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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) May 15, 2020 5 Intended status: Standards Track 6 Expires: November 16, 2020 8 OCSP Nonce Extension 9 draft-ietf-lamps-ocsp-nonce-02 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 November 16, 2020. 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 . . 4 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 . . . . . . . . . . . . . . . . . 5 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]). Following is the 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 updates the Section 4.4.1 of [RFC6960] which describes 117 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 minimum nonce length of 1 octet is defined to provide the 133 backward compatibility with clients following [RFC6960]. However the 134 newer OCSP clients MUST use length of at least 16 octets for Nonce 135 extension and the value of the nonce MUST be generated using a 136 cryptographically strong pseudorandom number generator. 138 Nonce ::= OCTET STRING(SIZE(1..32)) 140 3. Security Considerations 142 The security considerations of OCSP, in general, are described in the 143 [RFC6960]. The Nonce extension is used to avoid replay attacks 144 during the interval in which the previous OCSP response for a 145 certificate is not expired but the responder has a changed status for 146 that certificate. Including client's Nonce value in the OCSP 147 response makes sure that the response is the latest response from the 148 server and not an old copy. 150 3.1. Replay Attack 152 The Nonce extension is used to avoid replay attacks. Since the OCSP 153 responder may choose to not send the Nonce extension in the OCSP 154 response even if the client has sent the Nonce extension in the 155 request [RFC5019], a man in the middle (MITM) entity can intercept 156 the OCSP request and respond with an earlier response from the server 157 without the Nonce extension. This can be mitigated by the server 158 using a closer nextUpdate value in the OCSP response. 160 3.2. Nonce Collision 162 If the value of the nonce used by a client is not random enough, then 163 an attacker may prefetch responses with the predicted nonce and can 164 replay them, thus defeating the purpose of using nonce. Therefore 165 the client MUST use a nonce value that contains cryptographically 166 strong randomness and is freshly generated. Also if the length of 167 the nonce is very small e.g. 1 octet then an attacker can prefetch 168 responses with all the possible values of the nonce and replay a 169 matching nonce. A client SHOULD use 32 octets for the nonce length. 171 4. IANA Considerations 173 This document does not call for any IANA actions. 175 5. Changes to Appendix B. of RFC 6960 177 This section updates the ASN.1 definitions of the OCSP Nonce 178 extension in the Appendix B.1 and Appendix B.2 of the [RFC6960] The 179 Appendix B.1 defines OCSP using ASN.1 - 1998 Syntax and Appendix B.2 180 defines OCSP using ASN.1 - 2008 Syntax 182 5.1. Changes to Appendix B.1. OCSP in ASN.1 - 1998 Syntax 184 OLD Syntax: 186 The definition of OCSP Nonce Extension is not provided in the 187 Appendix B.1 of [RFC6960] for the ASN.1 - 1998 Syntax. 189 NEW Syntax: 191 Nonce ::= OCTET STRING(SIZE(1..32)) 193 5.2. Changes to Appendix B.2 OCSP in ASN.1 - 2008 Syntax 195 OLD Syntax: 197 re-ocsp-nonce EXTENSION ::= { SYNTAX OCTET STRING IDENTIFIED 198 BY id-pkix-ocsp-nonce } 200 NEW Syntax: 202 re-ocsp-nonce EXTENSION ::= { SYNTAX OCTET STRING(SIZE(1..32)) 203 IDENTIFIED BY id-pkix-ocsp-nonce } 205 6. References 207 6.1. Normative References 209 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 210 Requirement Levels", BCP 14, RFC 2119, 211 DOI 10.17487/RFC2119, March 1997, 212 . 214 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 215 2119 Key Words", DOI 10.17487/RFC8174, RFC 8174, BCP 14, 216 May 2017, . 218 [RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S., 219 Housley, R., and W. Polk, "Internet X.509 Public Key 220 Infrastructure Certificate and Certificate Revocation List 221 (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008, 222 . 224 [RFC6960] Santesson, S., Myers, M., Ankney, R., Malpani, A., 225 Galperin, S., and C. Adams, "X.509 Internet Public Key 226 Infrastructure Online Certificate Status Protocol - OCSP", 227 RFC 6960, DOI 10.17487/RFC6960, June 2013, 228 . 230 6.2. Informative References 232 [RFC4732] Handley, M., Ed., Rescorla, E., Ed., and IAB, "Internet 233 Denial-of-Service Considerations", RFC 4732, 234 DOI 10.17487/RFC4732, December 2006, 235 . 237 [RFC5019] Deacon, A. and R. Hurst, "The Lightweight Online 238 Certificate Status Protocol (OCSP) Profile for High-Volume 239 Environments", RFC 5019, DOI 10.17487/RFC5019, September 240 2007, . 242 Author's Address 244 Mohit Sahni (editor) 245 Palo Alto Networks 246 3000 Tannery Way 247 Santa Clara, CA 95054 248 US 250 Email: msahni@paloaltonetworks.com