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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 (==), 3 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) August 14, 2020 5 Intended status: Standards Track 6 Expires: February 15, 2021 8 OCSP Nonce Extension 9 draft-ietf-lamps-ocsp-nonce-03 11 Abstract 13 This document specifies the updated format of the Nonce extension in 14 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 in the OCSP request and response messages to 17 avoid replay attacks. This document updates the RFC 6960 19 Status of This Memo 21 This Internet-Draft is submitted in full conformance with the 22 provisions of BCP 78 and BCP 79. 24 Internet-Drafts are working documents of the Internet Engineering 25 Task Force (IETF). Note that other groups may also distribute 26 working documents as Internet-Drafts. The list of current Internet- 27 Drafts is at https://datatracker.ietf.org/drafts/current/. 29 Internet-Drafts are draft documents valid for a maximum of six months 30 and may be updated, replaced, or obsoleted by other documents at any 31 time. It is inappropriate to use Internet-Drafts as reference 32 material or to cite them other than as "work in progress." 34 This Internet-Draft will expire on February 15, 2021. 36 Copyright Notice 38 Copyright (c) 2020 IETF Trust and the persons identified as the 39 document authors. All rights reserved. 41 This document is subject to BCP 78 and the IETF Trust's Legal 42 Provisions Relating to IETF Documents 43 (https://trustee.ietf.org/license-info) in effect on the date of 44 publication of this document. Please review these documents 45 carefully, as they describe your rights and restrictions with respect 46 to this document. Code Components extracted from this document must 47 include Simplified BSD License text as described in Section 4.e of 48 the Trust Legal Provisions and are provided without warranty as 49 described in the Simplified BSD License. 51 Table of Contents 53 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 54 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 2 55 2. OCSP Extensions . . . . . . . . . . . . . . . . . . . . . . . 3 56 2.1. Nonce Extension . . . . . . . . . . . . . . . . . . . . . 3 57 3. Security Considerations . . . . . . . . . . . . . . . . . . . 4 58 3.1. Replay Attack . . . . . . . . . . . . . . . . . . . . . . 4 59 3.2. Nonce Collision . . . . . . . . . . . . . . . . . . . . . 4 60 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4 61 5. Changes to Appendix B. of RFC 6960 . . . . . . . . . . . . . 4 62 5.1. Changes to Appendix B.1. OCSP in ASN.1 - 1998 Syntax . . 5 63 5.2. Changes to Appendix B.2 OCSP in ASN.1 - 2008 Syntax . . . 5 64 6. References . . . . . . . . . . . . . . . . . . . . . . . . . 5 65 6.1. Normative References . . . . . . . . . . . . . . . . . . 5 66 6.2. Informative References . . . . . . . . . . . . . . . . . 6 67 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 6 69 1. Introduction 71 This document updates the usage and format of the Nonce extension 72 used in OCSP request and response messages. This extension was 73 previously defined in section 4.1.1 of [RFC6960]. The [RFC6960] does 74 not mention any minimum and maximum length of the nonce extension. 75 Due to not having an upper or lower limit of the length of the Nonce 76 extension, the OCSP responders that follow [RFC6960] may be 77 vulnerable to various attacks like Denial of Service attacks 78 [RFC4732], chosen prefix attacks to get a desired signature from the 79 OCSP responder and possible evasions that can use the Nonce extension 80 data for evasion. This document specifies a lower limit of 1 and an 81 upper limit of 32 to the length of the Nonce extension. This 82 document updates the [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 the OCSP request and response is defined in 95 the [RFC6960]. It also defines the standard extensions for OCSP 96 messages based on the extension model employed in X.509 version 3 97 certificates (see [RFC5280]). The following is a list of standard 98 extensions that can be used in the OCSP messages by the OCSP 99 responder and OCSP client. 101 * Nonce 102 * CRL References 103 * Acceptable Response Types 104 * Archive Cutoff 105 * CRL Entry Extensions 106 * Service Locator 107 * Preferred Signature Algorithms 108 * Extended Response Definition 110 This document only specifies the new format for Nonce extension and 111 does not change the specification of any of the other standard 112 extensions. 114 2.1. Nonce Extension 116 This section replaces the entirety of the Section 4.4.1 of [RFC6960] 117 which describes the OCSP Nonce extension. 119 The nonce cryptographically binds a request and a response to prevent 120 replay attacks. The nonce is included as one of the 121 requestExtensions in requests, while in responses it would be 122 included as one of the responseExtensions. In both the request and 123 the response, the nonce will be identified by the object identifier 124 id-pkix-ocsp-nonce, while the extnValue is the value of the nonce. 125 If Nonce extension is present then the length of nonce MUST be at 126 least 1 octet and can be up to 32 octets. 128 A server MUST reject any OCSP request having a Nonce extension with 129 length of more than 32 octets with the malformedRequest 130 OCSPResponseStatus as described in section 4.2.1 of [RFC6960] 132 The value of the nonce MUST be generated using a cryptographically 133 strong pseudorandom number generator. The OCSP clients SHOULD use a 134 length of 32 octets for the Nonce extension. The minimum nonce 135 length of 1 octet is defined to provide the backward compatibility 136 with older clients following [RFC6960] however, the newer OCSP 137 clients MUST use a length of at least 16 octets for Nonce extension. 138 The OCSP responder MAY choose to ignore Nonce extension for the 139 requests where length of the Nonce extension is less than 16 octets. 141 id-pkix-ocsp OBJECT IDENTIFIER ::= { id-ad-ocsp } 142 id-pkix-ocsp-nonce OBJECT IDENTIFIER ::= { id-pkix-ocsp 2 } 144 Nonce ::= OCTET STRING(SIZE(1..32)) 146 3. Security Considerations 148 The security considerations of OCSP, in general, are described in the 149 [RFC6960]. The Nonce extension is used to avoid replay attacks 150 during the interval in which the previous OCSP response for a 151 certificate is not expired but the responder has a changed status for 152 that certificate. Including client's Nonce value in the OCSP 153 response makes sure that the response is the latest response from the 154 server and not an old copy. 156 3.1. Replay Attack 158 The Nonce extension is used to avoid replay attacks. Since the OCSP 159 responder may choose to not send the Nonce extension in the OCSP 160 response even if the client has sent the Nonce extension in the 161 request [RFC5019], an on-path attacker can intercept the OCSP request 162 and respond with an earlier response from the server without the 163 Nonce extension. This can be mitigated by configuring the server to 164 use a short time interval between thisUpdate and nextUpdate fields in 165 the OCSP response. 167 3.2. Nonce Collision 169 If the value of the nonce used by a client in OCSP request is not 170 random enough, then an attacker may prefetch responses with the 171 predicted nonce and can replay them, thus defeating the purpose of 172 using nonce. Therefore the value of Nonce extension in the OCSP 173 request MUST contain cryptographically strong randomness and MUST be 174 freshly generated at the time of creating the OCSP request. Also if 175 the length of the nonce extension is too small e.g. 1 octet then an 176 on-path attacker can prefetch responses with all the possible values 177 of the nonce and replay a matching nonce. 179 4. IANA Considerations 181 This document does not call for any IANA actions. 183 5. Changes to Appendix B. of RFC 6960 185 This section updates the ASN.1 definitions of the OCSP Nonce 186 extension in the Appendix B.1 and Appendix B.2 of the [RFC6960] The 187 Appendix B.1 defines OCSP using ASN.1 - 1998 Syntax and Appendix B.2 188 defines OCSP using ASN.1 - 2008 Syntax 190 5.1. Changes to Appendix B.1. OCSP in ASN.1 - 1998 Syntax 192 OLD Syntax: 194 The definition of OCSP Nonce Extension is not provided in the 195 Appendix B.1 of [RFC6960] for the ASN.1 - 1998 Syntax. 197 NEW Syntax: 199 Nonce ::= OCTET STRING(SIZE(1..32)) 201 5.2. Changes to Appendix B.2 OCSP in ASN.1 - 2008 Syntax 203 OLD Syntax: 205 re-ocsp-nonce EXTENSION ::= { SYNTAX OCTET STRING IDENTIFIED 206 BY id-pkix-ocsp-nonce } 208 NEW Syntax: 210 re-ocsp-nonce EXTENSION ::= { SYNTAX OCTET STRING(SIZE(1..32)) 211 IDENTIFIED BY id-pkix-ocsp-nonce } 213 6. References 215 6.1. Normative References 217 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 218 Requirement Levels", BCP 14, RFC 2119, 219 DOI 10.17487/RFC2119, March 1997, 220 . 222 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 223 2119 Key Words", DOI 10.17487/RFC8174, RFC 8174, BCP 14, 224 May 2017, . 226 [RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S., 227 Housley, R., and W. Polk, "Internet X.509 Public Key 228 Infrastructure Certificate and Certificate Revocation List 229 (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008, 230 . 232 [RFC6960] Santesson, S., Myers, M., Ankney, R., Malpani, A., 233 Galperin, S., and C. Adams, "X.509 Internet Public Key 234 Infrastructure Online Certificate Status Protocol - OCSP", 235 RFC 6960, DOI 10.17487/RFC6960, June 2013, 236 . 238 6.2. Informative References 240 [RFC4732] Handley, M., Ed., Rescorla, E., Ed., and IAB, "Internet 241 Denial-of-Service Considerations", RFC 4732, 242 DOI 10.17487/RFC4732, December 2006, 243 . 245 [RFC5019] Deacon, A. and R. Hurst, "The Lightweight Online 246 Certificate Status Protocol (OCSP) Profile for High-Volume 247 Environments", RFC 5019, DOI 10.17487/RFC5019, September 248 2007, . 250 Author's Address 252 Mohit Sahni (editor) 253 Palo Alto Networks 254 3000 Tannery Way 255 Santa Clara, CA 95054 256 US 258 Email: msahni@paloaltonetworks.com