Subject: WG Last call, redux

From: Stephen Kent <[email-masked]>
Date: Thu, 22 Apr 1999 13:24:18 -0400

Folks,

At my request, the OCSP document underwent some revisions after WG last
call, and IESG approval.  Although the changes are largely editorial,
designed to eliminate possible ambiguities, at least one substantive change
was made and thus an abbreviated IETF and WG last call are being held, in
parallel.  The WG is being explicitly notified of this last call to
expedite the process, but the notice from the IETF Secretariat will set the
officical closing date for comments.

Steve
----------------------------------

PKIX Working Group                               Michael Myers(VeriSign)
draft-ietf-pkix-ocsp-08.txt                         Rich Ankney (CertCo)
                                             Ambarish Malpani (ValiCert)
                                            Slava Galperin (Teknowledge)
                                   Carlisle Adams (Entrust Technologies)

Expires in 6 months                                           March 1999

                X.509 Internet Public Key Infrastructure
               Online Certificate Status Protocol - OCSP
                     <draft-ietf-pkix-ocsp-08.txt>

1.  Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as
   Internet-Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet- Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

2.  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 3. 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

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   document (in uppercase, as shown) are to be interpreted as described
   in [RFC2119].

3.  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.

3.1  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.

3.2  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

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   servers and clients. The rest of this section pertains only to this
   basic response type.

   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

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   the certificate being requested.

3.3  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.

3.4  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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3.5  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.

3.6  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.

3.7  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.

4.  Functional Requirements

4.1  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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4.2  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.

5.  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

5.1  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.).

5.1.1  Request Syntax

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

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   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 }

   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.

5.1.2  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 5.4 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.

5.2  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.).

5.2.1  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 }

   OCSP responders SHALL be capable of producing responses of the id-

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   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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5.2.2  Notes on OCSP Responses

5.2.2.1  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 3.4).

   The producedAt time is the time at which this response was signed.

5.2.2.2  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.

5.2.2.2.1  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.

5.3  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.

5.4  Extensions

   This section defines some standard extensions, based on the extension
   model employed in X.509 version 3 certificates see [RFC2459]. Support

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   for all extensions is optional for both clients and responders.  For
   each extension, the definition indicates its syntax, processing
   performed by the OCSP Responder, and any extensions which are
   included in the corresponding response.

5.4.1  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 }

5.4.2  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.

5.4.3  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

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   response types this client can accept (e.g., id-pkix-ocsp-basic).

   id-pkix-ocsp-response  OBJECT IDENTIFIER ::= { id-pkix-ocsp 4 }

   AcceptableResponses ::= SEQUENCE OF OBJECT IDENTIFIER

   As noted in section 5.2.1, 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.

5.4.4  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).

5.4.5  CRL Entry Extensions

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

5.4.6  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

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   included as one of the singleRequestExtensions in requests.

   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.

6.  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.

7.  References

   [RFC2459] Internet X.509 Public Key Infrastructure Certificate and
             CRL Profile, R. Housley, W. Ford, W. Polk, D. Solo, RFC
             2459, January, 1999.

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      [HTTP] Hypertext Transfer Protocol -- HTTP/1.1, R. Fielding, J.
             Gettys, J. Mogul, H. Frystyk and T. Berners-Lee, RFC 2068,
             January 1997.

   [RFC2119] Key words for use in RFCs to Indicate Requirement Levels,
             S. Bradner, RFC 2119, March 1997.

       [URL] Uniform Resource Locators (URL), T. Berners-Lee, L.
             Masinter, M.  McCahill, 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).

8.  Author's Address

   Michael Myers
   VeriSign, Inc.
   1390 Shorebird Way
   Mountain View, CA 94019
   [email-masked]

   Rich Ankney
   CertCo, LLC
   13506 King Charles Dr.
   Chantilly, VA  20151
   [email-masked]

   Ambarish Malpani
   ValiCert, Inc.
   3160 W. Bayshore Drive
   Palo Alto, CA 94303
   [email-masked]
   650.567.5457

   Slava Galperin
   Teknowledge Corporation
   1810 Embarcadero Road
   Palo Alto, CA
   [email-masked]

   Carlisle Adams
   Entrust Technologies
   750 Heron Road, Suite E08
   Ottawa, Ontario
   K1V 1A7

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   Canada
   [email-masked]

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.

Appendix B:  OCSP in ASN.1

   OCSP DEFINITIONS EXPLICIT TAGS::=

   BEGIN

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   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 }

   CertID ::= SEQUENCE {
       hashAlgorithm            AlgorithmIdentifier,
       issuerNameHash     OCTET STRING, -- Hash of Issuer's DN
       issuerKeyHash      OCTET STRING, -- Hash of Issuers public key
       serialNumber       CertificateSerialNumber }

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   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,
      nextUpdate           [0]     EXPLICIT GeneralizedTime OPTIONAL,
      singleExtensions     [1]     EXPLICIT Extensions OPTIONAL }

   CertStatus ::= CHOICE {
       good                [0]     IMPLICIT NULL,
       revoked             [1]     IMPLICIT RevokedInfo,

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       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

Appendix C: MIME registrations

C.1 application/ocsp-request

   To: [email-masked]
   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

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   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 <[email-masked]>

   Intended usage: COMMON

   Author/Change controller:
   Ambarish Malpani <[email-masked]>

C.2 application/ocsp-response

   To: [email-masked]
   Subject: Registration of MIME media type application/ocsp-response

   MIME media type name: application

   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

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   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 <[email-masked]>

   Intended usage: COMMON

   Author/Change controller:
   Ambarish Malpani <[email-masked]>

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---

From: Paul Hoffman / IMC <[email-masked]>
Date: Thu, 22 Apr 1999 12:17:38 -0700

At 01:24 PM 4/22/99 -0400, Stephen Kent wrote:
>Although the changes are largely editorial,
>parallel.

Care to give us a hint about the changes so that we can look at them in 
context in the draft?

--Paul Hoffman, Director
--Internet Mail Consortium

---

From: Stephen Kent <[email-masked]>
Date: Fri, 23 Apr 1999 12:15:12 -0400

Several folks pointed out that I made the re-opening of last call into a
treasure hunt!  Sorry 'bout that.  I am away from the office and not easily
able to provide a diff, but I can describe the goal for the changes, which
resulted in both editorial and sunstantive modifications to the text.

The concern I raised with the OCSP authors was that it was not clear what
the hard and fast requirements were for CAs and clients with regard to
supporting three different ways that OCSP can be "enabled." I felt it
important to ensure that CAs and clients that claim comformance would
provide a set of confuguration controls that would allow interoperability,
if properly configured. So, the resvied text tries to make this perfectly
clear. The final form of the requirements, with some abstraction, is
sumarized below:

	- an OCSP-compliant CA SHALL be capable of issuing OCSP responses
that are signed ditrectly by the CA, and MUST be able to designate an OCSP
responder by issuing an appropriately marked certificate directly to the
responder.  the choice or direct vs. delegated OCSP responses is a local,
administrative option. the CA also SHALL be capable of putting the AIA
extension into certs when it is the intent that these certs will be checked
via OCSP, and MUST be capable of populating this extension with the OID
specifying OCSP access method and a URI for such access.  (This last part
was changed from a MAy to a MUST, which seems reasonable to ensure the goal
cited above.)

	- an OCSP-compliant client MUST be able to accept OCSP responses
via three different means: responses signed by the CA that issued the cert
in question, responses signed by a responder directly designated by that
CA, or via a locally designated responder.  It is a local administrative
choice as to which of these options if enabled. If local designation is
enabled, vendors have choices as to how fancy it gets, e.g., how many OCSP
responders are specified, how one knows which ones are authorized to
provide status for which sets of certs, etc.

Steve

---

From: Denis Pinkas <[email-masked]>
Date: Wed, 28 Apr 1999 15:45:02 +0200

The original title was "Re: WG Last call, redux".

Steve,

Thanks for giving the hint for the change. :-)

In the previous text, as it will be explained in detail, we were somewhat
inconsistent having a SHALL followed by a MAY.

The new text is proposing to keep the SHALL and change the MAY into a MUST.
I am basically proposing to change the SHALL into a SHOULD and keep the MAY.

Both solutions are consistent. :-)

It seems now the Pandora box is re-opened  :-) and we have a chance to fix the
issue.

First, let me duplicate the section from the version 08 so that people may save
time, if they wish to follow this thread.

In version -08

4.1  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 [RFC 2459], 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).

In version 07 we had:

4.1  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 [PKIX1], 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, MAY provide 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).

(...)

The « MAY » in the second paragraph has been changed into a « MUST ».

Leaving the text out for a moment, let us consider the following scenario:

A CA is started up with a CRL scheme. After one year of operation, the CA
wishes to offer an *additional* service available for *all* the certificates,
i.e. an On-line Certificate Status (OCS) Service.

For doing so, there is one single option: to revoke all the current
certificates and re-issue new certificates with the appropriate extension.

This is a BIG BANG situation. :-(

The consequences are quite important, among them, the size of the CRLs is going
to increase dramatically (there is no reason to stop that service).

The concern is that a smooth transition cannot occur. What can we do ? Is there
a panacea to this problem ?

Let us now take a closer look at the text. The last sentence of the fist
paragraph from 4.1 says: « Alternatively, the accessLocation for the OCSP
provider *may* be configured locally at the OCSP client. ». If this is the
case, then the extension is not used. If someone wanted to deploy a system by
configuring locally the system, CAs would nevertheless be mandated to support
the extension.  :-(

This is one argument for having SHALL changed into SHOULD, i.e. « In order to
convey to OCSP clients a well-known point of information access, CAs SHOULD
provide the capability to include the AuthorityInfoAccess extension »

When the local configuration is NOT used, let us now attempt to solve the BIG
BANG issue, and let us take a look at the text from RFC 2459.

« 4.2.2.1  Authority Information Access

The authority information access extension indicates how to access CA
information and services for the issuer of the certificate in which the
extension appears. Information and services may include on-line validation
services and CA policy data.  (The location of CRLs is not specified in this
extension; that information is provided by the cRLDistributionPoints
extension.)  This extension may be included in subject or CA certificates, and
it MUST be non-critical. »

The text allows the extension to be placed in CA certificate. To my knowledge,
a self-signed certificate is also a CA certificate. So it is possible to have
that extension is a self-signed certificate. The advantage is two folds:

1) the content of a self-signed certificate may change without affecting the
content of the leaf certificates or of the cross-certificates.

2) since the extension is not in a leaf certificate, then it makes leaf
certificates smaller (remember low-fat leaf certificates ?)

We have defined in CMP a protocol to allow a certificate rollover for trust
points, so we know how to handle the renewal of a self-signed certificate.

Now, I still guess that some people would like the current text when a CA is
started from the very beginning with an OCS service or when that service is
gradually offered to renewed certificates. So I would now propose some text
that handles all the three cases. Here is the new proposal for a text to fit
under 4.1.

« 4.1  Certificate Content

 In order to convey to OCSP clients a well-known point of information access,
CAs SHOULD provide the capability to include the AuthorityInfoAccess extension
(defined in [RFC2459], section 4.2.2.1) either in every certificate that can be
checked using OCSP or in a self-signed certificate.  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, MAY 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). »

Note: the other major change around this topic is in section 5.2.2.2
Authorized Responders:

In version 08 we have:

 (...)

While in version -07 we have:

   The key that signs a certificate's status information need not be the
   same key that signed the certificate. A certificate's issuer MAY
   explicitly delegate OCSP signing authority by issuing a certificate
   including an extendedKeyUsage extension in the OCSP signer's
   certificate containing the value id-kp-OCSPSigning.

Denis