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General Internet Engineering Task Force Online Certificate Status Protocol (OCSP) Nonce Extension This document updates the Nonce extension section of RFC-8954. Nonce extension is an optional extension for Online Certificate Status Protocol (OCSP) request and response messages. OCSP is used for checking the status of a certificate, and the Nonce extension is used to cryptographically bind an OCSP response message to a particular OCSP request message. Some environments use cryptographic algorithms that generate a Nonce that is longer than 32 octets. This document updates the maximum allowed length of Nonce to 128 octets.

Introduction Nonce extension was previously defined in Section 4.4.1 of and updated in . enforces the maximum Nonce length to 32 octets. To support cryptographic algorithms that generate a Nonce that is longer than 32 octets, this document updates the maximum allowed size of the Nonce to 128 octets. In addition, this document recommends that the OCSP client and responder use a Nonce with a minimum length of 32 octets.

Requirements Language 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 when, and only when, they appear in all capitals, as shown here.

OCSP Extensions The message formats for OCSP requests and responses are defined in and Nonce extension was updated in . also defines the standard extensions for OCSP messages based on the extension model employed in X.509 version 3 certificates (see ). replaces this section to enforce the minimum and maximum length for the Nonce value. This document extends the maximum allowed nonce length to 128 octets and does not change the specifications of any of the other standard extensions defined in [RFC6960].

Nonce Extension This section replaces the entirety of Section 2.1 of , 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; 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 the Nonce extension is present, then the length of the Nonce MUST be at least 1 octet and can be up to 128 octets. An OCSP client that implements this document SHOULD use a minimum length of 32 octets for Nonce in the Nonce extension. RFC 8954-compliant implementations will be unable to process nonces generated per the new specification with sizes in excess of what was permitted by RFC 8954. OCSP resonder that implements this document MUST reject any OCSP request that has a Nonce in the Nonce extension with a length of either 0 octets or more than 128 octets, with the malformedRequest OCSPResponseStatus as described in Section 4.2.1 of . Responders, supporting the Nonce extension, MUST accept lengths of at least 16 octets and MAY choose to ignore the Nonce extension for requests where the length of the nonce is less than 16 octets or more than 32 octets. The value of the Nonce MUST be generated using a cryptographically strong pseudorandom number generator (see ). The minimum Nonce length of 1 octet is defined to provide backward compatibility with older clients that follow . id-pkix-ocsp OBJECT IDENTIFIER ::= { id-ad-ocsp } id-pkix-ocsp-Nonce OBJECT IDENTIFIER ::= { id-pkix-ocsp 2 } Nonce ::= OCTET STRING(SIZE(1..128))

Security Considerations The security considerations of OCSP, in general, are described in . 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, a copy of that OCSP response can be used to indicate that the status of the certificate is still valid. Including a 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.

Replay Attack The Nonce extension is used to avoid replay attacks. Since the OCSP responder may choose not to send the Nonce extension in the OCSP response even if the client has sent the Nonce extension in the request , 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 the thisUpdate and nextUpdate fields in the OCSP response.

IANA Considerations For the ASN.1 Module in Appendix A.1, IANA is requested to assign an object identifier (OID) for the module identifier to replace TBD1. The OID for the module should be allocated in the "SMI Security for PKIX Module Identifier" registry (1.3.6.1.5.5.7.0), and the Description for the new OID should be set to "id-mod-ocsp-2024-88". For the ASN.1 Module in Appendix A.2, IANA is requested to assign an object identifier (OID) for the module identifier to replace TBD2. The OID for the module should be allocated in the "SMI Security for PKIX Module Identifier" registry (1.3.6.1.5.5.7.0), and the Description for the new OID should be set to "id-mod-ocsp-2024-08".

References Normative References Informative References RFC Errata RFC 6960

This section includes the ASN.1 modules for OCSP and replaces the entirity of Section 5 of . It addresses Errata id 5891 as well. Appendix A.1 includes an ASN.1 module that conforms to the 1998 version of ASN.1 for all syntax elements of OCSP. This module replaces the modules Appendix B.1 of . Appendix A.2 includes an ASN.1 module, corresponding to the module present in A.1, that conforms to the 2008 version of ASN.1. This module replaces the modules in Section 4 of and Appendix B.2 of . Although a 2008 ASN.1 module is provided, the module in Appendix A.1 remains the normative module as per the policy of the PKIX working group.

OCSP-2024-88 {iso(1) identified-organization(3) dod(6) internet(1) security(5) mechanisms(5) pkix(7) id-mod(0) id-mod-ocsp-2024-88(TBD1)} DEFINITIONS EXPLICIT TAGS ::= BEGIN IMPORTS -- PKIX Certificate Extensions AuthorityInfoAccessSyntax, CRLReason, GeneralName FROM PKIX1Implicit88 { iso(1) identified-organization(3) dod(6) internet(1) security(5) mechanisms(5) pkix(7) id-mod(0) id-pkix1-implicit(19) } Name, CertificateSerialNumber, Extensions, id-kp, id-ad-ocsp, Certificate, AlgorithmIdentifier FROM PKIX1Explicit88 { iso(1) identified-organization(3) dod(6) internet(1) security(5) mechanisms(5) pkix(7) id-mod(0) id-pkix1-explicit(18) }; OCSPRequest ::= SEQUENCE { tbsRequest TBSRequest, optionalSignature [0] EXPLICIT Signature OPTIONAL } TBSRequest ::= SEQUENCE { version [0] EXPLICIT Version DEFAULT v1, requestorName [1] EXPLICIT GeneralName OPTIONAL, requestList SEQUENCE OF Request, requestExtensions [2] EXPLICIT Extensions OPTIONAL } Signature ::= SEQUENCE { signatureAlgorithm AlgorithmIdentifier, signature BIT STRING, certs [0] EXPLICIT SEQUENCE OF Certificate OPTIONAL } Version ::= INTEGER { v1(0) } Nonce ::= OCTET STRING(SIZE(1..128)) Request ::= SEQUENCE { reqCert CertID, singleRequestExtensions [0] EXPLICIT Extensions OPTIONAL } CertID ::= SEQUENCE { hashAlgorithm AlgorithmIdentifier, issuerNameHash OCTET STRING, -- Hash of issuer's DN issuerKeyHash OCTET STRING, -- Hash of issuer's public key serialNumber CertificateSerialNumber } OCSPResponse ::= SEQUENCE { responseStatus OCSPResponseStatus, responseBytes [0] EXPLICIT ResponseBytes OPTIONAL } OCSPResponseStatus ::= ENUMERATED { successful (0), -- Response has valid confirmations malformedRequest (1), -- Illegal confirmation request internalError (2), -- Internal error in issuer tryLater (3), -- Try again later -- (4) is not used sigRequired (5), -- Must sign the request unauthorized (6) -- Request unauthorized } ResponseBytes ::= SEQUENCE { responseType OBJECT IDENTIFIER, response OCTET STRING } BasicOCSPResponse ::= SEQUENCE { tbsResponseData ResponseData, signatureAlgorithm AlgorithmIdentifier, signature BIT STRING, certs [0] EXPLICIT SEQUENCE OF Certificate OPTIONAL } ResponseData ::= SEQUENCE { version [0] EXPLICIT Version DEFAULT v1, responderID ResponderID, producedAt GeneralizedTime, responses SEQUENCE OF SingleResponse, responseExtensions [1] EXPLICIT Extensions OPTIONAL } ResponderID ::= CHOICE { byName [1] Name, byKey [2] KeyHash } KeyHash ::= OCTET STRING -- SHA-1 hash of responder's public key -- (i.e., the SHA-1 hash of the value of the -- BIT STRING subjectPublicKey [excluding -- the tag, length, and number of unused -- bits] in the responder's certificate) SingleResponse ::= SEQUENCE { certID CertID, certStatus CertStatus, thisUpdate GeneralizedTime, nextUpdate [0] EXPLICIT GeneralizedTime OPTIONAL, singleExtensions [1] EXPLICIT Extensions OPTIONAL } CertStatus ::= CHOICE { good [0] IMPLICIT NULL, revoked [1] IMPLICIT RevokedInfo, unknown [2] IMPLICIT UnknownInfo } RevokedInfo ::= SEQUENCE { revocationTime GeneralizedTime, revocationReason [0] EXPLICIT CRLReason OPTIONAL } UnknownInfo ::= NULL ArchiveCutoff ::= GeneralizedTime AcceptableResponses ::= SEQUENCE OF OBJECT IDENTIFIER ServiceLocator ::= SEQUENCE { issuer Name, locator AuthorityInfoAccessSyntax } CrlID ::= SEQUENCE { crlUrl [0] EXPLICIT IA5String OPTIONAL, crlNum [1] EXPLICIT INTEGER OPTIONAL, crlTime [2] EXPLICIT GeneralizedTime OPTIONAL } PreferredSignatureAlgorithms ::= SEQUENCE OF PreferredSignatureAlgorithm PreferredSignatureAlgorithm ::= SEQUENCE { sigIdentifier AlgorithmIdentifier, certIdentifier AlgorithmIdentifier OPTIONAL } -- Object Identifiers id-kp-OCSPSigning OBJECT IDENTIFIER ::= { id-kp 9 } id-pkix-ocsp OBJECT IDENTIFIER ::= { id-ad-ocsp } id-pkix-ocsp-basic OBJECT IDENTIFIER ::= { id-pkix-ocsp 1 } id-pkix-ocsp-nonce OBJECT IDENTIFIER ::= { id-pkix-ocsp 2 } id-pkix-ocsp-crl OBJECT IDENTIFIER ::= { id-pkix-ocsp 3 } id-pkix-ocsp-response OBJECT IDENTIFIER ::= { id-pkix-ocsp 4 } id-pkix-ocsp-nocheck OBJECT IDENTIFIER ::= { id-pkix-ocsp 5 } id-pkix-ocsp-archive-cutoff OBJECT IDENTIFIER ::= { id-pkix-ocsp 6 } id-pkix-ocsp-service-locator OBJECT IDENTIFIER ::= { id-pkix-ocsp 7 } id-pkix-ocsp-pref-sig-algs OBJECT IDENTIFIER ::= { id-pkix-ocsp 8 } id-pkix-ocsp-extended-revoke OBJECT IDENTIFIER ::= { id-pkix-ocsp 9 } END

OCSP-2024-08 {iso(1) identified-organization(3) dod(6) internet(1) security(5) mechanisms(5) pkix(7) id-mod(0) id-mod-ocsp-2024-08(TBD2)} DEFINITIONS EXPLICIT TAGS ::= BEGIN IMPORTS Extensions{}, EXTENSION, ATTRIBUTE FROM PKIX-CommonTypes-2009 -- From [RFC5912] {iso(1) identified-organization(3) dod(6) internet(1) security(5) mechanisms(5) pkix(7) id-mod(0) id-mod-pkixCommon-02(57)} AlgorithmIdentifier{}, DIGEST-ALGORITHM, SIGNATURE-ALGORITHM, PUBLIC-KEY FROM AlgorithmInformation-2009 -- From [RFC5912] {iso(1) identified-organization(3) dod(6) internet(1) security(5) mechanisms(5) pkix(7) id-mod(0) id-mod-algorithmInformation-02(58)} AuthorityInfoAccessSyntax, GeneralName, CrlEntryExtensions, CRLReason FROM PKIX1Implicit-2009 -- From [RFC5912] {iso(1) identified-organization(3) dod(6) internet(1) security(5) mechanisms(5) pkix(7) id-mod(0) id-mod-pkix1-implicit-02(59)} Name, CertificateSerialNumber, id-kp, id-ad-ocsp, Certificate FROM PKIX1Explicit-2009 -- From [RFC5912] {iso(1) identified-organization(3) dod(6) internet(1) security(5) mechanisms(5) pkix(7) id-mod(0) id-mod-pkix1-explicit-02(51)} sa-dsaWithSHA1, sa-rsaWithMD2, sa-rsaWithMD5, sa-rsaWithSHA1 FROM PKIXAlgs-2009 -- From [RFC5912] {iso(1) identified-organization(3) dod(6) internet(1) security(5) mechanisms(5) pkix(7) id-mod(0) id-mod-pkix1-algorithms2008-02(56)}; OCSPRequest ::= SEQUENCE { tbsRequest TBSRequest, optionalSignature [0] EXPLICIT Signature OPTIONAL } TBSRequest ::= SEQUENCE { version [0] EXPLICIT Version DEFAULT v1, requestorName [1] EXPLICIT GeneralName OPTIONAL, requestList SEQUENCE OF Request, requestExtensions [2] EXPLICIT Extensions {{re-ocsp-nonce | re-ocsp-response, ..., re-ocsp-preferred-signature-algorithms}} OPTIONAL } Signature ::= SEQUENCE { signatureAlgorithm AlgorithmIdentifier { SIGNATURE-ALGORITHM, {...}}, signature BIT STRING, certs [0] EXPLICIT SEQUENCE OF Certificate OPTIONAL } Version ::= INTEGER { v1(0) } Nonce ::= OCTET STRING(SIZE(1..128)) Request ::= SEQUENCE { reqCert CertID, singleRequestExtensions [0] EXPLICIT Extensions { {re-ocsp-service-locator, ...}} OPTIONAL } CertID ::= SEQUENCE { hashAlgorithm AlgorithmIdentifier {DIGEST-ALGORITHM, {...}}, issuerNameHash OCTET STRING, -- Hash of issuer's DN issuerKeyHash OCTET STRING, -- Hash of issuer's public key serialNumber CertificateSerialNumber } OCSPResponse ::= SEQUENCE { responseStatus OCSPResponseStatus, responseBytes [0] EXPLICIT ResponseBytes OPTIONAL } OCSPResponseStatus ::= ENUMERATED { successful (0), -- Response has valid confirmations malformedRequest (1), -- Illegal confirmation request internalError (2), -- Internal error in issuer tryLater (3), -- Try again later -- (4) is not used sigRequired (5), -- Must sign the request unauthorized (6) -- Request unauthorized } RESPONSE ::= TYPE-IDENTIFIER ResponseSet RESPONSE ::= {basicResponse, ...} ResponseBytes ::= SEQUENCE { responseType RESPONSE. &id ({ResponseSet}), response OCTET STRING (CONTAINING RESPONSE. &Type({ResponseSet}{@responseType}))} basicResponse RESPONSE ::= { BasicOCSPResponse IDENTIFIED BY id-pkix-ocsp-basic } BasicOCSPResponse ::= SEQUENCE { tbsResponseData ResponseData, signatureAlgorithm AlgorithmIdentifier{SIGNATURE-ALGORITHM, {sa-dsaWithSHA1 | sa-rsaWithSHA1 | sa-rsaWithMD5 | sa-rsaWithMD2, ...}}, signature BIT STRING, certs [0] EXPLICIT SEQUENCE OF Certificate OPTIONAL } ResponseData ::= SEQUENCE { version [0] EXPLICIT Version DEFAULT v1, responderID ResponderID, producedAt GeneralizedTime, responses SEQUENCE OF SingleResponse, responseExtensions [1] EXPLICIT Extensions {{re-ocsp-nonce, ..., re-ocsp-extended-revoke}} OPTIONAL } ResponderID ::= CHOICE { byName [1] Name, byKey [2] KeyHash } KeyHash ::= OCTET STRING -- SHA-1 hash of responder's public key -- (excluding the tag and length fields) SingleResponse ::= SEQUENCE { certID CertID, certStatus CertStatus, thisUpdate GeneralizedTime, nextUpdate [0] EXPLICIT GeneralizedTime OPTIONAL, singleExtensions [1] EXPLICIT Extensions{{re-ocsp-crl | re-ocsp-archive-cutoff | CrlEntryExtensions, ...} } OPTIONAL } CertStatus ::= CHOICE { good [0] IMPLICIT NULL, revoked [1] IMPLICIT RevokedInfo, unknown [2] IMPLICIT UnknownInfo } RevokedInfo ::= SEQUENCE { revocationTime GeneralizedTime, revocationReason [0] EXPLICIT CRLReason OPTIONAL } UnknownInfo ::= NULL ArchiveCutoff ::= GeneralizedTime AcceptableResponses ::= SEQUENCE OF RESPONSE.&id({ResponseSet}) ServiceLocator ::= SEQUENCE { issuer Name, locator AuthorityInfoAccessSyntax } CrlID ::= SEQUENCE { crlUrl [0] EXPLICIT IA5String OPTIONAL, crlNum [1] EXPLICIT INTEGER OPTIONAL, crlTime [2] EXPLICIT GeneralizedTime OPTIONAL } PreferredSignatureAlgorithms ::= SEQUENCE OF PreferredSignatureAlgorithm PreferredSignatureAlgorithm ::= SEQUENCE { sigIdentifier AlgorithmIdentifier{SIGNATURE-ALGORITHM, {...}}, certIdentifier AlgorithmIdentifier{PUBLIC-KEY, {...}} OPTIONAL } -- Certificate Extensions ext-ocsp-nocheck EXTENSION ::= { SYNTAX NULL IDENTIFIED BY id-pkix-ocsp-nocheck } -- Request Extensions re-ocsp-nonce EXTENSION ::= { SYNTAX Nonce IDENTIFIED BY id-pkix-ocsp-nonce } re-ocsp-response EXTENSION ::= { SYNTAX AcceptableResponses IDENTIFIED BY id-pkix-ocsp-response } re-ocsp-service-locator EXTENSION ::= { SYNTAX ServiceLocator IDENTIFIED BY id-pkix-ocsp-service-locator } re-ocsp-preferred-signature-algorithms EXTENSION ::= { SYNTAX PreferredSignatureAlgorithms IDENTIFIED BY id-pkix-ocsp-pref-sig-algs } -- Response Extensions re-ocsp-crl EXTENSION ::= { SYNTAX CrlID IDENTIFIED BY id-pkix-ocsp-crl } re-ocsp-archive-cutoff EXTENSION ::= { SYNTAX ArchiveCutoff IDENTIFIED BY id-pkix-ocsp-archive-cutoff } re-ocsp-extended-revoke EXTENSION ::= { SYNTAX NULL IDENTIFIED BY id-pkix-ocsp-extended-revoke } -- Object Identifiers id-kp-OCSPSigning OBJECT IDENTIFIER ::= { id-kp 9 } id-pkix-ocsp OBJECT IDENTIFIER ::= id-ad-ocsp id-pkix-ocsp-basic OBJECT IDENTIFIER ::= { id-pkix-ocsp 1 } id-pkix-ocsp-nonce OBJECT IDENTIFIER ::= { id-pkix-ocsp 2 } id-pkix-ocsp-crl OBJECT IDENTIFIER ::= { id-pkix-ocsp 3 } id-pkix-ocsp-response OBJECT IDENTIFIER ::= { id-pkix-ocsp 4 } id-pkix-ocsp-nocheck OBJECT IDENTIFIER ::= { id-pkix-ocsp 5 } id-pkix-ocsp-archive-cutoff OBJECT IDENTIFIER ::= { id-pkix-ocsp 6 } id-pkix-ocsp-service-locator OBJECT IDENTIFIER ::= { id-pkix-ocsp 7 } id-pkix-ocsp-pref-sig-algs OBJECT IDENTIFIER ::= { id-pkix-ocsp 8 } id-pkix-ocsp-extended-revoke OBJECT IDENTIFIER ::= { id-pkix-ocsp 9 } END