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RFC 2560

X.509 Internet Public Key Infrastructure Online Certificate Status Protocol - OCSP

Pages: 23
Obsoleted by:  6960
Updated by:  6277

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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].
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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: -- protocol version -- service request -- target certificate identifier -- 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.
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   All definitive response messages SHALL be digitally signed. The key
   used to sign the response MUST belong to one of the following:

   -- the CA who issued the certificate in question
   -- a Trusted Responder whose public key is trusted by the requester
   -- 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:

   -- version of the response syntax
   -- name of the responder
   -- responses for each of the certificates in a request
   -- optional extensions
   -- signature algorithm OID
   -- signature computed across hash of the response

   The response for each of the certificates in a request consists of

   -- target certificate identifier
   -- certificate status value
   -- response validity interval
   -- optional extensions

   This specification defines the following definitive response
   indicators for use in the certificate status value:

   -- good
   -- revoked
   -- 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.
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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: -- malformedRequest -- internalError -- tryLater -- sigRequired -- 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: - thisUpdate: The time at which the status being indicated is known to be correct - nextUpdate: The time at or before which newer information will be available about the status of the certificate - 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.
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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).
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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 {
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       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).
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   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 }
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   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
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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."
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   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: - 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 } - 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]. - 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
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   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).
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   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.
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   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.
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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).
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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
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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.
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Appendix B. OCSP in ASN.1

OCSP DEFINITIONS EXPLICIT TAGS::= BEGIN IMPORTS -- 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 }
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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
                         --(excluding the tag and length fields)

SingleResponse ::= SEQUENCE {
   certID                       CertID,
   certStatus                   CertStatus,
   thisUpdate                   GeneralizedTime,
ToP   noToC   RFC2560 - Page 20
   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
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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
ToP   noToC   RFC2560 - Page 22
   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>
ToP   noToC   RFC2560 - Page 23
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