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rfc:rfc2560

Network Working Group M. Myers Request for Comments: 2560 VeriSign Category: Standards Track R. Ankney

                                                                CertCo
                                                            A. Malpani
                                                              ValiCert
                                                           S. Galperin
                                                                My CFO
                                                              C. Adams
                                                  Entrust Technologies
                                                             June 1999
              X.509 Internet Public Key Infrastructure
             Online Certificate Status Protocol - OCSP

Status of this Memo

 This document specifies an Internet standards track protocol for the
 Internet community, and requests discussion and suggestions for
 improvements.  Please refer to the current edition of the "Internet
 Official Protocol Standards" (STD 1) for the standardization state
 and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

 Copyright (C) The Internet Society (1999).  All Rights Reserved.

1. Abstract

 This document specifies a protocol useful in determining the current
 status of a digital certificate without requiring CRLs. Additional
 mechanisms addressing PKIX operational requirements are specified in
 separate documents.
 An overview of the protocol is provided in section 2. Functional
 requirements are specified in section 4. Details of the protocol are
 in section 5. We cover security issues with the protocol in section
 6. Appendix A defines OCSP over HTTP, appendix B accumulates ASN.1
 syntactic elements and appendix C specifies the mime types for the
 messages.
 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
 document (in uppercase, as shown) are to be interpreted as described
 in [RFC2119].

Myers, et al. Standards Track [Page 1] RFC 2560 PKIX OCSP June 1999

2. Protocol Overview

 In lieu of or as a supplement to checking against a periodic CRL, it
 may be necessary to obtain timely information regarding the
 revocation status of a certificate (cf. [RFC2459], Section 3.3).
 Examples include high-value funds transfer or large stock trades.
 The Online Certificate Status Protocol (OCSP) enables applications to
 determine the (revocation) state of an identified certificate. OCSP
 may be used to satisfy some of the operational requirements of
 providing more timely revocation information than is possible with
 CRLs and may also be used to obtain additional status information. An
 OCSP client issues a status request to an OCSP responder and suspends
 acceptance of the certificate in question until the responder
 provides a response.
 This protocol specifies the data that needs to be exchanged between
 an application checking the status of a certificate and the server
 providing that status.

2.1 Request

 An OCSP request contains the following data:
  1. - protocol version
  2. - service request
  3. - target certificate identifier
  4. - optional extensions which MAY be processed by the OCSP Responder
 Upon receipt of a request, an OCSP Responder determines if:
 1. the message is well formed
 2. the responder is configured to provide the requested service and
 3. the request contains the information needed by the responder If
 any one of the prior conditions are not met, the OCSP responder
 produces an error message; otherwise, it returns a definitive
 response.

2.2 Response

 OCSP responses can be of various types.  An OCSP response consists of
 a response type and the bytes of the actual response. There is one
 basic type of OCSP response that MUST be supported by all OCSP
 servers and clients. The rest of this section pertains only to this
 basic response type.

Myers, et al. Standards Track [Page 2] RFC 2560 PKIX OCSP June 1999

 All definitive response messages SHALL be digitally signed. The key
 used to sign the response MUST belong to one of the following:
  1. - the CA who issued the certificate in question
  2. - a Trusted Responder whose public key is trusted by the requester
  3. - a CA Designated Responder (Authorized Responder) who holds a

specially marked certificate issued directly by the CA, indicating

    that the responder may issue OCSP responses for that CA
 A definitive response message is composed of:
  1. - version of the response syntax
  2. - name of the responder
  3. - responses for each of the certificates in a request
  4. - optional extensions
  5. - signature algorithm OID
  6. - signature computed across hash of the response
 The response for each of the certificates in a request consists of
  1. - target certificate identifier
  2. - certificate status value
  3. - response validity interval
  4. - optional extensions
 This specification defines the following definitive response
 indicators for use in the certificate status value:
  1. - good
  2. - revoked
  3. - unknown
 The "good" state indicates a positive response to the status inquiry.
 At a minimum, this positive response indicates that the certificate
 is not revoked, but does not necessarily mean that the certificate
 was ever issued or that the time at which the response was produced
 is within the certificate's validity interval. Response extensions
 may be used to convey additional information on assertions made by
 the responder regarding the status of the certificate such as
 positive statement about issuance, validity, etc.
 The "revoked" state indicates that the certificate has been revoked
 (either permanantly or temporarily (on hold)).
 The "unknown" state indicates that the responder doesn't know about
 the certificate being requested.

Myers, et al. Standards Track [Page 3] RFC 2560 PKIX OCSP June 1999

2.3 Exception Cases

 In case of errors, the OCSP Responder may return an error message.
 These messages are not signed. Errors can be of the following types:
  1. - malformedRequest
  2. - internalError
  3. - tryLater
  4. - sigRequired
  5. - unauthorized
 A server produces the "malformedRequest" response if the request
 received does not conform to the OCSP syntax.
 The response "internalError" indicates that the OCSP responder
 reached an inconsistent internal state. The query should be retried,
 potentially with another responder.
 In the event that the OCSP responder is operational, but unable to
 return a status for the requested certificate, the "tryLater"
 response can be used to indicate that the service exists, but is
 temporarily unable to respond.
 The response "sigRequired" is returned in cases where the server
 requires the client sign the request in order to construct a
 response.
 The response "unauthorized" is returned in cases where the client is
 not authorized to make this query to this server.

2.4 Semantics of thisUpdate, nextUpdate and producedAt

 Responses can contain three times in them - thisUpdate, nextUpdate
 and producedAt. The semantics of these fields are:
  1. thisUpdate: The time at which the status being indicated is known

to be correct

  1. nextUpdate: The time at or before which newer information will be

available about the status of the certificate

  1. producedAt: The time at which the OCSP responder signed this

response.

 If nextUpdate is not set, the responder is indicating that newer
 revocation information is available all the time.

Myers, et al. Standards Track [Page 4] RFC 2560 PKIX OCSP June 1999

2.5 Response Pre-production

 OCSP responders MAY pre-produce signed responses specifying the
 status of certificates at a specified time. The time at which the
 status was known to be correct SHALL be reflected in the thisUpdate
 field of the response. The time at or before which newer information
 will be available is reflected in the nextUpdate field, while the
 time at which the response was produced will appear in the producedAt
 field of the response.

2.6 OCSP Signature Authority Delegation

 The key that signs a certificate's status information need not be the
 same key that signed the certificate. A certificate's issuer
 explicitly delegates OCSP signing authority by issuing a certificate
 containing a unique value for extendedKeyUsage in the OCSP signer's
 certificate. This certificate MUST be issued directly to the
 responder by the cognizant CA.

2.7 CA Key Compromise

 If an OCSP responder knows that a particular CA's private key has
 been compromised, it MAY return the revoked state for all
 certificates issued by that CA.

3. Functional Requirements

3.1 Certificate Content

 In order to convey to OCSP clients a well-known point of information
 access, CAs SHALL provide the capability to include the
 AuthorityInfoAccess extension (defined in [RFC2459], section 4.2.2.1)
 in certificates that can be checked using OCSP.  Alternatively, the
 accessLocation for the OCSP provider may be configured locally at the
 OCSP client.
 CAs that support an OCSP service, either hosted locally or provided
 by an Authorized Responder, MUST provide for the inclusion of a value
 for a uniformResourceIndicator (URI) accessLocation and the OID value
 id-ad-ocsp for the accessMethod in the AccessDescription SEQUENCE.
 The value of the accessLocation field in the subject certificate
 defines the transport (e.g. HTTP) used to access the OCSP responder
 and may contain other transport dependent information (e.g. a URL).

Myers, et al. Standards Track [Page 5] RFC 2560 PKIX OCSP June 1999

3.2 Signed Response Acceptance Requirements

 Prior to accepting a signed response as valid, OCSP clients SHALL
 confirm that:
 1. The certificate identified in a received response corresponds to
 that which was identified in the corresponding request;
 2. The signature on the response is valid;
 3. The identity of the signer matches the intended recipient of the
 request.
 4. The signer is currently authorized to sign the response.
 5. The time at which the status being indicated is known to be
 correct (thisUpdate) is sufficiently recent.
 6. When available, the time at or before which newer information will
 be available about the status of the certificate (nextUpdate) is
 greater than the current time.

4. Detailed Protocol

 The ASN.1 syntax imports terms defined in [RFC2459]. For signature
 calculation, the data to be signed is encoded using the ASN.1
 distinguished encoding rules (DER) [X.690].
 ASN.1 EXPLICIT tagging is used as a default unless specified
 otherwise.
 The terms imported from elsewhere are: Extensions,
 CertificateSerialNumber, SubjectPublicKeyInfo, Name,
 AlgorithmIdentifier, CRLReason

4.1 Requests

 This section specifies the ASN.1 specification for a confirmation
 request. The actual formatting of the message could vary depending on
 the transport mechanism used (HTTP, SMTP, LDAP, etc.).

4.1.1 Request Syntax

 OCSPRequest     ::=     SEQUENCE {
     tbsRequest                  TBSRequest,
     optionalSignature   [0]     EXPLICIT Signature OPTIONAL }
 TBSRequest      ::=     SEQUENCE {

Myers, et al. Standards Track [Page 6] RFC 2560 PKIX OCSP June 1999

     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) }
 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 Issuers public key
     serialNumber        CertificateSerialNumber }
 issuerNameHash is the hash of the Issuer's distinguished name. The
 hash shall be calculated over the DER encoding of the issuer's name
 field in the certificate being checked. issuerKeyHash is the hash of
 the Issuer's public key. The hash shall be calculated over the value
 (excluding tag and length) of the subject public key field in the
 issuer's certificate. The hash algorithm used for both these hashes,
 is identified in hashAlgorithm. serialNumber is the serial number of
 the certificate for which status is being requested.

4.1.2 Notes on the Request Syntax

 The primary reason to use the hash of the CA's public key in addition
 to the hash of the CA's name, to identify the issuer, is that it is
 possible that two CAs may choose to use the same Name (uniqueness in
 the Name is a recommendation that cannot be enforced). Two CAs will
 never, however, have the same public key unless the CAs either
 explicitly decided to share their private key, or the key of one of
 the CAs was compromised.
 Support for any specific extension is OPTIONAL. The critical flag
 SHOULD NOT be set for any of them.  Section 4.4 suggests several
 useful extensions.  Additional extensions MAY be defined in
 additional RFCs. Unrecognized extensions MUST be ignored (unless they
 have the critical flag set and are not understood).

Myers, et al. Standards Track [Page 7] RFC 2560 PKIX OCSP June 1999

 The requestor MAY choose to sign the OCSP request. In that case, the
 signature is computed over the tbsRequest structure. If the request
 is signed, the requestor SHALL specify its name in the requestorName
 field. Also, for signed requests, the requestor MAY include
 certificates that help the OCSP responder verify the requestor's
 signature in the certs field of Signature.

4.2 Response Syntax

 This section specifies the ASN.1 specification for a confirmation
 response. The actual formatting of the message could vary depending
 on the transport mechanism used (HTTP, SMTP, LDAP, etc.).

4.2.1 ASN.1 Specification of the OCSP Response

 An OCSP response at a minimum consists of a responseStatus field
 indicating the processing status of the prior request. If the value
 of responseStatus is one of the error conditions, responseBytes are
 not set.
 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
 }
 The value for responseBytes consists of an OBJECT IDENTIFIER and a
 response syntax identified by that OID encoded as an OCTET STRING.
 ResponseBytes ::=       SEQUENCE {
     responseType   OBJECT IDENTIFIER,
     response       OCTET STRING }
 For a basic OCSP responder, responseType will be id-pkix-ocsp-basic.
 id-pkix-ocsp           OBJECT IDENTIFIER ::= { id-ad-ocsp }
 id-pkix-ocsp-basic     OBJECT IDENTIFIER ::= { id-pkix-ocsp 1 }

Myers, et al. Standards Track [Page 8] RFC 2560 PKIX OCSP June 1999

 OCSP responders SHALL be capable of producing responses of the id-
 pkix-ocsp-basic response type. Correspondingly, OCSP clients SHALL be
 capable of receiving and processing responses of the id-pkix-ocsp-
 basic response type.
 The value for response SHALL be the DER encoding of
 BasicOCSPResponse.
 BasicOCSPResponse       ::= SEQUENCE {
    tbsResponseData      ResponseData,
    signatureAlgorithm   AlgorithmIdentifier,
    signature            BIT STRING,
    certs                [0] EXPLICIT SEQUENCE OF Certificate OPTIONAL }
 The value for signature SHALL be computed on the hash of the DER
 encoding ResponseData.
 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
 (excluding the tag and length fields)
 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 -- this can be replaced with an enumeration

Myers, et al. Standards Track [Page 9] RFC 2560 PKIX OCSP June 1999

4.2.2 Notes on OCSP Responses

4.2.2.1 Time

 The thisUpdate and nextUpdate fields define a recommended validity
 interval. This interval corresponds to the {thisUpdate, nextUpdate}
 interval in CRLs. Responses whose nextUpdate value is earlier than
 the local system time value SHOULD be considered unreliable.
 Responses whose thisUpdate time is later than the local system time
 SHOULD be considered unreliable. Responses where the nextUpdate value
 is not set are equivalent to a CRL with no time for nextUpdate (see
 Section 2.4).
 The producedAt time is the time at which this response was signed.

4.2.2.2 Authorized Responders

 The key that signs a certificate's status information need not be the
 same key that signed the certificate. It is necessary however to
 ensure that the entity signing this information is authorized to do
 so.  Therefore, a certificate's issuer MUST either sign the OCSP
 responses itself or it MUST explicitly designate this authority to
 another entity.  OCSP signing delegation SHALL be designated by the
 inclusion of id-kp-OCSPSigning in an extendedKeyUsage certificate
 extension included in the OCSP response signer's certificate.  This
 certificate MUST be issued directly by the CA that issued the
 certificate in question.
 id-kp-OCSPSigning OBJECT IDENTIFIER ::= {id-kp 9}
 Systems or applications that rely on OCSP responses MUST be capable
 of detecting and enforcing use of the id-ad-ocspSigning value as
 described above. They MAY provide a means of locally configuring one
 or more OCSP signing authorities, and specifying the set of CAs for
 which each signing authority is trusted. They MUST reject the
 response if the certificate required to validate the signature on the
 response fails to meet at least one of the following criteria:
 1. Matches a local configuration of OCSP signing authority for the
 certificate in question; or
 2. Is the certificate of the CA that issued the certificate in
 question; or
 3. Includes a value of id-ad-ocspSigning in an ExtendedKeyUsage
 extension and is issued by the CA that issued the certificate in
 question."

Myers, et al. Standards Track [Page 10] RFC 2560 PKIX OCSP June 1999

 Additional acceptance or rejection criteria may apply to either the
 response itself or to the certificate used to validate the signature
 on the response.

4.2.2.2.1 Revocation Checking of an Authorized Responder

 Since an Authorized OCSP responder provides status information for
 one or more CAs, OCSP clients need to know how to check that an
 authorized responder's certificate has not been revoked. CAs may
 choose to deal with this problem in one of three ways:
  1. A CA may specify that an OCSP client can trust a responder for the

lifetime of the responder's certificate. The CA does so by including

 the extension id-pkix-ocsp-nocheck. This SHOULD be a non-critical
 extension. The value of the extension should be NULL. CAs issuing
 such a certificate should realized that a compromise of the
 responder's key, is as serious as the compromise of a CA key used to
 sign CRLs, at least for the validity period of this certificate. CA's
 may choose to issue this type of certificate with a very short
 lifetime and renew it frequently.
 id-pkix-ocsp-nocheck OBJECT IDENTIFIER ::= { id-pkix-ocsp 5 }
  1. A CA may specify how the responder's certificate be checked for

revocation. This can be done using CRL Distribution Points if the

 check should be done using CRLs or CRL Distribution Points, or
 Authority Information Access if the check should be done in some
 other way. Details for specifying either of these two mechanisms are
 available in [RFC2459].
  1. A CA may choose not to specify any method of revocation checking

for the responder's certificate, in which case, it would be up to the

 OCSP client's local security policy to decide whether that
 certificate should be checked for revocation or not.

4.3 Mandatory and Optional Cryptographic Algorithms

 Clients that request OCSP services SHALL be capable of processing
 responses signed used DSA keys identified by the DSA sig-alg-oid
 specified in section 7.2.2 of [RFC2459]. Clients SHOULD also be
 capable of processing RSA signatures as specified in section 7.2.1 of
 [RFC2459]. OCSP responders SHALL support the SHA1 hashing algorithm.

4.4 Extensions

 This section defines some standard extensions, based on the extension
 model employed in X.509 version 3 certificates see [RFC2459]. Support
 for all extensions is optional for both clients and responders.  For

Myers, et al. Standards Track [Page 11] RFC 2560 PKIX OCSP June 1999

 each extension, the definition indicates its syntax, processing
 performed by the OCSP Responder, and any extensions which are
 included in the corresponding response.

4.4.1 Nonce

 The nonce cryptographically binds a request and a response to prevent
 replay attacks. The nonce is included as one of the requestExtensions
 in requests, while 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.
 id-pkix-ocsp-nonce     OBJECT IDENTIFIER ::= { id-pkix-ocsp 2 }

4.4.2 CRL References

 It may be desirable for the OCSP responder to indicate the CRL on
 which a revoked or onHold certificate is found. This can be useful
 where OCSP is used between repositories, and also as an auditing
 mechanism. The CRL may be specified by a URL (the URL at which the
 CRL is available), a number (CRL number) or a time (the time at which
 the relevant CRL was created). These extensions will be specified as
 singleExtensions. The identifier for this extension will be id-pkix-
 ocsp-crl, while the value will be CrlID.
 id-pkix-ocsp-crl       OBJECT IDENTIFIER ::= { id-pkix-ocsp 3 }
 CrlID ::= SEQUENCE {
    crlUrl               [0]     EXPLICIT IA5String OPTIONAL,
    crlNum               [1]     EXPLICIT INTEGER OPTIONAL,
    crlTime              [2]     EXPLICIT GeneralizedTime OPTIONAL }
 For the choice crlUrl, the IA5String will specify the URL at which
 the CRL is available. For crlNum, the INTEGER will specify the value
 of the CRL number extension of the relevant CRL. For crlTime, the
 GeneralizedTime will indicate the time at which the relevant CRL was
 issued.

4.4.3 Acceptable Response Types

 An OCSP client MAY wish to specify the kinds of response types it
 understands. To do so, it SHOULD use an extension with the OID id-
 pkix-ocsp-response, and the value AcceptableResponses.  This
 extension is included as one of the requestExtensions in requests.
 The OIDs included in AcceptableResponses are the OIDs of the various
 response types this client can accept (e.g., id-pkix-ocsp-basic).

Myers, et al. Standards Track [Page 12] RFC 2560 PKIX OCSP June 1999

 id-pkix-ocsp-response  OBJECT IDENTIFIER ::= { id-pkix-ocsp 4 }
 AcceptableResponses ::= SEQUENCE OF OBJECT IDENTIFIER
 As noted in section 4.2.1, OCSP responders SHALL be capable of
 responding with responses of the id-pkix-ocsp-basic response type.
 Correspondingly, OCSP clients SHALL be capable of receiving and
 processing responses of the id-pkix-ocsp-basic response type.

4.4.4 Archive Cutoff

 An OCSP responder MAY choose to retain revocation information beyond
 a certificate's expiration. The date obtained by subtracting this
 retention interval value from the producedAt time in a response is
 defined as the certificate's "archive cutoff" date.
 OCSP-enabled applications would use an OCSP archive cutoff date to
 contribute to a proof that a digital signature was (or was not)
 reliable on the date it was produced even if the certificate needed
 to validate the signature has long since expired.
 OCSP servers that provide support for such historical reference
 SHOULD include an archive cutoff date extension in responses.  If
 included, this value SHALL be provided as an OCSP singleExtensions
 extension identified by id-pkix-ocsp-archive-cutoff and of syntax
 GeneralizedTime.
 id-pkix-ocsp-archive-cutoff  OBJECT IDENTIFIER ::= { id-pkix-ocsp 6 }
 ArchiveCutoff ::= GeneralizedTime
 To illustrate, if a server is operated with a 7-year retention
 interval policy and status was produced at time t1 then the value for
 ArchiveCutoff in the response would be (t1 - 7 years).

4.4.5 CRL Entry Extensions

 All the extensions specified as CRL Entry Extensions - in Section 5.3
 of [RFC2459] - are also supported as singleExtensions.

4.4.6 Service Locator

 An OCSP server may be operated in a mode whereby the server receives
 a request and routes it to the OCSP server which is known to be
 authoritative for the identified certificate.  The serviceLocator
 request extension is defined for this purpose.  This extension is
 included as one of the singleRequestExtensions in requests.

Myers, et al. Standards Track [Page 13] RFC 2560 PKIX OCSP June 1999

 id-pkix-ocsp-service-locator OBJECT IDENTIFIER ::= { id-pkix-ocsp 7 }
 ServiceLocator ::= SEQUENCE {
     issuer    Name,
     locator   AuthorityInfoAccessSyntax OPTIONAL }
 Values for these fields are obtained from the corresponding fields in
 the subject certificate.

5. Security Considerations

 For this service to be effective, certificate using systems must
 connect to the certificate status service provider. In the event such
 a connection cannot be obtained, certificate-using systems could
 implement CRL processing logic as a fall-back position.
 A denial of service vulnerability is evident with respect to a flood
 of queries. The production of a cryptographic signature significantly
 affects response generation cycle time, thereby exacerbating the
 situation. Unsigned error responses open up the protocol to another
 denial of service attack, where the attacker sends false error
 responses.
 The use of precomputed responses allows replay attacks in which an
 old (good) response is replayed prior to its expiration date but
 after the certificate has been revoked. Deployments of OCSP should
 carefully evaluate the benefit of precomputed responses against the
 probability of a replay attack and the costs associated with its
 successful execution.
 Requests do not contain the responder they are directed to. This
 allows an attacker to replay a request to any number of OCSP
 responders.
 The reliance of HTTP caching in some deployment scenarios may result
 in unexpected results if intermediate servers are incorrectly
 configured or are known to possess cache management faults.
 Implementors are advised to take the reliability of HTTP cache
 mechanisms into account when deploying OCSP over HTTP.

Myers, et al. Standards Track [Page 14] RFC 2560 PKIX OCSP June 1999

6. References

 [RFC2459] Housley, R., Ford, W., Polk, W. and D. Solo, "Internet
           X.509 Public Key Infrastructure Certificate and CRL
           Profile", RFC 2459, January 1999.
 [HTTP]    Fielding, R., Gettys, J., Mogul, J., Frystyk, H. and T.
           Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1", RFC
           2068, January 1997.
 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
           Requirement Levels", BCP 14, RFC 2119, March 1997.
 [URL]     Berners-Lee, T., Masinter, L. and M. McCahill, "Uniform
           Resource Locators (URL)", RFC 1738, December 1994.
 [X.690]   ITU-T Recommendation X.690 (1994) | ISO/IEC 8825-1:1995,
           Information Technology - ASN.1 encoding rules:
           Specification of Basic Encoding Rules (BER), Canonical
           Encoding Rules (CER) and Distinguished Encoding Rules
           (DER).

Myers, et al. Standards Track [Page 15] RFC 2560 PKIX OCSP June 1999

7. Authors' Addresses

 Michael Myers
 VeriSign, Inc.
 1350 Charleston Road
 Mountain View, CA 94043
 EMail: mmyers@verisign.com
 Rich Ankney
 CertCo, LLC
 13506 King Charles Dr.
 Chantilly, VA  20151
 EMail: rankney@erols.com
 Ambarish Malpani
 ValiCert, Inc.
 1215 Terra Bella Ave.
 Mountain View, CA 94043
 Phone: 650.567.5457
 EMail: ambarish@valicert.com
 Slava Galperin
 My CFO, Inc.
 1945 Charleston Road
 Mountain View, CA
 EMail: galperin@mycfo.com
 Carlisle Adams
 Entrust Technologies
 750 Heron Road, Suite E08
 Ottawa, Ontario
 K1V 1A7
 Canada
 EMail: cadams@entrust.com

Myers, et al. Standards Track [Page 16] RFC 2560 PKIX OCSP June 1999

Appendix A.

A.1 OCSP over HTTP

 This section describes the formatting that will be done to the
 request and response to support HTTP.

A.1.1 Request

 HTTP based OCSP requests can use either the GET or the POST method to
 submit their requests. To enable HTTP caching, small requests (that
 after encoding are less than 255 bytes), MAY be submitted using GET.
 If HTTP caching is not important, or the request is greater than 255
 bytes, the request SHOULD be submitted using POST.  Where privacy is
 a requirement, OCSP transactions exchanged using HTTP MAY be
 protected using either TLS/SSL or some other lower layer protocol.
 An OCSP request using the GET method is constructed as follows:
 GET {url}/{url-encoding of base-64 encoding of the DER encoding of
 the OCSPRequest}
 where {url} may be derived from the value of AuthorityInfoAccess or
 other local configuration of the OCSP client.
 An OCSP request using the POST method is constructed as follows: The
 Content-Type header has the value "application/ocsp-request" while
 the body of the message is the binary value of the DER encoding of
 the OCSPRequest.

A.1.2 Response

 An HTTP-based OCSP response is composed of the appropriate HTTP
 headers, followed by the binary value of the DER encoding of the
 OCSPResponse. The Content-Type header has the value
 "application/ocsp-response". The Content-Length header SHOULD specify
 the length of the response. Other HTTP headers MAY be present and MAY
 be ignored if not understood by the requestor.

Myers, et al. Standards Track [Page 17] RFC 2560 PKIX OCSP June 1999

Appendix B. OCSP in ASN.1

OCSP DEFINITIONS EXPLICIT TAGS::=

BEGIN

IMPORTS

  1. - Directory Authentication Framework (X.509)

Certificate, AlgorithmIdentifier, CRLReason

           FROM AuthenticationFramework { joint-iso-itu-t ds(5)
                    module(1) authenticationFramework(7) 3 }

– PKIX Certificate Extensions

           AuthorityInfoAccessSyntax
        FROM PKIX1Implicit88 {iso(1) identified-organization(3)
                dod(6) internet(1) security(5) mechanisms(5) pkix(7)
                id-mod(0) id-pkix1-implicit-88(2)}
        Name, GeneralName, CertificateSerialNumber, Extensions,
         id-kp, id-ad-ocsp
           FROM PKIX1Explicit88 {iso(1) identified-organization(3)
                dod(6) internet(1) security(5) mechanisms(5) pkix(7)
                id-mod(0) id-pkix1-explicit-88(1)};

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) }

Request ::= SEQUENCE {

  reqCert                    CertID,
  singleRequestExtensions    [0] EXPLICIT Extensions OPTIONAL }

Myers, et al. Standards Track [Page 18] RFC 2560 PKIX OCSP June 1999

CertID ::= SEQUENCE {

  hashAlgorithm            AlgorithmIdentifier,
  issuerNameHash     OCTET STRING, -- Hash of Issuer's DN
  issuerKeyHash      OCTET STRING, -- Hash of Issuers 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

  1. -(excluding the tag and length fields)

SingleResponse ::= SEQUENCE {

 certID                       CertID,
 certStatus                   CertStatus,
 thisUpdate                   GeneralizedTime,

Myers, et al. Standards Track [Page 19] RFC 2560 PKIX OCSP June 1999

 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 – this can be replaced with an enumeration

ArchiveCutoff ::= GeneralizedTime

AcceptableResponses ::= SEQUENCE OF OBJECT IDENTIFIER

ServiceLocator ::= SEQUENCE {

  issuer    Name,
  locator   AuthorityInfoAccessSyntax }

– 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 }

END

Myers, et al. Standards Track [Page 20] RFC 2560 PKIX OCSP June 1999

Appendix C. MIME registrations

C.1 application/ocsp-request

 To: ietf-types@iana.org
 Subject: Registration of MIME media type application/ocsp-request
 MIME media type name: application
 MIME subtype name: ocsp-request
 Required parameters: None
 Optional parameters: None
 Encoding considerations: binary
 Security considerations: Carries a  request for information. This
 request may optionally be cryptographically signed.
 Interoperability considerations: None
 Published specification: IETF PKIX Working Group Draft on Online
 Certificate Status Protocol - OCSP
 Applications which use this media type: OCSP clients
 Additional information:
    Magic number(s): None
    File extension(s): .ORQ
    Macintosh File Type Code(s): none
 Person & email address to contact for further information:
 Ambarish Malpani <ambarish@valicert.com>
 Intended usage: COMMON
 Author/Change controller:
 Ambarish Malpani <ambarish@valicert.com>

C.2 application/ocsp-response

 To: ietf-types@iana.org
 Subject: Registration of MIME media type application/ocsp-response
 MIME media type name: application

Myers, et al. Standards Track [Page 21] RFC 2560 PKIX OCSP June 1999

 MIME subtype name: ocsp-response
 Required parameters: None
 Optional parameters: None
 Encoding considerations: binary
 Security considerations: Carries a cryptographically signed response
 Interoperability considerations: None
 Published specification: IETF PKIX Working Group Draft on Online
 Certificate Status Protocol - OCSP
 Applications which use this media type: OCSP servers
 Additional information:
 Magic number(s): None
 File extension(s): .ORS
 Macintosh File Type Code(s): none
 Person & email address to contact for further information:
 Ambarish Malpani <ambarish@valicert.com>
 Intended usage: COMMON
 Author/Change controller:
 Ambarish Malpani <ambarish@valicert.com>

Myers, et al. Standards Track [Page 22] RFC 2560 PKIX OCSP June 1999

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Myers, et al. Standards Track [Page 23]

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