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Internet Draft                                       Ambarish Malpani
draft-ietf-pkix-scvp-03.txt                                  ValiCert
June 12, 2000                                             Paul Hoffman
Expires in six months                                  VPN Consortium

          Simple Certificate Validation Protocol (SCVP)

Status of this memo

This document is an Internet-Draft and is in full conformance with all
provisions of Section 10 of RFC 2026.

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

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

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

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


Abstract

The SCVP protocol allows a client to offload certificate handling to a
server. The server can give a variety of valuable information about the
certificate, such as whether or not the certificate is valid, a chain
to a trusted certificate, and so on. SCVP has many purposes, including
simplifying client implementations and allowing companies to centralize
their trust and policy managment.


1. Introduction

Certificate validation is a difficult problem. 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 must be reduced. There are a variety of
applications that can use public key certificates but are burdened by
the overhead of validating the certificates when all the application
really wants is the public key and name from the certificate, and a
determination of whether or not the certificate may be used for a
particular purpose. There are other applications that can perform
certificate path validation but have no reliable method of obtaining a
current chain to a trusted certificate.

1.1 SCVP overview and requirements

The primary goals of SCVP are to make it easier for  applications to
deploy systems using a PKI and to allow centralization of administering
PKI policies. Parts of SCVP can be used by clients that do much of the
PKI processing themselves and simply want a useful but untrusted server
that will collect information for them. Other parts can be used by
clients that have complete trust in the server to both offload the work
of certificate validation and to ensure that policies are enforced in a
consistent fashion across an enterprise.

Untrusted SCVP servers can give client the certificate chains needed
for path validation. They can also give clients revocation information
such as CRLs and OCSP responses that the client can use in the client's
path validation. These services can be valuable to client systems that
do not include the protocols needed to find and download all of the
intermediate certificates, CRLs, and OCSP responses needed for the
client to perform complete path validation.

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

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

- The client is in an enterprise that wants to centralize its PKI
validation policies, such as which root certificates are trusted and
which types of policy checking are performed during 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 [MUSTSHOULD].

1.3 Open Issues

The following is a list of issues that were raised on earlier versions
of this document that have not been fully dealt with here. Comments on
these issues are particularly welcome.

- Extensions can be marked as critical. The usefulness and problems of
criticality have been long debated and there has not been a great deal
of consensus. In SCVP, marking a request extension as critical says to
the server "don't give me an answer unless you understand this
extension", and marking a response extension as critical says "don't
use this response unless you understand this extension". Without the
critical bit in the extensions, either the semantics of extensions
would have to be changed to essentially say "all extensions are
critical" (which is overkill for some extensions that might really be
optional), or the semantics would have to be changed to say "you can
never rely on the other party understanding an extension", which would
limit the usefulness of some extensions.

- All responses are signed. There may be cases where the server
doesn't want to sign the responses, such as on messages that
are only error responses, or where the message is travelling over a
medium that is already known to be secure.


2. Protocol

The SCVP protocol uses a simple request-response model. That is, a SCVP
client creates a single request and sends it to the server; the server
creates a single response and sends it to the client. Typical use of
SCVP is expected to be over HTTP, and possibly email. This document
registers MIME types for SCVP requests and responses.


3. Requests

A SCVP client's request to the server MUST be a single FullRequest
item. The FullRequest item contains the entire request. A FullRequest
item is carried in an application/scvp-request MIME body part.

3.1 FullRequest

The FullRequest item encapsulates the client's request. The FullRequest
item contains a PSRequest item, and an optional RequestSignature item.

3.2 PSRequest

The PSRequest item contains the part of the client's request.
The PSRequest item
contains a Version item, a Query item, a TypesOfCheck item, and a
WantBack item. It can also contain an optional RequestNonce item and
an optional ReqExtensions item. (The "PS" in PSRequest means "possibly
signed".)

A signed request can be used to authenticate the client to the
server and for non-repudiation of the client's request, such as for
accounting purposes. A server might require all requests to be signed
if the server did not want to respond to request unless they were from
authenticated clients. A server might want to allow unsigned requests
if the server is authenticating in some other fashion (such as by
IP address).

In this specification, the item(s) in the Query item are certificates.
The TypesOfCheck item tells the server what types of checking it should
do on the item(s) in the Query item. The WantBack item tells the server
what the client wants to know about the item(s). ReqExtensions in the
PSRequest item are used to extend the request, such as to request a
different type of item.

3.3 Version

The Version item tells the version of SCVP used in a request or a
response. The value of the Version item for this specification is 1.

3.4 Query

The Query item specifies the object of the request. One type of object
is defined in this specification: CertsQuery. (Other types of queries
might be specified in the future.) The CertsQuery is a request for
information on one or more certificates. A CertsQuery contains a list
of certificates, and can also contain zero or one of each of the
following items: ValidityTime, IntermediateCerts, TrustedCerts,
RevocationInfo, PolicyID, ConfigurationIdentifier, and QueryExtensions.

The list of certificates in the Query item tells the server the
certificate(s) the client wants a reply for. The optional ValidityTime
item tells the time at which the client wants to know about. The
optional IntermediateCerts, TrustedCerts, RevocationInfo, PolicyID, and
ConfigurationIdentifier items tell the server how to process the
request.

3.5 CertBundle

The CertBundle item contains one or more Certs. The order of
the Cert(s) in the bundle is not important.

3.6 Cert

The Cert item contains a complete certificate. The Cert item
contains an identifier for the type of certificate and the octets of
the certificate itself. One type of certificate, for PKIX [PKIX], is
defined, but other types of certificates (such as for OpenPGP
[OpenPGP]) may be defined in the future.

3.8 QueryExtensions

The QueryExtensions item specifies a list of extensions to the SCVP
protocol, for example to request additional information about the
certificate(s) in the CertsQuery. The QueryExtensions item contains a
sequence of Extension items, each of which contain an ExtnID item,
a Critical item, and an ExtnValue item.

3.9 ExtnID

The ExtnID item is an identifier for the extension. It contains
the OID of the extension.

3.10 Critical

The Critical item tells whether the extension is critical. The
values for the item are:

False  Not critical
True   Critical

In a request, if the Critical item is true, the server MUST
NOT process the request unless it understands the extension. In a
reply, if the Critical item is true, the client MUST NOT
process the reply unless it understands the extension.

3.11 ExtnValue

The ExtnValue item gives the value of an extension. It
contains a sequence of octets.

3.12 IntermediateCerts

The IntermediateCerts item specifies to the server the intermediate
certificates that the server MAY use when forming a certificate chain.
The certificates in the IntermediateCerts item can be used by the
server in addition to any other certificates that the server knows of
when building chains. The IntermediateCerts item contains a list of
certificates. The certificates in the IntermediateCerts MUST NOT be
self-signed certificates.

The purpose of the IntermediateCerts item is to help the server create
validation chains.

3.13 TrustedCerts

The TrustedCerts item specifies to the server the trusted certificates
that the server MUST use. If a TrustedCerts item is included in a
CertsQuery item, the server MUST NOT use any certificate chain anchors
other than the certificates in the TrustedCerts item when forming a
certificate chain for validation. The TrustedCerts item contains a
CertBundle item.

3.14 RevocationInfo

The RevocationInfo item specifies to the server revocation information
such as CRLs and OCSP [OCSP] responses that the server MAY use when
validating certificate chains. The purpose of the RevocationInfo item
is to provide revocation information to the server that the server may
not have access to, such as an OCSP response that the client received
along with the certificate. Note that the information in the
RevocationInfo item might not be used by the server, such as if the
information is for certificates that the server does not use in chain
building.

The types of revocation proof that can be provided are:
- CRL
- OCSP response

[[[Need to specify the format of the extensions for both CRLs and
for OCSP responses.]]]

3.15 PolicyID

The PolicyID item specifies to the server the policy ID that the server
MUST use when forming a certificate chain. The PolicyID item contains
a URL that, when resolved, defines the policy.

3.16 ConfigurationIdentifier

The ConfigurationIdentifier item tells the server the SCVP options that
the client wants the server to use. The client can use this option
instead of specifying other SCVP configuration such as PolicyID,
TrustedCerts, RevocationInfo, and so on. The value of this item is
determined by private agreement between the client and the server and
is not specified in this document. For example, the value might be the
hash of some set of options, or it might be a short identifier for a
common set of options. Further, the server might want to have
identifiers that indicate that some settings are used in addition to
others given in the request; in this way, the configuration identifier
might be a shorthand for some SCVP options.

3.17 TypesOfCheck

The TypesOfCheck item describes the kind of checking that the client
wants the server to do on the certificate(s) in the Query item. If the
TypesOfCheck item is given in a request, it can contain one or more
types of checks. For each type of check specified in the request, the
server MUST perform all the checks requested, or return an error.

The types of checks are:
- Path validation to a trusted root
- Revocation status
Note that revocation status check inherently includes path validation.

3.18 WantBack

The WantBack item describes the kind of information the client wants
from the server for the certificate(s) in the Query item. If the
WantBack item is given in a request, it can contain one or more types
of information. For each type of information specified in the request,
the server MUST return information on what it found during the check.

The types of information that can be requested are:
- Certificate chain used to validate the certificate
- Proof of revocation status

For example, a request might include a TypesOfCheck item that does not
specify path validation, and include a WantBack item that specifies the
certificate chain used to validate. The response would not include a
status for the validation, but would include a certificate chain that
the server thinks might validate. This set of options might be used by
a client that wants to do its own path validation.

3.19 ValidityTime

The ValidityTime indicates the time for which the client wants the
information to be relevant. Not specifying a ValidityTime means that
the server should use the current time. For example, when asking for
validation of a certificate, the client might ask "was this certificate
valid at this time". The information in the CertReply item in the
response MUST be formatted as if the server created the response at the
time indicated in the ValidityTime, if the server doesn't have
historical information about that time, it MAY either return an error
or return information for a later time. A client MUST be able to handle
responses that have ThisUpdate items that are later than the requested
ValidityTime.

3.20 RequestNonce

The RequestNonce item is an identifier generated by the client for the
request; the server MUST return the same RequestNonce in the signed
part of the server's response. The RequestNonce item is simply a
sequence of octets. The client SHOULD include a RequestNonce item in
every request to prevent an attacker acting as a man-in-the-middle from
replaying old responses from the server. The value of the nonce SHOULD
change with every request sent from the client.

3.22 RequestSignature

The RequestSignature item is the signature of the PSRequest item. The
details of how a RequestSignature is computed is defined in the
specific sections which describe how a request/response is represented
in various formats.


4. Responses

A SCVP server's response to the client MUST be a single FullResponse
item. The FullResponse item contains the entire response. A
FullResponse item is carried in an application/scvp-response MIME body
part.

4.1 FullResponse

The FullResponse item encapsulates the server's response. The
FullResponse item contains a PSResponse item and an optional
ResponseSignature item.

4.2 PSResponse

The PSResponse item contains the part of the server's response that is
signed by the ResponseSignature item. The item contains a Version
item, a ProducedAt item, a ResponseStatus item, and a RequestHash
item. The item can also contain an optional ReplyObjects item, an
optional RequestNonce item, and an optional RespExtensions item. The
PSResponse item MUST contain exactly one CertReply item for each
certificate requested in the request. The RequestNonce item MUST be
included if the request had a RequestNonce item.

4.3 ProducedAt

The ProducedAt item tells the time at which the whole response was
produced. The ProducedAt item represents the date at UTC.

4.4 ResponseStatus

The ResponseStatus item gives status information to the 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 optional string may be used to transmit status information, but it
is optional. The client MAY choose to display the string to the client.
However, because there is no way to know the languages understood by
the user, the string may be of little or no use to them.

The complete list of status codes for the ResponseStatus item is:

0  The request was fully processable
1  The request included unrecognized items; continuing

10  Too busy; try again later

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; aborting
23  The key given in the RequestSignature is not recognized
24  The signature did not match the body of the request
25  The encoding was not understood
26  The request was not authorized

4.4a RequestHash

The RequestHash item is the SHA-1 hash of the PSRequest item. The
RequestHash item serves the following purposes:

- It helps a client know that the request was  not maliciously modified
  when the client gets the response back

- It allows the client to associate a response with a request when
  using connectionless protocols

The purpose of the RequestHash is not for authentication of the
client.

The server MUST return the RequestHash item in the response.

4.5 ReplyObjects

The ReplyObjects item returns objects to the client. In this
specification, the ReplyObjects item is always a CertReply, which tells
the client about a single certificate from the request. The CertReply
item contains a Cert item identifying the certificate, a
ReplyStatus item, a ThisUpdate item, and a NextUpdate item. There may
also be the following optional items: ValidationStatus,
RevocationStatus, PublicKey, CertSubject, ValidationChain,
RevocationProof, and SingleReplyExtensions.

The presence or absence of the ValidationStatus, RevocationStatus,
PublicKey, CertSubject, ValidationChain, and RevocationProof items in
the CertReply item is controlled by the TypesOfCheck, and WantBack
items in the request. A server MUST include one of the above items for
each related item requested in the TypesOfCheck, and WantBack items.

4.6 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 certificate.

The complete list of status codes for the ReplyStatus item is:

0  Success: a definitive answer follows
1  Failure: the certificate type is not recognized
2  Failure: an item wanted in TypesOfCheck is not recognized
3  Failure: an item wanted in WantBack is not recognized
4  Failure: the certificate was malformed
5  Failure: the mandatory PolicyID is not recognized
6  Failure: the ConfigurationIdentifier is not recognized
7  Failure: unauthorized request

Status code 4 is used to tell the client that the request was properly
formed but the certificate in question was not. This is useful to
clients that cannot parse a certificate.

4.7 ThisUpdate

The ThisUpdate item tells the time at which the information in the
CertReply was correct. The ThisUpdate item represents the date as
UTC.

4.8 NextUpdate

The NextUpdate item tells the time until which the server expects the
information in the CertReply to be valid. The NextUpdate item
represents the date at UTC. [[[Is there a desire for another item that
says "the server takes liability for this response up to this
particular time?]]]

4.9 ReplyTypesOfCheck

The ReplyTypesOfCheck contains the responses to the client's
TypesOfCheck item in the request. It has the same form as the
Extensions item, and the OIDs in the ReplyTypesOfCheck item MUST match
the OIDS in the TypesOfCheck item.

The value for path validation to a trusted root, {type-arc 0}, can be
one of the following:

0  Valid
1  Not valid
2  Unknown

The value for the revocation status, {type-arc 1}, can be one of the
following:

0  Good
1  Revoked
2  Unknown

4.10 ReplyWantBack

The ReplyWantBack contains the responses to the client's WantBack item
in the request. It has the same form as the Extensions item, and the
OIDs in the ReplyWantBack item MUST match the OIDS in the WantBack
item.

The value for the certificate chain used to validate the certificate
in the request, {want-arc 1}, is a CertBundle item.

The value for the proof of revocation status, {want-arc 2}, is a
RevocationProof item.

4.11 RevocationProof

The RevocationProof item gives the client the proof that the server
used to check revocation. The structure of the RevocationProof item is
the same as an Extensions item. The OIDs in the RevocationProof item
are the same as those in the RevocationInfo item.

4.12 ResponseSignature

The ResponseSignature item is the signature of the PSResponse item.

The client SHOULD check the signature on every signed message it
receives from the server. In order to check the signature, the client
MUST know and rely on the public signing key of the server. The client
could have obtained the server's public key through an out-of-band
mechanism of direct trust or through a certificate that chains to a
root that the client trusts to delegate this type of authority.


5. ASN.1 Syntax for SCVP

This section defines the syntax for SCVP messages. The semantics for
the messages are defined in sections 2, 3, and 4.

5.1 Signatures in ASN.1

Signatures in ASN.1 are done over the DER encoding of the
PSRequest/PSResponse item. The Name is the distinguished name of the
signer. The SignatureAlgorithm is the
algorithm used to sign the request, and a SignatureBits item that is
the signature itself. The signature may also contain an
optional CertBundle that represents a chain of certs to verify the key used
to sign the request.

5.1.1 SignatureAlgorithm

The SignatureAlgorithm identifies the algorithm used to sign a request
or response. The SigningAlgorithm item contains the OID of the
algorithm and any necessary parameters for the algorithm.

5.1.2 SignatureBits

The SignatureBits item holds the octets of a signature. The structure
of the SignatureBits item is determined by the value of the
SignatureAlgorithm item.

5.2 ASN.1 Module definition

SCVP DEFINITIONS EXPLICIT TAGS ::=

BEGIN

IMPORTS

      -- Directory Authentication Framework (X.509)
             Certificate, AlgorithmIdentifier
             FROM AuthenticationFramework { joint-iso-itu-t ds(5)
                      module(1) authenticationFramework(7) 3 }

      -- PKIX Imports
          Name, Extensions,
             FROM PKIX1Explicit88 {iso(1) identified-organization(3)
                  dod(6) internet(1) security(5) mechanisms(5) pkix(7)
                  id-mod(0) id-pkix1-explicit-88(1)};

FullRequest ::= SEQUENCE {
    psRequest            PSRequest,
    requestSignature     [0] Signature OPTIONAL
}

PSRequest ::= SEQUENCE {
    version                 INTEGER,
    query                   Query,
    typesOfCheck            TypesOfCheck,
    wantBack                WantBack,
    requestNonce        [1] OCTET STRING OPTIONAL,
    reqExtensions       [2] Extensions OPTIONAL
}

Query ::= CHOICE {
    certsQuery       [0] CertsQuery
}

CertsQuery ::= SEQUENCE {
    queriedCerts          SEQUENCE SIZE (1..MAX) OF Cert,
    validityTime      [0] GeneralizedTime OPTIONAL,
    intermediateCerts [1] SEQUENCE SIZE (1..MAX) OF Cert OPTIONAL,
    trustedCerts      [2] CertBundle OPTIONAL,
    revocationInfo    [3] Extensions OPTIONAL,
    policyID          [4] UTF8String OPTIONAL,
    configurationIdentifier [5] OBJECT IDENTIFIER OPTIONAL,
    queryExtensions        [6] Extensions OPTIONAL
}

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

Cert ::= CHOICE {
    pkixCert        [0] Certificate
}

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

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


Signature ::= SEQUENCE {
    signerName               Name,
    signatureAlgorithm       AlgorithmIdentifier,
    signatureBits            BIT STRING,
    certs                [0] CertBundle OPTIONAL
}

FullResponse ::= SEQUENCE {
    psResponse            PSResponse,
    responseSignature     [0] Signature OPTIONAL
}

PSResponse ::= SEQUENCE {
    version               INTEGER,
    producedAt            GeneralizedTime,
    responseStatus        ResponseStatus,
    requestHash           OCTET STRING,
    replyObjects      [0] ReplyObjects OPTIONAL,
    requestNonce      [2] OCTET STRING OPTIONAL,
    respExtensions        [3] Extensions OPTIONAL
}

ResponseStatus ::= SEQUENCE {
    statusCode          INTEGER,
    errorMessage    [0] UTF8String OPTIONAL
}

ReplyObjects ::= CHOICE {
    certReplies     [0] SEQUENCE SIZE (1..MAX) OF CertReply
}

CertReply ::= SEQUENCE {
    cert                  Cert,
    replyStatus           ReplyStatus,
    thisUpdate            GeneralizedTime,
    nextUpdate            GeneralizedTime,
    replyTypesOfCheck [0] Extensions OPTIONAL,
    replyWantBack     [1] Extensions OPTIONAL,
    singleReplyExtensions        [2] Extensions OPTIONAL
}

ReplyStatus ::= ENUMERATED {
    success                  (0),
    certTypeUnrecognized     (1),
    typeOfCheckUnrecognized  (2),
    wantBackUnrecognized     (3),
    certMalformed            (4),
    policyIDUnrecognized     (5),
    configInfoUnrecognized   (6),
    unauthorizedRequest      (7)
}

-- Need to include type-arc, want-arc, and revinfo-arc

END

6. XML Syntax for SCVP

This section defines the syntax for SCVP messages. The semantics for
the messages are defined in sections 2, 3, and 4.

TODO: We need to import the XML DSig data into our DTD.  We also need
to provide more information about the format of the elements which map
to PCDATA.

Note: this is the second attempt at XML for SCVP. We invite any comments
on it.

6.1 Signatures in XML

Signatures are done using [XMLDSIG].

6.2 Namespaces

The XML namespace [XML-ns] URI that MUST be used by implementations of
this (dated) specification is:

   xmlns="http://www.ietf.org/pkixwg/01/scvp"

6.3 XML Request/Response syntax

<!-- Need to specify the namespace for SCVP. Also, need to include
        the DTD for XMLDSIG -->


<?xml version="1.0" encoding="UTF-8"?>

<!ELEMENT FullRequest ( PSRequest,
                 RequestSignature? )>

<!ELEMENT RequestSignature (Signature)>
<!ELEMENT PSRequest ( Version,
                        Query,
                        TypesOfCheck,
                        WantBack,
                        RequestNonce?,
                        ReqExtensions? )>
<!ATTLIST PSRequest
    Id     ID      #IMPLIED >

<!ELEMENT ReqExtensions (Extension+)>

<!ELEMENT Query ( CertsQuery ) >

<!ELEMENT CertsQuery ( QueriedCerts,
                        ValidityTime?,
                        IntermediateCerts?,
                        TrustedCerts?,
                        RevocationInfo?,
                        PolicyID?,
                        ConfigurationIdentifier?,
                        QueryExtensions? )>

<!ELEMENT QueryExtensions (Extension+)>

<!ELEMENT QueriedCerts ( Cert+ )>

<!ELEMENT ValidityTime ( GeneralizedTime )>

<!ELEMENT IntermediateCerts ( Cert+ )>

<!ELEMENT TrustedCerts ( CertBundle )>

<!ELEMENT RevocationInfo ( Extension+ )>

<!ELEMENT PolicyID ( #PCDATA )>

<!ELEMENT Version ( #PCDATA )>

<!ELEMENT ConfigurationIdentifier ( ObjID )>

<!ELEMENT CertBundle ( Cert+ )>

<!ELEMENT Cert ( X509Certificate )>

<!ELEMENT ObjID ( #PCDATA )>

<!ELEMENT GeneralizedTime ( #PCDATA )>

<!ELEMENT TypesOfCheck ( ObjID+ )>

<!ELEMENT WantBack ( ObjID+ )>

<!ELEMENT RequestNonce ( #PCDATA )>

<!ELEMENT Extensions ( Extension+ )>

<!ELEMENT Extension ( ExtnID,
                       ExtnValue )>
<!ATTLIST Extension critical ( true | false ) "false">

<!ELEMENT ExtnID ( ObjID )>



<!ELEMENT ExtnValue ( #PCDATA )>

<!ELEMENT FullResponse ( PSResponse,
                      ResponseSignature? )>

<!ELEMENT ResponseSignature (Signature)>

<!ELEMENT PSResponse ( Version,
                         ProducedAt,
                         ResponseStatus,
                         RequestHash,
                         ReplyObjects?,
                         RequestNonce?,
                         RespExtensions? )>

<!ATTLIST PSResponse
    Id     ID      #IMPLIED >

<!ELEMENT ProducedAt ( GeneralizedTime )>

<!ELEMENT ResponseStatus ( StatusCode,
                            ErrorMessage? )>

<!ELEMENT RequestHash ( #PCDATA )>

<!ELEMENT StatusCode ( #PCDATA )>

<!ELEMENT ErrorMessage ( #PCDATA )>

<!ELEMENT ReplyObjects ( CertReplies )>

<!ELEMENT RespExtensions (Extension+)>

<!ELEMENT CertReplies ( CertReply+ )>

<!ELEMENT CertReply ( Cert,
                       ReplyStatus,
                       ThisUpdate,
                       NextUpdate,
                       ReplyTypesOfCheck?,
                       ReplyWantBack?,
                       SingleReplyExtensions? )>

<!ELEMENT ThisUpdate ( GeneralizedTime )>

<!ELEMENT NextUpdate ( GeneralizedTime )>

<!ELEMENT ReplyTypesOfCheck ( Extensions )>

<!ELEMENT ReplyWantBack ( Extensions )>

<!ELEMENT ReplyStatus EMPTY>
<!ATTLIST ReplyStatus value ( success |
                   certTypeUnrecognized |
                   typeOfCheckUnrecognized |
                   WantBackUnrecognized |
                   CertMalformed |
                   PolicyIDUnrecogized |
                   ConfigInfoUnrecognized |
                   UnauthorizedRequest)
                   "success" >


<!ELEMENT SingleReplyExtensions (Extension+)>



6.3 Example of XML syntax

<?xml version="1.0" encoding="UTF-8"?>

<!DOCTYPE FullRequest SYSTEM "scvp.dtd">

    <FullRequest xmlns="http://www.ietf.org/pkixwg/01/scvp">
        <PSRequest Id="SCVPReq">
            <Version>1</Version>
            <Query>
                <CertsQuery>
                    <QueriedCerts>
                        <Cert>
                            <X509Certificate>
                            MIICEzCCAb0CAgfYMA0GCSqGSIb3D
                            QEBBAUAMIGTMQswCQYDVQQGEwJLTz
                            . . .
                            oeedsN6iA4IhpA4Ev2rWiM92OoKag
                            UvVGaQoBuDkz7JfYNw==
                            </X509Certificate>
                        </Cert>
                    </QueriedCerts>

                    <ValidityTime>
                        <GeneralizedTime>19991232235959
                        </GeneralizedTime>
                    </ValidityTime>

                    <IntermediateCerts>
                        <Cert>
                            <X509Certificate>
                            MIICEzCCAb0CAgfYMA0GCSqGSIb3D
                            QEBBAUAMIGTMQswCQYDVQQGEwJLTz
                            . . .
                            oeedsN6iA4IhpA4Ev2rWiM92OoKag
                            UvVGaQoBuDkz7JfYNw==
                            </X509Certificate>
                        </Cert>

                    </IntermediateCerts>

                </CertsQuery>
            </Query>

            <TypesOfCheck>
                <ObjID>1.3.5.5.5.2.5.2</ObjID>
            </TypesOfCheck>

            <WantBack>
                <ObjID>1.3.5.5.5.2.5.2</ObjID>
            </WantBack>
            <RequestNonce>2888475218934</RequestNonce>
            <ReqExtensions>
                <Extension critical="true">
                    <ExtnID><ObjID>1.5.4.5.9.12.1</ObjID></ExtnID>
                    <ExtnValue>192812</ExtnValue>
                </Extension>
            </ReqExtensions>

        </PSRequest>

        <RequestSignature> <Signature xmlns="http://www.w3.org/2000/02/xmldsig#">
            <SignedInfo Id="v5">
            <CanonicalizationMethod Algorithm=
                "http://www.w3.org/1999/07/WD-xml-c14n-19990729"/>
            <SignatureMethod Algorithm=
                "http://www.w3.org/2000/01/xmldsig/dsa"/>
            <Reference URI="#SCVPReq">
            <Transforms>
                <Transform Algorithm=
                    "http://www.w3.org/2000/01/xmldsig/null">
                </Transform>
            </Transforms>
            <DigestMethod Algorithm=
                "http://www.w3.org/2000/01/xmldsig/sha1"/>
            <DigestValue>a23bcd43</DigestValue>
            </Reference>
        </SignedInfo>
        <SignatureValue>dd2323dd</SignatureValue>
        <KeyInfo Id="v10">
            <X509Data>
                <X509IssuerSerial>
                    <X509IssuerName>C=US, ST=Illinois, L=Chicago, O=Aromatic
                    Penguin Playing Basketball, OU=Certificate
                    Authority, CN=www.ceramic.com</X509IssuerName>
                    <X509SerialNumber>2007 </X509SerialNumber>
                </X509IssuerSerial>
                <X509Certificate>
                MIICITCCAcsCAgfXMA0GCSqGSIb3DQEBBAUAMIGaMQswCQYDVQQG
                EwJVUzERMA8GA1UECBMISWxsaW5vaXMxEDAOBgNVBAcTB0NoaWNh
                . . .
                bD2d2MixUSENihcgGbCEikUpNrMREO/eYkyKsiqmzAxlr3Tu/eKB
                NBeu
                </X509Certificate>
            </X509Data>
        </KeyInfo>
        </Signature> </RequestSignature>
    </FullRequest>


TODO: Need to add an example of a response


7. Security Considerations

A client that trusts a server's responses for validation of
certificates 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. Thus, an SCVP
server must be protected at least as well as the weakest root server
that the SCVP server trusts.

If the client does not check the signature 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. This attack does not affect the usefulness of some responses (such
as a response that returns a certificate path that the client will
validate itself) but does affect things such as a validation response.

If the client does not include a RequestNonce item, or if the client
does not check that the RequestNonce in the reply matches that in the
request, an attacker can replay previous responses from the server.
This attack can also be mounted, even with signed requests, if the
server does not keep track of previous RequestNonce items.

If the server does not require some sort of authorization (such as
signed requests), an attacker can get the server to reply 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.


A. References

[MUSTSHOULD] "Key words for use in RFCs to Indicate Requirement
Levels", RFC 2119.

[OCSP] "PKIX Online Certificate Status Protocol (OCSP)", RFC 2560.

[OpenPGP] "OpenPGP Message Format", RFC 2440.

[PKIX] "PKIX Certificate and CRL Profile", RFC 2459.

[SHA-1] "Secure Hash Standard", NIST FIPS publication 180-1, April
1995.

[UTF8] "UTF-8, a transformation format of ISO 10646", RFC 2279.

[XMLDSIG] NEED THE REFERENCE


B. Acknowledgments

The lively debate in the PKIX Working Group also had a significant
impact on the types of items described in this protocol. Denis Pinkas
suggested some additional requirements for the protocol, and Mike Myers
helped point out sections that needed clarification.


C. Changes Between Versions of This Document

C.1 Differences between -00 and -01

1: Rewrote to both narrow focus and to explain the goals more fully.

1.1: Removed second paragraph.

2: Removed the discussion of the two syntaxes.

3: Reorganized the section to put the Extensions items after the
CertsQuery items. The section numbers below are from the -00 draft.
Throughout the section, made RequestHash mandatory instead of optional.
Added RevocationInfo item. Changed CertID to CertHash throughout.
Fixed the names of the parts of the signature to match the text.

3.1: Split the item into a TBSRequest followed by the hash and/or
signature. Changed the order of the extensions item so that all the
optional items were together. Changed CertsQuery into Query. Added the
ValidityTime item.

3.3: Redefined Extension to be Extensions to be more similar to
Extensions in PKIX. Other wording changes.

3.5: Gave more explanation for the ExtensionCritical bit, and made
the values boolean. Note that this item may disappear, depending
on discussion of the open issue on it.

3.7: Changed CertsQuery into Query and described the one defined
instance as CertsQuery. Moved the TypesOfCheck and WantBack from the
Query and up one level to the TBSRequest.

3.9: Removed OpenPGP cert, but allowed for it to be added back in the
future.

3.10: Removed OpenPGP cert hash, but allowed for it to be added back in
the future.

3.11 Made TypesOfCheck OIDs.

3.12: Made WantBack OIDs. Removed the public key and the names.

3.10: Added sentence about when a client might include a CertHash item
in the TrustedRoots.

3.13: Clarified use of IntermediateCerts

3.18: Added wording that the RequestHash should not be used for
authentication.

3.19: Changed wording to make it clear that RequestSignature was needed
only for authentication of the client.

3.23: Clarified purpose of KeyID.

4: The section numbers below are from the -00 draft. Throughout the
section, made returning the RequestHash mandatory because it is now
mandatory in the request.

4.1: Split the item into a TBSResponse followed by the hash and/or
signature. Made ResponseSignature mandatory. Made the items returned in
the form of Extensions to match the fact that TypesOfCheck and WantBack
are now sequences of OIDs.

4.3: Made the status code a single number.

4.4 Removed the subject names and public keys. Added NextUpdate.

4.10: Clarified that CertSubject for PKIX certs must contain both the
subject name and the subjectAltName.

4.13: Made ResponseSignature mandatory; this might be changed back to
optional for some types of responses in a future revision of the spec.
Added a discussion of how the client can get the server's signing key.

Old 5: Removed tiny syntax, renumbered old 6 to 5.

5: Added note about semantics in 2-4.
Split FullRequest into FullRequest and TBSRequest.
Moved the extensions item in FullRequest.
Changed the certsQuery to Query.
Move TypesOfCheck and WantBack up to TBSRequest.
Made TypesOfCheck and WantBack SEQUENCE of OIDs.
Added ValidityTime.
Changed "CertID" to "CertHash".
Made the status code a single number.
Added reminder in CertItem about full certs.
Changed order of Signature items.
Split FullResponse into FullResponse and TBSResponse.
Added ReplyTypesOfChecks and ReplyWantBack items.
Added Extensions item and sub-items.

7: Updated to reflect mandatory RequestHash and ResponseSignature.
Added explicit words about compromise of the SCVP server. Removed the
first paragraph because it was confusing and will be fixed in later
versions of the draft.

A: Added reference to OCSP.

D: Updated.

C.2 Difference between -01 and -02

Abstract: Updated to include design goals.

Throughout: Changed TBSRequest to PSRequest. Changed UsageID to
PolicyID. Changed Greenwich Mean Time to UTC.

1.2: Changed wording to match RFC 2119.

1.3: Removed first open issue (cert hashes) because we removed cert
hashes. Removed third open issue (optional response signing) because
the draft now clarifies which responses must be signed and which ones
don't. Added new open issue (making signatures on responses optional).

3.1: Removed the RequestHash from the request.

3.2: Removed the RequestHash from the request. Added explanation of
PSRequest name. Added SignerName here.

3.4: Added note about other types of queries being added in the future.

3.5: Removed CertHash.

3.7: Removed the CertHash item. Filled in the hole that would have been
created with SignerName from below.

3.10: Minor edit to last line.

3.12: Removed most of the second paragraph because it was confusing.

3.14: Removed the arc stuff.

3.15: Made the PolicyID be a URL instead of an OID.

3.17: Removed the arc stuff. Also added last sentence after the list.

3.18: Removed the arc stuff.

3.19: Removed the surperfluous NextUpdate from the last sentence.
Detailed what no ValidityTime request means. Changed what should happen
if the client requests information for a time that the server does not
have.

3.21: Changed last sentence to indicate that the RequestHash is only
returned in the response, not sent in the request.

3.22: Removed the last sentence because the RequestHash is only
returned in the response, not sent in the request. Moved the second
paragraph up to 3.2 to make it clearer why someone might or might not
sign their request. Got rid of the optional KeyID. Removed the
SignerName.

3.23: Moved SignerName up in the document to 3.7. Renumbered the rest
of this section.

3.26: Got rid of KeyID item.

4.2: Added SignerName here.

4.4: Got rid of 11 and 12 and made the description of 10 more sensible.
Changed 25 to "encoding not understood".

4.5: Removed the last sentence because it was confusing.

4.9: Got rid of "temporarily unknown".

4.12: Made the response signature optional in the first sentence of the
second paragraph. Got rid of KeyID. Removed the SignerName.

5: Removed RequestHash from FullRequest. Removed CertItem and made
CertBundle a SEQUENCE OF Cert. Changed type of policyID to UTF8string
to hold the URL. Got rid of KeyID. Moved signerName out of Signature
and into PSRequest and TBSResponse, and made it optional.

6: Added the XML syntax and example.

7: Removed the second paragraph because it dealt with RequestHash in
the request.

C.3 Difference between -02 and -03

1. Changed TBSResponse and TBSRequest to PSResponse and
PSRequest. Made signatures optional in both requests and responses.

2. Added a tag to the optional signatures in both requests and
responses.

3. Changed RevocationInfos to RevocationInfo.

4. Removed CertHash completely.

5. Simplified section 3.5, since FullCert has gone away

6. Replaced section 3.6 to talk about Cert, rather than FullCert

7. Replaced ExtensionParameter with ExtensionValue in Section 3.11.

8. Made sure that all SEQUENCE OF are SEQUENCE SIZE (1..MAX) OF

9. Import Extension and used the same definition for Extension as in
RFC2459

10. Replace "trusted root" with "trusted certificate", because a
server or client might decide to put its trust in a certificate that
might not be self-signed. Replaced trustedRoot with trustedCert.

11. Fixed once occurance of definition of requestNonce

12. Removed scvp, scvpReq and scvpResp tags in the XML.

13. Removed the last 2 sentences of the second paragraph Section 3.4

14. Changed last sentence of section 3.13, since you have have multiple
cert chains for a certificate even if there is no cross certification.

15. Changed last sentence of section 3.17.

16. Moved section 3.21 to the response section - 4.4a. We need to
renumber all sections when we are close to being done.

17. Added a default value for the attribute value of ReplyStatus in
the XML.

18. Added IMPORTS to the ASN.1 module.

19. Gave the extensions in different places different names.

20. Changed the way criticality is specified for Extension in XML

21. Added the mime type registration requests

22. Added appendix E and moved Author Information to appendix F

23. Moved signerName from the PSRequest and PSResponse to the
signature part.

24. Removed the second paragraph in section 3.13.

25. Changed a line in section 3.14, first para (about where a client
may have obtained an OCSP response to send to the SCVP server).

26. Got rid of the multiple places where we say what is signed by the
RequestSignature or ResponseSignature (e.g. section 3.1 and 3.2). Also
simplified the definition of the RequestSignature and
ResponseSignature in sections 3 and 4. The should be defined in detail
in the encoding sections.

D. MIME Registrations

D.1 application/scvp-request

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

   MIME media type name: application

   MIME subtype name: scvp-request

   Required parameters: None

   Optional parameters: None

   Encoding considerations: binary or XML

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

   Interoperability considerations: None

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

   Applications which 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@valicert.com>

   Intended usage: COMMON

   Author/Change controller:
   Ambarish Malpani <ambarish@valicert.com>

D.2 application/scvp-response

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

   MIME media type name: application

   MIME subtype name: scvp-response

   Required parameters: None

   Optional parameters: None
   Encoding considerations: binary or XML

   Security considerations: Carries a cryptographically signed response

   Interoperability considerations: None

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

   Applications which use this media type: SCVP servers

   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@valicert.com>

   Intended usage: COMMON

   Author/Change controller:
   Ambarish Malpani <ambarish@valicert.com>

E. SCVP data format

E.1 SCVP over HTTP

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

E.1.1 Request

   HTTP based SCVP requests can 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/scvp-request"
   while 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 DER encoding of the FullRequest, or XML encoding of
   FullRequest. Other HTTP headers MAY be present and MAY
   be ignored if not understood by the requestor.


E.1.2 Response

   An HTTP-based SCVP response is composed of the appropriate HTTP
   headers, followed by the binary value of the DER encoding of the
   FullResponse or XML encoding of FullResponse. The Content-Type
   header MUST have the value "application/scvp-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.


F. Author Contact Information

Ambarish Malpani
ValiCert, Inc.
339 N. Bernardo Ave.
Mountain View, CA 94043
ambarish@valicert.com

Paul Hoffman
VPN Consortium
127 Segre Place
Santa Cruz, CA  95060 USA
paul.hoffman@vpnc.org


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