a short time interval between the thisUpdate and nextUpdate 154 fields in the OCSP response. 156 3.2. Nonce Collision 158 If the value of nonce used by a client in OCSP request is 159 predictable, then an attacker may prefetch responses with the 160 predicted nonce and can replay them, thus defeating the purpose of 161 using nonce. Therefore the value of Nonce extension in the OCSP 162 request MUST contain cryptographically strong randomness and MUST be 163 freshly generated at the time of creating the OCSP request. Also if 164 the length of nonce is too small e.g. 1 octet then an on-path 165 attacker can prefetch responses with all the possible values of nonce 166 and replay a matching nonce. 168 4. IANA Considerations 170 This document does not call for any IANA actions. 172 5. Changes to Appendix B. of RFC 6960 174 This section updates the ASN.1 definitions of the OCSP Nonce 175 extension in Appendix B.1 and Appendix B.2 of [RFC6960] The 176 Appendix B.1 defines OCSP using ASN.1 - 1998 Syntax and Appendix B.2 177 defines OCSP using ASN.1 - 2008 Syntax 179 5.1. Changes to Appendix B.1. OCSP in ASN.1 - 1998 Syntax 181 OLD Syntax: 183 The definition of OCSP Nonce Extension is not provided in 184 Appendix B.1 of [RFC6960] for the ASN.1 - 1998 Syntax. 186 NEW Syntax: 188 Nonce ::= OCTET STRING(SIZE(1..32)) 190 5.2. Changes to Appendix B.2 OCSP in ASN.1 - 2008 Syntax 192 OLD Syntax: 194 re-ocsp-nonce EXTENSION ::= { SYNTAX OCTET STRING IDENTIFIED 195 BY id-pkix-ocsp-nonce } 197 NEW Syntax: 199 re-ocsp-nonce EXTENSION ::= { SYNTAX OCTET STRING(SIZE(1..32)) 200 IDENTIFIED BY id-pkix-ocsp-nonce } 202 6. References 204 6.1. Normative References 206 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 207 Requirement Levels", BCP 14, RFC 2119, 208 DOI 10.17487/RFC2119, March 1997, 209 . 211 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 212 2119 Key Words", DOI 10.17487/RFC8174, RFC 8174, BCP 14, 213 May 2017, . 215 [RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S., 216 Housley, R., and W. Polk, "Internet X.509 Public Key 217 Infrastructure Certificate and Certificate Revocation List 218 (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008, 219 . 221 [RFC6960] Santesson, S., Myers, M., Ankney, R., Malpani, A., 222 Galperin, S., and C. Adams, "X.509 Internet Public Key 223 Infrastructure Online Certificate Status Protocol - OCSP", 224 RFC 6960, DOI 10.17487/RFC6960, June 2013, 225 . 227 6.2. Informative References 229 [RFC4086] Eastlake 3rd, D., Schiller, J., and S. Crocker, 230 "Randomness Requirements for Security", BCP 106, RFC 4086, 231 DOI 10.17487/RFC4086, June 2005, 232 . 234 [RFC4732] Handley, M., Ed., Rescorla, E., Ed., and IAB, "Internet 235 Denial-of-Service Considerations", RFC 4732, 236 DOI 10.17487/RFC4732, December 2006, 237 . 239 [RFC5019] Deacon, A. and R. Hurst, "The Lightweight Online 240 Certificate Status Protocol (OCSP) Profile for High-Volume 241 Environments", RFC 5019, DOI 10.17487/RFC5019, September 242 2007, . 244 Author's Address 246 Mohit Sahni (editor) 247 Palo Alto Networks 248 3000 Tannery Way 249 Santa Clara, CA 95054 250 US 252 Email: msahni@paloaltonetworks.com