Internet Draft                   Adams, Sylvester, Zolotarev, Zuccherato
PKIX Working Group        October 15, 1999        expires April 15, 2000


                Internet X.509 Public Key Infrastructure
          Data Validation and Certification Server Protocols
                      <draft-ietf-pkix-dcs-03.txt>


Status of this Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups. Note that other
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   Internet-Drafts are draft documents valid for a maximum of six months
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   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt

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

Abstract

   This document describes a general data validation and certification
   service and the protocols to be used when communicating with it.  The
   Data Validation and Certification Server is a Trusted Third Party
   (TTP) that can be used as one component in building reliable non-
   repudiation services (see [ISONR]).

   Useful Data Validation and Certification Server responsibilities in a
   PKI are to validate signed documents and to assert the validity of
   public key certificates at a given time.

   We give examples of how to use the Data Certification Server to
   extend the lifetime of a signature beyond key expiry or revocation
   and to query the Data Certification Server regarding the status of a
   public key certificate.

   <draft>Note: The initial drafts of this protocol used the
   abbreviation DCS instead of DVCS.</draft>



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   The key words "MUST", "MUST NOT", "REQUIRED", "SHOULD", "SHOULD NOT",
   "RECOMMENDED", "MAY", and "OPTIONAL" in this document (in uppercase,
   as shown) are to be interpreted as described in [RFC2119].

   <draft>A complete list of ASN.1 will be added in an appendix.</draft>

1. Introduction

   A Data Validation  Server (DVCS) is a Trusted Third Party (TTP)
   providing data validation  services, asserting correctness of
   digitally signed documents, validity of public key certificates, and
   possession of data.

   As a result of the assertion, a DVCS generates a Data Validation
   Certificate (DVC) The data validation certificate can be used for
   constructing evidence of non-repudiation, relating to the validity
   and correctness of an entity's claim to possess data, the validity
   and revocation status of an entity's public key certificate and the
   validity and correctness of a digitally signed document.

   DVCS services do not replace the usage of CRLs and OCSP for public
   key certificate revocation checking in large open environments, due
   to concerns about the scalability of this protocol.  It should be
   rather used to support non-repudiation or to supplement more
   traditional services concerning paperless document environments.  The
   presence of a data validation certificate supports non-repudiation in
   two ways. It provides evidence that a digitally signed document or
   public key certificate was valid at the time indicated in the dvc.
   The dvc for a public key certificate can be used even after the
   public key certificate expires and its revocation information is no
   longer or not easily available; it is assumed that verifying the
   validity of a dvc is easier, since the population is smaller.  The
   production of a data validation certificate in response to a signed
   request for validation  of a signed document or public key
   certificate also provides evidence that due diligence was performed
   by the requester in validating a digital signature or public key
   certificate.

2. DVCS Services

   The current specification defines 4 types of validation and
   certification services:

   - Certification of Possession of Data (cpd),
   - Certification of Claim of Possession of Data (ccpd),
   - Validation of Digitally Signed Document (vsd), and
   - Validation of Public Key Certificates (vpkc).




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   A DVCS is REQUIRED to support at least a subset of these services.

   On completion of each service, the DVCS produces a data validation
   certificate - a signed document containing the validation results and
   trustworthy time information.

2.1 Certification Possession of Data

   The Certification of Possession of Data service provides evidence
   that the requester possessed data at the time indicated and that the
   actual data where presented to the Data Validation Server.

2.2 Certification of Claim of possession of Data

   The Certification Claim of Possession service is similar to the
   previous one, except that the requester does not present the data
   itself but a message digest. This service is similar to time stamping
   services as described in [TSP].

2.3 Validation of Digitally Signed Documents

   The Validation of Digitally Signed Document service is used when
   validity of a signed document is to be asserted.

   The DVCS verifies all signatures attached to the signed document
   using all appropriate status information and public key certificates.
   The DVCS verifies the mathematical correctness of all signatures
   attached to the document and also checks whether the signing entities
   can be trusted, for example by validating the full certification path
   from the signing entities to a trusted point (e.g., the DVCS's CA, or
   the root CA in a hierarchy).

   The DVCS may be able to rely on relevant CRLs or may need to
   supplement this with access to more current status information from
   the CAs for example by accessing to an OCSP service, a trusted
   directory service, or other DVCS services.

   The DVCS will perform verification of all signatures attached to the
   signed document. A failure of the verification of one of the
   signatures does not necessarily result in the failure of the entire
   certification, and vice versa, a global failure may occur if the
   document has an insufficient number of signatures.

2.4 Validation of Public Key Certificates

   The Validation of Public Key Certificates service is used to verify
   and assert the validity (according to [RFC2459]) of one or more
   public key certificates at the specified time.



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   When verifying a public key certificate, the DVCS verifies that the
   certificate included in the request is a valid certificate and
   determines its revocation status at a specified time.  DVS checks the
   full certification path from the certificate's issuer to a trusted
   point.  Again the DVCS MAY be able to rely on external information
   (CRL, OCSP, DVCS).

3. Data Certification Server usage and scenarii.

   It is outside the scope of this document to completely describe
   different operational scenarii, or usages for DVCS.

   See Appendix B and C for a set of some basic examples and use cases.

   The Validate Signed Document service can be used to support non-
   repudiation services, to allow use of the signed document beyond
   public key certificate revocation or expiry, or simply to delegate
   signature validation to a trusted central (company wide) service.

   The Validate Public Key Certificate service can be used when timely
   information regarding a certificate's revocation status is required
   (e.g. high value funds transfer or the compromise of a highly
   sensitive key) or when evidence supporting non-repudiation is
   required.

   A data validation certificate may be used to simplify the validation
   of a signature beyond the expiry or subsequent revocation of the
   signing certificate: a Data validation certificate used as an
   authenticated attribute in a signature includes an additional
   assertion about the usability of a certificate that was used for
   signing. In order to validate such a signature it may be sufficient
   to only validate the data validation certificate.

   A data validation certificate for a key exchange certificate may
   contain additional certificates to be used as a simple method to
   indicate to a client to encrypt a session key for additional
   authorised entities (e.g., to support company wide recovery).

   The Certification of Claim of Possession of Dataservice is equivalent
   to the services described in [TSP].

   The Certification of Possession of Data service can be used to assert
   legal deposit of documents, or to implement archival services as a
   trusted third party service.

   The Data Validation and Certification Server Protocols can be used in
   different service contexts. Examples include company-wide centralised
   services (verification of signatures, certification of company



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   certificates), service to cooperate in a multi-organisation
   community, or general third party services for time stamping or data
   archival.

   An important application of DVCS is an enterprise environment where
   all security decision are based on company wide rules.  A company
   wide DVCS service can be used to delegate all technical decisions
   (e.g., path validation, trust configuration) to a centrally managed
   service.

   In all cases, the trust that PKI entities have in the Data Validation
   and Certification Server is transferred to the contents of the Data
   Validation Certificate  (just as trust in a CA is transferred to the
   public key certificates that it issues).

   A DVCS service may be combined with or use archiving and logging
   systems, in order to serve as a strong building block in non-
   repudiation services. In this sense it can be regarded as an Evidence
   Recording Authority [ISO-NR].

4. Functional Requirements for DVCS

   The DVCS MUST

   1. provide a signed receipt in the form of a data validation
      certificate to the requester, as defined by policy. The DVCS
      service definition and the policy define how much information that
      has been used by the DVCS service to generate the response will be
      included in a data validation certificate, e.g., public key
      certificates, CRLs, and responses from other OCSP servers, TSA and
      DVCS.

   2. indicate in the data validation certificate whether or not the
      signed document, the public key certificate(s), or the data were
      validated, and, if not, the reason why the verification failed.

   3. include a strictly monotonously increasing serial number in each
      data validation certificate.

   4. include a time of day value or a time stamp token into each data
      validation certificate.

   5. sign each data certification token using a key generated
      exclusively for this purpose, have this property of the key
      indicated in the corresponding public key certificate, and include
      a reference to this certificate as a signed attributes in the
      signature.




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   6. check the validity of its own signing key and certificate before
      delivering data validation certificates and MUST not deliver data
      validation certificate in case of failure.

   A DVCS SHOULD include within each data validation certificate a
   policy identifier to determine the trust and validation policy used
   for DVC's signature.

   The [TSA] defines additional requirements: If the DVCS protocol is
   used as a replacement for the services defined in [TSA], any
   additional requirement of [TSA] apply to that service.

5. Data Certification Server Transactions

   A DVCS transaction begins with a client preparing a Data
   Certification Request.  The request always contains data for which
   validity, correctness or possession is to be certified.  It may be
   required that a requestor signs a request, to prove that it came from
   a valid DVCS service's subscriber.  The DVCS client chooses an
   appropriate transport mechanism to convey the requests to a DVCS. It
   may be necessary to choose a transport mechanism providing
   confidentiality and, in particular, allowing authentication of the
   DVCS by the requestor, e.g. TLS or encryption.

   If the request is valid, the DVCS performs all necessary
   verifications steps, and generates a Data Validation Certificate
   (DVC), and sends a response message containing the DVC back to the
   requestor.  The Data Validation Certificate is formed as a signed
   document (CMS SignedData).

   If the request was invalid, the DVCS generates a response message
   containing an appropriate error notification.

   Upon receiving the response, the requesting entity SHOULD verify its
   validity, i.e. it contains the correct time, the correct name for the
   DVCS, the correct request information and message imprint, a valid
   signature, and satisfactory status, service and policy fields.

   When verifying validity of a DVC, it is up to the requestor's
   application to check whether a DVCS's signing certificate was valid.
   Depending on the usage environment, different methods (online or out
   of band, CRLs, DVCS, OCSP...) may have to be used.

   After all checks passed, the data validation certificate can be used
   to authenticate the correctness or possession of the corresponding
   data.

6. Identification of the DVCS



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   A DVCS tags several element using OIDs. In order to provide a common
   root the following OID s defined

   id-dvcs OBJECT IDENTIFIER ::= { id-pkix [TBS]}

   The DVCS MUST sign all data certification messages with a key
   reserved explicitly for that purpose.  The corresponding certificate
   MUST contain the extended key usage field extension as defined in
   [RFC2459] Section 4.2.1.14 with KeyPurposeID having value id-dvcs-kp.
   This extension MUST be marked as critical. The Data Validation
   Certificate MUST contain an ESSCertID authenticated attribute for the
   certificate used by the DVCS for signing.

   id-dvcs-kp   OBJECT IDENTIFIER ::= { id-dvcs 1 }

   Consistent key usage bits:  digitalSignature, nonRepudiation

   A DVCS's certificate MAY contain an Authority Information Access
   extension [RFC2459] in order to convey the method of contacting the
   DVCS.  The accessMethod field in this extension MUST contain the OID
   id-dvcs-ad:

   id-dvcs-ad    OBJECT IDENTIFIER ::= { id-dvcs 2 }

   The value of the field 'accessLocation' field defines the transport
   (e.g.  an URL) used to access the DVCS.

7. Common Data Types

   There are several common data types that occur in the request and the
   response data structures. These data types are either defined by this
   document or imported from other sources. This chapter defines and
   describes these types and lists their usages.

7.1 DigestInfo:

   This element is defind in [RFC2315]. Since the status of that
   document is informational, the definition is repeated here:

   DigestInfo ::= SEQUENCE {
       digestAlgorithm   DigestAlgorithmIdentifier,
       digest            Digest
   }

   Digest ::= OCTET STRING

   The fields of type DigestInfo have the following meanings:




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   - The field 'digestAlgorithm' identifies the message-digest algorithm
     (and any associated parameters) under which data are digested.

   - The field 'digest' is the result of the message-digesting process.

   A DigestInfo is used in two places:

   - as a data portion for the ccpd service, and

   - in all a data validation certificates to hold a digest of the data
     portion of the corresponding request or a copy of the data field
     for a ccpd service.

7.2. Nonce

   Requests and responses may include Nonce values.  A Nonce in the
   request is returned as is in the response. The DVCS may create an
   addition Nonce in the response.

   The following definition is used:

   Nonce ::= INTEGER

7.3. Time Values

   Indicators of time can be present in requests and responses.  In the
   most simple form, the time is represented as GeneralizedTime where
   fractions of seconds are allowed.

   An alternate form is a timeStampToken from a TSA, or as a DVC (or
   some other token) from another third party service.  When using third
   party tokens, it is a matter of policy whether a DVCS tries to
   interpret or validate a timeStampToken.

   DVCSTime ::= CHOICE  {
        genTime                      GeneralizedTime,
        timeStampToken               SignedData
   }

   Future versions of the protocol MAY include additional time formats.

   Time values generated by the DVCS are increasing but not necessarily
   unique using the order defined by serial numbers.

7.4. PKIStatusInfo

   This structure is defined in [RFC2510]. It is used as component of
   the 'chain' field of a TargetEtcChain structure, and as a global



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   status indicator in the DVCSResponse structure. Every occurrence of
   PKIStatusInfo is generated by the responding DVCS to reflect the
   result of some local verification.

7.5. TargetEtcChain

   A TargetEtcChain structure contains certificates and other indicators
   to describe either (in a request for a cpkc service) information to
   be validated, or the result of the verifications. The structure may
   also contain information about policies and policy mappings.

   The details about how to fill in and to interpret the structure are
   defined later for each service.

   The 'pathProcInput' field contains information about policies and
   policy mapping to be used or used during a validation.

   In a response, the 'pkistatus' and 'certstatus' choices can only
   occur in in the 'chain' sequence.  If present, they contain the
   result of a local verification of the immediately preceding element,
   or of the target value, if it is the first element in the 'chain'
   sequence. If no 'pkistatus' or 'certstatus' is present, the DVCS
   considers all elements in the 'chain' as trustworthy. Note, that
   there may be for example an OCSP response or DVC indicating an
   invalid certificate.

   TargetEtcChain ::= SEQUENCE {
        target                       CertEtcToken,
        chain                        [0] SEQUENCE SIZE (1..MAX) OF
                                        CertEtcToken OPTIONAL,
        pathProcInput                [1] PathProcInput OPTIONAL
   }

   PathProcInput ::= SEQUENCE {
        acceptablePolicySet          SEQUENCE SIZE (1..MAX) OF
                                        PolicyInformation,
        inhibitPolicyMapping         BOOLEAN DEFAULT FALSE,
        explicitPolicyReqd           BOOLEAN DEFAULT FALSE
   }

   CertEtcToken ::= CHOICE {
        certificate                  [0] Certificate ,
        oscpcertid                   [1] CertId ,
        esscertid                    [2] ESSCertId ,
        datacert                     [3] SignedData ,
        oscpresponse                 [4] OCSPResponse,
        crl                          [5] CertificateList,
        certstatus                   [6] CertStatus,



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        pkistatus                    [7] PKIStatusField ,
        extension                    Extension
   }

   Certificate, PolicyInformation and CertificateList are defined in
   [RFC2459]. ESSCertId is defined in [RFC2634]. CertiId, OCSPResponse
   and CertStatus are defined in [RFC2560]. PKIStatusField is defined in
   [RFC2510].

   The choice 'datacert' can contain a data validation certificate, or a
   timeStamp, or other assertions.

   The choices 'datacert', 'ocspresponse' and 'crl' are provided by
   services external to the responding DVCS. The choices 'certStatus'
   and 'pkistatus' reflect decisions made directly by the responding
   DVCS.

   As a replacement for certificates, certification identifiers
   (ESSCertId, CertId) MAY be used in requests and responses, if this is
   sufficient to perform the service, e.g., when the corresponding
   certificates are provided elsewhere in a request or response (as part
   of the SignedData type).

7.6. DVCSReqInfo

   A DVCSReqInfo data structure contains general information about the
   data validation and certification request. This structure occurs in a
   request, and is also included in a corresponding data validation
   certificate.

   DVCSReqInfo ::= SEQUENCE  {
           service                      ServiceType,
           requester                    [0] GeneralNames OPTIONAL,
           reqPolicy                    [1] PolicyInformation OPTIONAL,
           DVCS                         [2] GeneralNames OPTIONAL,
           dataLocator                  [3] GeneralName OPTIONAL,
           nonce                        Nonce OPTIONAL,
           reqTime                      DVCSTime OPTIONAL,
           extensions                   Extensions OPTIONAL
   }

   The ServiceType type enumerates the DVCS service type of a request.
   See chapter 2 for the description of the services.

   ServiceType ::= INTEGER  { cpd(1), vsd(2), cpkc(3), ccpd(4) }






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7.7. GeneralNames

   There are several occurences of sequences of GeneralName. For
   syntactical conveniance the following type is defined here:

   GeneralNames ::= SEQUENCE OF GeneralName

   GeneralName is imported from [RFC2459].

8. Data Validation and Certification Requests

   A data certification request is a SignedData construct of [RFC2630].
   The contenttype indicated in the eContentType of the encapContentInfo
   is of type id-ct-DVCSReqData signalling a DVCSReqData as eContent of
   the encapContentInfo (carried as an octet string).

   id-ct-DVCSReqData  OBJECT IDENTIFIER ::= { id-dvcs 3 }

   A data certification request MAY contain several SignerInfo
   structures, and countersignature attributes depending on operational
   environments. When an end user client creates the request, there is
   one or zero SignerInfo. A relaying DVCS MAY add an additional
   signature or a countersignature attribute.

   The content of a request consists of a description of the desired
   service and additional parameters, the data to be validated, and an
   optional identifier of the request.

   DVCSRequest ::= SEQUENCE  {
       reqInfo                    DVCSReqInfo,
       data                       Data,
       transactionIdentifier      GeneralName OPTIONAL
   }

   The 'DVCSRequest.reqInfo' element contains general information about
   the request. It is filled in by the requester as follows:

   - The field 'service' contains the requested service.

   - The value of the 'requester' field indicates the requesting entity.
     If the field is present, and the request is signed, it MUST match
     the identity (subjectName or subjectAltName extension) of the
     corresponding signature certificate, unless the request is signed
     by a DVCS when relaying a request to another server.

     When acting as a relay to DVCS MAY its own identity in the request
     relayed to another service provider, and it MAY remove the initial
     value.



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   - The 'reqPolicy' field SHOULD indicate the policy under which the
     validation is requested. This field MUST be checked by the DVCS to
     verify agreement with its own policy. The absence of this field
     indicates that any policy is acceptable.

   - The 'dvcs' field MAY be used to indicate a list a DVCS which are to
     be contacted to provide (additional) information or to perform
     additional operations necessary to produce the response. It is up
     to the DVCS policy whether to honor this field or not, and to
     define which choice of a general name is acceptable (e.g. an URL or
     a DN). The DVCS MAY use local information to use additional
     external services.

   - The 'dataLocator' field MAY be used to indicate where a copy of the
     'data' field of the request or supplementary information can be
     obtained. The DVCS does not use this field for its own operation,
     the exact interpretation of this field is defined by applications.

   - The 'nonce' field MAY be used to provide additional protection
     against replay or content guessing attacks.

   - The 'reqTime' field MAY be used to indicate the time for which the
     requested service should be performed. For a vsd and cpkc service,
     it specifies the time for which the validity of a signed document
     or certicates is to be asserted. For the other service, the field
     is ignored by the DVCS.  If the field is absent, the current time
     is assumed.

   - The 'extensions' field MAY be used to include additional
     information. Extensions may be marked critical or not in order to
     indicate whether the DVCS is supposed to understand them. This
     document does not define extensions.

   The DVCSRequest.data contains service-specific content, defined by
   each particular service provided by the DVCS.

   Depending on the requested service type, the field may contain a
   signed document, a list of certificates, a message digest or
   arbitrary data.

   The following type is used:

   Data ::= CHOICE {
         message           [0] OCTET STRING ,
         messageImprint    [1] DigestInfo,
         certs             [2] SEQUENCE SIZE (1..MAX) OF
                                  TargetEtcChain
   }



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   The requester fills the 'data' element as follows:

   - For a vsd service request, the requestor encapsulates a CMS
     SignedData object in the value octets of the 'message' choice.

     It is up to the requester to decide whether and how to provide any
     certificate that may be needed to verify the signature(s) in the
     signedData object. A requester MAY add certificates to the
     encapsulated signedData object or in the certificate is of the
     request.


   - For a cpkc service request the 'certs' choice is used.

     Each certificate to be verified MUST be included in a separate
     instance of TargetEtcChain.  The 'TargetEtcChain.target' field
     SHALL contain the certificate to be verified.  The
     'TargetEtcChain.chain' field, if present, MUST indicate the chain
     of trust to be used when certifying the certificate.  The
     'TargetEtcChain.pathProcInput' field, if present, indicates the
     acceptable policy set and initial settings for explicit-policy-
     indicator and inhibit-policy-mapping indicators to be used in X.509
     public key certificate path validation (see [RFC2459]).

     Only the Certificate, ESSCertId, CertId or Extension choices of the
     TargetEtcChain can be used in the request.

     The requester is responsible for providing sufficient information
     to the DVCS to identify the corresponding certificates.

   - For a ccpd service the 'messageImprint' choice is used.

     The hash algorithm indicated in the hashAlgorithm field SHOULD be a
     "strong" hash algorithm (that is, it SHOULD be one-way and
     collision resistant). It is up to the Data Certification Server to
     decide whether or not the given hash algorithm is sufficiently
     "strong" (based on the current state of knowledge in cryptanalysis
     and the current state of the art in computational resources, for
     example).

   - For a cpd service the 'message' choice is used.

     The field contains requester-specific data with any type of
     content.  The DVCS does not inspect, modify, or take any particular
     action based on the particular content of the 'message' field.

   The field 'DVCSRequest.transactionIdentifier' MAY be used in order to
   associate DVCS responses containing error messages, to requests.  For



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   example, in a mail based environment, the parameter could be a copy
   of a messageid.  Note, that the transactionIdentifier is not
   necessary for associating a request with a valid data validation
   certificate.

9. DVCS Responses

   This chapters describes the data structures that are created by a
   DVCS to indicate the results of validation and certification
   requests.

   A DVCS Response structure is generated by the DVCS as a result of
   processing of the data validation and certification request.

   A Data Validation response is a SignedData construct of [RFC2630].
   The contenttype indicated in the eContentType of the encapContentInfo
   is of type id-ct-DVCSResponseData, signalling a DVCSResponse as
   eContent of the encapContentInfo (carried as an octet string).

   id-ct-DVCSResponseData OBJECT IDENTIFIER ::= { id-dvcs 4 }

   The DVCS MUST use a key, which is specifically allocated for the
   purpose of DVCS signing, with a proper extendedKeyUsage set in a
   corresponding certificate.

   In a critical situation when a DVCS cannot produce a valid signature
   (if the DVCS's signing key is known to be compromised, for example),
   the DVCSResponse, containing the error notification, MUSTS be
   generated as a signedData with no signerInfo attached.  Receiving
   unsigned DVCSResponse MUST be treated by the clients as critical and
   fatal error, and the content of the message should not be implicitly
   trusted.

   A valid response can contain one of the following:

   1. A Data Validation Certificate (DVC), delivering the results of
      data validation operations, performed by the DVCS.

   2. An error notification. This may happen when a request fails due to
      a parsing error, requester authentication failure, or anything
      else that prevented the server from executing the request.

   The following type is used:

   DVCSResponse ::= CHOICE
   {
       dvcErrorNote        [0] DVErrorNote,
       dvCertInfo          [1] DVCertInfo



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   }

9.1. DVCS Error Notification

   A DVCS Error Notification is a CMS signedData object containing a
   DVCSResponse with a 'dvErrorNote' choice.

   DVErrorNote ::= SEQUENCE {
       DVTransStatus           PKIStatusInfo ,
       transactionIdentifier   GeneralName OPTIONAL }

   The PKIStatusInfo is defined in the [RFC2511].  For the purposes of
   communicating the DVErrorNote, the following subset of PKIFailureInfo
   values is used:

   PKIFailureInfo ::= BITSTRING  {

        badRequest       (2),
        -- transaction not permitted or supported
        badTime          (3),
        -- messageTime was not sufficiently close to the system time,
        -- as defined by local policy
        badDataFormat    (5),
        -- the data submitted has the wrong format
        wrongAuthority   (6),
        -- the DVCS indicated in the request is different from the
        -- one creating the response token
        incorrectData    (7),
        --the requester's data (i.e.  signature) is incorrect
   )

   In the DVErrorNote, the PKIStatus field of the PKIStatusInfo must be
   set to REJECTED.

   The 'statusString' field of PKIStatusInfo can be used to accommodate
   extra text, such as a reason for the failure, for example "I have
   gone out of service".  The DVCS initialises the
   'DVErrorNote.transactionIdentifier' with a copy of the
   'DVCSRequest.transactionIdentifier' field of the corresponding
   request.

   In certain circumstances, a DVCS may not be able to produce a valid
   response to a request (for example, if it is unable to compute
   signatures for a period of time).  In these situations the DVCS MAY
   create a response with an DVErrorNote but no signature.

   DVCS clients SHOULD NOT trust unsigned responses. A DVCS client MAY
   trust unsigned responses, if the communication channel provides for



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   server authentication (e.g. by services defined by TLS [RFC2246]).

9.2. Data Validation Certificate

   A Data Validation Certificate is a signedData object containing a
   DVCSResponse with a dvCertInfo choice.

   DVCertInfo::= SEQUENCE  {
            nonce               Nonce OPTIONAL,
            dvReqInfo           DVCSReqInfo,
            messageImprint      DigestInfo,
            serialNumber        Integer,
            respTime            DVCSTime,
            dvStatus            [0] PKIStatusInfo OPTIONAL,
            policy              [1] PolicyInformation OPTIONAL,
            reqSignature        [2] SignerInfos OPTIONAL,
            certs               [3] SEQUENCE OF TargetEtcChain OPTIONAL,
            extensions          [4] Extensions OPTIONAL }

   The DVCertInfo structure is returned as a result of successful
   execution of data validation service. It contains the results of the
   data validation, a reference to the original request, and other
   parameters. Please note that 'successful execution' does not
   necessarily mean that the validation itself was successful - a
   DVCertInfo may contain both the 'valid' and 'invalid' results.

   The DVCS creates a DVCertInfo as follows:

   - The 'DVCertInfo.nonce' field MAY be used to protect against replay
     attacks.

   - The 'dvReqInfo' is essentially a copy of the 'reqInfo' field of the
     corresponding request. The DVCS MAY modify the fields 'dvcs' and
     'requester' of the ReqInfo structure, e.g., if the request was
     processed by a chain of DVCS, if the request to indicate DVCS.

   - The 'DVCertInfo.messageImprint' field is computed from the 'data'
     field of the corresponding request as follows:

     For the 'certs' choice (the 'vpkc' service), the digest is computed
     over the DER encoded data value. For a 'message' choice (the 'vsd'
     and the 'vpd' services) the digest is computed over the value
     octets (not including tag and length octets) of the OCTET STRING.
     It is up to the DVCS to choose an appropriate digest algorithm.

     For a 'messageImprint' choice (the 'vcpd' service), the
     'messageImprint'
      of the DVCSRequest is copied as is.



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   - The 'DVCertInfo.serialNumber' field contains a unique identifier of
     the request.

   - The field 'respTime' indicates a time value associated to the
     response.  The value MAY be a locally generated one, or a signed
     TimeStampToken (TST) or DVC obtained from an external service.

   - The field 'DVCertInfo.dvStatus' reflects a collective result of the
     validation.

     If the field is missing, it is an equvivalent of the SUCCESS
     status.

     For a vkpc, if the status field is present and set to SUCCESS, it
     indicates that all certificates were successfully validated. If it
     is present and set to FAILED, it indicates that all or some of the
     certificates failed validation, and the specific status of the
     'certs' should be investigated, at least of the elements of the
     'certs' TargetEtcChain structures MUST have a failure status.

     If the field 'dvStatus' does not indicate success ('granted' or
     'granted with mods') the element 'failInfo' MAY indicate the reason
     for the failure.  Note that the field 'certs' MAY contain
     additional information about verification failures.

     A failure of the verification of one of the signatures does not
     necessarily result in failing to validate a signed document. For
     example, as long as a sufficient number of signature was
     successfully verified, a DVC with status `grantedWithMods` may be
     produced.  A DVC with status `granted` MUST only be produced if all
     signatures verified successfully.

     The field MUST be present, and the status must be set to WAITING,
     if no final response can be immediately available.

     In case of failure, the requester can further investigate the cause
     of the failure, by looking into the TargetEtcChain fields.
     'CertEtctoken.pkistatus' fields will indicate which item(s) has
     failed or succeeded the validation and for what reason.


   - The 'DVCertInfo.policy' field indicates the policy under which the
     DVCS operates.

   - If present, 'DVCertInfo.reqSignature' MUST be the same value as the
     signerInfos field of the corresponding request. It is a policy
     decision whether to include this field.




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   - The 'DVCertInfo.certs' field contains the results is the
     verifications made by the DVCS. For the cpkc service each element
     contains a copy of a corresponding field of the request plus the
     result of the verfications or external certification. For a vsd
     service each element contains the result of the validation of one
     signature of the signed document to be validated.

     In case of a global status of waiting, the DVCS MAY choose to
     return an invidual status of waiting in some of the certs element,
     or not to return such a TargetEtcChain at all.

     The 'acceptablePolicySet' sequence  indicate the policies and
     mappings that were processed during X.509 public key certificate
     path validation.  PolicyMappingsSyntax is defined in [RFC2459].


   - The 'extensions' field MAY be used to return additional information
     to the client. Extensions MAY be marked critical or not in order to
     indicate whether the client is supposed to understand them. This
     document does not define extensions.


10. Transports

   There is no mandatory transport mechanism in this document.  All
   mechanisms are optional.

10.1 DVCS Protocol via HTTP or HTTPS

   This subsection specifies a means for conveying ASN.1-encoded
   messages for the DVCS protocol exchanges via the HyperText Transfer
   Protocol.

   The DER encoded DVCS requests and responses are encapsulated using a
   simple MIME object with Content-Type application/dvcs and an
   appropriate Content-Transfer-Encoding.

   This MIME object can be sent and received using common HTTP
   processing engines over WWW links and provides a simple browser-
   server transport for DVCS messages.

10.2 File Based Data Protocol

   A file containing a data validation and certification message MUST
   contain only the DER  encoding of one PKI message, i.e. there MUST be
   no extraneous header or trailer information in the file.

   Such files can be used to transport data certification messages using



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   for example, FTP.

10.3 Data Certification Server Protocol Using Email

   This section specifies a means for conveying ASN.1-encoded messages
   for the protocol exchanges described in Section 4 via Internet mail.

   The DER encoded DVCS requests and responses are encapsulated using a
   simple MIME object with Content-Type application/dvcs with an
   appropriate Content-Transfer-Encoding.

   This MIME object can be sent and received using MIME processing
   engines and provides a simple Internet mail transport for Data
   Validation and Certification Server messages.

11. Security Considerations

   This entire chapter discusses security considerations.

   When designing a data validation and certification service, the
   following considerations have been identified that have an impact
   upon the validity or "trust" in the data validation certificate.

   It is imperative that the Data Certification Server's key be guarded
   with proper security and controls in order to minimize the
   possibility of compromise.  Nevertheless, in case the private key
   does become compromised, an audit trail of all the DVC generated by
   the DVCS SHOULD be kept as a means to help discriminate between
   genuine and false DVCs.

   When confidentiality and server authentication is required, requests
   and responses MAY be protected using appropriate mechanisms (e.g. CMS
   encapsulation [RFC 2630] or TLS [RFC2246]).

   Client identification and authentication MAY use services defined by
   TLS [RFC2246]) instead of using a signed request if either the client
   identity is not confidential information, or protected by lower layer
   means.

12. Patent Information

   The following United States Patents related to data validation and
   certification services, listed in chronological order, are known by
   the authors to exist at this time. This may not be an exhaustive
   list. Other patents may exist or be issued at any time. Implementers
   of the DVCS protocol and applications using the protocol SHOULD
   perform their own patent search and determine whether or not any
   encumberences exist on their implementation.



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   # 4,309,569     Method of Providing Digital Signatures
   (issued) January 5, 1982
   (inventor) Ralph C.  Merkle
   (assignee) The Board of Trustees of the Leland Stanford Junior
   University

   # 5,001,752     Public/Key Date-Time Notary Facility
   (issued) March 19, 1991
   (inventor) Addison M.  Fischer

   # 5,022,080     Electronic Notary
   (issued) June 4, 1991
   (inventors) Robert T.  Durst, Kevin D.  Hunter

   # 5,136,643     Public/Key Date-Time Notary Facility
   (issued) August 4, 1992
   (inventor) Addison M.  Fischer
   (Note: This is a continuation of patent # 5,001,752.)

   # 5,136,646     Digital Document Time-Stamping with Catenate Certificate
   (issued) August 4, 1992
   (inventors) Stuart A.  Haber, Wakefield S.  Stornetta Jr.
   (assignee) Bell Communications Research, Inc.,

   # 5,136,647     Method for Secure Time-Stamping of Digital Documents
   (issued) August 4, 1992
   (inventors) Stuart A.  Haber, Wakefield S.  Stornetta Jr.
   (assignee) Bell Communications Research, Inc.,

   # 5,373,561     Method of Extending the Validity of a Cryptographic
   Certificate
   (issued) December 13, 1994
   (inventors) Stuart A.  Haber, Wakefield S.  Stornetta Jr.
   (assignee) Bell Communications Research, Inc.,

   # 5,422,95 Personal Date/Time Notary Device
   (issued) June 6, 1995
   (inventor) Addison M.  Fischer

   # 5,781,629     Digital Document Authentication System
   (issued) July 14, 1998
   (inventor) Stuart A. Haber, Wakefield S. Stornetta Jr.
   (assignee) Surety Technologies, Inc.,


10. References

   [RFC2119] "Key words for use in RFCs to Indicate Requirement Levels",



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   RFC 2119.

   [TSA] C.  Adams, P. Cain, D. Pinkas, R. Zuccherato, "Internet X.509
   Public Key Infrastructure, Time Stamp Protocols," draft-ietf-pkix-
   time-stamp-02.txt, 1999 (work in progress).

   [RFC2510] C. Adams, S. Farrell, "Internet X.509 Public Key
   Infrastructure, Certificate Management Protocols," RFC-2510, 1999.

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

   [RFC2630] R. Housley, "Cryptographic Message Syntax", RFC-2630, June
   1999.

   [ISONR] ISO/IEC 10181-5:  Security Frameworks in Open Systems. Non-
   Repudiation Framework.

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

   [RFC2511] M. Myers, C. Adams, D. Solo, D. Kemp "Internet X.509
   Certificate Request Message Format," RFC-2511, March 1999.

   [RFC2246] T. Dierks, C. Allen, "The TLS Protocol, Version 1.0," RFC
   2246, January 1999.

   [RFC2634] P. Hoffman, "Enhanced Security Services for S/MIME", RFC
   2634, June 1999

   [RFC2560] M. Myers, R. Ankney, A. Malpani, S. Galperin, C. Adams,
   "X.509 Internet Public Key Infrastructure Online Certificate Status
   Protocol", RFC 2560, June 1999.

11. Authors' Addresses

   Carlisle Adams
   Entrust Technologies
   750 Heron Road
   Ottawa, Ontario
   K1V 1A7
   CANADA
   cadams@entrust.com

   Peter Sylvester
   EdelWeb SA
   33 avenue du Maine



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   F-75755 Paris Cedex 15
   FRANCE
   peter.sylvester@edelweb.fr

   Michael Zolotarev
   Baltimore Technologies Pty Limited,
   5th Floor, 1 James Place,
   North Sydney, NSW 2060.
   AUSTRALIA
   mzolotarev@baltimore.com

   Robert Zuccherato
   Entrust Technologies
   750 Heron Road
   Ottawa, Ontario
   K1V 1A7
   CANADA
   robert.zuccherato@entrust.com


APPENDIX A - PKCS #9 Attribute

   We define a PKCS #9 [PKCS9] attribute type. The attribute type has
   ASN.1 type SignedData and contains a data validation certificate.

   The object identifier id-dvcs-dvc identifies the data valication
   certificate attribute type.

   id-dvcs-dvc     OBJECT IDENTIFIER ::= { id-dvcs 5 }

   The attribute may be used as a authenticated or unauthenticated
   attribute in CMS SignedData documents.

APPENDIX B - Signed document validation.

   We present some examples of a possible use of DVCS in the context of
   validation of signed documents.

B.1 Signed document validation

   The example covers the case where a DVCS is used by a signer to
   obtain a proof that a document's structure, including one or more
   attached signatures, is/was correct, after the document was signed.

   The DVC can be produced either by a DVCS that is trusted by the
   signer, or by a DVCS that is trusted by an intended verifier of the
   document.




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   The signer uses the obtained DVC as an evidence that its intentions
   were good and it produced a signed document using the
   environment(keys, algorithms, etc) that was known to be OK.

   It produces a stand-alone document that can be used to extend the
   life of a signature.  This example assumes that we have total trust
   in the Data Validation and Certification Server.

   Signature algorithms and keys have a finite lifetime.  Therefore,
   signatures have a finite lifetime.  The Data Certification Server can
   be used to extend the lifetime of a signature.

   In order to extend the lifetime of a signature in this way, the
   following technique can be used:


   1) The signature needs to be certified:

      The signed message is presented to the Data Validation and
      Certification Server in a 'vsd' service request.

      The DVCS verifies that the signature and certificates are valid at
      that time by checking expiry dates, status information, or DVCs,
      and returns a DVC.

   2) The DVC SHOULD be verified.

      The signature of the Data Validation and Certification Server in
      data certification token SHALL be verified using the Data
      Certification Server's valid verification key.

   A signer's signing key (and therefore, its signature) is only valid
   until some specified time T1.  The DVCS's signing key (and therefore,
   its signature) is valid until some specified time T2 that is
   (usually) after time T1.  Without certification, the signer's
   signature would only be valid until time T1.  With certification, the
   signer's signature remains valid until time T2, regardless of
   subsequent revocation or expiry at time T1.

   If the signature of the DVCS is valid, the trust we have in the DVCS
   allows us to conclude that the original signature on the data was
   valid at the time included in the DVC.

   The DVCS signing key MUST be of a sufficient length to allow for a
   sufficiently long lifetime.  Even if this is done, the key will have
   a finite lifetime.  Since data validation certificates are just
   another type of signed documents, they can be validated using
   (another) DVCS.



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APPENDIX C - Verifying the Status of a Public Key Certificate

   We now present two examples of how to produce a data validation
   certificate that can be used to assert that a public key certificate
   is valid, trusted, and can be used for a particular purpose.

   A client wants to use a given public key certificate either to use it
   to sign a document or to use it for document encryption.

   A DVCS MUST have access to current information regarding public
   certificate status, it can therefore be used to verify the revocation
   status of a certificate at the current time.

   The following technique can be used:


   A) The public key certificate needs to be validated.

      The certificate is presented to the Data Certification Server
      using a 'vpkc' service.

      The Data Validation and Certification Server verifies that the
      public key certificate is valid and that it hasn't been revoked
      and then returns a data validation certificate.

   B) The data validation certificate MUST be verified.

      The signature of the Data Certification Server in the data
      certification token SHALL be verified using the Data Validation
      and Certification Server's valid certificate.

   C) The public key certificate is used:

   C.1) A clients's own public key certificate (i.e., the corresponding
        private key) can be used to add a signature to a document. The
        signing certificate and the data validation certificate can be
        added as signed attributes to the signature.

        A data validation certificate can now be used during the
        validation signatures using the key contained in the public key
        certificate. This service provided by the DVCS can be thought of
        as a supplement to the usual method of checking revocation
        status.

        In other words, signature validation at a later time does not
        necessarily require access to the revocation status of the
        user's signing certificate, access to a DVCS service and
        validation of the DVC is sufficient to verify a signature. Note



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        that the DVC does not tell when the signature had been created,
        it only indicates when the signing certificate was valid.

   C.2) A public key certificate for key exchange can be used after
        having obtained a data validation certification certificate to
        encrypt data. The DVC can be stored with the data and/or stored
        by the creator of the encrypted document.

        If an intended recipient of the document claims that the creator
        did not use an appropriate encryption key, the DVC (obtained by
        a recipient's DVCS) can be used as evidence that the recipient's
        DVCS has authorized the usage of the public key.


Appendix D - MIME Registration

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

   MIME media type name: application

   MIME subtype name: dvcs

   Required parameters: None

   Optional parameters: None

   Encoding considerations: binary or Base64

   Security considerations: Carries a request for a data validation and
   certification service and the response. A request may be
   cryptographically signed. The response will be cryptographically
   signed.

   Interoperability considerations: None

   Published specification: IETF PKIX Working Group Draft on Data
   Validation and Certification Server Protocols

   Applications which use this media type: Data Validation and
   Certification Server clients

   Additional information:

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




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   Person & email address to contact for further information: Peter
   Sylvester <peter.sylvester@edelweb.fr>

   Intended usage: COMMON

   Author/Change controller: Peter Sylvester
   <peter.sylvester@edelweb.fr>

Appendix E - Acknowledgements

   This text is based on initial work from Robert Zuccerato and Carlisle
   Adams, both at Entrust Technologies, and from Denis Pinkas at Bull,
   for time stamping, notary and data certification services.

Appendix F - Full Copyright Statement

   Copyright (C) The Internet Society 1999. All Rights Reserved.  This
   document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works. However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process shall be
   followed, or as required to translate it into languages other than
   English.

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns. This
   document and the information contained herein is provided on an "AS
   IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK
   FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT
   LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL
   NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY
   OR FITNESS FOR A PARTICULAR PURPOSE.












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