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Internet Draft                                              T. Freeman
draft-ietf-pkix-scvp-18.txt                             Microsoft Corp
February 2005                                               R. Housley
Expires in six months                                   Vigil Security
                                                            A. Malpani
                                           Malpani Consulting Services
                                                             D. Cooper
                                                                  NIST
                                                               T. Polk
                                                                  NIST

           Simple Certificate Validation Protocol (SCVP)


Status of this Memo

   By submitting this Internet-Draft, I certify that any applicable
   patent or other IPR claims of which I am aware have been disclosed,
   or will be disclosed, and any of which I become aware will be
   disclosed, in accordance with RFC 3668.

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

   Internet-Drafts are draft documents valid for a maximum of six months
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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than a "work in progress."

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

   The list of Internet-Draft Shadow Directories can be accessed at
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Copyright Notice

   Copyright (C) The Internet Society (2005). All Rights Reserved.

Abstract

   SCVP allows a client to delegate certificate path construction and
   certificate path validation to a server.  The path construction or
   validation (e.g. making sure that none of the certificates in the
   path are revoked) is performed according to a validation policy,
   which contains one or more trust anchors.  It allows simplification
   of client implementations and use of a set of predefined validation
   policies.


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Table of Contents

1 Introduction..................................................5
 1.1 SCVP overview and requirements.............................5
 1.2 Terminology................................................6
 1.3 Validation Policies........................................6
 1.4 Validation Algorithm.......................................7
 1.5 Validation Requirements....................................8
2 Protocol Overview.............................................8
3 Validation Request............................................9
 3.1 cvRequestVersion..........................................12
 3.2 query.....................................................12
   3.2.1 queriedCerts..........................................13
   3.2.2 checks................................................13
   3.2.3 wantBack..............................................15
   3.2.4 validationPolicy......................................17
     3.2.4.1 validationPolRef..................................18
       3.2.4.1.1 Default Validation Policy.....................19
     3.2.4.2 validationAlg.....................................19
       3.2.4.2.1 Basic Validation Algorithm....................19
       3.2.4.2.2 Basic Validation Algorithm Errors.............20
       3.2.4.2.3 Name Validation Algorithm.....................21
       3.2.4.2.4 Name Validation Algorithm Errors..............22
     3.2.4.3 userPolicySet.....................................23
     3.2.4.4 inhibitPolicyMapping..............................23
     3.2.4.5 requireExplicitPolicy.............................23
     3.2.4.6 inhibitAnyPolicy..................................23
     3.2.4.7 trustAnchors......................................24
     3.2.4.8 keyUsages.........................................24
     3.2.4.9 extendedKeyUsages.................................25
   3.2.5 responseFlags.........................................26
     3.2.5.1 fullRequestInResponse.............................26
     3.2.5.2 responseValidationPolByRef........................26
     3.2.5.3 protectResponse...................................27
     3.2.5.4 cachedResponse....................................27
   3.2.6 serverContextInfo.....................................28
   3.2.7 valididationTime......................................28
   3.2.8 intermediateCerts.....................................29
   3.2.9 revInfos..............................................30
   3.2.10 producedAt...........................................30
   3.2.11 queryExtensions......................................31
     3.2.11.1 extnID...........................................31
     3.2.11.2 critical.........................................31
     3.2.11.3 extnValue........................................31
 3.3 requestorRef..............................................31
 3.4 requestNonce..............................................32
 3.5 requestorName.............................................32
 3.6 requestExtensions.........................................33
   3.6.1 extnID................................................33


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   3.6.2 critical..............................................33
   3.6.3 extnValue.............................................33
 3.7 SCVP Request Authentication...............................33
4 Validation Response..........................................34
 4.1 cvResponseVersion.........................................37
 4.2 policyID..................................................37
 4.3 producedAt................................................37
 4.4 responseStatus............................................38
 4.5 respValidationPolicy......................................40
   4.5.1 validationPolicy......................................40
   4.5.2 validationPolicyAttr..................................40
 4.6 requestRef................................................41
   4.6.1 requestHash...........................................41
   4.6.2 fullRequest...........................................42
 4.7 requestorRef..............................................42
 4.8 requestorName.............................................42
 4.9 replyObjects..............................................42
   4.9.1 cert..................................................43
   4.9.2 replyStatus...........................................44
   4.9.3 replyValTime..........................................45
   4.9.4 replyChecks...........................................45
   4.9.5 replyWantBacks........................................47
   4.9.6 validationErrors......................................49
   4.9.7 nextUpdate............................................49
   4.9.8 certReplyExtensions...................................49
 4.10 respNonce................................................49
 4.11 serverContextInfo........................................50
 4.12 cvResponseExtensions.....................................50
 4.13 SCVP Response Validation.................................51
   4.13.1 Simple Key Validation................................51
   4.13.2 SCVP Server Certificate Validation...................51
5 Server Policy Request........................................52
 5.1 vpRequestVersion..........................................52
 5.2 requestNonce..............................................52
6 Validation Policy Response...................................53
 6.1 vpResponseVersion.........................................54
 6.2 maxCVRequestVersion.......................................54
 6.3 maxVPRequestVersion.......................................55
 6.4 defaultPolicyID...........................................55
 6.5 thisUpdate................................................55
 6.6 nextUpdate and requestNonce...............................55
 6.7 validationPolicies........................................56
 6.8 validationAlgs............................................56
 6.9 authPolicies..............................................56
 6.10 responseTypes............................................56
 6.11 revocationInfoTypes......................................56
 6.12 defaultPolicyValues......................................57
 6.13 serverPublicKeys.........................................57
 6.14 clockSkew................................................57


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7 SCVP Server Relay............................................57
8 SCVP ASN.1 Module............................................58
9 Security Considerations......................................66
10 References..................................................68
 10.1 Normative References.....................................68
 10.2 Informative References...................................69
11 Acknowledgments.............................................70
Appendix A -- MIME Registrations...............................70
 A.1  application/cv-request...................................70
 A.2  application/cv-response..................................71
 A.3  application/vp-request...................................72
 A.4  application/vp-response..................................73
Appendix B -- SCVP over HTTP...................................73
 B.1  SCVP Request.............................................73
 B.2  SCVP Response............................................74
 B.3  SCVP Policy Request......................................74
 B.4  SCVP Policy Response.....................................75
Appendix C -- Author Contact Information.......................75
































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1  Introduction

   Certificate validation is complex.  If certificate handling is to be
   widely deployed in a variety of applications and environments, the
   amount of processing an application needs to perform before it can
   accept a certificate needs to be reduced.  There are a variety of
   applications that can make use of public key certificates, but these
   applications are burdened with the overhead of constructing and
   validating the certification paths.  SCVP reduces this overhead for
   two classes of certificate-using applications.

   The first class of applications wants just two things: confirmation
   that the public key belongs to the identity named in the certificate
   and confirmation that the public key can be used for the intended
   purpose.  Such clients can completely delegate certification path
   construction and validation to the SCVP server.  This is often
   referred to as delegated path validation (DPV).

   The second class of applications can perform certification path
   validation, but they lack a reliable or efficient method of
   constructing a valid certification path.  Such clients delegate
   certification path construction to the SCVP server, but not
   validation of the returned certification path.  This is often
   referred to as delegated path discovery (DPD).

1.1  SCVP overview and requirements

   SCVP meets the mandatory requirements documented in [RQMTS].

   The primary goals of SCVP are to make it easier to deploy PKI-enabled
   applications and to allow central administration of PKI policies
   within an organization.  SCVP can be used by clients that do much of
   the certificate processing themselves but simply want an untrusted
   server to collect information for them.  However, when the client has
   complete trust in the SCVP server, SCVP can be used to delegate the
   work of certification path construction and validation, and SCVP can
   be used to ensure that policies are consistently enforced throughout
   an organization.

   Untrusted SCVP servers can provide clients the certification paths.
   They can also provide clients the revocation information, such as
   CRLs and OCSP responses, that the clients need to validate the
   certification paths constructed by the SCVP server.  These services
   can be valuable to clients that do not include the protocols needed
   to find and download intermediate certificates, CRLs, and OCSP
   responses.




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   Trusted SCVP servers can perform certification path construction and
   validation for the client.  For a client that uses these services,
   the client inherently trusts the SCVP server as much as it would its
   own certification path validation software (if it contained such
   software).  There are two main reasons that a client may want to
   trust such an SCVP server:

     1. The client does not want to incur the overhead of including
        certification path validation software and running it for each
        certificate it receives.

     2. The client is in an organization or community that wants to
        centralize its PKI policies.  These policies might dictate that
        particular trust anchors are to be used and the types of policy
        checking that are to be performed during certification path
        validation.

1.2  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [STDWORDS].

1.3  Validation Policies

   A validation policy (as defined in RFC 3379 [RQMTS]) specifies the
   rules and parameters to be used by the SCVP server when validating a
   certificate.  In SCVP, the validation policy to be used by the server
   can either be fully referenced in the request by the client (and thus
   no additional parameters are necessary) or it can be referenced in
   the request by the client with additional parameters.

   Policy definitions can be quite long and complex, and some policies
   may allow for the setting of a few parameters.  The request can
   therefore be very simple if an OBJECT IDENTIFIER (OID) or URI is used
   to specify both the algorithm to be used and all the associated
   parameters of the validation policy.  The request can be more complex
   if the validation policy fixes many of the parameters but allows the
   client to specify some of them.  When the validation policy defines
   every parameter necessary, an SCVP request needs only to contain the
   certificate to be validated, the referenced validation policy, and
   any run-time parameters for the request.

   A server publishes the references of the validation policies it
   supports.  When these policies have parameters that may be
   overridden, the server communicates the default values for these
   parameters as well.  The client can simplify the request by omitting
   a parameter from a request if the default value published by the
   server for a given validation policy reference is acceptable.


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   However, if there is a desire to demonstrate to someone else that a
   specific validation policy with all its parameters has been used, the
   client will need to ask the server for the inclusion of the full
   validation policy with all the parameters in the response.

   The inputs to the basic certification path processing algorithm used
   by SCVP are defined by [PKIX-1] in section 6.1.1 and comprise:

    Certificate to be validated (by value or by reference);

    Validation time;

    Set of Trust Anchors (by value or by reference);

    The initial policy set;

    Initial inhibit policy mapping setting;

    Initial inhibit anyPolicy setting; and

    Initial require explicit policy setting.

   The basic certification path processing algorithm also supports the
   following parameters, which are defined in [PKIX-1] section 4:

     The usage of the key contained in the certificate (e.g., key
     encipherment, key agreement, signature); and

     Other application-specific purposes for which the certified public
     key may be used.

1.4  Validation Algorithm

   The validation algorithm is determined by agreement between the
   client and the server and is represented as an OID.  The algorithm
   defines the checking that will be performed by the server to
   determine whether the certificate is valid.  A validation algorithm
   is one of the parameters to a validation policy.  SCVP defines a
   basic validation algorithm which implements the certification path
   validation algorithm as defined in [PKIX-1].  New validation
   algorithms can be specified that define additional checks if needed.
   These new validation algorithms may specify additional parameters.
   The values for these parameters may be defined by any validation
   policy that uses the algorithm or may be included by the client in
   the request.

   Application-specific validation algorithms in addition to those
   defined in this document can be defined to meet specific requirements
   not covered by the basic validation algorithm.  The validation


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   algorithms documented here should serve as a guide for the
   development of further application-specific validation algorithms.
   For example, a new application-specific validation algorithm might
   require the presence of a particular name form in the subject
   alternative name extension of the certificate.

1.5  Validation Requirements

   For a certification path to be considered valid under a particular
   validation policy it MUST be a valid certification path as defined in
   [PKIX-1] and all validation policy constraints that apply to the
   certification path MUST be verified.

   Revocation checking is one aspect of certification path validation
   defined in [PKIX-1].  However, revocation checking is an optional
   feature in [PKIX-1], and revocation information is distributed in
   multiple formats.  Clients specify in requests whether revocation
   checking should be performed and whether revocation information
   should be returned in the response.

   Servers MUST be capable of indicating the sources of revocation
   information that they are capable of processing:

     1.  full CRLs (or full Authority Revocation Lists);

     2.  OCSP responses, using [OCSP];

     3.  delta CRLs; and

     4.  indirect CRLs.

2  Protocol Overview

   SCVP uses a simple request-response model.  That is, the SCVP client
   creates a request and sends it to the SCVP server, and then the SCVP
   server creates a single response and sends it to the client.  The
   typical use of SCVP is expected to be over HTTP [HTTP], but it can
   also be used with email or any other protocol that can transport
   digitally signed objects.  Appendices A and B provide the details
   necessary to use SCVP with HTTP.

   SCVP includes two request-response pairs.  The primary request-
   response pair handles certificate validation.  The secondary request-
   response pair is used to determine the list of validation policies
   and default parameters supported by a specific SCVP server.

   Section 3 defines the certificate validation request.

   Section 4 defines the corresponding certificate validation response.


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   Section 5 defines the validation policies request.

   Section 6 defines the corresponding validation policies response.

   Appendix A registers MIME types for SCVP requests and responses, and
   Appendix B describes the use of these MIME types with HTTP.

3  Validation Request

   An SCVP client request to the server MUST be a single CVRequest item.
   When a CVRequest is encapsulated in a MIME body part, application/cv-
   request MUST be used.

   There are two forms of SCVP request: unprotected and protected.  A
   protected request is used to authenticate the client to the server or
   to provide anonymous client integrity over the request-response pair.
   The protection is provided by a digital signature or message
   authentication code (MAC).  In the later case, the MAC key is derived
   using a key agreement algorithm, such as Diffie-Hellman.  If the
   client's public key is contained in a certificate, then it may be
   used to authenticate the client.  More commonly, the client's key
   agreement public key will be ephemeral, supporting anonymous client
   integrity.

   A server MAY require all requests to be protected, and a server MAY
   discard all unprotected requests.  Alternatively, a server MAY choose
   to process unprotected requests.

   The unprotected request consists of a CVRequest encapsulated in a CMS
   ContentInfo [CMS].  An overview of these structures is provided below
   and is only intended as illustrative.  The definitive ASN.1 is found
   in [CMS].  Many details are not shown, but the way that SCVP makes
   use of CMS is clearly illustrated.

     ContentInfo {
       contentType        id-ct-scvp-certValRequest,
                                    -- (1.2.840.113549.1.9.16.1.10)
       content            CVRequest }

   The protected request consists of a CVRequest encapsulated in either
   a SignedData or AuthenticatedData, which is in turn encapsulated in a
   ContentInfo.  SignedData is used when the request is digitally
   signed.  AuthenticatedData is used with a message authentication code
   (MAC).  An overview of these structures is provided below.  Again,
   many details are not shown, but the way that SCVP makes use of CMS is
   clearly illustrated.

   SignedData example:


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     ContentInfo {
       contentType        id-signedData, -- (1.2.840.113549.1.7.2)
       content            SignedData }

     SignedData {
       version            CMSVersion,
       digestAlgorithms   DigestAlgorithmIdentifiers,
       encapContentInfo   EncapsulatedContentInfo,
       certificates       [0] IMPLICIT CertificateSet, -- Optional
       crls               [1] IMPLICIT CertificateRevocationLists,
                                    -- Optional
       signerInfos        SET OF SignerInfo } -- Only one in SCVP

     SignerInfo {
       version            CMSVersion,
       sid                SignerIdentifier,
       digestAlgorithm    DigestAlgorithmIdentifier,
       signedAttrs        SignedAttributes, -- Required in SCVP
       signatureAlgorithm SignatureAlgorithmIdentifier,
       signature          SignatureValue,
       unsignedAttrs      UnsignedAttributes } -- not used in SCVP

     EncapsulatedContentInfo {
       eContentType       id-ct-scvp-certValRequest,
                                     -- (1.2.840.113549.1.9.16.1.10)
       eContent           OCTET STRING } -- Contains CVRequest

   AuthenticatedData example:

     ContentInfo {
       contentType       id-ct-authData,
                                    -- (1.2.840.113549.1.9.16.1.2)
       content           AuthenticatedData }

     AuthenticatedData {
       version           CMSVersion,
       originatorInfo    OriginatorInfo, -- Optional
       recipientInfos    RecipientInfos, -- Only SCVP server
       macAlgorithm      MessageAuthenticationCodeAlgorithm,
       digestAlgorithm   DigestAlgorithmIdentifier, -- Optional
       encapContentInfo  EncapsulatedContentInfo,
       authAttrs         AuthAttributes, -- Required in SCVP
       mac               MessageAuthenticationCode,
       unauthAttrs       UnauthAttributes } -- not used in SCVP

     EncapsulatedContentInfo {
       eContentType       id-ct-scvp-certValRequest,
                                     -- (1.2.840.113549.1.9.16.1.10)


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       eContent           OCTET STRING } -- Contains CVRequest

   All SCVP clients MUST support SignedData for signed requests and
   responses.  SCVP clients SHOULD support AuthenticatedData for MAC
   protected requests and responses.

   If the client uses SignedData it MUST have a public key that has been
   bound to a subject identity by a certificate that conforms to the
   PKIX profile [PKIX-1] and that certificate MUST be suitable for
   signing the SCVP request.  That is:

       1. If the key usage extension is present, either the digital
          signature or the non-repudiation bit MUST be asserted.

       2. If the extended key usage extension is present, it MUST
          contain either the SCVP client OID (see Section 3.7) or
          another OID acceptable to the SCVP server.

   The client MUST put an unambiguous reference to its certificate in
   the SignedData that encapsulates the request.  The client SHOULD
   include its certificate in the request, but MAY omit the certificate
   to reduce the size of the request.  The client MAY include other
   certificates in the request to aid the validation of its certificates
   by the SCVP server.

   The client MUST put its key agreement public key or an unambiguous
   reference to a certificate that contains its key agreement public key
   in the AuthenticatedData that encapsulates the request.  If an
   ephemeral key agreement key pair is used, then the ephemeral key
   agreement public key is carried in the originatorKey field of
   KeyAgreeRecipientInfo, which requires the client to obtain the
   server's key agreement public key before computing the message
   authentication code (MAC).

   The syntax and semantics for SignedData, AuthenticatedData, and
   ContentInfo are defined in [CMS].  The syntax and semantics for
   CVRequest are defined below.  The CVRequest item contains the client
   request.  The CVRequest contains the cvRequestVersion and query
   items; the CVRequest MAY also contain the requestorRef, requestNonce,
   requestorName, and requestExtensions items.

   The CVRequest MUST have the following syntax:

     CVRequest ::= SEQUENCE {
       cvRequestVersion        INTEGER DEFAULT 1,
       query                   Query,
       requestorRef        [0] SEQUENCE SIZE (1..MAX) OF OCTET STRING
                                 OPTIONAL,
       requestNonce        [1] OCTET STRING OPTIONAL,


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       requestorName       [2] GeneralName OPTIONAL,
       requestExtensions   [3] Extensions OPTIONAL }

   Each of the items within the CVRequest is described in the following
   sections.

3.1  cvRequestVersion

   The cvRequestVersion item defines the version of the SCVP CVRequest
   used in a request.  The subsequent response MUST use the same version
   number.  The value of the cvRequestVersion item MUST be one (1) for a
   client implementing this specification.  Future updates to this
   specification must specify other values if there are any changes to
   syntax or semantics.

3.2  query

   The query item specifies one or more certificates that are the
   subject of the request; the certificates can be either public key
   certificates [PKIX-1] or attribute certificates [PKIX-AC].  A query
   MUST contain a queriedCerts item as well as one checks, one wantBack,
   and one validationPolicy item; a query MAY also contain
   responseFlags, serverContextInfo, validationTime, intermediateCerts,
   revInfos, producedAt, and queryExtensions items.

   Query MUST have the following syntax:

     Query ::= SEQUENCE {
       queriedCerts            CertReferences,
       checks                  CertChecks,
       wantBack                WantBack,
       validationPolicy        ValidationPolicy,
       responseFlags           ResponseFlags OPTIONAL,
       serverContextInfo   [2] OCTET STRING OPTIONAL,
       validationTime      [3] GeneralizedTime OPTIONAL,
       intermediateCerts   [4] CertBundle OPTIONAL,
       revInfos            [5] RevocationInfos OPTIONAL,
       producedAt          [6] GeneralizedTime OPTIONAL,
       queryExtensions     [7] Extensions OPTIONAL }

   The list of certificate references in the queriedCerts item tells the
   server the certificate(s) for which the client wants information.
   The checks item specifies the checking that the client wants
   performed.  The wantBack item specifies the objects that the client
   wants the server to return in the response.  The validationPolicy
   item specifies the validation policy that the client wants the server
   to employ.  The responseFlags item allows the client to request
   optional features for the response.  The serverContextInfo item tells
   the server that additional information from a previous request-


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   response is desired.  The validationTime item tells the date and time
   relative to which the client wants the server to perform the checks.
   The intermediateCerts and revInfos items provide context for the
   client request.  The queryExtensions item provides for future
   expansion of the query syntax.  The syntax and semantics of each of
   these items is discussed in the following sections.

3.2.1  queriedCerts

   The queriedCerts field is a SEQUENCE of one or more certificates,
   each of which is a subject of the request.  The specified
   certificates are either public key certificates or attribute
   certificates; if more than one certificate is specified, all must be
   of the same type.  Each certificate is either directly included or it
   is referenced.  When referenced, a SHA-1 hash value [SHA-1] of the
   referenced item is included to ensure that the SCVP client and the
   SCVP server both obtain the same certificate when the referenced
   certificate is fetched.  Certificate references use the ESSCertID
   type defined in [ESS].  A single request MAY contain both directly
   included and referenced certificates.

   CertReferences has the following syntax:

     CertReferences ::= CHOICE {
       pkcRefs           [0] SEQUENCE SIZE (1..MAX) OF PKCReference,
       acRefs            [1] SEQUENCE SIZE (1..MAX) OF ACReference }

     PKCReference ::= CHOICE {
       cert              [0] Certificate,
       pkcRef            [1] ESSCertID }

     ACReference ::= CHOICE {
       attrCert          [2] AttributeCertificate,
       acRef             [3] ESSCertID }

   The ASN.1 definition of Certificate is imported from [PKIX-1]; the
   definition of AttributeCertificate is imported from [PKIX-AC]; and
   the definition of ESSCertID is imported from [ESS].

3.2.2  checks

   The checks item describes the checking that the SCVP client wants the
   SCVP server to perform on the certificate(s) in the queriedCerts
   item.  The checks item contains a sequence of object identifiers
   (OIDs).  Each OID tells the SCVP server what checking the client
   expects the server to perform.  For each check specified in the
   request, the SCVP server MUST perform all of the requested checks, or
   return an error.  A server may choose to perform additional checks
   (e.g., a server that is only asked to build a validated certification


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   path may choose to also perform revocation status checks), although
   the server cannot indicate in the response that the additional checks
   have been performed.

   The checks item uses the CertChecks type, which has the following
   syntax:

     CertChecks ::= SEQUENCE SIZE (1..MAX) OF OBJECT IDENTIFIER

   For public key certificates, the following checks are defined:

    - id-stc-build-pkc-path: Build a prospective certification path to
       a trust anchor (as defined in section 6.1 of [PKIX-1]);

    - id-stc-build-valid-pkc-path: Build a validated certification path
       to a trust anchor (revocation checking not required);

    - id-stc-build-status-checked-pkc-path: Build a validated
       certification path to a trust anchor and perform revocation
       status checks on the certification path.

   Conforming SCVP server implementations MUST support the id-stc-build-
   pkc-path check.  Conforming SCVP server implementations that support
   delegated path validation (DPV) as defined in [RQMTS] MUST support
   the id-stc-build-valid-pkc-path and id-stc-build-status-checked-pkc-
   path checks.

   For attribute certificates, the following checks are defined:

    - id-stc-build-aa-path: Build a certification path to a trust
       anchor for the AC issuer;

    - id-stc-build-valid-aa-path: Build a validated certification path
       to a trust anchor for the AC issuer;

    - id-stc-build-status-checked-aa-path: Build a validated
       certification path to a trust anchor for the AC issuer and
       perform revocation status checks on the certification path for
       the AC issuer;

    - id-stc-status-check-ac-and-build-status-checked-aa-path: Build a
       validated certification path to a trust anchor for the AC issuer
       and perform revocation status checks on the AC as well as the
       certification path for the AC issuer.

   Conforming SCVP server implementations MAY support the attribute
   certificates checks.

   For these purposes, the following OIDs are defined:


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     id-stc OBJECT IDENTIFIER ::= { iso(1) identified-organization(3)
             dod(6) internet(1) security(5) mechanisms(5) pkix(7) 17 }


     id-stc-build-pkc-path         OBJECT IDENTIFIER ::= { id-stc 1 }
     id-stc-build-valid-pkc-path   OBJECT IDENTIFIER ::= { id-stc 2 }
     id-stc-build-status-checked-pkc-path
                                   OBJECT IDENTIFIER ::= { id-stc 3 }
     id-stc-build-aa-path          OBJECT IDENTIFIER ::= { id-stc 4 }
     id-stc-build-valid-aa-path    OBJECT IDENTIFIER ::= { id-stc 5 }
     id-stc-build-status-checked-aa-path
                                   OBJECT IDENTIFIER ::= { id-stc 6 }
     id-stc-status-check-ac-and-build-status-checked-aa-path
                                   OBJECT IDENTIFIER ::= { id-stc 7 }

3.2.3  wantBack

   The wantBack item describes the kind of information the SCVP client
   wants from the SCVP server for the certificate(s) in the queriedCerts
   item.  The wantBack item MUST contain a sequence of object
   identifiers (OIDs).  Each OID tells the SCVP server what the client
   wants to know about the queriedCerts item.  For each type of
   information specified in the request, the server MUST return
   information regarding its finding (in a successful response).

   For example, a request might include a checks item that only
   specifies certification path building and include a wantBack item
   that requests the return of the certification path built by the
   server.  In this case, the response would not include a status for
   the validation of the certification path, but it would include a
   certification path that the server considers to be valid.  A client
   that wants to perform its own certification path validation might use
   a request of this form.

   Alternatively, a request might include a checks item that requests
   the server to build a certification path and validate it, including
   revocation checking, and include a wantBack item that requests the
   return of the status.  In this case, the response would include only
   a status for the validation of the certification path.  A client that
   completely delegates certification path validation might use a
   request of this form.

   The wantBack item uses the WantBack type, which has the following
   syntax:

     WantBack ::= SEQUENCE SIZE (1..MAX) OF OBJECT IDENTIFIER




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   For public key certificates, the types of information that can be
   requested are:

    - id-swb-pkc-cert: The certificate that was the subject of the
       request;

    - id-swb-pkc-best-cert-path: The certification path built for the
       certificate including the certificate that was validated;

    - id-swb-pkc-revocation-info: Proof of revocation status for each
       certificate in the certification path;

    - id-swb-pkc-cert-status: Status indication;

    - id-swb-pkc-public-key-info: The public key from the certificate;
       and

    - id-swb-pkc-all-cert-paths: A set of certification paths for the
       certificate.

   The SCVP protocol provides two methods for a client to obtain
   multiple certification paths for a certificate.  The client could use
   serverContextInfo to request one path at a time (see section 3.2.6).
   After obtaining each path, the client could submit the
   serverContextInfo from the previous request to obtain another path
   until the client either found a suitable path or the server indicated
   (by not returning a serverContextInfo) that no more paths were
   available.  Alternatively, the client could send a single request
   with an id-swb-pkc-all-cert-paths wantBack, in which case the server
   would return all of the available paths in a single response.

   The server may, at its discretion, limit the number of paths that it
   returns in response to the id-swb-pkc-all-cert-paths.  When the
   request includes an id-swb-pkc-all-cert-paths wantBack, the response
   should not include a serverContextInfo.

   For attribute certificates, the types of information that can be
   requested are:

    - id-swb-ac-cert: The attribute certificate that was the subject of
       the request;

    - id-swb-aa-cert-path: The certification path built for the AC
       issuer certificate;

    - id-swb-ac-revocation-info: Proof of revocation status for each
       certificate in the AC issuer certification path;




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    - id-swb-aa-revocation-info: Proof of revocation status for the
       attribute certificate; and

    - id-swb-ac-cert-status: Status indication.


   For these purposes, the following OIDs are defined:

     id-swb OBJECT IDENTIFIER ::= { iso(1) identified-organization(3)
             dod(6) internet(1) security(5) mechanisms(5) pkix(7) 18 }

     id-swb-pkc-best-cert-path      OBJECT IDENTIFIER ::= { id-swb 1 }
     id-swb-pkc-revocation-info     OBJECT IDENTIFIER ::= { id-swb 2 }
     id-swb-pkc-cert-status         OBJECT IDENTIFIER ::= { id-swb 3 }
     id-swb-pkc-public-key-info     OBJECT IDENTIFIER ::= { id-swb 4 }
     id-swb-aa-cert-path            OBJECT IDENTIFIER ::= { id-swb 5 }
     id-swb-aa-revocation-info      OBJECT IDENTIFIER ::= { id-swb 6 }
     id-swb-ac-revocation-info      OBJECT IDENTIFIER ::= { id-swb 7 }
     id-swb-ac-cert-status          OBJECT IDENTIFIER ::= { id-swb 8 }
     id-swb-pkc-cert                OBJECT IDENTIFIER ::= { id-swb 10}
     id-swb-ac-cert                 OBJECT IDENTIFIER ::= { id-swb 11}
     id-swb-pkc-all-cert-paths      OBJECT IDENTIFIER ::= { id-swb 12}

3.2.4  validationPolicy

   The validationPolicy item defines the validation policy that the
   client wants the SCVP server to use during certificate validation.
   If this policy cannot be used for any reason, then the server MUST
   return an error response.

   A validation policy MUST define default values for all parameters
   necessary for processing an SCVP request.  For each parameter, a
   validation policy may either allow the client to specify a non-
   default value or forbid the use of a non-default value.  If the
   client wishes to use the default values for all of the parameters,
   then the client need only supply a reference to the policy in this
   item.  If the client wishes to use non-default values for one or more
   parameters, then the client supplies a reference to the policy plus
   whatever parameters are necessary to complete the request in this
   item.  If there are any conflicts between the policy referenced in
   the request and any supplied parameter values in the request, then
   the server MUST return an error response.

   The syntax of the validationPolicy item is:

     ValidationPolicy ::= SEQUENCE {
       validationPolRef          ValidationPolRef,
       validationAlg         [0] ValidationAlg OPTIONAL,
       userPolicySet         [1] SEQUENCE SIZE (1..MAX) OF OBJECT


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                                   IDENTIFIER OPTIONAL,
       inhibitPolicyMapping  [2] BOOLEAN OPTIONAL,
       requireExplicitPolicy [3] BOOLEAN OPTIONAL,
       inhibitAnyPolicy      [4] BOOLEAN OPTIONAL,
       trustAnchors          [5] TrustAnchors OPTIONAL,
       keyUsages             [6] KeyUsages OPTIONAL,
       extendedKeyUsages     [7] SEQUENCE OF KeyPurposeId OPTIONAL}

   The validationPolRef item is required, but the remaining items are
   optional.  The optional items are used to provide validation policy
   parameters.  When the client uses the validation policy's default
   values for all parameters, all of the optional items are absent.  The
   validationAlg item specifies the validation algorithm.  The
   userPolicySet item provides an acceptable set of certificate
   policies.  The inhibitPolicyMapping item inhibits certificate policy
   mapping during certification path validation.  The
   requireExplicitPolicy item requires at least one valid certificate
   policy in the certificate policies extension.  The inhibitAnyPolicy
   item indicates whether the anyPolicy certificate policy OID is
   processed or ignored when evaluating certificate policy.  The
   trustAnchors item indicates the trust anchors that are acceptable to
   the client.  The keyUsages item indicates the technical usage of the
   public key that is to be confirmed by the server as acceptable.  The
   extendedKeyUsages item indicates the application-specific usage of
   the public key that is to be confirmed by the server as acceptable.
   The syntax and semantics of each of these items is discussed in the
   following sections.

3.2.4.1  validationPolRef

   The reference to the validation policy can be either an OID or a URI.
   In either case, the client and server have agreed that the value
   represents a particular validation policy.  The URI can point to a
   human readable definition of the policy to facilitate correct
   configuration.

   The syntax of the ValidationPolRef item is:

     ValidationPolRef::= CHOICE {
       valPolRefByOID         OBJECT IDENTIFIER,
       valPolRefByURI         IA5String}

   There is no requirement for either the client or the server to
   dereference the URI during SCVP request processing.  The URI is
   simply used as a reference for the validation policy.  Clients and
   server MAY dereference the URI as part of configuration.  See Section
   9 for security considerations that apply when referencing policies
   using URIs.



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3.2.4.1.1  Default Validation Policy

   The client can request the SCVP server's default validation policy or
   another validation policy.  The object identifier to identify the
   default validation policy is:

     id-svp OBJECT IDENTIFIER ::= { iso(1) identified-organization(3)
            dod(6) internet(1) security(5) mechanisms(5) pkix(7) 19 }

     id-svp-defaultValPolicy OBJECT IDENTIFIER ::= { id-svp 1 }

   The default validation policy MUST use the basic validation algorithm
   as its default validation algorithm (see section 3.2.4.2.1).

   When using the default validation policy, the client can override any
   of the default parameter values by supplying a specific value in the
   request.  The SCVP server MUST make use of the provided parameter
   values or return an error response.

   Conforming implementations of SCVP servers MUST support the default
   policy.  However, an SCVP server may be configured to send an error
   response to all requests using the default policy to meet local
   security requirements.

3.2.4.2  validationAlg

   The optional validationAlg item defines the validation algorithm to
   be used by the SCVP server during certificate validation.  The value
   of this item can be determined by agreement between the client and
   the server.  The validation algorithm is represented by an object
   identifier.

   The syntax of the validationAlg is:

     ValidationAlg ::= SEQUENCE {
       valAlgId              OBJECT IDENTIFIER,
       parameters            ANY DEFINED BY valAlgId OPTIONAL }

   The following section specifies the basic validation algorithm and
   the name validation algorithm.

   SCVP clients and servers MUST support both validation algorithms
   defined in this section.  Other validation algorithms can be
   specified in other documents for use with specific applications.
   SCVP clients and servers MAY support any such validation algorithms.

3.2.4.2.1  Basic Validation Algorithm




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   The client can request use of the SCVP basic validation algorithm or
   another algorithm.  For identity certificates, the basic validation
   algorithm MUST implement the certification path validation algorithm
   as defined in section 6 of [PKIX-1].  For attribute certificates, the
   basic validation algorithm MUST implement certificate path validation
   as defined in section 5 of [PKIX-AC].  Other validation algorithms
   MAY implement functions over and above those in the basic algorithm,
   but validation algorithms MUST generate results compliant with the
   basic validation algorithm.  That is, none of the validation
   requirements in the basic algorithm may be omitted from any newly
   defined validation algorithms.  However, other validation algorithms
   MAY reject paths that are valid using the basic validation algorithm.
   The object identifier to identify the basic validation algorithm is:

     id-svp-basicValAlg OBJECT IDENTIFIER ::= { id-svp 3 }

   When id-svp-basicValAlg appears in valAlgId, the parameters item MUST
   be absent.

3.2.4.2.2  Basic Validation Algorithm Errors

   The following errors are defined for the basic validation algorithm
   for inclusion in the validationErrors item in the response (see
   section 4.9.6).  These errors can be used by any other validation
   algorithm since all validation algorithms MUST implement the
   functionality of the basic validation algorithm.

     id-bvae OBJECT IDENTIFIER ::= id-svp-basicValAlg

     id-bvae-expired              OBJECT IDENTIFIER ::= { id-bvae 1 }
     id-bvae-not-yet-valid        OBJECT IDENTIFIER ::= { id-bvae 2 }
     id-bvae-wrong-anchor         OBJECT IDENTIFIER ::= { id-bvae 3 }
     id-bvae-invalid-key-usage    OBJECT IDENTIFIER ::= { id-bvae 10 }
     id-bvae-invalid-purpose      OBJECT IDENTIFIER ::= { id-bvae 11 }
     id-bvae-revoked              OBJECT IDENTIFIER ::= { id-bvae 16 }

   The id-bvae-expired value means that the validation time used for the
   request was later than the notAfter time in the end certificate (the
   certificate specified in the queriedCerts item).

   The id-bvae-not-yet-valid value means that the validation time used
   for the request was before the notBefore time in the end certificate.

   The id-bvae-wrong-anchor value means that a certification path could
   not be constructed for the client specified trust anchor(s), but a
   path exists for one of the trust anchors specified in the server's
   default validation policy.

   The id-bvae-invalid-key-usage value means that the keyUsage extension
   (PKIX-1 section 4.2.1.3) in the end certificate does not satisfy the

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   validation policy.  For example, the keyUsage extension in the
   certificate may assert only the keyEncipherment bit, but the
   validation policy specifies in the keyUsages field that
   digitalSignature is required.

   The id-bvae-invalid-purpose value means that the extended key usage
   extension (PKIX-1 section 4.2.1.13) in the end certificate does not
   satisfy the validation policy.

   The id-bvae-revoked value means that the end certificate was revoked.

3.2.4.2.3  Name Validation Algorithm

   The name validation is a refinement of the basic validation algorithm
   that allows the client to specify one or more subject names that MUST
   appear in the end certificate.  The name validation algorithm allows
   the client to supply an application identifier and a name to the
   server.  The application identifier defines the name matching rules
   to use in comparing the name supplied in the request with the names
   in the certificate.

     id-svp-nameValAlg OBJECT IDENTIFIER ::= { id-svp 2 }

   When the id-svp-nameValAlg appears as a valAlgId, the parameters MUST
   use the NameValidationAlgParms syntax:

     NameValidationAlgParms ::= SEQUENCE {
       nameCompAlgId     OBJECT IDENTIFIER,
       validationNames   GeneralNames }

   GeneralNames is defined in [PKIX-1].

   If more than one name is supplied in the validationNames value, all
   names MUST be of the same type.  The certificate must contain a
   matching name for each of the names supplied in validationNames
   according to the name matching rules associated with the
   nameCompAlgId.  This specification defines three sets of name
   matching rules.

   If the nameCompAlgId supplied in the request is id-nva-dnCompAlg,
   then GeneralNames supplied in the request MUST be a directoryName,
   and the matching rules to be used are defined in [PKIX-1].  The
   certificate must contain a matching name in either the subject field
   or a directoryName in the subjectAltName extension.  This
   specification defines the OID for id-nva-dnCompAlg as follows:

     id-nva-dnCompAlg   OBJECT IDENTIFIER ::= { id-svp 4 }




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   If the nameCompAlgId supplied in the request is id-kp-serverAuth
   [PKIX-1], then GeneralNames supplied in the request MUST be a
   dNSName, and the matching rules to be used are defined in [HTTP-TLS].

   If the nameCompAlgId supplied in the request is id-kp-mailProtection
   [PKIX-1], then GeneralNames supplied in the request MUST be an
   rfc822Name, and the matching rules are defined in [SMIME-CERT].

   Conforming SCVP servers MUST support the name validation algorithm
   and the matching rules associated with id-nva-dnCompAlg, id-kp-
   serverAuth, id-kp-mailProtection.  SCVP server MAY support other name
   matching rules.

3.2.4.2.4  Name Validation Algorithm Errors

   The following errors are defined for the Name Validation Algorithm:

     id-nvae OBJECT IDENTIFIER ::= id-svp-nameValAlg

     id-nvae-name-mismatch    OBJECT IDENTIFIER ::= { id-nvae 1 }
     id-nvae-no-name          OBJECT IDENTIFIER ::= { id-nvae 2 }
     id-nvae-unknown-alg      OBJECT IDENTIFIER ::= { id-nvae 3 }
     id-nvae-bad-name         OBJECT IDENTIFIER ::= { id-nvae 4 }
     id-nvae-bad-name-type    OBJECT IDENTIFIER ::= { id-nvae 5 }
     id-nvae-mixed-names      OBJECT IDENTIFIER ::= { id-nvae 6 }

   The id-nvae-name-mismatch value means the client supplied a name with
   the request, which the server recognized and the server found
   corresponding name type in the certificate, but was unable to find a
   match to the name supplied.  For example, the client supplied a DNS
   name of example1.com, the certificate contained a DNS name of
   example.com.

   The id-nvae-no-name value means the client supplied a name with the
   request, which the server recognized, but the server could not find
   the corresponding name type in the certificate.  For example, the
   client supplied a DNS name of example1.com, the certificate only
   contained a rfc822Name of user@example.com.

   The id-nvae-unknown-alg value means the client supplied a
   nameCompAlgId which the server does not recognize.

   The id-nvae-bad-name value means the client supplied either an empty
   or malformed name in the request.

   The id-nvae-bad-name-type value means the client supplied an
   inappropriate name type for the application identifier.  For example,
   the client specified a nameCompAlgId of id-kp-serverAuth, and an
   rfc822Name of user@example.com.


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   The id-nvae-mixed-names value means the client supplied multiple
   names in the request of different types.

3.2.4.3  userPolicySet

   The userPolicySet item specifies a list of certificate policy
   identifiers that the SCVP server MUST use when constructing and
   validating a certification path.  The userPolicySet item specifies
   the user-initial-policy-set as defined in Section 6 of [PKIX-1].  A
   userPolicySet containing the anyPolicy OID indicates a user-initial-
   policy-set of any-policy.

   SCVP clients SHOULD support userPolicySet item in requests, and SCVP
   servers MUST support userPolicySet item in requests.

3.2.4.4  inhibitPolicyMapping

   The inihibitPolicyMapping item specifies an input to the
   certification path validation algorithm, and it controls whether
   policy mapping is allowed during certification path validation (see
   [PKIX-1], section 6.1.1).  If the client wants the server to inhibit
   policy mapping, inhibitPolicyMapping is set to TRUE in the request.

   SCVP clients MAY support inhibiting policy mapping.  SCVP servers
   SHOULD support inhibiting policy mapping.

3.2.4.5  requireExplicitPolicy

   The requireExplicitPolicy item specifies an input to the
   certification path validation algorithm, and it controls whether
   there must be at least one valid policy in the certificate policies
   extension (see [PKIX-1], section 6.1.1).  If the client wants the
   server to require at least one policy, requireExplicitPolicy is set
   to TRUE in the request.

   SCVP clients MAY support requiring explicit policies.  SCVP servers
   SHOULD support requiring explicit policies.

3.2.4.6  inhibitAnyPolicy

   The inhibitAnyPolicy item specifies an input to the certification
   path validation algorithm (see [PKIX-1], section 6.1.1), and it
   controls whether the anyPolicy OID is processed or ignored when
   evaluating certificate policy.  If the client wants the server to
   ignore the anyPolicy OID, inhibitAnyPolicy MUST be set to TRUE in the
   request.




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   SCVP clients MAY support ignoring the anyPolicy OID.  SCVP servers
   SHOULD support ignoring the anyPolicy OID.

3.2.4.7  trustAnchors

   The trustAnchors item specifies the trust anchors at which the
   certification path must terminate if the path is to be considered
   valid by the SCVP server for the request.  If a trustAnchors item is
   present, the server MUST NOT consider any certification paths ending
   in other trust anchors as valid.

   The TrustAnchors type contains one or more trust anchor
   specifications.  A certificate reference can be used to identify the
   trust anchor by certificate hash and optionally a distinguished name
   with serial number.  Alternatively, trust anchors can be provided
   directly.  The order of trust anchor specifications within the
   sequence is not important.  Any CA certificate that meets the
   requirements of [PKIX-1] for signing certificates can be provided as
   a trust anchor.  If a trust anchor is supplied which does not meet
   these requirements, the server MUST return an error response.

   The trust anchor itself, regardless of its form, MUST NOT be included
   in any certification path returned by the SCVP server.

   TrustAnchors has the following syntax:

     TrustAnchors ::= SEQUENCE SIZE (1..MAX) OF PKCReference

   SCVP server MUST support trustAnchors.  SCVP clients SHOULD support
   trustAnchors.

3.2.4.8  keyUsages

   The key usage extension [PKIX-1, section 4.2.1.3] in the certificate
   defines the technical purpose (such as encipherment, signature, and
   certificate signing) of the key contained in the certificate.  If the
   client wishes to confirm the technical usage, then it can communicate
   the usage it wants to validate by the same structure using the same
   semantics as defined in [PKIX-1].  For example, if the client
   obtained the certificate in the context of a digital signature, it
   can confirm this use by including a keyUsage structure with the
   digital signature bit set.

     KeyUsages ::= CHOICE {
       anyKeyUsage         NULL,
       requiredKeyUsages   SEQUENCE SIZE (1..MAX) OF KeyUsage }





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   The keyUsages item may indicate either the particular key usages that
   are required by the client (using requiredKeyUsages) or that the
   client does not require any particular key usage (using anyKeyUsage).

   The requiredKeyUsages item can contain one or more keyUsage
   definitions to allow the client to search for a set of patterns any
   one of which is acceptable to the client.  If the client wishes to
   match against multiple possibilities then the client passes in a
   sequence of possible patterns.  Each keyUsage can contain a set of
   one or more bits set in the request, all bits MUST be present in the
   certificate to match against an instance of the keyUsage in the SCVP
   request.  If the certificate key usage extension contains more usages
   than requested, then the certificate MUST be considered a match.  For
   example, if a client wishes to check for either digital signature or
   non-repudiation, then the client provides two keyUsage values, one
   with digital signature set and the other with non-repudiation set.
   If the key usage extension is absent from the certificate, the
   certificate MUST be considered good for all usages and therefore any
   pattern in the SCVP request will match.

   SCVP clients SHOULD support keyUsages, and SCVP servers MUST support
   keyUsages.

3.2.4.9  extendedKeyUsages

   The extended key usage extension [PKIX-1, section 4.2.1.13] defines
   more specific technical purposes, in addition to or in place of the
   purposes indicated in the key usage extension, for which the
   certified public key may be used.  If the client wishes to confirm
   the extended key usage, then it can communicate the usage it wants to
   validate by the same extension using the same semantics as defined in
   [PKIX-1].  For example, if the client obtained the certificate in the
   context of a TLS server, it can confirm this usage by including the
   extended key usage structure with the id-kp-serverAuth object
   identifier.  If the extension is absent or is present and asserts the
   anyExtendedKeyUsage OID, then all usages specified in the request are
   a match.  If the extension is present and more than one usage is set
   in the request, all usages MUST be present in the certificate.  If
   the certificate extension contains more usages than requested, then
   the certificate MUST be considered a match.

   Where the client does not require any particular extended key usage,
   the client can specify an empty SEQUENCE.  This may be used to
   override extended key usage requirements imposed in the validation
   policy specified by validationPolRef.

   SCVP clients SHOULD support extendedKeyUsages, and SCVP servers MUST
   support extendedKeyUsages.



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3.2.5  responseFlags

   The optional response flags item allows the client to indicate which
   optional features in the CVResponse it wants the server to include.
   If the default values for all of the flags are used, then the
   response flags item MUST NOT be included in the request.

   The syntax of the responseFlags is:

     ResponseFlags ::= SEQUENCE {
       fullRequestInResponse      [0] BOOLEAN DEFAULT FALSE,
       responseValidationPolByRef [1] BOOLEAN DEFAULT TRUE,
       protectResponse            [2] BOOLEAN DEFAULT TRUE,
       cachedResponse             [3] BOOLEAN DEFAULT TRUE }

   Each of the response flags is described in the following sections.

3.2.5.1  fullRequestInResponse

   By default, the server includes a hash of the request in non-cached
   responses to allow the client to identify the response.  If the
   client wants the server to include the full request in the non-cached
   response, fullRequestInResponse is set to TRUE.  The main reason a
   client would request the server to include the full request in the
   response is to archive the request-response exchange in a single
   object.  That is, the client wants to archive a single object that
   includes both request and response.

   SCVP clients and servers MUST support the default behavior.  SCVP
   clients MAY support requesting and processing the full request.  SCVP
   servers SHOULD support returning the full request.

3.2.5.2  responseValidationPolByRef

   The responseValidationPolByRef item controls whether the response
   includes just a reference to the policy or a reference to the policy
   plus all the parameters by value of the policy used to process the
   request.  The response MUST contain a reference to the validation
   policy.  If the client wants the validation policy parameters to be
   also included by value, then responseValidationPolByRef is set to
   FALSE.  The main reason a client would request the server to include
   validation policy to be included by value is to archive the request-
   response exchange in a single object.  That is, the client wants to
   archive the CVResponse and have it include every aspect of the
   validation policy.

   SCVP clients and servers MUST support the default behavior.  SCVP
   clients MAY support requesting and processing the validation policy



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   by values.  SVCP server SHOULD support returning the validation
   policy by values.

3.2.5.3  protectResponse

   The protectResponse item indicates whether the client requires the
   server to protect the response.  If the client is performing full
   certification path validation on the response and it is not concerned
   about the source of the response, then the client does not benefit
   from a digital signature or MAC on the response.  In this case, the
   client can indicate to the server that protecting the message is
   unnecessary.  However, the server is always permitted to return a
   protected response.

   SCVP clients that support delegated path discovery (DPD) as defined
   in [RQMTS] MUST support setting this value to FALSE.

   SCVP clients that support delegated path validation (DPV) as defined
   in [RQMTS] require an authenticated response.  Unless a protected
   transport mechanism (such a TLS) is used, such clients MUST always
   set this value to TRUE or omit the responseFlags item entirely, which
   requires the server to return a protected response.

   SCVP servers MUST support returning protected responses, and SCVP
   servers SHOULD support returning unprotected responses.  Based on
   local policy, the server can be configured to return protected or
   unprotected responses if this value is set to FALSE.  If based on
   local policy the server is unable to return protected responses, then
   the server MUST return an error if this value is set to TRUE.

3.2.5.4  cachedResponse

   The cachedResponse item indicates whether the client will accept a
   cached response.  To enhance performance and limit the exposure of
   signing keys, an SCVP service may be designed to cache responses
   until new revocation information is expected.  Where cachedResponse
   is set to TRUE, the client will accept a previously cached response.

   Clients may insist on creation of a fresh response to protect against
   a replay attack and ensure information is up to date.  Where
   cachedResponse is FALSE, the client will not accept a cached
   response.  To ensure that a response is fresh, the client MUST also
   include the requestNonce as defined in Section 3.4.

   Servers MUST process the cachedResponse flag.  Where cachedResponse
   is FALSE, servers that cannot produce fresh responses MUST reply with
   an error message.  Servers MAY choose to provide fresh responses even
   where cachedResponse is set to TRUE.



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3.2.6  serverContextInfo

   The optional serverContextInfo item, if present, contains context
   from a previous request-response exchange with the same SCVP server.
   It allows the server to return more than one certification path for
   the same certificate to the client.  For example, if a server
   constructs a particular certification path for a certificate, but the
   client finds it unacceptable, the client can then send the same query
   back to the server with the serverContextInfo from the first
   response, and the server will be able to provide a different
   certification path (if another one can be found).

   Contents of the serverContextInfo are opaque to the SCVP client.
   That is, the client only knows that it needs to return the value
   provided by the server with the subsequent request to get a different
   certification path.  Note that the subsequent query needs to be
   identical to the previous query with the exception of the following:

    - requestNonce;

    - serverContextInfo; and

    - the client's digital signature or MAC on the request.

   SCVP clients MAY support serverContextInfo, and SCVP servers SHOULD
   support serverContextInfo.

3.2.7  valididationTime

   The optional validationTime item, if present, tells the date and time
   relative to which the SCVP client wants the server to perform the
   checks.  If the validationTime is not present, the server MUST
   perform the validation using the date and time at which the server
   processes the request.  If the validationTime is present, it MUST be
   encoded as GeneralizedTime.  The validationTime provided MUST be a
   retrospective time since the server can only perform a validity check
   using the current time (default) or previous time.  A server can
   ignore the validationTime provided in the request if the time is
   within the clock skew of the server's current time.

   The revocation status information is obtained with respect to the
   validation time.  When specifying a validation time other than the
   current time, the validation time should not necessarily be identical
   to the time when the private key was used.  The validation time
   specified by the client may be adjusted to compensate for:

     1) time for the end-entity to realize that its private key has
        been or could possibly be compromised, and/or



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      2) time for the end-entity to report the key compromise, and/or

      3) time for the revocation authority to process the revocation
         request from the end-entity, and/or

      4) time for the revocation authority to update and distribute the
         revocation status information.

   GeneralizedTime values MUST be expressed in Universal Coordinated
   Time (UTC) (which is also known as Greenwich Mean Time and Zulu time)
   and MUST include seconds (i.e., times are YYYYMMDDHHMMSSZ), even when
   the number of seconds is zero.  GeneralizedTime values MUST NOT
   include fractional seconds.

   The information in the corresponding CertReply item in the response
   MUST be formatted as if the server created the response at the time
   indicated in the validationTime.  However, if the server does not
   have appropriate historical information, the server MUST return an
   error response.

   SCVP servers MUST apply a clock skew to the validity time to allow
   for minor time synchronization errors.  The default value is 10
   minutes.  If the server uses a value other than the default it MUST
   include the clock skew value in the validation policy response.

   SCVP clients MAY support validationTime other than the current time.
   SCVP servers MUST support using its current time, and SHOULD support
   the client setting the validationTime in the request.

3.2.8  intermediateCerts

   The optional intermediateCerts item may help the SCVP server create
   valid certification paths.  The intermediateCerts item, when present,
   provides certificates that the server MAY use when forming a
   certification path.  When building certification paths, the server
   MAY use the certificates in the intermediateCerts item in addition to
   any other certificates that the server can access.  When present, the
   intermediateCerts item MUST contain at least one certificate, and the
   intermediateCerts item MUST be structured as a CertBundle.  The
   certificates in the intermediateCerts item MUST NOT be considered as
   valid by the server just because they are present in this item.

   The CertBundle type contains one or more certificates.  The order of
   the entries in the bundle is not important.  CertBundle has the
   following syntax:

     CertBundle ::= SEQUENCE SIZE (1..MAX) OF Certificate




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   SCVP clients SHOULD support intermediateCerts, and SCVP servers MUST
   support intermediateCerts.

3.2.9  revInfos

   The optional revInfos item specifies revocation information such as
   CRLs, delta CRLs [PKIX-1], and OCSP responses [OCSP] that the SCVP
   server MAY use when validating certification paths.  The purpose of
   the revInfos item is to provide revocation information to which the
   server might not otherwise have access, such as an OCSP response that
   the client received along with the certificate.  Note that the
   information in the revInfos item might not be used by the server.
   For example, the revocation information might be associated with
   certificates that the server does not use in the certification path
   that it constructs.

   Clients SHOULD be courteous to the SCVP server by separating CRLs and
   delta CRLs.  However, since the two share a common syntax, SCVP
   servers SHOULD accept delta CRLs even if they are identified as
   regular CRLs by the SCVP client.

   CRLs, delta CRLs, and OCSP responses can be provided as revocation
   information.  If needed, additional object identifiers can be
   assigned for additional revocation information types in the future.

   The revInfos item uses the RevocationInfos type, which has the
   following syntax:

     RevocationInfos ::= SEQUENCE SIZE (1..MAX) OF RevocationInfo

     RevocationInfo ::= CHOICE {
       crl                    [0] CertificateList,
       delta-crl              [1] CertificateList,
       ocsp                   [2] OCSPResponse,
       other                  [3] OtherRevInfo }

     OtherRevInfo ::= SEQUENCE {
       riType                     OBJECT IDENTIFIER,
       riValue                    ANY DEFINED BY riType }

3.2.10  producedAt

   The client MAY allow the server to use a cached SCVP response.  When
   doing so, the client MAY use the producedAt item to express
   requirements on the freshness of the cached response.  The producedAt
   item tells the earliest date and time at which an acceptable cached
   response could have been produced.  The producedAt item represents
   the date and time in UTC, using the GeneralizedTime type.  The value
   in the producedAt item is independent of the validation time.


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   GeneralizedTime value MUST be expressed in UTC, as defined in section
   3.2.7.

   SCVP client MAY support using producedAt values in the request.  SCVP
   server MAY support the producedAt values in the request.  SCVP
   servers that support cached responses SHOULD support the producedAt
   value in requests.

3.2.11  queryExtensions

   The optional queryExtensions item contains Extensions.  If present,
   each extension in the sequence extends the query.  This specification
   does not define any extensions; the facility is provided to allow
   future specifications to extend SCVP.  The syntax for extensions is
   imported from [PKIX-1].  The queryExtensions item, when present, MUST
   contain a sequence of extension items, and each of the extensions
   MUST contain extnID, critical, and extnValue items.  Each of these is
   described in the following sections.

3.2.11.1  extnID

   The extnID item is an identifier for the extension.  It contains the
   object identifier that names the extension.

3.2.11.2  critical

   The critical item is a BOOLEAN.  Each extension is designated as
   either critical (with a value of TRUE) or non-critical (with a value
   of FALSE).  By default, the extension is non-critical.  An SCVP
   server MUST reject the query if it encounters a critical extension
   that it does not recognize; however, a non-critical extension MAY be
   ignored if it is not recognized, but MUST be processed if it is
   recognized.

3.2.11.3  extnValue

   The extnValue item is an octet string, which contains the extension
   value.  An ASN.1 type is specified for each extension, identified by
   the associated extnID object identifier.

3.3  requestorRef

   The optional requestorRef item contains a SEQUENCE of OCTET STRINGs
   identifying SCVP servers, and it is intended for use in environments
   where SCVP relay is employed.  As described in [RQMTS], in some
   network environments an SCVP server might not be able to obtain all
   of the information that it needs to process a request.  However, the
   SCVP server might be configured to use the services of one or more


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   other SCVP servers to fulfill all requests.  In such cases, the
   client is unaware that the queried SCVP server is using the services
   of other SCVP servers, and the client-queried SCVP server acts as an
   SCVP client to another SCVP server.  Unlike the original client, the
   SCVP server is expected to have moderate computing and memory
   resources, enabling the use of relay, re-direct or multicasting
   mechanisms.  The requestorRef item is used to detect looping in some
   configurations.  The value and use of requestorRef is defined in
   section 7.  To detect loops, the server MUST inspect the sequence of
   octet strings, looking for values that it inserted as a client.

   If the SCVP client includes a requestorRef value in the request, then
   the SCVP server MUST return the same value in a non-cached response.
   The SCVP server MAY omit the requestorRef value from cached SCVP
   responses.

   The requestorRef item MUST be a sequence of octet strings.  No
   provisions are made to ensure uniqueness of the requestorRef octet
   strings.

3.4  requestNonce

   The optional requestNonce item contains a request identifier
   generated by the SCVP client.  If the client includes a requestNonce
   value in the request, it is expressing a preference that the SCVP
   server SHOULD return a non-cached response.  If the server returns a
   non-cached response it MUST include the value of requestNonce from
   the request in the response as the respNonce field; however, the
   server MAY return a cached response which MUST NOT have a respNonce.

   If the client includes a requestNonce and also sets the
   cachedResponse flag to FALSE as defined in section 3.2.5.4, the
   client is indicating that the SCVP server MUST return either a non-
   cached response including the respNonce or an error response.  The
   client SHOULD include a requestNonce item in every request to prevent
   an attacker from acting as a man-in-the-middle by replaying old
   responses from the server.  The requestNonce value SHOULD change with
   every request sent by the client.

   The client MUST NOT set the cachedResponse flag to FALSE without also
   including a requestNonce.  A server receiving such a request SHOULD
   return an invalidRequest error response.

   The requestNonce item, if present, MUST be an octet string that was
   generated exclusively for this request.

3.5  requestorName




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   The optional requestorName item is used by the client to include an
   identifier in the request.  The client MAY include this information
   for the DPV server to copy into the response.

   SCVP servers MUST be able to process requests that include this
   field.

3.6  requestExtensions

   The OPTIONAL requestExtensions item contains Extensions.  If present,
   each Extension in the sequence extends the request.  This
   specification does not define any extensions; the facility is
   provided to allow future specifications to extend SCVP.  The syntax
   for Extensions is imported from [PKIX-1].  The requestExtensions
   item, when present, MUST contain a sequence of extension items, and
   each of extension MUST contain extnID, critical, and extnValue items.
   Each of these is described in the following sections.

3.6.1  extnID

   The extnID item is an identifier for the extension.  It contains the
   object identifier that names the extension.

3.6.2  critical

   The critical item is a BOOLEAN.  Each extension is designated as
   either critical (with a value of TRUE) or non-critical (with a value
   of FALSE).  By default, the extension is non-critical.  An SCVP
   server MUST reject the query if it encounters a critical extension it
   does not recognize. A non-critical extension MAY be ignored if it is
   not recognized, but MUST be processed if it is recognized.

3.6.3  extnValue

   The extnValue item contains an octet string.  Within the octet string
   is the extension value.  An ASN.1 type is specified for each
   extension, identified by the associated extnID object identifier.

3.7  SCVP Request Authentication

   It is a matter of local policy what validation policy the server uses
   when authenticating requests.  When authenticating protected SCVP
   requests, the SCVP servers SHOULD use the validation algorithm
   defined in section 6 of [PKIX-1].

   If the certificate used to validate a SignedData validation request
   includes the key usage extension [PKIX-1, section 4.2.1.3], it MUST
   have either the digital signature bit set, the non-repudiation bit
   set, or both bits set.


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   If the certificate used to validate an AuthenticatedData validation
   request includes the key usage extension, it MUST have the key
   agreement bit set.

   If the certificate used on a validation request contains the extended
   key usage extension [PKIX-1, section 4.2.1.13], the server SHALL
   verify that it contains the SCVP client OID or another OID acceptable
   to the server.  The SCVP client OID is defined as follows:

     id-kp OBJECT IDENTIFIER ::= { id-pkix 3 }

     id-kp-scvpClient             OBJECT IDENTIFIER ::= { id-kp 16 }

   If a protected request fails to meet the validation policy of the
   server, it MUST be treated as an unauthenticated request.

4  Validation Response

   An SCVP server response to the client MUST be a single CVResponse
   item.  When a CVResponse is encapsulated in a MIME body part,
   application/cv-response MUST be used.

   There are a number of forms of an SCVP response:

    1. A success response to a request made over a protected transport
       such as TLS.  These responses SHOULD NOT be protected by the
       server.

    2. A success response to a request that has protectResponse set to
       FALSE.  These responses SHOULD NOT be protected by the server.

    3. The server MUST protect all other success responses.  If the
       server is unable to return a protected success response due to
       local policy, then it MUST return an error response.

    4. An error response to a request made over a protected transport
       such as TLS.  These responses SHOULD NOT be protected by the
       server

    5. An error response to a request that has protectResponse set to
       FALSE.  These responses SHOULD NOT be protected by the server.

    6. An error response to an authenticated request.  The server MUST
       protect these responses.

    7. An error response to an AuthenticatedData request where MAC is
       valid.  The server MUST protect these responses.

    8. All other error responses MUST NOT be protected by the server.


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   Successful responses are made when the server has fully complied with
   the request.  That is, the server was able to build a certification
   path using the referenced or supplied validation policy, and it was
   able to comply with all the requested parameters.  If the server is
   unable to perform validations using the required validation policy or
   the request contains an unsupported option, then the server MUST
   return an error response.

   For protected requests and responses, SCVP servers MUST support
   SignedData and SHOULD support AuthenticatedData.  It is a matter of
   local policy which types are used.

   If the server is making a protected response to a protected request,
   then the server MUST use the same protection mechanism (SignedData or
   AuthenticatedData) as in the request.

   An overview of the structure used for an unprotected response is
   provided below.  Many details are not shown, but the way that SCVP
   makes use of CMS is clearly illustrated.

     ContentInfo {
       contentType        id-ct-scvp-certValResponse,
                                   -- (1.2.840.113549.1.9.16.1.11)
       content            CVResponse }

   The protected response consists of a CVResponse encapsulated in
   either a SignedData or an AuthenticatedData, which is in turn
   encapsulated in a ContentInfo.  An overview of the structure used for
   a protected response is provided below.  As above, many details are
   not shown, but the way that SCVP makes use of CMS is clearly
   illustrated.

   SignedData Example:

     ContentInfo {
       contentType        id-signedData, -- (1.2.840.113549.1.7.2)
       content            SignedData }

     SignedData {
       version                CMSVersion,
       digestAlgorithms       DigestAlgorithmIdentifiers,
       encapContentInfo       EncapsulatedContentInfo,
       certificates       [0] IMPLICIT CertificateSet OPTIONAL,
                                    -- MUST include server cert
       crls               [1] IMPLICIT CertificateRevocationLists
                                    OPTIONAL,
       signerInfos            SET OF SignerInfos } -- Only one in SCVP



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     SignerInfo {
       version                CMSVersion,
       sid                    SignerIdentifier,
       digestAlgorithm        DigestAlgorithmIdentifier,
       signedAttrs            SignedAttributes, -- Required by CMS
       signatureAlgorithm     SignatureAlgorithmIdentifier,
       signature              SignatureValue,
       unsignedAttrs          UnsignedAttributes } -- Not used in SCVP

     EncapsulatedContentInfo {
       eContentType       id-ct-scvp-certValResponse,
                                     -- (1.2.840.113549.1.9.16.1.11)
       eContent           OCTET STRING } -- Contains CVResponse

   AuthenticatedData Example:

     ContentInfo {
       contentType       id-ct-authData,
                                    -- (1.2.840.113549.1.9.16.1.2)
       content           AuthenticatedData }

     AuthenticatedData ::= SEQUENCE {
       version                 CMSVersion,
       originatorInfo          OriginatorInfo,
       recipientInfos          RecipientInfos, -- Only for SCVP client
       macAlgorithm            MessageAuthenticationCodeAlgorithm,
       digestAlgorithm         DigestAlgorithmIdentifier,
       encapContentInfo        EncapsulatedContentInfo,
       authAttrs               AuthAttributes, -- Required by CMS
       mac                     MessageAuthenticationCode,
       unauthAttrs             UnauthAttributes } -- Not used in SCVP

     EncapsulatedContentInfo {
       eContentType       id-ct-scvp-certValResponse,
                                     -- (1.2.840.113549.1.9.16.1.11)
       eContent           OCTET STRING } -- Contains CVResponse

   The SCVP server MUST include its own certificate in the certificates
   field within SignedData.  Other certificates MAY also be included.
   The SCVP server MAY also provide one or more CRLs in the crls field
   within SignedData.

   The signedAttrs field within SignerInfo MUST include the content-type
   and message-digest attributes defined in [CMS], and it SHOULD include
   the signing-certificate attribute as defined in [ESS].  Within the
   signing-certificate attribute, the first certificate identified in
   the sequence of certificate identifiers MUST be the certificate of
   the SCVP server.  The inclusion of other certificate identifiers in



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   the signing-certificate attribute is OPTIONAL.  The inclusion of
   policies in the signing-certificate is OPTIONAL.

   The CVResponse item contains the server's response.  The CVResponse
   MUST contain the cvResponseVersion, policyID, producedAt, and
   responseStatus items.  The CVResponse MAY also contain the
   respValidationPolicy, requestRef, requestorRef, requestorName,
   replyObjects, respNonce, serverContextInfo, and cvResponseExtensions
   items.  The replyObjects item MUST contain exactly one CertReply item
   for each certificate requested.  The requestorRef item MUST be
   included if the request included a requestorRef item.  The respNonce
   item MUST be included if the request included a requestNonce item and
   a non-cached response is provided.

   The CVResponse MUST have the following syntax:

     CVResponse ::= SEQUENCE {
       cvResponseVersion         INTEGER,
       policyID                  INTEGER,
       producedAt                GeneralizedTime,
       responseStatus            ResponseStatus,
       respValidationPolicy  [0] RespValidationPolicy OPTIONAL,
       requestRef            [1] RequestReference OPTIONAL,
       requestorRef          [2] SEQUENCE SIZE (1..MAX) OF OCTET
                                   STRING OPTIONAL,
       requestorName         [3] GeneralNames OPTIONAL,
       replyObjects          [4] ReplyObjects OPTIONAL,
       respNonce             [5] OCTET STRING OPTIONAL,
       serverContextInfo     [6] OCTET STRING OPTIONAL,
       cvResponseExtensions  [7] Extensions OPTIONAL }

4.1  cvResponseVersion

   The syntax and semantics of cvResponseVersion are the same as
   cvRequestVersion as described in section 3.1.  The cvResponseVersion
   MUST match the cvRequestVersion in the request.  If the server cannot
   generate a response with a matching version number, then the server
   MUST return an error response that indicates the highest version
   number that the server supports as the version number.

4.2  policyID

   The policy ID representing the version of the default validation
   policy that was used by the SCVP server when it processed the
   request.  See section 6.4 for details.

4.3  producedAt




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   The producedAt item tells the date and time at which the SCVP server
   generated the response.  The producedAt item MUST be expressed in
   UTC, and it MUST be interpreted as defined in section 3.2.7.  This
   value is independent of the validation time.

4.4  responseStatus

   The responseStatus item gives status information to the SCVP client
   about its request.  The responseStatus item has a numeric status code
   and an optional string that is a sequence of characters from the
   ISO/IEC 10646-1 character set encoded with the UTF-8 transformation
   format defined in [UTF8].

   The string MAY be used to transmit status information.  The client
   MAY choose to display the string to a human user.  However, because
   there is often no way to know the languages understood by a human
   user, the string may be of little or no assistance.

   The responseStatus item uses the ResponseStatus type, which has the
   following syntax:

     ResponseStatus ::= SEQUENCE {
       statusCode            CVStatusCode DEFAULT okay,
       errorMessage          UTF8String OPTIONAL }

     CVStatusCode ::= ENUMERATED {
       okay                               (0),
       skipUnrecognizedItems              (1),
       tooBusy                           (10),
       invalidRequest                    (11),
       internalError                     (12),
       badStructure                      (20),
       unsupportedVersion                (21),
       abortUnrecognizedItems            (22),
       unrecognizedSigKey                (23),
       badSignatureOrMAC                 (24),
       unableToDecode                    (25),
       notAuthorized                     (26),
       unsupportedChecks                 (27),
       unsupportedWantBacks              (28),
       unsupportedSignatureOrMAC         (29),
       invalidSignatureOrMAC             (30),
       relayingLoop                      (40),
       unrecognizedValPol                (50),
       unrecognizedValAlg                (51),
       fullRequestInResponseUnsupported  (52),
       fullPolResponseUnsupported        (53),
       inhibitPolicyMappingUnsuported    (54),
       requireExplicitPolicyUnsupported  (55),


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       inhibitAnyPolicyUnsupported       (56),
       validityTimeUnsupported           (57),
       unrecognizedCritQueryExt          (63),
       unrecognizedCritRequestExt        (64) }

   The CVStatusCode values have the following meaning:

    0 The request was fully processed.
    1 The request included some unrecognized non-critical extensions;
       however, processing was able to continue ignoring them.
    10 Too busy; try again later.
    11 The server was able to decode the request, but there was some
       other problem with the request.
    12 An internal server error occurred.
    20 The structure of the request was wrong.
    21 The version of request is not supported by this server.
    22 The request included unrecognized items, and the server was not
       able to continue processing.
    23 The server could not validate the key used to protect the
       request.
    24 The signature or message authentication code did not match the
       body of the request.
    25 The encoding was not understood.
    26 The request was not authorized.
    27 The request included unsupported checks items, and the server
       was not able to continue processing.
    28 The request included unsupported want back items, and the server
       was not able to continue processing.
    29 The server does not support the signature or message
       authentication code algorithm used by the client to protect the
       request.
    30 The server could not validate the client's signature or message
       authentication code on the request.
    40 The request was previously relayed by the same server.
    50 The request contained an unrecognized validation policy
       reference.
    51 The request contained an unrecognized validation algorithm OID.
    52 The server does not support returning the full request in the
       response.
    53 The server does not support returning the full validation policy
       by value in the response.
    54 The server does not support inhibiting policy mapping.
    55 The server does not support requiring explicit policy.
    56 The server does not support ignoring the anyPolicy certificate
       policy OID.
    57 The server only validates requests using current time.
    63 The query item in the request contains a critical extension
       whose OID is not recognized.



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    64 The request contains a critical request extension whose OID is
       not recognized.

   Status codes 0-9 are reserved for codes that indicate the request was
   processed by the server and therefore MUST be sent in a success
   response.  Status codes 10 and above indicate an error and MUST
   therefore be sent in an error response.

4.5  respValidationPolicy

   The respValidationPolicy item contains either a reference to the full
   validation policy or the full policy by value used by the server to
   validate the request.  It MUST be present in success responses and
   MUST NOT be present in error responses.  The choice between returning
   the policy by reference or by value is controlled by the
   responseValidationPolByRef item in the request.  The resultant
   validation policy is the union of the following:

     1. Values from the request.

     2. For values that are not explicitly included in the request,
        values from the validation policy specified by reference in
        the request.

   The RespValidationPolicy syntax is:

     RespValidationPolicy ::= SEQUENCE {
       validationPolicy       ValidationPolicy,
       validationPolicyAttr   SEQUENCE SIZE (1..MAX) OF Attribute
                                OPTIONAL }

4.5.1  validationPolicy

   The validationPolicy item is defined in section 3.2.4.  When
   responseValidationPolByRef is set to FALSE in the request, all fields
   in the validationPolicy item MUST be populated.  When
   responseValidationPolByRef is set to TRUE, OPTIONAL fields in the
   validationPolicy item only need to be populated for items for which
   the value in the request differs from the value from the referenced
   validation policy.

4.5.2  validationPolicyAttr

   The validationPolicyAttr item MAY contain Attributes.  If present,
   each attribute in the sequence extends the policy values for the
   validation policy.  This specification does not define any
   attributes.  The facility is provided to allow future specifications
   to extend SCVP.  The syntax for Attribute is imported from [CMS].



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4.6  requestRef

   The requestRef item allows the SCVP client to identify the request
   that corresponds to this response from the server.  It associates the
   response to a particular request using either a hash of the request
   or a copy of CVRequest from the request.  The hash is calculated as
   described in [CMS] for SignedData and AuthenticatedData.  That is, it
   covers the encapsulated content and authenticated attributes but not
   the unauthenticated attributes.

   The requestRef item does not provide authentication, but does allow
   the client to determine that the request was not maliciously
   modified.

   The requestRef item allows the client to associate a response with a
   request.  The requestNonce provides an alternative mechanism for
   matching requests and responses.  When the fullRequest alternative is
   used, the response provides a single data structure that is suitable
   for archive of the transaction.

   The requestRef item uses the RequestReference type, which has the
   following syntax:

     RequestReference ::= CHOICE {
       requestHash       [0] HashValue, -- hash of CVRequest
       fullRequest       [1] CVRequest }

   SCVP clients MUST support requestHash, and they MAY support
   fullRequest.  SCVP servers MUST support using requestHash, and they
   SHOULD support using fullRequest.

4.6.1  requestHash

   The requestHash item is the hash of the CVRequest.  By default, SHA-1
   is used as the one-way hash function, but others can be used.  The
   requestHash item serves two purposes.  First, it allows a client to
   determine that the request was not maliciously modified.  Second, it
   allows the client to associate a response with a request when using
   connectionless protocols.  The requestNonce provides an alternative
   mechanism for matching requests and responses.

   The requestHash item uses the HashValue type, which has the following
   syntax:

     HashValue ::= SEQUENCE {
       algorithm             AlgorithmIdentifier DEFAULT { sha-1 },
       value                 OCTET STRING }

     sha-1 OBJECT IDENTIFIER ::= { iso(1) identified-organization(3)
         oiw(14) secsig(3) algorithm(2) 26 }

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   The algorithm identifier for SHA-1 is imported from [PKIX-ALG].  It
   is repeated here for convenience.

4.6.2  fullRequest

   Like requestHash, the fullRequest alternative allows a client to
   determine that the request was not maliciously modified.  It also
   provides a single data structure that is suitable for archive of the
   transaction.

   The fullRequest item uses the CVRequest type.  The syntax and
   semantics of the CVRequest type are described in section 3.

4.7  requestorRef

   The optional requestorRef item is used by the client to identify the
   original requestor in cases where SCVP relay is used.  The value is
   only of local significance to the client.  If the SCVP client
   includes a requestorRef value in the request, then the SCVP server
   MUST return the same value if the server is generating a non-cached
   response.

4.8  requestorName

   The optional requestorName item is used by the server to return one
   or more identities associated with the client in the response.

   The SCVP server MAY choose to include any or all of the following:
      (1) the identity asserted by the client in the requestorName field
          of the request,
      (2) an authenticated identity for the client from a certificate or
          other credential used to authenticate the request, or
      (3) a client identifier from an out-of-band mechanism.
   Alternatively, the SCVP server MAY omit this item.

   In the case of non-cached responses to authenticated requests, the
   SCVP server SHOULD return a requestor name.

   SCVP servers that support authenticated requests SHOULD support this
   item.

   SCVP clients MUST be able to process responses that include this
   field, although the item value might not impact the processing in any
   manner.

4.9  replyObjects




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   The replyObjects item returns requested objects to the SCVP client,
   each of which tells the client about a single certificate from the
   request.  The replyObjects item MUST be present in the response,
   unless the response is reporting an error.  The CertReply item MUST
   contain cert, replyStatus, replyValTime, replyChecks, and
   replyWantBacks items; and the CertReply item MAY contain the
   validationErrors, nextUpdate, and certReplyExtensions items.

   A success response MUST contain one CertReply for each certificate
   specified in the queriedCerts item in the request.  The order is
   important.  The first CertReply in the sequence MUST correspond to
   the first certificate in the request; the second CertReply in the
   sequence MUST correspond to the second certificate in the request;
   and so on.

   The checks item in the request determines the content of the
   replyChecks item in the response.  The wantBack item in the request
   determines the content of the replyWantBacks item in the response.
   The queryExtensions items in the request controls the absence or the
   presence and content of the certReplyExtensions item in the response.

   The replyObjects item uses the ReplyObjects type, which has the
   following syntax:

     ReplyObjects ::= SEQUENCE SIZE (1..MAX) OF CertReply

     CertReply ::= SEQUENCE {
       cert                       CertReference,
       replyStatus                ReplyStatus DEFAULT success,
       replyValTime               GeneralizedTime,
       replyChecks                ReplyChecks,
       replyWantBacks             ReplyWantBacks,
       validationErrors       [0] SEQUENCE SIZE (1..MAX) OF
                                    OBJECT IDENTIFIER OPTIONAL,
       nextUpdate             [1] GeneralizedTime OPTIONAL,
       certReplyExtensions    [2] Extensions OPTIONAL }

4.9.1  cert

   The cert item contains either the certificate or a reference to the
   certificate about which the client is requesting information.  If the
   certificate was specified by reference in the request, the request
   included either the id-swb-pkc-cert or id-swb-aa-cert wantBack, and
   the server was able to obtain the referenced certificate then this
   item MUST include the certificate.  Otherwise, this item MUST include
   the same value as was used in the queriedCerts item in the request.

   CertReference has the following syntax:



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     CertReference ::= CHOICE {
       pkc                   PKCReference,
       ac                    ACReference }

4.9.2  replyStatus

   The replyStatus item gives status information to the client about the
   request for the specific certificate.  Note that the responseStatus
   item is different than the replyStatus item.  The responseStatus item
   is the status of the whole request, while the replyStatus item is the
   status for the individual query item.

   The replyStatus item uses the ReplyStatus type, which has the
   following syntax:

     ReplyStatus ::= ENUMERATED {
         success                  (0),
         malformedPKC             (1),
         malformedAC              (2),
         unavailableValidityTime  (3),
         referenceCertHashFail    (4),
         certPathConstructFail    (5),
         certPathNotValid         (6),
         certPathNotValidNow      (7),
         wantBackUnsatisfied      (8) }

   The meaning of the various ReplyStatus values are:

    0 Success: all checks were performed successfully.
    1 Failure: the public key certificate was malformed.
    2 Failure: the attribute certificate was malformed.
    3 Failure: historical data for the requested validity time is not
       available.
    4 Failure: the server could not locate the reference certificate or
       the referenced certificate did not match the hash value provided.
    5 Failure: no certification path could be constructed.
    6 Failure: the constructed certification path is not valid with
       respect to the validation policy.
    7 Failure: the constructed certification path is not valid with
       respect to the validation policy, but a query at a later time
       may be successful.
    8 Failure: all checks were performed successfully, however one or
       more of the wantBacks could not be satisfied.

   Codes 1 and 2 are used to tell the client that the request was
   properly formed, but the certificate in question was not.  This is
   especially useful to clients that do not parse certificates.




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   Code 7 is used to tell the client that a valid certification path was
   found with the exception that a certificate in the path is on hold,
   current revocation information is unavailable, or the validation time
   precedes the notBefore time in one or more certificates in the path.

   For codes 1, 2, 3, and 4, the replyChecks and replyWantBacks items
   are not populated (i.e., they MUST be an empty sequence).  For codes
   5, 6, 7, and 8 replyChecks MUST include an entry corresponding to
   each check in the request; the replyWantBacks item is not populated.

4.9.3  replyValTime

   The replyValTime item tells the time at which the information in the
   CertReply was correct.  The replyValTime item represents the date and
   time in UTC, using GeneralizedTime type.  The encoding rules for
   GeneralizedTime in section 3.2.7 MUST be used.

   Within the request, the optional validityTime item tells the date and
   time relative to which the SCVP client wants the server to perform
   the checks.  If the validityTime is not present, the server MUST
   respond as if the client provided the date and time at which the
   server processes the request.

   The information in the CertReply item MUST be formatted as if the
   server created this portion of the response at the time indicated in
   the validityTime item of the query.  However, if the server does not
   have appropriate historical information, the server MAY either return
   an error or return information for a later time.

4.9.4  replyChecks

   The replyChecks item contains the responses to the checks item in the
   query.  The replyChecks item includes the object identifier (OID)
   from the query and an integer.  The value of the integer indicates
   whether the requested check was successful.  The OIDs in the checks
   item of the query are used to identify the corresponding replyChecks
   values.  The OIDs in the replyChecks item MUST match the OIDs in the
   checks item in the request.

   The replyChecks item uses the ReplyChecks type, which has the
   following syntax:

     ReplyChecks ::= SEQUENCE OF ReplyCheck

     ReplyCheck ::= SEQUENCE {
       check                      OBJECT IDENTIFIER,
       status                     INTEGER DEFAULT 0 }




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   The status value for public key certification path building to a
   trusted root, { id-stc 1 }, can be one of the following:

       0: Built a path
       1: Could not build a path

   The status value for public key certification path building to a
   trusted root along with simple validation processing, { id-stc 2 },
   can be one of the following:

       0: Valid
       1: Not valid

   The status value for public key certification path building to a
   trusted root along with complete status checking, { id-stc 3 }, can
   be one of the following:

       0: Valid
       1: Not valid
       2: Revocation Offline
       3: Revocation Unavailable
       4: No known source for revocation information

   Revocation offline means that the server or distribution point for
   the revocation information was connected to successfully without a
   network error but either no data was returned or if data was returned
   it was stale.  Revocation unavailable means that a network error was
   returned when an attempt was made to reach the server or distribution
   point.  No known source for revocation information means that the
   server was able to build a valid certification path but was unable to
   locate a source for revocation information for one or more
   certificates in the path.

   The status value for AC issuer certification path building to a
   trusted root, { id-stc 4 }, can be one of the following:

       0: Built a path
       1: Could not build a path

   The status value for AC issuer certification path building to a
   trusted root along with simple validation processing, { id-stc 5 },
   can be one of the following:

       0: Valid
       1: Not valid

   The status value for AC issuer certification path building to a
   trusted root along with complete status checking, { id-stc 6 }, can
   be one of the following:


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       0: Valid
       1: Not Valid
       2: Revocation Offline
       3: Revocation Unavailable
       4: No known source for revocation information

   The status value for revocation status checking of an AC as well as
   AC issuer certification path building to a trusted root along with
   complete status checking, { id-stc 7 }, can be one of the following:

       0: Valid
       1: Not Valid
       2: Revocation Offline
       3: Revocation Unavailable
       4: No known source for revocation information

4.9.5  replyWantBacks

   The replyWantBacks item contains the responses to the wantBack item
   in the request.  The replyWantBacks item includes the object
   identifier (OID) from the wantBack item in the request and an octet
   string.  Within the octet string is the requested value.  The OIDs in
   the wantBack item in the request are used to identify the
   corresponding reply value.  The OIDs in the replyWantBacks item MUST
   match the OIDs in the wantBack item in the request.

   The replyWantBacks item uses the ReplyWantBacks type, which has the
   following syntax:

     ReplyWantBacks ::= SEQUENCE OF ReplyWantBack

     ReplyWantBack::= SEQUENCE {
       wb                         OBJECT IDENTIFIER,
       value                      OCTET STRING }

   The octet string value for the certification path used to verify the
   certificate in the request, { id-swb 1 }, contains the CertBundle
   type.  The syntax and semantics of the CertBundle type are described
   in section 3.2.8.  This CertBundle includes all the certificates in
   the path, starting with the end certificate and ending with the
   certificate issued by the trust anchor.  If proof of revocation
   status was also requested, the CertBundle also contains any
   additional certificates used to validate the revocation information.
   These certificates follow the certificate issued by the trust anchor
   in the sequence.





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   The octet string value for the proof of revocation status, { id-swb
   2 }, contains the RevocationInfos type.  The syntax and semantics of
   the RevocationInfos type are described in section 3.2.9.

   The octet string value for the public key certificate status, { id-
   swb 3 }, contains an ASN.1 BOOLEAN type.  The value will be TRUE if
   the certificate is valid, and the value will be FALSE if the
   certificate is not valid.

   The octet string value for the public key information, { id-swb 4 },
   contains the SubjectPublicKeyInfo type.  The syntax and semantics of
   the SubjectPublicKeyInfo type are described in [PKIX-1].

   The octet string value for the AC issuer certification path used to
   verify the certificate in the request, { id-swb 5 }, contains the
   CertBundle type.  The syntax and semantics of the CertBundle type are
   described in section 3.2.8.  This CertBundle includes all the
   certificates in the path, beginning with the AC issuer certificate
   and ending with the certificate issued by the trust anchor.  If proof
   of revocation status was also requested, the CertBundle also contains
   any additional certificates used to validate the revocation
   information.  These certificates follow the certificate issued by the
   trust anchor in the sequence.

   The octet string value for the proof of revocation status of the AC
   issuer certification path, { id-swb 6 }, contains the RevocationInfos
   type.  The syntax and semantics of the RevocationInfos type are
   described in section 3.2.9.

   The octet string value for the proof of revocation status of the
   attribute certificate, { id-swb 7 }, contains the RevocationInfos
   type.  The syntax and semantics of the RevocationInfos type are
   described in section 3.2.9.

   The octet string value for the attribute certificate status, { id-swb
   8 }, contains an ASN.1 BOOLEAN type.  The value will be TRUE if the
   certificate is valid, and the value will be FALSE if the certificate
   is not valid.

   The octet string value for returning all paths, { id-swb 12 },
   contains an ASN.1 type CertBundles, as defined below.  The syntax and
   semantics of the CertBundle type are described in section 3.2.8.
   Each CertBundle includes all the certificates in one path, starting
   the end certificate and ending with the certificate issued by the
   trust anchor.  If proof of revocation status was also requested, the
   CertBundle also contains any additional certificates used to validate
   the revocation information for that path.  These certificates follow
   the certificate issued by the trust anchor in the sequence.



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        CertBundles ::= SEQUENCE SIZE (1..MAX) OF CertBundle

4.9.6  validationErrors

   The validationErrors item MUST only be present in failure responses.
   If present, it MUST contain one or more OIDs representing the reason
   the validation failed (validation errors for the basic validation
   algorithm and name validation algorithm are defined in sections
   3.2.4.2.2 and 3.2.4.2.4).  The validationErrors item SHOULD only be
   included when the replyStatus is 3, 5, 6, 7, or 8.  SCVP servers are
   not required to specify all of the reasons that validation failed.
   SCVP clients MUST NOT assume that the OIDs included in
   validationErrors represent all of the validation errors for the
   certification path.

4.9.7  nextUpdate

   The nextUpdate item tells the time at which the server expects a
   refresh of information regarding the validity of the certificate to
   become available.  The nextUpdate item is especially interesting if
   the certificate revocation status information is not available or the
   certificate is suspended.  The nextUpdate item represents the date
   and time in UTC, using the GeneralizedTime type.  The encoding rules
   for GeneralizedTime in section 3.2.7 MUST be used.

4.9.8  certReplyExtensions

   The certReplyExtensions contains the responses to the queryExtensions
   item in the request.  The certReplyExtensions item uses the
   Extensions type defined in [PKIX-1].  The object identifiers (OIDs)
   in the queryExtensions item in the request are used to identify the
   corresponding reply values.  The certReplyExtensions item, when
   present, contains a sequence of Extension items, each of which
   contains an extnID item, a critical item, and an extnValue item.

   The extnID item is an identifier for the extension.  It contains the
   OID that names the extension, and it MUST match one of the OIDs in
   the queryExtensions item in the request.

   The critical item is a BOOLEAN, and it MUST be set to FALSE.

   The extnValue item contains an OCTET STRING.  Within the OCTET STRING
   is the extension value.  An ASN.1 type is specified for each
   extension, identified by the associated extnID object identifier.

4.10  respNonce

   The respNonce item contains an identifier to bind the request to the
   response.


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     If the client includes a requestNonce value in the request and the
     server is generating a specific non-cached response to the request
     then the server MUST return the same value in the response.

     If the server is using a cached response to the request then it
     MUST omit the respNonce field.

     If the server is returning a specific non-cached response to a
     request without a nonce, then the server MAY include a message
     specific nonce.  For digitally signed messages, the server MAY use
     the value of the message-digest attribute in the signedAttrs within
     SignerInfo of the request as the value in the respNonce field.

   The requestNonce item uses the octet string type.

   Client SHOULD support respNonce and servers MUST support respNonce.

4.11  serverContextInfo

   The serverContextInfo item in a response is a mechanism for the
   server to pass some opaque context information to the client.  If the
   client does not like the certification path returned, it can make a
   new query and pass along this context information.

   Section 3.2.6 contains information about the client's usage of this
   item.

   The context information is opaque to the client, but it provides
   information to the server that ensures that a different certification
   path will be returned (if another one can be found).  The context
   information could indicate state on the server or it could contain a
   sequence of hashes of certification paths that have already been
   returned to the client.  The protocol does not dictate any structure
   or requirements for this item.  However, implementers should review
   the Security Considerations section of this document before selecting
   a structure.

   Servers that are incapable of returning additional paths MUST NOT
   include the serverContextInfo item in the response.

4.12  cvResponseExtensions

   If present, the CVResponseExtensions item contains a sequence of
   Extensions that extend the response.  This specification does not
   define any extensions.  The facility is provided to allow future
   specifications to extend SCVP.  The syntax for Extensions is imported
   from [PKIX-1].  The cvResponseExtensions item, when present, contains



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   a sequence of Extension items, each of which contains an extnID item,
   a critical item, and an extnValue item.

   The extnID item is an identifier for the extension.  It contains the
   object identifier (OID) that names the extension.

   The critical item is a BOOLEAN.  Each extension is designated as
   either critical (with a value of TRUE) or non-critical (with a value
   of FALSE).  An SCVP client MUST reject the response if it encounters
   a critical extension it does not recognize; however, a non-critical
   extension MAY be ignored if it is not recognized.

   The extnValue item contains an OCTET STRING.  Within the OCTET STRING
   is the extension value.  An ASN.1 type is specified for each
   extension, identified by the associated extnID object identifier.

4.13  SCVP Response Validation

   There are two mechanisms for validation of SCVP responses, one based
   on the client's knowledge of a specific SCVP server key and the other
   based on validation of the certificate corresponding to the private
   key used to protect the SCVP response.

4.13.1  Simple Key Validation

   The simple key validation method is where the SCVP client has a local
   policy of one or more SCVP server keys that directly identify the set
   of valid SCVP servers.  Mechanisms for storage of server keys or
   identifiers are a local matter.  For example, a client could store
   cryptographic hashes of public keys used to verify SignedData
   responses.  Alternatively, a client could store shared symmetric keys
   used to verify MACs in AuthenticatedData responses.

   Simple key validation MUST be used by SCVP clients that cannot
   validate PKIX-1 certificates and are therefore making delegated path
   validation requests to the SCVP server [RQTMS]. It is a matter of
   local policy with these clients whether to use SignedData or
   AuthenticatedData.  Simple key validation MAY be used by other SCVP
   clients for other reasons.

4.13.2  SCVP Server Certificate Validation

   It is a matter of local policy what validation policy the client uses
   when validating responses.  When validating protected SCVP responses,
   SCVP clients SHOULD use the validation algorithm defined in section 6
   of [PKIX-1].

   If the certificate used to sign the validation policy responses and
   SignedData validation responses contains the key usage extension


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   [PKIX-1 section 4.2.1.3] it MUST have either the digital signature
   bit set, the non-repudiation bit set, or both bits set.

   If the certificate for AuthenticatedData validation responses
   contains the key usage extension it MUST have the key agreement bit
   set.

   If the certificate used on a validation policy response or a
   validation response contains the extended key usage extension [PKIX-1
   section 4.2.1.13] it MUST contain the following OID:

     id-kp-scvpServer             OBJECT IDENTIFIER ::= { id-kp 15 }

5  Server Policy Request

   An SCVP client uses the ValPolRequest item to request information
   about an SCVP server's policies and configuration information,
   including the list of validation policies supported by the SCVP
   server.  When a ValPolRequest is encapsulated in a MIME body part, it
   MUST be carried in an application/vp-request MIME body part.

   The request consists of a ValPolRequest encapsulated in a
   ContentInfo.  The client does not sign the request.

     ContentInfo {
       contentType        id-ct-scvp-valPolRequest,
                                     -- (1.2.840.113549.1.9.16.1.12)
       content            ValPolRequest }

   The ValPolRequest type has the following syntax:

     ValPolRequest ::= SEQUENCE {
       vpRequestVersion           INTEGER DEFAULT 1,
       requestNonce               OCTET STRING }

5.1  vpRequestVersion

   The syntax and semantics of vpRequestVersion are the same as
   cvRequestVersion as described in section 3.1.

5.2  requestNonce

   The requestNonce item contains a request identifier generated by the
   SCVP client.  If the server returns a specific response it MUST
   include the requestNonce from the request in the response, but the
   server MAY return a cached response which MUST NOT include a
   requestNonce.




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6  Validation Policy Response

   In response to a ValPolRequest, the SCVP server provides a
   ValPolResponse.  The ValPolResponse MAY not be unique to any
   ValPolRequest, so may be reused by the server in response to multiple
   ValPolRequests.  The ValPolResponse also has an indication of how
   frequently the ValPolResponse may be reissued.  The server MUST sign
   the response using its digital signature certificate.  When a
   ValPolResponse is encapsulated in a MIME body part, it MUST be
   carried in an application/vp-response MIME body part.

   The response consists of a ValPolResponse encapsulated in a
   SignedData, which is in turn encapsulated in a ContentInfo.  An
   overview of the structure used for the response is provided below.
   Many details are not shown, but the way that SCVP makes use of CMS is
   clearly illustrated.

     ContentInfo {
       contentType        id-signedData, -- (1.2.840.113549.1.7.2)
       content            SignedData }

     SignedData {
       version                CMSVersion,
       digestAlgorithms       DigestAlgorithmIdentifiers,
       encapContentInfo       EncapsulatedContentInfo,
       certificates       [0] IMPLICIT CertificateSet OPTIONAL,
                                    -- MUST include server cert
       crls               [1] IMPLICIT CertificateRevocationLists
                                    OPTIONAL,
    signerInfos            SET OF SignerInfos } -- Only one in SCVP

     SignerInfo {
       version                CMSVersion,
       sid                    SignerIdentifier,
       digestAlgorithm        DigestAlgorithmIdentifier,
       signedAttrs            SignedAttributes, -- Required by CMS
       signatureAlgorithm     SignatureAlgorithmIdentifier,
       signature              SignatureValue,
       unsignedAttrs          UnsignedAttributes } -- Not used in SCVP

     EncapsulatedContentInfo {
       eContentType       id-ct-scvp-valPolResponse,
                                     -- (1.2.840.113549.1.9.16.1.13)
       eContent           OCTET STRING } -- Contains ValPolResponse

   The ValPolResponse type has the following syntax:

     ValPolResponse ::= SEQUENCE {
       vpResponseVersion                INTEGER,


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       maxCVResponseVersion             INTEGER,
       maxVPResponseVersion             INTEGER,
       defaultPolicyID                  INTEGER,
       thisUpdate                       GeneralizedTime,
       nextUpdate                       GeneralizedTime OPTIONAL,
       validationPolices                SEQUENCE OF ValidationPolRef,
       validationAlgs                   SEQUENCE OF OBJECT IDENTIFIER,
       authPolicies                     SEQUENCE OF AuthPolicy,
       responseTypes                    ResponseTypes,
       defaultPolicyValues              RespValidationPolicy,
       revocationInfoTypes              RevocationInfoTypes,
       serverPublicKeys                 SEQUENCE OF KeyAgreePublicKey
                                          OPTIONAL,
       clockSkew                        INTEGER DEFAULT 10,
       requestNonce                     OCTET STRING OPTIONAL }

     ResponseTypes  ::= ENUMERATED {
       cached-only                (0),
       non-cached-only            (1),
       cached-and-non-cached      (2) }

     RevocationInfoTypes ::= BIT STRING {
       fullCRLs                   (0),
       deltaCRLs                  (1),
       indirectCRLs               (2),
       oCSPResponses              (3) }

   SCVP clients that support validation policy requests MUST support
   validation policy responses.  SCVP servers MUST support validation
   policy responses.

   SCVP servers MUST support cached policy responses and MAY support
   specific responses to policy requests.

6.1  vpResponseVersion

   The syntax and semantics of the vpResponseVersion item are the same
   as cvRequestVersion as described in section 3.1.  The
   vpResponseVersion used MUST be the same as the vpRequestVersion
   unless the client has used a value greater than the values the server
   supports.  If the client submits a vpRequestVersion greater than the
   version supported by the server, the server MUST return a
   vpResponseVersion using the highest version number the server
   supports as the version number.

6.2  maxCVRequestVersion

   The maxCVRequestVersion defines the maximum version number for CV
   requests that the server supports.


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6.3  maxVPRequestVersion

   The maxVPRequestVersion defines the maximum version number for VP
   requests that the server supports.

6.4  defaultPolicyID

   An integer that uniquely represents the version of the default
   validation policy as represented by the validationPolicy,
   validationAlg, authPolicies, and clockSkew.  If any of these values
   change, the server MUST create a new ValPolResponse with a new
   defaultPolicyID.  If the policy and therefore the defaultPolicyID has
   not changed, then the server may reuse defaultPolicyID across
   multiple ValPolResponse messages.  However if the server, having
   changed the policy, then reverts to an earlier policy, the server
   MUST NOT revert the policy ID as well, but MUST select another unique
   value.

6.5  thisUpdate

   This field indicates the signing date and time of this policy
   response.

   GeneralizedTime values MUST be expressed Greenwich Mean Time (Zulu)
   and interpreted as defined in section 3.2.7.

6.6  nextUpdate and requestNonce

   These fields are used to indicate whether policy responses are
   specific to policy requests.  Where policy responses are cached,
   these fields indicate when the information will be updated.  The
   optional nextUpdate field indicates the time by which the next policy
   response will be published.  The optional requestNonce field links
   the response to a specific request by returning the nonce provided in
   the request.

   If the nextUpdate field is omitted it indicates a non-cached response
   generated in response to a specific request (i.e. the ValPolResponse
   is bound to a specific request).  If this field is omitted the
   requestNonce field MUST be present and MUST include the requestNonce
   value from the request.

   If the nextUpdate field is present it indicates a cached response
   that is not bound to a specific request.  An SCVP server MUST
   periodically generate a new response as defined by the next update
   time, but MAY use the same ValPolResponse to respond to multiple
   requests.  Thes requestNonce is omitted if the nextUpdate field is
   present.


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   It is a matter of local server policy to return a cached or non-
   cached specific response.

   GeneralizedTime values in nextUpdate MUST be expressed Greenwich Mean
   Time (Zulu) as specified in section 3.2.7.

6.7  validationPolicies

   The validationPolicies item contains a sequence of ValidationPolRef
   representing the validation policies supported by the server.  It is
   a matter of local policy if the server wishes to process requests
   using the default validation policy, and if it does not, then it MUST
   NOT include the id-svp-defaultValPolicy in this list.

6.8  validationAlgs

   The validationAlgs item contains a sequence of OIDs.  Each OID
   identifies a validation algorithm supported by the server.

6.9  authPolicies

   The authPolicies item contains a sequence of policy references for
   authenticating to the SCVP server.

   The reference to the authentication policy can be either an OID where
   the client and server have agreed the OID to represent an
   authentication policy or a URI where the URI points to a human
   readable definition of the policy.  The list of policies is intended
   to document to the client if authentication is required for some
   requests and if so how.

     AuthPolicy ::= CHOICE {
       authPolRefByOID     OBJECT IDENTIFIER,
       authPolRefByURI     IA5String }

6.10  responseTypes

   responseTypes allows the server to publish the range of response
   types it supports.  Cached only means the server will only return
   cached responses to requests.  Non-cached only means the server will
   return a specific response to the request i.e. containing the
   requestor's nonce.  Both means the server will return either,
   depending on the request.

6.11  revocationInfoTypes

   revocationInfoTypes allows the server to indicate the sources of
   revocation information that it is capable of processing.  For each


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   bit in the RevocationInfoTypes bit string, the server MUST set the
   bit to one if it is capable of processing the corresponding
   revocation information type and to zero if it can not.

6.12  defaultPolicyValues

   This is the default validation policy used by the server.  It
   contains a RespValidationPolicy, which is defined in section 4.5.
   All OPTIONAL fields in the validationPolicy field MUST be populated.
   A server will use these default values when the request references
   the default validation policy and the client does not override the
   default values by supplying other values in the request.

   This allows the client to optimize the request by omitting parameters
   that match the server default values.

6.13  serverPublicKeys

   The serverPublicKeys item is a sequence of one or more key agreement
   public keys and associated parameters.  It is used by clients making
   AuthenticatedData requests to the server.  Each item in the
   serverPublicKeys sequence is of the KeyAgreePublicKey type:

     KeyAgreePublicKey ::= SEQUENCE {
       algorithm            AlgorithmIdentifier,
       publicKey            BIT STRING }

   The KeyAgreePublicKey includes the algorithm identifier and the
   server's public key.  SCVP servers that support the key agreement
   mode of AuthenticatedData for SCVP requests MUST support
   serverPublicKeys and the Diffie-Hellman key agreement algorithm as
   specified in [PKIX-ALG].  SCVP servers that support serverPublicKeys
   MUST support the 1024-bit MODP group key (group 2) as defined in
   [IKE].  SCVP servers that support serverPublicKeys MAY support other
   Diffie-Hellman groups [IKE-GROUPS], as well as other key agreement
   algorithms.

6.14  clockSkew

   The clockSkew item is the number of minutes the server will allow for
   clock skew.  The default value of 10 minutes.

7  SCVP Server Relay

   In some network environments, especially ones that include firewalls,
   an SCVP server might not be able to obtain all of the information
   that it needs to process a request.  However, the server might be
   configured to use the services of one or more other SCVP servers to
   fulfill all requests.  In such cases, the SCVP client is unaware that


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   the initial SCVP server is using the services of other SCVP servers.
   The initial SCVP server acts as a client to another SCVP server.
   Unlike the original client, the SCVP server is expected to have
   moderate computing and memory resources.   This section describes
   SCVP server-to-SCVP server exchanges.  This section does not impose
   any requirements on SCVP clients that are not also SCVP servers.
   Further, this section does not impose any requirements on SCVP
   servers that do not relay requests to other SCVP servers.

   When one SCVP server relays a request to another server, in an
   incorrectly configured system of servers, it is possible that the
   same request will be relayed back again.  Any SCVP server that relays
   requests MUST implement the conventions described in this section to
   detect and break loops.

   When an SCVP server relays a request, the request MUST include the
   requestorRef item.  If the request to be relayed already contains a
   requestorRef item, then the server-generated request MUST contain a
   requestorRef item constructed from this value followed by an octet
   string that contains an identifier of the SCVP server.  If the
   request to be relayed does not contain a requestorRef item, then the
   server-generated request MUST contain a requestorRef item that
   includes a single octet string that contains an identifier of the
   SCVP server.

   To prevent false loop detection, servers should use identifiers that
   are unique within their network of cooperating SCVP servers.  SCVP
   servers that support relay SHOULD populate this item with the DNS
   name of the server or the distinguished name in the server's
   certificate.  SCVP servers MAY choose other procedures for generating
   identifiers that are unique within their community.

   When an SVCP server receives a request that contains a requestorRef
   item, the server MUST check the sequence of octet strings in the
   requestorRef item for its own identifier.  If the server discovers
   its own identifier in the requestor item, it MUST respond with an
   error, setting the cvResponseStatus to 40.

   When an SCVP server generates a non-cached response to a relayed
   request, the server MUST include the requestorRef item from the
   request in the response.

8  SCVP ASN.1 Module

   This section defines the syntax for SCVP request-response pairs.  The
   semantics for the messages are defined in sections 3, 4, 5, and 6.
   The SCVP ASN.1 module follows.

   SCVP


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     { iso(1) identified-organization(3) dod(6) internet(1)
       security(5) mechanisms(5) pkix(7) id-mod(0) 21 }

   DEFINITIONS IMPLICIT TAGS ::= BEGIN

   IMPORTS

   AlgorithmIdentifier, Attribute, Certificate, Extensions,
   -- Import UTF8String if required by compiler
   -- UTF8String, -- CertificateList
     FROM PKIX1Explicit88 -- RFC 3280
     { iso(1) identified-organization(3) dod(6) internet(1)
       security(5) mechanisms(5) pkix(7) id-mod(0) 18 }

   GeneralNames, GeneralName, KeyUsage, KeyPurposeId
     FROM PKIX1Implicit88 -- RFC 3280
     { iso(1) identified-organization(3) dod(6) internet(1)
       security(5) mechanisms(5) pkix(7) id-mod(0) 19 }

   AttributeCertificate
     FROM PKIXAttributeCertificate -- RFC 3281
     { iso(1) identified-organization(3) dod(6) internet(1)
       security(5) mechanisms(5) pkix(7) id-mod(0) 12 }

   ESSCertID
     FROM ExtendedSecurityServices -- RFC 2634
     { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1)
       pkcs-9(9) smime(16) modules(0) 2 }

   OCSPResponse
     FROM OCSP -- RFC 2560
     { iso(1) identified-organization(3) dod(6) internet(1)
       security(5) mechanisms(5) pkix(7) id-mod(0) 14 } ;


   -- SCVP Certificate Validation Request

   id-ct OBJECT IDENTIFIER ::= { iso(1) member-body(2)
             us(840) rsadsi(113549) pkcs(1) pkcs9(9)
             id-smime(16) 1 }

   id-ct-scvp-certValRequest OBJECT IDENTIFIER ::= { id-ct 10 }

   CVRequest ::= SEQUENCE {
     cvRequestVersion           INTEGER DEFAULT 1,
     query                      Query,
     requestorRef           [0] SEQUENCE SIZE (1..MAX) OF OCTET STRING
                                  OPTIONAL,


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     requestNonce           [1] OCTET STRING OPTIONAL,
     requestorName          [2] GeneralName OPTIONAL,
     reqestExtensions       [3] Extensions OPTIONAL }

   Query ::= SEQUENCE {
     queriedCerts             CertReferences,
     checks                   CertChecks,
     wantBack                 WantBack,
     validationPolicy         ValidationPolicy,
     responseFlags            ResponseFlags OPTIONAL,
     serverContextInfo    [2] OCTET STRING OPTIONAL,
     validationTime       [3] GeneralizedTime OPTIONAL,
     intermediateCerts    [4] CertBundle OPTIONAL,
     revInfos             [5] RevocationInfos OPTIONAL,
     producedAt           [6] GeneralizedTime OPTIONAL,
     queryExtensions      [7] Extensions OPTIONAL }

   CertReferences ::= CHOICE {
     pkcRefs              [0] SEQUENCE SIZE (1..MAX) OF PKCReference,
     acRefs               [1] SEQUENCE SIZE (1..MAX) OF ACReference }

   CertReference::= CHOICE {
     pkc                        PKCReference,
     ac                         ACReference }

   PKCReference ::= CHOICE {
     cert                   [0] Certificate,
     pkcRef                 [1] ESSCertID }

   ACReference ::= CHOICE {
     attrCert               [2] AttributeCertificate,
     acRef                  [3] ESSCertID }

   ValidationPolicy ::= SEQUENCE {
     validationPolRef           ValidationPolRef,
     validationAlg          [0] ValidationAlg OPTIONAL,
     userPolicySet          [1] SEQUENCE SIZE (1..MAX) OF OBJECT
                                  IDENTIFIER OPTIONAL,
     inhibitPolicyMapping   [2] BOOLEAN OPTIONAL,
     requireExplicitPolicy  [3] BOOLEAN OPTIONAL,
     inhibitAnyPolicy       [4] BOOLEAN OPTIONAL,
     trustAnchors           [5] TrustAnchors OPTIONAL,
     keyUsages              [6] KeyUsages OPTIONAL,
     extendedKeyUsages      [7] SEQUENCE OF KeyPurposeId OPTIONAL }


   CertChecks ::= SEQUENCE SIZE (1..MAX) OF OBJECT IDENTIFIER

   WantBack ::= SEQUENCE SIZE (1..MAX) OF OBJECT IDENTIFIER


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   ValidationPolRef ::= CHOICE {
     valPolRefByOID         OBJECT IDENTIFIER,
     valPolRefByURI         IA5String }

   ValidationAlg ::= SEQUENCE {
     valAlgId               OBJECT IDENTIFIER,
     parameters             ANY DEFINED BY valAlgId OPTIONAL }

   NameValidationAlgParms ::= SEQUENCE {
     nameCompAlgId          OBJECT IDENTIFIER,
     validationNames        GeneralNames }

   TrustAnchors ::= SEQUENCE SIZE (1..MAX) OF PKCReference

   KeyUsages ::= CHOICE {
     anyKeyUsage         NULL,
     requiredKeyUsages   SEQUENCE SIZE (1..MAX) OF KeyUsage }

   KeyAgreePublicKey ::= SEQUENCE {
     algorithm           AlgorithmIdentifier,
     publicKey           BIT STRING }

   ResponseFlags ::= SEQUENCE {
     fullRequestInResponse      [0] BOOLEAN DEFAULT FALSE,
     responseValidationPolByRef [1] BOOLEAN DEFAULT TRUE,
     protectResponse            [2] BOOLEAN DEFAULT TRUE,
     cachedResponse             [3] BOOLEAN DEFAULT TRUE }

   CertBundle ::= SEQUENCE SIZE (1..MAX) OF Certificate

   RevocationInfos ::= SEQUENCE SIZE (1..MAX) OF RevocationInfo

   RevocationInfo ::= CHOICE {
     crl                    [0] CertificateList,
     delta-crl              [1] CertificateList,
     ocsp                   [2] OCSPResponse,
     other                  [3] OtherRevInfo }

   OtherRevInfo ::= SEQUENCE {
     riType                     OBJECT IDENTIFIER,
     riValue                    ANY DEFINED BY riType }


   -- SCVP Certificate Validation Response

   id-ct-scvp-certValResponse OBJECT IDENTIFIER ::= { id-ct 11 }

   CVResponse ::= SEQUENCE {


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     cvResponseVersion          INTEGER,
     policyID                   INTEGER,
     producedAt                 GeneralizedTime,
     responseStatus             ResponseStatus,
     respValidationPolicy   [0] RespValidationPolicy OPTIONAL,
     requestRef             [1] RequestReference OPTIONAL,
     requestorRef           [2] SEQUENCE SIZE (1..MAX) OF OCTET STRING
                                  OPTIONAL,
     requestorName          [3] GeneralNames OPTIONAL,
     replyObjects           [4] ReplyObjects OPTIONAL,
     respNonce              [5] OCTET STRING OPTIONAL,
     serverContextInfo      [6] OCTET STRING OPTIONAL,
     cvResponseExtensions   [7] Extensions OPTIONAL }

   ResponseStatus ::= SEQUENCE {
       statusCode               CVStatusCode DEFAULT okay,
       errorMessage             UTF8String OPTIONAL }

   CVStatusCode ::= ENUMERATED {
     okay                               (0),
     skipUnrecognizedItems              (1),
     tooBusy                           (10),
     invalidREquest                    (11),
     internalError                     (12),
     badStructure                      (20),
     unsupportedVersion                (21),
     abortUnrecognizedItems            (22),
     unrecognizedSigKey                (23),
     badSignatureOrMAC                 (24),
     unableToDecode                    (25),
     notAuthorized                     (26),
     unsupportedChecks                 (27),
     unsupportedWantBacks              (28),
     unsupportedSignatureOrMAC         (29),
     invalidSignatureOrMAC             (30),
     relayingLoop                      (40),
     unrecognizedValPol                (50),
     unrecognizedValAlg                (51),
     fullRequestInResponseUnsupported  (52),
     fullPolResponseUnsupported        (53),
     inhibitPolicyMappingUnsupported   (54),
     requireExplicitPolicyUnsupported  (55),
     inhibitAnyPolicyUnsupported       (56),
     validityTimeUnsupported           (57),
     unrecognizedCritQueryExt          (63),
     unrecognizedCriticalRequestExt    (64) }

   RespValidationPolicy ::= SEQUENCE {
     validationPolicy       ValidationPolicy,


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     validationPolicyAttr   SEQUENCE SIZE (1..MAX) OF Attribute
                              OPTIONAL }

   RequestReference ::= CHOICE {
     requestHash        [0] HashValue, -- hash of CVRequest
     fullRequest        [1] CVRequest }

   HashValue ::= SEQUENCE {
     algorithm              AlgorithmIdentifier DEFAULT { sha-1 },
     value                  OCTET STRING }

   sha-1 OBJECT IDENTIFIER ::= { iso(1) identified-organization(3)
             oiw(14) secsig(3) algorithm(2) 26 }

   ReplyObjects ::= SEQUENCE SIZE (1..MAX) OF CertReply

   CertReply ::= SEQUENCE {
     cert                       CertReference,
     replyStatus                ReplyStatus DEFAULT success,
     replyValTime               GeneralizedTime,
     replyChecks                ReplyChecks,
     replyWantBacks             ReplyWantBacks,
     validationErrors       [0] SEQUENCE SIZE (1..MAX) OF
                                  OBJECT IDENTIFIER OPTIONAL,
     nextUpdate             [1] GeneralizedTime OPTIONAL,
     certReplyExtensions    [2] Extensions OPTIONAL }

   ReplyStatus ::= ENUMERATED {
     success                    (0),
     malformedPKC               (1),
     malformedAC                (2),
     unavailableValidityTime    (3),
     referenceCertHashFail      (4),
     certPathConstructFail      (5),
     certPathNotValid           (6),
     certPathNotValidNow        (7),
     wantBackUnsatisfied        (8) }

   ReplyChecks ::= SEQUENCE OF ReplyCheck

   ReplyCheck ::= SEQUENCE {
     check                      OBJECT IDENTIFIER,
     status                     INTEGER DEFAULT 0 }

   ReplyWantBacks ::= SEQUENCE OF ReplyWantBack

   ReplyWantBack::= SEQUENCE {
     wb                         OBJECT IDENTIFIER,
     value                      OCTET STRING }


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   CertBundles ::= SEQUENCE SIZE (1..MAX) OF CertBundle

   -- SCVP Validation Policies Request

   id-ct-scvp-valPolRequest     OBJECT IDENTIFIER ::= { id-ct 12 }

   ValPolRequest ::= SEQUENCE {
     vpRequestVersion           INTEGER DEFAULT 1,
     requestNonce               OCTET STRING }

   -- SCVP Validation Policies Response

   id-ct-scvp-valPolResponse OBJECT IDENTIFIER ::= { id-ct 13 }

   ValPolResponse ::= SEQUENCE {
     vpResponseVersion                INTEGER,
     maxCVResponseVersion             INTEGER,
     maxVPResponseVersion             INTEGER,
     defaultPolicyID                  INTEGER,
     thisUpdate                       GeneralizedTime,
     nextUpdate                       GeneralizedTime OPTIONAL,
     validationPolices                SEQUENCE OF ValidationPolRef,
     validationAlgs                   SEQUENCE OF OBJECT IDENTIFIER,
     authPolicies                     SEQUENCE OF AuthPolicy,
     responseTypes                    ResponseTypes,
     defaultPolicyValues              RespValidationPolicy,
     revocationInfoTypes              RevocationInfoTypes,
     serverPublicKeys                 SEQUENCE OF KeyAgreePublicKey
                                        OPTIONAL,
     clockSkew                        INTEGER DEFAULT 10,
     requestNonce                     OCTET STRING OPTIONAL }

   ResponseTypes  ::= ENUMERATED {
     cached-only                (0),
     non-cached-only            (1),
     cached-and-non-cached      (2) }

   RevocationInfoTypes ::= BIT STRING {
     fullCRLs                   (0),
     deltaCRLs                  (1),
     indirectCRLs               (2),
     oCSPResponses              (3) }

   AuthPolicy ::= CHOICE {
     authPolRefByOID       OBJECT IDENTIFIER,
     authPolRefByURI       IA5String }

   -- SCVP Check Identifiers


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   id-stc OBJECT IDENTIFIER ::= { iso(1) identified-organization(3)
             dod(6) internet(1) security(5) mechanisms(5) pkix(7) 17 }

   id-stc-build-pkc-path        OBJECT IDENTIFIER ::= { id-stc 1 }
   id-stc-build-valid-pkc-path  OBJECT IDENTIFIER ::= { id-stc 2 }
   id-stc-build-status-checked-pkc-path
                                OBJECT IDENTIFIER ::= { id-stc 3 }
   id-stc-build-aa-path         OBJECT IDENTIFIER ::= { id-stc 4 }
   id-stc-build-valid-aa-path   OBJECT IDENTIFIER ::= { id-stc 5 }
   id-stc-build-status-checked-aa-path
                                OBJECT IDENTIFIER ::= { id-stc 6 }
   id-stc-status-check-ac-and-build-status-checked-aa-path
                                OBJECT IDENTIFIER ::= { id-stc 7 }

   -- SCVP WantBack Identifiers

   id-swb OBJECT IDENTIFIER ::= { iso(1) identified-organization(3)
             dod(6) internet(1) security(5) mechanisms(5) pkix(7) 18 }

   id-swb-pkc-best-cert-path       OBJECT IDENTIFIER ::= { id-swb 1 }
   id-swb-pkc-revocation-info      OBJECT IDENTIFIER ::= { id-swb 2 }
   id-swb-pkc-cert-status          OBJECT IDENTIFIER ::= { id-swb 3 }
   id-swb-pkc-public-key-info      OBJECT IDENTIFIER ::= { id-swb 4 }
   id-swb-aa-cert-path             OBJECT IDENTIFIER ::= { id-swb 5 }
   id-swb-aa-revocation-info       OBJECT IDENTIFIER ::= { id-swb 6 }
   id-swb-ac-revocation-info       OBJECT IDENTIFIER ::= { id-swb 7 }
   id-swb-ac-cert-status           OBJECT IDENTIFIER ::= { id-swb 8 }
   id-swb-pkc-cert                 OBJECT IDENTIFIER ::= { id-swb 10}
   id-swb-ac-cert                  OBJECT IDENTIFIER ::= { id-swb 11}
   id-swb-pkc-all-cert-paths       OBJECT IDENTIFIER ::= { id-swb 12}

   -- SCVP Validation Policy and Algorithm Identifiers

   id-svp OBJECT IDENTIFIER ::= { iso(1) identified-organization(3)
             dod(6) internet(1) security(5) mechanisms(5) pkix(7) 19 }

   id-svp-defaultValPolicy OBJECT IDENTIFIER ::= { id-svp 1 }

   -- SCVP Basic Validation Algorithm Identifier

   id-svp-basicValAlg OBJECT IDENTIFIER ::= { id-svp 3 }

   -- SCVP Basic Validation Algorithm Errors

   id-bvae OBJECT IDENTIFIER ::= id-svp-basicValAlg

   id-bvae-expired              OBJECT IDENTIFIER ::= { id-bvae 1 }
   id-bvae-not-yet-valid        OBJECT IDENTIFIER ::= { id-bvae 2 }


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   id-bvae-wrong-anchor         OBJECT IDENTIFIER ::= { id-bvae 3 }
   id-bvae-invalid-key-usage    OBJECT IDENTIFIER ::= { id-bvae 10 }
   id-bvae-invalid-purpose      OBJECT IDENTIFIER ::= { id-bvae 11 }
   id-bvae-revoked              OBJECT IDENTIFIER ::= { id-bvae 16 }

   -- SCVP Name Validation Algorithm Identifier

   id-svp-nameValAlg OBJECT IDENTIFIER ::= { id-svp 2 }

   -- SCVP Name Validation Algorithm DN comparison algorithm

   id-nva-dnCompAlg   OBJECT IDENTIFIER ::= { id-svp 4 }

   -- SCVP Name Validation Algorithm Errors

   id-nvae OBJECT IDENTIFIER ::= id-svp-nameValAlg

   id-nvae-name-mismatch          OBJECT IDENTIFIER ::= { id-nvae 1 }
   id-nvae-no-name                OBJECT IDENTIFIER ::= { id-nvae 2 }
   id-nvae-unknown-alg            OBJECT IDENTIFIER ::= { id-nvae 3 }
   id-nvae-bad-name               OBJECT IDENTIFIER ::= { id-nvae 4 }
   id-nvae-bad-name-type          OBJECT IDENTIFIER ::= { id-nvae 5 }
   id-nvae-mixed-names            OBJECT IDENTIFIER ::= { id-nvae 6 }

   -- SCVP Extended Key Usage Key Purpose Identifiers

   id-kp OBJECT IDENTIFIER ::= { iso(1) identified-organization(3)
             dod(6) internet(1) security(5) mechanisms(5) pkix(7) 3 }

   id-kp-scvpServer               OBJECT IDENTIFIER ::= { id-kp 15 }

   id-kp-scvpClient               OBJECT IDENTIFIER ::= { id-kp 16 }


   END

9  Security Considerations

   For security considerations specific to the Cryptographic Message
   Syntax message formats, see [CMS].  For security considerations
   specific to the process of PKI certificate path validation, see
   [PKIX-1].

   A client that trusts a server's response for validation of a
   certificate inherently trusts that server as much as it would trust
   its own validation software.  This means that if an attacker
   compromises a trusted SCVP server, the attacker can change the
   validation processing for every client that relies on that server.



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   Thus, an SCVP server must be protected at least as well as the trust
   anchors that the SCVP server trusts.

   Clients MUST verify that the response matches their original request.
   Clients need to ensure that the server has performed the appropriate
   checks for the correct certificates under the requested validation
   policy for the specified validation time, and that the response
   includes the requested want backs and meets the client's freshness
   requirements.

   When the SCVP response is used to determine the validity of a
   certificate, the client MUST validate the digital signature or MAC on
   the response to ensure that the expected SCVP server generated it.
   If the client does not check the digital signature or MAC on the
   response, a man-in-the-middle attack could fool the client into
   believing modified responses from the server, or responses to
   questions the client did not ask.

   If the client does not include a requestNonce item, or if the client
   does not check that the requestNonce in the response matches the
   value in the request, an attacker can replay previous responses from
   the SCVP server.

   If the server does not require some sort of authorization (such as
   signed requests), an attacker can get the server to respond to
   arbitrary requests.  Such responses may give the attacker information
   about weaknesses in the server or about the timeliness of the
   server's checking.  This information may be valuable for a future
   attack.

   If the server uses the serverContextInfo item to indicate some server
   state associated with a requestor, implementers must take appropriate
   measures against denial of service attacks where an attacker sends in
   a lot of requests at one time to force the server to keep a lot of
   state information.

   SCVP does not include any confidentiality mechanisms.  If
   confidentiality is needed, it can be achieved with a lower-layer
   security protocol.

   The only validation policy references that are truly persistent are
   OIDs.  If the ownership of the policy could in any way be an issue,
   then OIDs should be the reference type of choice.  However in many
   situations, even though URIs are technically non-persistent, the use
   of a URI is much more readily understood because of its widespread
   use elsewhere, and with many organizations they may be viewed as
   persistent for practical purposes. Therefore, in these situations use
   of a URI may be more attractive.



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   If an SCVP client is not operating on a network with good physical
   protection, it must ensure that there is integrity over the SCVP
   request-response pair.  The client can ensure integrity by using a
   protected transport such as TLS.  It can ensure integrity by using
   MACs or digital signatures to individually protect the request and
   response messages.

   If an SCVP client populates the userPolicySet in a request with a
   value other than anyPolicy, but does not set the
   requireExplicitPolicy flag, the server may return an affirmative
   answer for paths that do not satisfy any of the specified policies.
   In general, when a client populates the userPolicySet in a request
   with a value other than anyPolicy, the requireExplicitPolicy flag
   should also be set.  This guarantees that all valid paths satisfy at
   least one of the requested policies.

   In SCVP, historical validation of a certificate returns the known
   status of the certificate at the time specified in validationTime.
   This may be used to demonstrate due diligence, but does not
   necessarily provide the most complete information.  A certificate may
   have been revoked after the time specified in validationTime, but the
   revocation notice may specify an invalidity date that precedes the
   validationTime.  The SCVP server would provide an affirmative
   response even though the most current information available indicates
   the certificate should not be trusted at that time.  SCVP clients may
   wish to specify a validationTime later than the actual time of
   interest to mitigate this risk.

10  References

   Normative and informative references are provided.

10.1  Normative References

  [STDWORDS] Bradner, S., "Key words for use in RFCs to Indicate
             Requirement Levels", BCP 14, RFC 2119, March 1997.
             http://www.ietf.org/rfc/rfc2119.txt

  [CMS] Housley, R., "Cryptographic Message Syntax", RFC 2630,June 1999.
             http://www.ietf.org/rfc/rfc2630.txt

  [OCSP] Myers, M., Ankney, R., Malpani, A., Galperin, S. and C. Adams,
             "X.509 Internet Public Key Infrastructure - Online
             Certificate Status Protocol - OCSP", RFC 2560, June 1999.
             http://www.ietf.org/rfc/rfc2560.txt

  [PKIX-1] Housley, R., Polk, T, Ford, W.  and Solo, D., "Internet
             X.509 Public Key Infrastructure Certificate and
             Certificate Revocation List (CRL) Profile", RFC 3280,


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             April 2002.
             http://www.ietf.org/rfc/rfc3280.txt

  [PKIX-AC] Farrell, S., and R.  Housley, "An Internet Attribute
             Certificate Profile for Authorization", RFC 3281, April
             2002.
             http://www.ietf.org/rfc/rfc3281.txt

  [PKIX-ALG] Polk, W., Housley, R.  and L.  Bassham, "Algorithms and
             Identifiers for the Internet X.509 Public Key
             Infrastructure Certificate and Certificate Revocation List
             (CRL) Profile", RFC 3279, April 2002.
             http://www.ietf.org/rfc/rfc3280.txt

  [SHA-1]  National Institute of Standards and Technology, "Secure Hash
             Standard", NIST FIPS Pub 180-1, April 1995.

  [UTF8] Yergeau, F., "UTF-8, a transformation format of ISO 10646", RFC
             2279, January 1998.
             http://www.ietf.org/rfc/rfc2279.txt

  [ESS] Hoffman, P., "Enhanced Security Services for S/MIME", RFC 2634,
             June 1999.
             http://www.ietf.org/rfc/rfc2634.txt

  [HTTP-TLS] Rescorla, E., "HTTP Over TLS", RFC2818, May 2000.
             http://www.ietf.org/rfc/rfc2818.txt

  [SMIME-CERT] B. Ramsdell, Ed. "Secure/Multipurpose Internet Mail
             Extensions (S/MIME) Version 3.1 Certificate Handling"
             RFC3850, July 2004.
             http://www.ietf.org/rfc/rfc3850.txt

  [IKE] D. Harkins, D. Carrel. "The Internet Key Exchange"
             RFC2409, November 1998
             http://www.ietf.org/rfc/rfc2409.txt

10.2  Informative References

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

  [IKE-GROUPS] T. Kivinen, M. Kojo "More Modular Exponential (MODP)
             Diffie-Hellman groups for Internet Key Exchange (IKE)
             RFC3526, May 2003
             http://www.ietf.org/rfc/rfc3526.txt




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  [RQMTS]  Pinkas, D., and R.  Housley, "Delegated Path Validation and
             Delegated Path Discovery Protocol Requirements", RFC 3379,
             September 2002.

11  Acknowledgments

   The lively debate in the PKIX Working Group has made a significant
   impact on this protocol.  Special thanks to the following for their
   contributions to this standard and diligence in greatly improving
   this document.

    Paul Hoffman
    Denis Pinkas
    Phillip Hallam-Baker
    Mike Myers
    Frank Balluffi
    Ameya Talwalkar
    John Thielens
    Peter Sylvester
    Yuriy Dzambasow
    Sean P. Turner
    Wen-Cheng Wang
    Francis Dupont
    Dave Engberg
    Faisal Maqsood


   Thanks also to working group chair Steve Kent for his support and
   help.

Appendix A -- MIME Registrations

   Four MIME type registrations are provided in this appendix.

 A.1  application/cv-request

   To: ietf-types@iana.org
   Subject: Registration of MIME media type application/cv-request

   MIME media type name: application

   MIME subtype name: cv-request

   Required parameters: format

   Optional parameters: None

   Encoding considerations: binary



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   Security considerations: Carries a request for information.  This
   request may optionally be cryptographically protected.

   Interoperability considerations: None

   Published specification: IETF PKIX Working Group Draft on Simple
   Certificate Validation Protocol (SCVP)

   Applications that use this media type: SCVP clients

   Additional information:
       Magic number(s): None
       File extension(s): .SCQ
       Macintosh File Type Code(s): none

   Person & email address to contact for further information:
   Ambarish Malpani <ambarish@malpani.biz>

   Intended usage: COMMON

   Author/Change controller:
   Ambarish Malpani <ambarish@malpani.biz>

 A.2  application/cv-response

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

   MIME media type name: application

   MIME subtype name: cv-response

   Required parameters: format

   Optional parameters: None

   Encoding considerations: binary

   Security considerations: The client may require that this response be
   cryptographically protected, or may choose to use secure transport
   mechanism.  DPD responses may be unprotected, but the client
   validates the information provided in the request.

   Interoperability considerations: None

   Published specification: IETF PKIX Working Group Draft on Simple
   Certificate Validation Protocol (SCVP)

   Applications that use this media type: SCVP servers


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   Additional information:

       Magic number(s): None
       File extension(s): .SCS
       Macintosh File Type Code(s): none

   Person & email address to contact for further information:
   Ambarish Malpani <ambarish@malpani.biz>

   Intended usage: COMMON

   Author/Change controller: Ambarish Malpani <ambarish@malpani.biz>

 A.3  application/vp-request

   To: ietf-types@iana.org
   Subject: Registration of MIME media type application/vp-request

   MIME media type name: application

   MIME subtype name: vp-request

   Required parameters: format

   Optional parameters: None

   Encoding considerations: binary

   Security considerations: Carries a request for information.

   Interoperability considerations: None

   Published specification: IETF PKIX Working Group Draft on Simple
   Certificate Validation Protocol (SCVP)

   Applications that use this media type: SCVP clients

   Additional information:

       Magic number(s): None
       File extension(s): .SPQ
       Macintosh File Type Code(s): none

   Person & email address to contact for further information:
   Ambarish Malpani <ambarish@malpani.biz>

   Intended usage: COMMON



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   Author/Change controller: Ambarish Malpani <ambarish@malpani.biz>

 A.4  application/vp-response

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

   MIME media type name: application

   MIME subtype name: vp-response

   Required parameters: format

   Optional parameters: None

   Encoding considerations: Binary

   Security considerations: None

   Interoperability considerations: None

   Published specification: IETF PKIX Working Group Draft on Simple
   Certificate Validation Protocol (SCVP)

   Applications that use this media type: SCVP servers

   Additional information:
       Magic number(s): None
       File extension(s): .SPP
       Macintosh File Type Code(s): none

   Person & email address to contact for further information:
   Ambarish Malpani <ambarish@malpani.biz>

   Intended usage: COMMON

   Author/Change controller:
   Ambarish Malpani <ambarish@malpani.biz>

Appendix B  -- SCVP over HTTP

   This appendix describes the formatting conventions for the SCVP
   request and response when carried by HTTP.

B.1  SCVP Request

   HTTP based SCVP requests can use the POST method to submit their
   requests.  Where privacy is a requirement, SCVP transactions



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   exchanged using HTTP MAY be protected using either TLS/SSL or some
   other lower layer protocol.

   An SCVP request using the POST method is constructed as follows:

       The Content-Type header MUST have the value "application/cv-
       request".

       The Content-Length header MUST be present and have the exact
       length of the request.

       The body of the message is the binary value of the BER encoding
       of the CVRequest, wrapped in a CMS body as described in
       Section 3.  Other HTTP headers MAY be present and MAY be
       ignored if not understood by the requestor.

   Sample Content-Type headers are:
          Content-Type: application/cv- request

B.2  SCVP Response

   An HTTP-based SCVP response is composed of the appropriate HTTP
   headers, followed by the binary value of the BER encoding of the
   CVResponse, wrapped in a CMS body as described in Section 4.

   The Content-Type header MUST have the value "application/cv-
   response".

   The Content-Length header MUST be present and specify the length of
   the response.

   Other HTTP headers MAY be present and MAY be ignored if not
   understood by the requestor.

B.3  SCVP Policy Request

   HTTP based SCVP policy requests can use the POST method to submit
   their requests.  Where privacy is a requirement, SCVP transactions
   exchanged using HTTP MAY be protected using either TLS/SSL or some
   other lower layer protocol.

   An SCVP request using the POST method is constructed as follows:

       The Content-Type header MUST have the value "application/vp-
       request".

       The Content-Length header MUST be present and have the exact
       length of the request.



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       The body of the message is the binary value of the BER encoding
       of the ValPolRequest, wrapped in a CMS body as described in
       Section 5.  Other HTTP headers MAY be present and
       MAY be ignored if not understood by the requestor.

   Sample Content-Type headers are:
          Content-Type: application/vp-request

B.4  SCVP Policy Response

   An HTTP-based SCVP policy response is composed of the appropriate
   HTTP headers, followed by the binary value of the BER encoding of the
   ValPolResponse, wrapped in a CMS body as described in Section 6.

   The Content-Type header MUST have the value "application/vp-
   response".

   The Content-Length header MUST be present and specify the length of
   the response.

   Other HTTP headers MAY be present and MAY be ignored if not
   understood by the requestor.


Appendix C  -- Author Contact Information

   Trevor Freeman
   Microsoft Corporation,
   One Microsoft way.
   Redmond, WA 98052
   USA.
   trevorf@microsoft.com

   Russell Housley
   Vigil Security, LLC
   918 Spring Knoll Drive
   Herndon, VA 20170
   USA
   housley@Vigilsec.com

   Ambarish Malpani
   Malpani Consulting Services
   ambarish@malpani.biz

   David Cooper
   National Institute of Standards and Technology
   100 Bureau Drive, Mail Stop 8930
   Gaithersburg, MD 20899-8930
   david.cooper@nist.gov


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   Tim Polk
   National Institute of Standards and Technology
   100 Bureau Drive, Mail Stop 8930
   Gaithersburg, MD 20899-8930
   tim.polk@nist.gov


   Full Copyright Statement

   "Copyright (C) The Internet Society (2005).  This document is subject
   to the rights, licenses and restrictions contained in BCP 78, and
   except as set forth therein, the authors retain all their rights."

   "This document and the information contained herein are provided on
   An "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE
   REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE
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   This document and translations of it may be copied and furnished to
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   kind, provided that the above copyright notice and this paragraph
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