Certificate Management over CMS (CMC)

1.1. Protocol Requirements

The protocol must be based as much as possible on the existing CMS, PKCS #10 [PKCS10] and CRMF (Certificate Request Message Format) [CRMF] specifications.¶

The protocol must support the current industry practice of a PKCS #10 certification request followed by a PKCS#7 "certs-only" response as a subset of the protocol.¶

The protocol must easily support the multi-key enrollment protocols required by S/MIME and other groups.¶

The protocol must supply a way of doing all enrollment operations in a single round-trip. When this is not possible the number of round-trips is to be minimized.¶

The protocol must be designed such that all key generation can occur on the client.¶

Support must exist for the mandatory algorithms used by S/MIME. Support should exist for all other algorithms cited by the S/MIME core documents.¶

The protocol must contain Proof-of-Possession (POP) methods. Optional provisions for multiple-round-trip POP will be made if necessary.¶

The protocol must support deferred and pending responses to enrollment requests for cases where external procedures are required to issue a certificate.¶

1.2. Requirements Terminology

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.¶

1.3. Changes from RFC 2797

We have done a major overhaul on the layout of the document. This included two different steps. Firstly we removed some sections from the document and moved them to two other documents. Information on how to transport our messages are now found in [CMC-TRANS]. Information on which controls and sections of this document must be implemented along with which algorithms are required can now be found in [CMC-COMPL].¶

A number of new controls have been added in this version:¶

• Extended CMC Status Info Section 6.1.1¶

• Publish Trust Anchors Section 6.15¶

• Authenticate Data Section 6.16¶

• Batch Request and Response Processing Section 6.17¶

• Publication Information Section 6.18¶

• Modify Certification Request Section 6.5.1¶

• Control Processed Section 6.19¶

• Identity Proof Section 6.2.2¶

• Identity POP Link Witness V2 Section 6.3.1.1¶

1.4. Updates Made by RFC 6402

Two new controls have been added:¶

• RA Identity Witness allows for an RA to perform identity checking using the identity and shared-secret, and then tell any following servers that the identity check was successfully performed.¶

• Response Body allows for an RA to identify a nested response for an EE to process.¶

Created a new attribute, Change Subject Name, that allows a client to request a change in the subject name and subject alternate name fields in a certificate.¶

Added Extended Key Usages for CMC to distinguish server types.¶

Defined a new Subject Information Access type to hold locations to contact the CMC server.¶

Clarified that the use of a pre-existing certificate is not limited to just renewal and rekey messages and is required for support. This formalizes a requirement for the ability to do renewal and rekey that previously was implicit.¶

1.5. Changes Since RFC 6402

--02 todo:¶

• Address management of KEM certificate¶

• Add module to support PBKDF2¶

--01 version changes:¶

• Changed RFC 5273 references to draft-mandel-lamps-rfc5273bis¶

• Changed RFC 5274 references to draft-mandel-lamps-rfc5274bis¶

• Added missing "OBJECT IDENTIFIER" to declarations throughout mainbody to match ASN.1 module¶

• Rework Section 1.3¶

• Update CMC Control Attribute Table¶

• Updates ASN.1 to use 2002 ASN.1 module baseed on [CMC-Updates]¶

• To support adopting SHA-256 and HMAC-SHA256:¶

  • Add maca-hMAC-SHA256 to POPAlgs¶

  • Add mda-sha256 to WitnessAlgs¶

  • Add maca-hMAC-SHA256 and mda-sha256 to example in Appendix B¶

• Merged [erratum2731]¶

• Merged [erratum4775]¶

• Mereged [erratum7379]¶

• Merged [erratum7628]¶

• Merged [erratum7629]¶

--00 version changes:¶

• Added "Updates Made by RFC 6402" section¶

• Merged [CMC-Updates] text¶

• Merged [erratum2063]¶

• Merged [erratum7627]¶

• Updated and moved Acknowledgments¶

2.1. Terminology

There are several different terms, abbreviations, and acronyms used in this document. These are defined here, in no particular order, for convenience and consistency of usage:¶

• • End-Entity (EE) refers to the entity that owns a key pair and for whom a certificate is issued.¶

• • Registration Authority (RA) or Local RA (LRA) refers to an entity that acts as an intermediary between the EE and the CA. Multiple RAs can exist between the end-entity and the Certification Authority. RAs may perform additional services such as key generation or key archival. This document uses the term RA for both RA and LRA.¶

• • Certification Authority (CA) refers to the entity that issues certificates.¶

• • Client refers to an entity that creates a PKI Request. In this document, both RAs and EEs can be clients.¶

• • Server refers to the entities that process PKI Requests and create PKI Responses. In this document, both CAs and RAs can be servers.¶

• • PKCS #10 refers to the Public Key Cryptography Standard #10 [PKCS10] which defines a certification request syntax.¶

• • CRMF refers to the Certificate Request Message Format RFC [CRMF]. CMC uses this certification request syntax defined in this document as part of the protocol.¶

• • CMS refers to the Cryptographic Message Syntax RFC [CMS]. This document provides for basic cryptographic services including encryption and signing with and without key management.¶

• • PKI Request/Response refers to the requests/responses described in this document. PKI Requests include certification requests, revocation requests, etc. PKI Responses include certs-only messages, failure messages, etc.¶

• • Proof-of-Identity refers to the client proving they are who they say that they are to the server.¶

• • Enrollment or certification request refers to the process of a client requesting a certificate. A certification request is a subset of the PKI Requests.¶

• • Proof-of-Possession (POP) refers to a value that can be used to prove that the private key corresponding to a public key is in the possession and can be used by an end-entity. The different types of POP are:¶

• • • Signature provides the required POP by a signature operation over some data.¶

• • • Direct provides the required POP operation by an encrypted challenge/response mechanism.¶

• • • Indirect provides the required POP operation by returning the issued certificate in an encrypted state. (This method is not used by CMC.)¶

• • • Publish provides the required POP operation by providing the private key to the certificate issuer. (This method is not currently used by CMC. It would be used by Key Generation or Key Escrow extensions.)¶

• • • Attested provides the required POP operation by allowing a trusted entity to assert that the POP has been proven by one of the above methods.¶

• • Object IDentifier (OID) is a primitive type in Abstract Syntax Notation One (ASN.1).¶

2.2. Protocol Requests/Responses

Figure 1 shows the Simple PKI Requests and Responses. The contents of Simple PKI Request and Response are detailed in Section 3.1 and Section 4.1.¶

Simple PKI Request                      Simple PKI Response
-------------------------               --------------------------

 +----------+                            +------------------+
 | PKCS #10 |                            | CMS ContentInfo  |
 +----------+--------------+             +------------------+------+
 | Certification Request   |             | CMS Signed Data,        |
 |                         |             |   no SignerInfo         |
 | Subject Name            |             |                         |
 | Subject Public Key Info |             | SignedData contains one |
 |   (K_PUB)               |             | or more certificates in |
 | Attributes              |             | the certificates field  |
 |                         |             | Relevant CA certs and   |
 +-----------+-------------+             | CRLs can be included    |
             | signed with |             | as well.                |
             | matching    |             |                         |
             | K_PRIV      |             | encapsulatedContentInfo |
             +-------------+             | is absent.              |
                                         +--------------+----------+
                                                        | unsigned |
                                                        +----------+

             Figure 1: Simple PKI Requests and Responses

Figure 2 shows the Full PKI Requests and Responses. The contents of the Full PKI Request and Response are detailed in Section 3.2 and Section 4.2.¶

Full PKI Request                        Full PKI Response
-----------------------                 ------------------------
 +----------------+                      +----------------+
 | CMS ContentInfo|                      | CMS ContentInfo|
 | CMS SignedData |                      | CMS SignedData |
 |   or Auth Data |                      |   or Auth Data |
 |     object     |                      |     object     |
 +----------------+--------+             +----------------+--------+
 |                         |             |                         |
 | PKIData                 |             | PKIResponse             |
 |                         |             |                         |
 | Sequence of:            |             | Sequence of:            |
 | <enrollment control>*   |             | <enrollment control>*   |
 | <certification request>*|             | <CMS object>*           |
 | <CMS object>*           |             | <other message>*        |
 | <other message>*        |             |                         |
 |                         |             | where * == zero or more |
 | where * == zero or more |             |                         |
 |                         |             | All certificates issued |
 | Certification requests  |             | as part of the response |
 | are CRMF, PKCS #10, or  |             | are included in the     |
 | Other.                  |             | "certificates" field    |
 |                         |             | of the SignedData.      |
 +-------+-----------------+             | Relevant CA certs and   |
         | signed (keypair |             | CRLs can be included as |
         | used may be pre-|             | well.                   |
         | existing or     |             |                         |
         | identified in   |             +---------+---------------+
         | the request)    |                       | signed by the |
         +-----------------+                       | CA or an LRA  |
                                                   +---------------+

          Figure 2: Full PKI Requests and Responses

3.1. Simple PKI Request

A Simple PKI Request uses the PKCS #10 syntax CertificationRequest [PKCS10].¶

When a server processes a Simple PKI Request, the PKI Response returned is:¶

• • Simple PKI Response on success.¶

• • Full PKI Response on failure. The server MAY choose not to return a PKI Response in this case.¶

The Simple PKI Request MUST NOT be used if a proof-of-identity needs to be included.¶

The Simple PKI Request cannot be used if the private key is not capable of producing some type of signature (i.e., Diffie-Hellman (DH) keys can use the signature algorithms in [DH-POP] for production of the signature).¶

The Simple PKI Request cannot be used for any of the advanced services specified in this document.¶

The client MAY incorporate one or more X.509v3 extensions in any certification request based on PKCS #10 as an ExtensionReq attribute. The ExtensionReq attribute is defined as:¶

  ExtensionReq ::= SEQUENCE SIZE (1..MAX) OF Extension

where Extension is imported from [PKIXCERT] and ExtensionReq is identified by:¶

  id-ExtensionReq OBJECT IDENTIFIER ::= { iso(1) member-body(2)
    us(840) rsadsi(113549) pkcs(1) pkcs-9(9) 14 }

Servers MUST be able to process all extensions defined, but not prohibited, in [PKIXCERT]. Servers are not required to be able to process other X.509v3 extensions transmitted using this protocol, nor are they required to be able to process private extensions. Servers are not required to put all client-requested extensions into a certificate. Servers are permitted to modify client-requested extensions. Servers MUST NOT alter an extension so as to invalidate the original intent of a client-requested extension. (For example, changing key usage from keyAgreement to digitalSignature.) If a certification request is denied due to the inability to handle a requested extension and a PKI Response is returned, the server MUST return a PKI Response with a CMCFailInfo value with the value unsupportedExt.¶

3.2. Full PKI Request

The Full PKI Request provides the most functionality and flexibility.¶

The Full PKI Request is encapsulated in either a SignedData or an AuthenticatedData with an encapsulated content type of 'id-cct-PKIData' (Section 3.2.1).¶

When a server processes a Full PKI Request, a PKI Response MUST be returned. The PKI Response returned is:¶

• • Simple PKI Response if the enrollment was successful and only certificates are returned. (A CMCStatusInfoV2 control with success is implied.)¶

• • Full PKI Response if the enrollment was successful and information is returned in addition to certificates, if the enrollment is pending, or if the enrollment failed.¶

If SignedData is used, the signature can be generated using either the private key material of an embedded signature certification request (i.e., included in the TaggedRequest tcr or crm fields) or a previously certified signature key. If the private key of a signature certification request is used, then:¶

1. The certification request containing the corresponding public key MUST include a Subject Key Identifier extension.¶

2. The subjectKeyIdentifier form of the signerIdentifier in SignerInfo MUST be used.¶

3. The value of the subjectKeyIdentifier form of SignerInfo MUST be the Subject Key Identifier specified in the corresponding certification request. (The subjectKeyIdentifier form of SignerInfo is used here because no certificates have yet been issued for the signing key.) If the request key is used for signing, there MUST be only one SignerInfo in the SignedData.¶

If AuthenticatedData is used, then:¶

1. The Password Recipient Info option of RecipientInfo MUST be used.¶

2. A randomly generated key is used to compute the Message Authentication Code (MAC) value on the encapsulated content.¶

3. The input for the key derivation algorithm is a concatenation of the identifier (encoded as UTF8) and the shared-secret.¶

When creating a PKI Request to renew or rekey a certificate:¶

1. The Identification and Identity Proof controls are absent. The same information is provided by the use of an existing certificate from a CA when signing the PKI Request. In this case, the CA that issued the original certificate and the CA the request is made to will usually be the same, but could have a common operator.¶

2. CAs and RAs can impose additional restrictions on the signing certificate used. They may require that the most recently issued signing certificate for a client be used.¶

3. Some CAs may prevent renewal operations (i.e., reuse of the same keys). In this case the CA MUST return a PKI Response with noKeyReuse as the CMCFailInfo failure code.¶

  id-cct-PKIData OBJECT IDENTIFIER ::= { id-pkix id-cct(12) 2 }

  PKIData ::= SEQUENCE {
    controlSequence    SEQUENCE SIZE(0..MAX) OF TaggedAttribute,
    reqSequence        SEQUENCE SIZE(0..MAX) OF TaggedRequest,
    cmsSequence        SEQUENCE SIZE(0..MAX) OF TaggedContentInfo,
    otherMsgSequence   SEQUENCE SIZE(0..MAX) OF OtherMsg
  }

  TaggedAttribute ::= SEQUENCE {
    bodyPartID         BodyPartID,
    attrType           OBJECT IDENTIFIER,
    attrValues         SET OF AttributeValue
  }

  AttributeValue ::= ANY

  TaggedRequest ::= CHOICE {
    tcr               [0] TaggedCertificationRequest,
    crm               [1] CertReqMsg,
    orm               [2] SEQUENCE {
      bodyPartID            BodyPartID,
      requestMessageType    OBJECT IDENTIFIER,
      requestMessageValue   ANY DEFINED BY requestMessageType
    }
  }

  TaggedCertificationRequest ::= SEQUENCE {
    bodyPartID            BodyPartID,
    certificationRequest  CertificationRequest
  }

  CertReqMsg ::= SEQUENCE {
    certReq   CertRequest,
    popo      ProofOfPossession  OPTIONAL,
    -- content depends upon key type
    regInfo   SEQUENCE SIZE(1..MAX) OF
                AttributeTypeAndValue OPTIONAL }

  CertRequest ::= SEQUENCE {
    certReqId     INTEGER,
                    -- ID for matching request and reply
    certTemplate  CertTemplate,
                    -- Selected fields of cert to be issued
    controls      Controls OPTIONAL }
                    -- Attributes affecting issuance

  CertTemplate ::= SEQUENCE {
    version      [0] Version               OPTIONAL,
    serialNumber [1] INTEGER               OPTIONAL,
    signingAlg   [2] AlgorithmIdentifier   OPTIONAL,
    issuer       [3] Name                  OPTIONAL,
    validity     [4] OptionalValidity      OPTIONAL,
    subject      [5] Name                  OPTIONAL,
    publicKey    [6] SubjectPublicKeyInfo  OPTIONAL,
    issuerUID    [7] UniqueIdentifier      OPTIONAL,
    subjectUID   [8] UniqueIdentifier      OPTIONAL,
    extensions   [9] Extensions            OPTIONAL }

  TaggedContentInfo ::= SEQUENCE {
    bodyPartID              BodyPartID,
    contentInfo             ContentInfo
  }

  OtherMsg ::= SEQUENCE {
    bodyPartID        BodyPartID,
    otherMsgType      OBJECT IDENTIFIER,
    otherMsgValue     ANY DEFINED BY otherMsgType }

  bodyIdMax INTEGER ::= 4294967295

  BodyPartID ::= INTEGER(0..bodyIdMax)

  BodyPartList ::= SEQUENCE SIZE (1..MAX) OF BodyPartID

  BodyPartPath ::= SEQUENCE SIZE (1..MAX) OF BodyPartID

  id-aa-cmc-unsignedData OBJECT IDENTIFIER ::= { id-aa 34 }

  CMCUnsignedData ::= SEQUENCE {
    bodyPartPath        BodyPartPath,
    identifier          OBJECT IDENTIFIER,
    content             ANY DEFINED BY identifier
  }

4.1. Simple PKI Response

Clients MUST be able to process the Simple PKI Response. The Simple PKI Response consists of a SignedData with no EncapsulatedContentInfo and no SignerInfo. The certificates requested in the PKI Response are returned in the certificate field of the SignedData.¶

Clients MUST NOT assume the certificates are in any order. Servers SHOULD include all intermediate certificates needed to form complete certification paths to one or more trust anchors, not just the newly issued certificate(s). The server MAY additionally return CRLs in the CRL bag. Servers MAY include the self-signed certificates. Clients MUST NOT implicitly trust included self-signed certificate(s) merely due to its presence in the certificate bag. In the event clients receive a new self-signed certificate from the server, clients SHOULD provide a mechanism to enable the user to use the certificate as a trust anchor. (The Publish Trust Anchors control (Section 6.15) should be used in the event that the server intends the client to accept one or more certificates as trust anchors. This requires the use of the Full PKI Response message.)¶

4.2. Full PKI Response

Clients MUST be able to process a Full PKI Response.¶

The Full PKI Response consists of a SignedData or AuthenticatedData encapsulating a PKIResponse content type. The certificates issued in a PKI Response are returned in the certificates field of the immediately encapsulating SignedData.¶

Clients MUST NOT assume the certificates are in any order. Servers SHOULD include all intermediate certificates needed to form complete chains to one or more trust anchors, not just the newly issued certificate(s). The server MAY additionally return CRLs in the CRL bag. Servers MAY include self-signed certificates. Clients MUST NOT implicitly trust included self-signed certificate(s) merely due to its presence in the certificate bag. In the event clients receive a new self-signed certificate from the server, clients MAY provide a mechanism to enable the user to explicitly use the certificate as a trust anchor. (The Publish Trust Anchors control (Section 6.15) exists for the purpose of allowing for distribution of trust anchor certificates. If a trusted anchor publishes a new trusted anchor, this is one case where automated trust of the new trust anchor could be allowed.)¶

  id-cct-PKIResponse OBJECT IDENTIFIER ::= { id-pkix id-cct(12) 3  }

  PKIResponse ::= SEQUENCE {
    controlSequence   SEQUENCE SIZE(0..MAX) OF TaggedAttribute,
    cmsSequence       SEQUENCE SIZE(0..MAX) OF TaggedContentInfo,
    otherMsgSequence  SEQUENCE SIZE(0..MAX) OF OtherMsg
    }

    ReponseBody ::= PKIResponse

6.1. CMC Status Info Controls

The CMC Status Info controls return information about the status of a client/server request/response. Two controls are described in this section. The Extended CMC Status Info control is the preferred control; the CMC Status Info control is included for backwards compatibility with RFC 2797.¶

Servers MAY emit multiple CMC status info controls referring to a single body part. Clients MUST be able to deal with multiple CMC status info controls in a PKI Response. Servers MUST use the Extended CMC Status Info control, but MAY additionally use the CMC Status Info control. Clients MUST be able to process the Extended¶

CMC Status Info control.¶

  id-cmc-statusInfoV2 OBJECT IDENTIFIER ::= { id-cmc 25 }

   CMCStatusInfoV2 ::= SEQUENCE {
      cMCStatus             CMCStatus,
      bodyList              SEQUENCE SIZE (1..MAX) OF
                              BodyPartReference,
      statusString          UTF8String OPTIONAL,
      otherInfo             OtherStatusInfo OPTIONAL
   }

   OtherStatusInfo ::= CHOICE {
      failInfo              CMCFailInfo,
      pendInfo              PendInfo,
      extendedFailInfo      ExtendedFailInfo
   }

   PendInfo ::= SEQUENCE {
      pendToken           OCTET STRING,
      pendTime            GeneralizedTime
   }

   ExtendedFailInfo ::= SEQUENCE {
      failInfoOID            OBJECT IDENTIFIER,
      failInfoValue          ANY DEFINED BY failInfoOID
   }

  BodyPartReference ::= CHOICE {
    bodyPartID           BodyPartID,
    bodyPartPath         BodyPartPath
   }

  id-cmc-statusInfo OBJECT IDENTIFIER ::= { id-cmc 1 }

  CMCStatusInfo ::= SEQUENCE {
    cMCStatus           CMCStatus,
    bodyList            BodyPartList,
    statusString        UTF8String OPTIONAL,
    otherInfo           CHOICE {
      failInfo            CMCFailInfo,
      pendInfo            PendInfo } OPTIONAL
    }

  CMCStatus ::= INTEGER {
    success                (0),
    -- reserved            (1),
    failed                 (2),
    pending                (3),
    noSupport              (4),
    confirmRequired        (5),
    popRequired            (6),
    partial                (7)
    }

  CMCFailInfo ::= INTEGER {
    badAlg            (0),
    badMessageCheck   (1),
    badRequest        (2),
    badTime           (3),
    badCertId         (4),
    unsupportedExt     (5),
    mustArchiveKeys   (6),
    badIdentity       (7),
    popRequired       (8),
    popFailed         (9),
    noKeyReuse        (10),
    internalCAError   (11),
    tryLater          (12),
    authDataFail      (13)
    }

6.2. Identification and Identity Proof Controls

Some CAs and RAs require that a proof-of-identity be included in a certification request. Many different ways of doing this exist with different degrees of security and reliability. Most are familiar with a bank's request to provide your mother's maiden name as a form of identity proof. The reasoning behind requiring a proof-of- identity can be found in Appendix C of [CRMF].¶

CMC provides a method to prove the client's identity based on a client/server shared-secret. If clients support the Full PKI Request, clients MUST implement this method of identity proof (Section 6.2.2). Servers MUST provide this method, but MAY additionally support bilateral methods of similar strength.¶

This document also provides an Identification control (Section 6.2.3). This control is a simple method to allow a client to state who they are to the server. Generally, a shared-secret AND an identifier of that shared-secret are passed from the server to the client. The identifier is placed in the Identification control, and the shared-secret is used to compute the Identity Proof control.¶

  id-cmc-identityProofV2 OBJECT IDENTIFIER ::= { id-cmc 34 }

  IdentifyProofV2 ::= SEQUENCE {
    hashAlgID        AlgorithmIdentifier,
    macAlgID         AlgorithmIdentifier,
    witness          OCTET STRING
    }

  id-cmc-identityProof OBJECT IDENTIFIER ::= { id-cmc 3 }

  IdentifyProof ::= OCTET STRING

  id-cmc-identification OBJECT IDENTIFIER ::= { id-cmc 2 }

  Identification ::= UTF8String

6.3. Linking Identity and POP Information

In a CMC Full PKI Request, identity proof information about the client is carried in the certificate associated with the signature of the SignedData containing the certification requests, one of the two identity proof controls or the MAC computed for the AuthenticatedData containing the certification requests. Proof-of-possession (POP) information for key pairs, however, is carried separately for each PKCS #10 or CRMF certification request. (For keys capable of generating a digital signature, the POP is provided by the signature on the PKCS #10 or CRMF request. For encryption-only keys, the controls described in Section 6.7 are used.) In order to prevent substitution-style attacks, the protocol must guarantee that the same entity supplied both the POP and proof-of-identity information.¶

We describe three mechanisms for linking identity and POP information: witness values cryptographically derived from a shared- secret (Section 6.3.1), shared-secret/subject name matching (Section 6.3.2) , and subject name matching to an existing certificate (Section 6.3.3) . Clients and servers MUST support the witness value and the certificate linking techniques. Clients and servers MAY support shared-secret/name matching or MAY support other bilateral techniques of similar strength. The idea behind the first two mechanisms is to force the client to sign some data into each certification request that can be directly associated with the shared-secret; this will defeat attempts to include certification requests from different entities in a single Full PKI Request.¶

  id-cmc-popLinkWitnessV2 OBJECT IDENTIFIER ::= { id-cmc 33 }

  PopLinkWitnessV2 ::= SEQUENCE {
    keyGenAlgorithm   AlgorithmIdentifier,
    macAlgorithm      AlgorithmIdentifier,
    witness           OCTET STRING
    }

  id-cmc-popLinkWitness OBJECT IDENTIFIER ::= { id-cmc 23 }

  PopLinkWitness ::= OCTET STRING

  id-cmc-popLinkRandom OBJECT IDENTIFIER ::= { id-cmc 22 }

  PopLinkRandom ::= OCTET STRING

6.4. Data Return Control

The Data Return control allows clients to send arbitrary data (usually some type of internal state information) to the server and to have the data returned as part of the Full PKI Response. Data placed in a Data Return control is considered to be opaque to the server. The same control is used for both Full PKI Requests and Responses. If the Data Return control appears in a Full PKI Request, the server MUST return it as part of the PKI Response.¶

In the event that the information in the Data Return control needs to be confidential, it is expected that the client would apply some type of encryption to the contained data, but the details of this are outside the scope of this specification.¶

The Data Return control is identified by the OID:¶

  id-cmc-dataReturn OBJECT IDENTIFIER ::= { id-cmc 4 }

The Data Return control has the ASN.1 definition:¶

  DataReturn ::= OCTET STRING

A client could use this control to place an identifier marking the exact source of the private key material. This might be the identifier of a hardware device containing the private key.¶

6.5. RA Certificate Modification Controls

These controls exist for RAs to be able to modify the contents of a certification request. Modifications might be necessary for various reasons. These include addition of certificate extensions or modification of subject and/or subject alternative names.¶

Two controls exist for this purpose. The first control, Modify Certification Request (Section 6.5.1), allows the RA to replace or remove any field in the certificate. The second control, Add Extensions (Section 6.5.2), only allows for the addition of extensions.¶

  id-cmc-modCertTemplate OBJECT IDENTIFIER ::= { id-cmc 31 }

  ModCertTemplate ::= SEQUENCE {
    pkiDataReference             BodyPartPath,
    certReferences               BodyPartList,
    replace                      BOOLEAN DEFAULT TRUE,
    certTemplate                 CertTemplate
    }

id-cmc-addExtensions OBJECT IDENTIFIER ::= { id-cmc 8 }

  AddExtensions ::= SEQUENCE {
    pkiDataReference             BodyPartID,
    certReferences               SEQUENCE OF BodyPartID,
    extensions                   SEQUENCE OF Extension
    }

6.6. Transaction Identifier Control and Sender and Recipient Nonce Controls

Transactions are identified and tracked with a transaction identifier. If used, clients generate transaction identifiers and retain their value until the server responds with a Full PKI Response that completes the transaction. Servers correspondingly include received transaction identifiers in the Full PKI Response.¶

The Transaction Identifier control is identified by the OID:¶

  id-cmc-transactionId  OBJECT IDENTIFIER ::= { id-cmc 5 }

The Transaction Identifier control has the ASN.1 definition:¶

  TransactionId ::= INTEGER

The Transaction Identifier control identifies a given transaction. It is used by client and server to manage the state of an operation. Clients MAY include a Transaction Identifier control in a request. If the original request contains a Transaction Identifier control, all subsequent requests and responses MUST include the same Transaction Identifier control.¶

Replay protection is supported through the use of the Sender and Recipient Nonce controls. If nonces are used, in the first message of a transaction, a Recipient Nonce control is not transmitted; a Sender Nonce control is included by the transaction originator and retained for later reference. The recipient of a Sender Nonce control reflects this value back to the originator as a Recipient Nonce control and includes its own Sender Nonce control. Upon receipt by the transaction originator of this response, the transaction originator compares the value of Recipient Nonce control to its retained value. If the values match, the message can be accepted for further security processing. The received value for a Sender Nonce control is also retained for inclusion in the next message associated with the same transaction.¶

The Sender Nonce and Recipient Nonce controls are identified by the OIDs:¶

  id-cmc-senderNonce    OBJECT IDENTIFIER ::= { id-cmc 6 }
  id-cmc-recipientNonce OBJECT IDENTIFIER ::= { id-cmc 7 }

The Sender Nonce control has the ASN.1 definition:¶

  SenderNonce ::= OCTET STRING

The Recipient Nonce control has the ASN.1 definition:¶

  RecipientNonce ::= OCTET STRING

Clients MAY include a Sender Nonce control in the initial PKI Request. If a message includes a Sender Nonce control, the response MUST include the transmitted value of the previously received Sender Nonce control as a Recipient Nonce control and include a new value as its Sender Nonce control.¶

6.7. Encrypted and Decrypted POP Controls

Servers MAY require that this POP method be used only if another POP method is unavailable. Servers SHOULD reject all certification requests contained within a PKIData if any required POP is missing for any element within the PKIData.¶

Many servers require proof that the entity that generated the certification request actually possesses the corresponding private component of the key pair. For keys that can be used as signature keys, signing the certification request with the private key serves as a POP on that key pair. With keys that can only be used for encryption operations, POP MUST be performed by forcing the client to decrypt a value. See Section 5 of [CRMF] for a detailed discussion of POP.¶

By necessity, POP for encryption-only keys cannot be done in one round-trip, since there are four distinct steps:¶

1. Client tells the server about the public component of a new encryption key pair.¶

2. Server sends the client a POP challenge, encrypted with the presented public encryption key.¶

3. Client decrypts the POP challenge using the private key that corresponds to the presented public key and sends the plaintext back to the server.¶

4. Server validates the decrypted POP challenge and continues processing the certification request.¶

CMC defines two different controls. The first deals with the encrypted challenge sent from the server to the user in Step 2. The second deals with the decrypted challenge sent from the client to the server in Step 3.¶

The Encrypted POP control is used to send the encrypted challenge from the server to the client as part of the PKIResponse. (Note that it is assumed that the message sent in Step 1 above is a Full PKI Request and that the response in Step 2 is a Full PKI Response including a CMCFailInfo specifying that a POP is explicitly required, and providing the POP challenge in the encryptedPOP control.)¶

The Encrypted POP control is identified by the OID:¶

    id-cmc-encryptedPOP OBJECT IDENTIFIER ::= { id-cmc 9 }

The Encrypted POP control has the ASN.1 definition:¶

  EncryptedPOP ::= SEQUENCE {
    request        TaggedRequest,
    cms            ContentInfo,
    thePOPAlgID    AlgorithmIdentifier,
    witnessAlgID   AlgorithmIdentifier,
    witness        OCTET STRING
    }

The Decrypted POP control is identified by the OID:¶

  id-cmc-decryptedPOP  OBJECT IDENTIFIER ::= { id-cmc 10 }

The Decrypted POP control has the ASN.1 definition:¶

  DecryptedPOP ::= SEQUENCE {
    bodyPartID     BodyPartID,
    thePOPAlgID    AlgorithmIdentifier,
    thePOP         OCTET STRING
    }

The encrypted POP algorithm works as follows:¶

1. The server randomly generates the POP Proof Value and associates it with the request.¶

2. The server returns the Encrypted POP control with the following fields set:¶

   • request is the original certification request (it is included here so the client need not keep a copy of the request).¶

   • cms is an EnvelopedData, the encapsulated content type being id- data and the content being the POP Proof Value; this value needs to be long enough that one cannot reverse the value from the witness hash. If the certification request contains a Subject Key Identifier (SKI) extension, then the recipient identifier SHOULD be the SKI. If the issuerAndSerialNumber form is used, the IssuerName MUST be encoded as NULL and the SerialNumber as the bodyPartID of the certification request.¶

   • thePOPAlgID identifies the algorithm to be used in computing the return POP value.¶

   • witnessAlgID identifies the hash algorithm used on the POP Proof Value to create the field witness.¶

   • witness is the hashed value of the POP Proof Value.¶

3. The client decrypts the cms field to obtain the POP Proof Value. The client computes H(POP Proof Value) using the witnessAlgID and compares to the value of witness. If the values do not compare or the decryption is not successful, the client MUST abort the enrollment process. The client aborts the process by sending a request containing a CMC Status Info control with CMCFailInfo value of popFailed.¶

4. The client creates the Decrypted POP control as part of a new PKIData. The fields in the DecryptedPOP are:¶

   • bodyPartID refers to the certification request in the new PKI Request.¶

   • thePOPAlgID is copied from the encryptedPOP.¶

   • thePOP contains the possession proof. This value is computed by thePOPAlgID using the POP Proof Value and the request.¶

5. The server then re-computes the value of thePOP from its cached value and the request and compares to the value of thePOP. If the values do not match, the server MUST NOT issue the certificate. The server MAY re-issue a new challenge or MAY fail the request altogether.¶

When defining the algorithms for thePOPAlgID and witnessAlgID, care must be taken to ensure that the result of witnessAlgID is not a useful value to shortcut the computation with thePOPAlgID. The POP Proof Value is used as the secret value in the HMAC algorithm and the request is used as the data. If the POP Proof Value is greater than 64 bytes, only the first 64 bytes of the POP Proof Value is used as the secret.¶

One potential problem with the algorithm above is the amount of state that a CA needs to keep in order to verify the returned POP value. The following describes one of many possible ways of addressing the problem by reducing the amount of state kept on the CA to a single (or small set) of values.¶

1. Server generates random seed x, constant across all requests. (The value of x would normally be altered on a regular basis and kept for a short time afterwards.)¶

2. For certification request R, server computes y = F(x,R). F can be, for example, HMAC-SHA1(x,R). All that's important for statelessness is that y be consistently computable with only known state constant x and function F, other inputs coming from the certification request structure. y should not be predictable based on knowledge of R, thus the use of a one-way function like HMAC-SHA1.¶

6.8. RA POP Witness Control

In a certification request scenario that involves an RA, the CA may allow (or require) that the RA perform the POP protocol with the entity that generated the certification request. In this case, the RA needs a way to inform the CA that it has done the POP. The RA POP Witness control addresses this issue.¶

The RA POP Witness control is identified by the OID:¶

  id-cmc-lraPOPWitness OBJECT IDENTIFIER ::= { id-cmc 11 }

The RA POP Witness control has the ASN.1 definition:¶

  LraPopWitness ::= SEQUENCE {
    pkiDataBodyid   BodyPartID,
    bodyIds         SEQUENCE of BodyPartID
    }

The fields in LraPOPWitness have the following meaning:¶

• • pkiDataBodyid contains the body part identifier of the nested TaggedContentInfo containing the client's Full PKI Request. pkiDataBodyid is set to 0 if the request is in the current PKIData.¶

• • bodyIds is a list of certification requests for which the RA has performed an out-of-band authentication. The method of authentication could be archival of private key material, challenge-response, or other means.¶

If a certification server does not allow an RA to do the POP verification, it returns a CMCFailInfo with the value of popFailed. The CA MUST NOT start a challenge-response to re-verify the POP itself.¶

6.9. Get Certificate Control

Everything described in this section is optional to implement.¶

The Get Certificate control is used to retrieve a previously issued certificate from a certificate repository. A CA, an RA, or an independent service may provide this repository. The clients expected to use this facility are those where a fully deployed directory is either infeasible or undesirable.¶

The Get Certificate control is identified by the OID:¶

  id-cmc-getCert OBJECT IDENTIFIER ::= { id-cmc 15 }

The Get Certificate control has the ASN.1 definition:¶

  GetCert ::= SEQUENCE {
    issuerName    GeneralName,
    serialNumber  INTEGER }

The fields in GetCert have the following meaning:¶

• • issuerName is the name of the certificate issuer.¶

• • serialNumber identifies the certificate to be retrieved.¶

The server that responds to this request places the requested certificate in the certificates field of a SignedData. If the Get Certificate control is the only control in a Full PKI Request, the response should be a Simple PKI Response.¶

6.10. Get CRL Control

Everything described in this section is optional to implement.¶

The Get CRL control is used to retrieve CRLs from a repository of CRLs. A CA, an RA, or an independent service may provide this repository. The clients expected to use this facility are those where a fully deployed directory is either infeasible or undesirable.¶

The Get CRL control is identified by the OID:¶

  id-cmc-getCRL OBJECT IDENTIFIER ::= { id-cmc 16 }

The Get CRL control has the ASN.1 definition:¶

  GetCRL ::= SEQUENCE {
    issuerName    Name,
    cRLName       GeneralName OPTIONAL,
    time          GeneralizedTime OPTIONAL,
    reasons       ReasonFlags OPTIONAL }

The fields in a GetCRL have the following meanings:¶

• • issuerName is the name of the CRL issuer.¶

• • cRLName may be the value of CRLDistributionPoints in the subject certificate or equivalent value in the event the certificate does not contain such a value.¶

• • time is used by the client to specify from among potentially several issues of CRL that one whose thisUpdate value is less than but nearest to the specified time. In the absence of a time component, the CA always returns with the most recent CRL.¶

• • reasons is used to specify from among CRLs partitioned by revocation reason. Implementers should bear in mind that while a specific revocation request has a single CRLReason code -- and consequently entries in the CRL would have a single CRLReason code value -- a single CRL can aggregate information for one or more reasonFlags.¶

A server responding to this request places the requested CRL in the crls field of a SignedData. If the Get CRL control is the only control in a Full PKI Request, the response should be a Simple PKI Response.¶

6.11. Revocation Request Control

The Revocation Request control is used to request that a certificate be revoked.¶

The Revocation Request control is identified by the OID:¶

  id-cmc-revokeRequest OBJECT IDENTIFIER ::= { id-cmc 17 }

The Revocation Request control has the ASN.1 definition:¶

  RevokeRequest ::= SEQUENCE {
    issuerName      Name,
    serialNumber    INTEGER,
    reason          CRLReason,
    invalidityDate  GeneralizedTime OPTIONAL,
    sharedSecret    OCTET STRING OPTIONAL,
    comment         UTF8string OPTIONAL }

The fields of RevokeRequest have the following meaning:¶

• • issuerName is the issuerName of the certificate to be revoked.¶

• • serialNumber is the serial number of the certificate to be revoked.¶

• • reason is the suggested CRLReason code for why the certificate is being revoked. The CA can use this value at its discretion in building the CRL.¶

• • invalidityDate is the suggested value for the Invalidity Date CRL Extension. The CA can use this value at its discretion in building the CRL.¶

• • sharedSecret is a secret value registered by the EE when the certificate was obtained to allow for revocation of a certificate in the event of key loss.¶

comment is a human-readable comment.¶

For a revocation request to be reliable in the event of a dispute, a strong proof-of-origin is required. However, in the instance when an EE has lost use of its signature private key, it is impossible for the EE to produce a digital signature (prior to the certification of a new signature key pair). The Revoke Request control allows the EE to send the CA a shared-secret that may be used as an alternative authenticator in the instance of loss of use of the EE's signature private key. The acceptability of this practice is a matter of local security policy.¶

It is possible to sign the revocation for the lost certificate with a different certificate in some circumstances. A client can sign a revocation for an encryption key with a signing certificate if the name information matches. Similarly, an administrator or RA can be assigned the ability to revoke the certificate of a third party. Acceptance of the revocation by the server depends on local policy in these cases.¶

Clients MUST provide the capability to produce a digitally signed Revocation Request control. Clients SHOULD be capable of producing an unsigned Revocation Request control containing the EE shared- secret (the unsigned message consisting of a SignedData with no signatures). If a client provides shared-secret-based self- revocation, the client MUST be capable of producing a Revocation Request control containing the shared-secret. Servers MUST be capable of accepting both forms of revocation requests.¶

The structure of an unsigned, shared-secret-based revocation request is a matter of local implementation. The shared-secret does not need to be encrypted when sent in a Revocation Request control. The shared-secret has a one-time use (i.e., it is used to request revocation of the certificate), and public knowledge of the shared- secret after the certificate has been revoked is not a problem. Clients need to inform users that the same shared-secret SHOULD NOT be used for multiple certificates.¶

A Full PKI Response MUST be returned for a revocation request.¶

6.12. Registration and Response Information Controls

The Registration Information control allows for clients to pass additional information as part of a Full PKI Request.¶

The Registration Information control is identified by the OID:¶

  id-cmc-regInfo OBJECT IDENTIFIER ::= { id-cmc 18 }

The Registration Information control has the ASN.1 definition:¶

  RegInfo ::= OCTET STRING

The content of this data is based on bilateral agreement between the client and server.¶

The Response Information control allows a server to return additional information as part of a Full PKI Response.¶

The Response Information control is identified by the OID:¶

  id-cmc-responseInfo  OBJECT IDENTIFIER ::= { id-cmc 19 }

The Response Information control has the ASN.1 definition:¶

  ResponseInfo ::= OCTET STRING

The content of this data is based on bilateral agreement between the client and server.¶

6.13. Query Pending Control

In some environments, process requirements for manual intervention or other identity checks can delay the return of the certificate. The Query Pending control allows clients to query a server about the state of a pending certification request. The server returns a pendToken as part of the Extended CMC Status Info and the CMC Status Info controls (in the otherInfo field). The client copies the pendToken into the Query Pending control to identify the correct certification request to the server. The server returns a suggested time for the client to query for the state of a pending certification request.¶

The Query Pending control is identified by the OID:¶

  id-cmc-queryPending  OBJECT IDENTIFIER ::= { id-cmc 21 }

The Query Pending control has the ASN.1 definition:¶

  QueryPending ::= OCTET STRING

If a server returns a pending or partial CMCStatusInfo (the transaction is still pending), the otherInfo MAY be omitted. If the otherInfo is not omitted, the value of 'pendInfo' MUST be the same as the original pendInfo value.¶

6.14. Confirm Certificate Acceptance Control

Some CAs require that clients give a positive confirmation that the certificates issued to the EE are acceptable. The Confirm Certificate Acceptance control is used for that purpose. If the CMC Status Info on a PKI Response is confirmRequired, then the client MUST return a Confirm Certificate Acceptance control contained in a Full PKI Request.¶

Clients SHOULD wait for the PKI Response from the server that the confirmation has been received before using the certificate for any purpose.¶

The Confirm Certificate Acceptance control is identified by the OID:¶

  id-cmc-confirmCertAcceptance  OBJECT IDENTIFIER ::= { id-cmc 24 }

The Confirm Certificate Acceptance control has the ASN.1 definition:¶

  CMCCertId ::= IssuerAndSerialNumber

CMCCertId contains the issuer and serial number of the certificate being accepted.¶

Servers MUST return a Full PKI Response for a Confirm Certificate Acceptance control.¶

Note that if the CA includes this control, there will be two full round-trips of messages.¶

1. The client sends the certification request to the CA.¶

2. The CA returns a Full PKI Response with the certificate and this control.¶

3. The client sends a Full PKI Request to the CA with an Extended CMC Status Info control accepting and a Confirm Certificate Acceptance control or an Extended CMC Status Info control rejecting the certificate.¶

4. The CA sends a Full PKI Response to the client with an Extended CMC Status Info of success.¶

6.15. Publish Trust Anchors Control

The Publish Trust Anchors control allows for the distribution of set trust anchors from a central authority to an EE. The same control is also used to update the set of trust anchors. Trust anchors are distributed in the form of certificates. These are expected, but not required, to be self-signed certificates. Information is extracted from these certificates to set the inputs to the certificates validation algorithm in Section 6.1.1 of [PKIXCERT].¶

The Publish Trust Anchors control is identified by the OID:¶

  id-cmc-trustedAnchors  OBJECT IDENTIFIER ::= { id-cmc 26 }

The Publish Trust Anchors control has the ASN.1 definition:¶

  PublishTrustAnchors ::= SEQUENCE {
    seqNumber      INTEGER,
    hashAlgorithm  AlgorithmIdentifier,
    anchorHashes   SEQUENCE OF OCTET STRING
  }

The fields in PublishTrustAnchors have the following meaning:¶

• • seqNumber is an integer indicating the location within a sequence of updates.¶

• • hashAlgorithm is the identifier and parameters for the hash algorithm that is used in computing the values of the anchorHashes field. All implementations MUST implement SHA-1 for this field.¶

• • anchorHashes are the hashes for the certificates that are to be treated as trust anchors by the client. The actual certificates are transported in the certificate bag of the containing SignedData structure.¶

While it is recommended that the sender place the certificates that are to be trusted in the PKI Response, it is not required as the certificates should be obtainable using normal discovery techniques.¶

Prior to accepting the trust anchors changes, a client MUST at least do the following: validate the signature on the PKI Response to a current trusted anchor, check with policy to ensure that the signer is permitted to use the control, validate that the authenticated publish time in the signature is near to the current time, and validate that the sequence number is greater than the previously used one.¶

In the event that multiple agents publish a set of trust anchors, it is up to local policy to determine how the different trust anchors should be combined. Clients SHOULD be able to handle the update of multiple trust anchors independently.¶

Note:

Clients that handle this control must use extreme care in validating that the operation is permissible. Incorrect handling of this control allows for an attacker to change the set of trust anchors on the client.¶

6.16. Authenticated Data Control

The Authenticated Data control allows a server to provide data back to the client in an authenticated manner. This control uses the Authenticated Data structure to allow for validation of the data. This control is used where the client has a shared-secret and a secret identifier with the server, but where a trust anchor has not yet been downloaded onto the client so that a signing certificate for the server cannot be validated. The specific case that this control was created for use with is the Publish Trust Anchors control (Section 6.15), but it may be used in other cases as well.¶

The Authenticated Data control is identified by the OID:¶

  id-cmc-authData OBJECT IDENTIFIER ::= { id-cmc 27 }

The Authenticated Data control has the ASN.1 definition:¶

  AuthPublish ::= BodyPartID

AuthPublish is a body part identifier that refers to a member of the cmsSequence element for the current PKI Response or PKI Data. The cmsSequence element is AuthenticatedData. The encapsulated content is an id-cct-PKIData. The controls in the controlSequence need to be processed if the authentication succeeds. (One example is the Publish Trust Anchors control in Section 6.15.)¶

If the authentication operation fails, the CMCFailInfo authDataFail is returned.¶

6.17. Batch Request and Response Controls

These controls allow for an RA to collect multiple requests together into a single Full PKI Request and forward it to a CA. The server would then process the requests and return the results in a Full PKI Response.¶

The Batch Request control is identified by the OID:¶

  id-cmc-batchRequests OBJECT IDENTIFIER ::= { id-cmc 28 }

The Batch Response control is identified by the OID:¶

  id-cmc-batchResponses OBJECT IDENTIFIER ::= { id-cmc 29 }

Both the Batch Request and Batch Response controls have the ASN.1 definition:¶

  BodyPartList ::= SEQUENCE of BodyPartID

The data associated with these controls is a set of body part identifiers. Each request/response is placed as an individual entry in the cmcSequence of the new PKIData/PKIResponse. The body part identifiers of these entries are then placed in the body part list associated with the control.¶

When a server processes a Batch Request control, it MAY return the responses in one or more PKI Responses. A CMCStatus value of partial is returned on all but the last PKI Response. The CMCStatus would be success if the Batch Requests control was processed; the responses are created with their own CMCStatus code. Errors on individual requests are not propagated up to the top level.¶

When a PKI Response with a CMCStatus value of partial is returned, the Query Pending control (Section 6.13) is used to retrieve additional results. The returned status includes a suggested time after which the client should ask for the additional results.¶

6.18. Publication Information Control

The Publication Information control allows for modifying publication of already issued certificates, both for publishing and removal from publication. A common usage for this control is to remove an existing certificate from publication during a rekey operation. This control should always be processed after the issuance of new certificates and revocation requests. This control should not be processed if a certificate failed to be issued.¶

The Publication Information control is identified by the OID:¶

  id-cmc-publishCert OBJECT IDENTIFIER ::= { id-cmc 30 }

The Publication Information control has the ASN.1 definition:¶

  CMCPublicationInfo ::= SEQUENCE {
    hashAlg     AlgorithmIdentifier,
    certHashes      SEQUENCE of OCTET STRING,
    pubInfo         PKIPublicationInfo
    }

  PKIPublicationInfo ::= SEQUENCE {
    action     INTEGER {
                        dontPublish (0),
                        pleasePublish (1) },
    pubInfos  SEQUENCE SIZE (1..MAX) OF SinglePubInfo OPTIONAL }

    -- pubInfos MUST NOT be present if action is "dontPublish"
    -- (if action is "pleasePublish" and pubInfos is omitted,
    -- "dontCare" is assumed)

  SinglePubInfo ::= SEQUENCE {
    pubMethod    INTEGER {
                         dontCare    (0),
                         x500        (1),
                         web         (2),
                         ldap        (3) },
     pubLocation  GeneralName OPTIONAL }
  }

The fields in CMCPublicationInfo have the following meaning:¶

• • hashAlg is the algorithm identifier of the hash algorithm used to compute the values in certHashes.¶

• • certHashes are the hashes of the certificates for which publication is to change.¶

• • pubInfo is the information where and how the certificates should be published. The fields in pubInfo (taken from [CRMF]) have the following meanings:¶

• • • action indicates the action the service should take. It has two values:¶

• • • • dontPublish indicates that the PKI should not publish the certificate (this may indicate that the requester intends to publish the certificate him/herself). dontPublish has the added connotation of removing from publication the certificate if it is already published.¶

• • • • pleasePublish indicates that the PKI MAY publish the certificate using whatever means it chooses unless pubInfos is present. Omission of the CMC Publication Info control results in the same behavior.¶

• • • pubInfos pubInfos indicates how (e.g., X500, Web, IP Address) the PKI SHOULD publish the certificate.¶

A single certificate SHOULD NOT appear in more than one Publication Information control. The behavior is undefined in the event that it does.¶

6.19. Control Processed Control

The Control Processed control allows an RA to indicate to subsequent control processors that a specific control has already been processed. This permits an RA in the middle of a processing stream to process a control defined either in a local context or in a subsequent document.¶

The Control Processed control is identified by the OID:¶

  id-cmc-controlProcessed  OBJECT IDENTIFIER ::= { id-cmc 32 }

The Control Processed control has the ASN.1 definition:¶

  ControlList ::= SEQUENCE {
    bodyList        SEQUENCE SIZE (1..MAX) OF BodyPartReference
  }

• • bodyList is a series of body part identifiers that form a path to each of the controls that were processed by the RA. This control is only needed for those controls that are not part of this standard and thus would cause an error condition of a server attempting to deal with a control not defined in this document. No error status is needed since an error causes the RA to return the request to the client with the error rather than passing the request on to the next server in the processing list.¶

6.20. RA Identity Proof Witness Control

The RA Identity Proof Witness control allows an RA to indicate to subsequent control processors that all of the identity proof requirements have been met. This permits the identity proof to be performed at a location closer to the end-entity. For example, the identity proof could be done at multiple physical locations, while the CA could operate on a company-wide basis. The RA performs the identity proof, and potentially other tasks that require the secret to be used, while the CA is prevented from knowing the secret. If the identity proof fails, then the RA returns an error to the client denoting that fact.¶

The RA Identity Proof Witness control is identified by the OID:¶

 id-cmc-raIdentityWitness OBJECT IDENTIFIER ::= { id-cmc 35 }

The RA Identity Proof Witness control has the ASN.1 definition:¶

  cmc-raIdentityWitness CMC-CONTROL ::=
    { BodyPartPath IDENTIFIED BY id-cmc-raIdentityWitness }

• • cmc-raIdentityWitness is a CMC-CONTROL associating the object identifier id-cmc-raIdentityWitness and the type BodyPartPath. This object is omitted from the 1988 module. The object is added to the object set Cmc-Control-Set. The control is permitted to appear only in the control sequence of a PKIData object. It MUST NOT appear in the control sequence of a PKIResponse. The control is permitted to be used only by an RA. The control may appear multiple times in a control sequence with each occurrence pointing to a different object.¶

• • id-cmc-raIdentityWitness is the object identifier used to identify this CMC control.¶

• • BodyPartPath is the type structure associated with the control. The syntax of BodyPartPath is defined in Section 3.2.2. The path contains a sequence of body part identifiers leading to one of the following items:¶

• • • Identity Proof control if the RA verified the identity proof in this control.¶

• • • Identity Proof Version 2 control if the RA verified the identity proof in this control.¶

• • • Full PKI Request if the RA performed an out-of-band identity proof for this request. The request SHOULD NOT contain either Identity Proof control.¶

• • • Simple PKI Request if the RA performed an out-of-band identity proof for this request.¶

The RA Identity Proof Witness control will frequently be associated with a Modify Certification Request control, which changes the name fields in the associated certification requests. This is because the RA knows the actual name to be assigned to the entity requesting the certificate, and the end-entity does not yet have the details of the name. (The association would be set up by the operator at the time the shared-secret was generated by the RA.)¶

When this control is placed in a message, it is RECOMMENDED that the Control Processed control be placed in the body sequence as well. Using the explicit new control, rather than implicitly relying on the Control Processed control is important due to the need to know explicitly which identity proofs have been performed. The new control also allows an RA to state that out-of-band identity proofs have been performed.¶

When the identity proof is performed by an RA, the RA also MUST validate the linking between the identity proof and the name information wrapped inside of the key proof-of-possession.¶

6.21. Response Body Control

The Response Body Control is designed to enable an RA to inform an EE that there is an embedded response message that MUST be processed as part of the processing of this message. This control is designed to be used in a couple of different cases where an RA has done some additional processing for the certification request, e.g., as key generation. When an RA performs key generation on behalf of an EE, the RA MUST respond with both the original response message from the certificate issuer (containing the certificate issuance) as part of the response generated by the RA (containing the new key). Another case where this is useful is when the secret is shared between the RA and the EE (rather than between the CA and the EE) and the RA returns the Publish Trust Anchors control (to populate the correct trust points).¶

The Response Body Control is identified by the OID:¶

  id-cmc-responseBody OBJECT IDENTIFIER ::= { id-cmc 37 }

The Response Body Control has the ASN.1 definition:¶

  cmc-responseBody CMC-CONTROL ::= {
     BodyPartPath IDENTIFIED BY id-cmc-responseBody
  }

• • cmc-responseBody is a CMC-CONTROL associating the object identifier id-cmc-responseBody with the type BodyPartPath. This object is omitted from the 1988 module. The object is added to the object set Cmc-Control-Set. The control is permitted to appear only in the control sequence of a PKIResponse. The control MUST NOT appear in the control sequence of a PKIData. It is expected that only an intermediary RA will use this control; a CA generally does not need the control as it is creating the original innermost message.¶

• • id-cmc-responseBody is the object identifier used to identify this CMC control.¶

• • BodyPartPath is the type structure associated with the control. The syntax of BodyPartPath is defined in Section 3.2.2. The path contains a sequence of body part identifiers leading to a cmsSequence item which contains a PKIResponse within it.¶

7.1. Change Subject Name Attribute

The Client Name Change Request attribute is designed for a client to ask for a change in its name as part of a certification request. Because of security issues, this cannot be done in the simple way of just changing the requested subject name in the certificate template. The name in the certification request MUST match the name in the certificate used to verify the request, in order that identity and possession proofs are correctly applied.¶

The relevant ASN.1 for the Client Name Change Request attribute is as follows:¶

  at-cmc-changeSubjectName ATTRIBUTE ::=
    { ChangeSubjectName IDENTIFIED BY id-cmc-changeSubjectName }

  id-cmc-changeSubjectName OBJECT IDENTIFIER ::= { id-cmc 36 }

  ChangeSubjectName ::= SEQUENCE {
    subject             Name OPTIONAL,
    subjectAlt          SubjectAltName OPTIONAL
  }
  (WITH COMPONENTS {..., subject PRESENT} |
    COMPONENTS {..., subjectAlt PRESENT} )

The attribute is designed to be used as an ATTRIBUTE object. As such, the attribute is placed in one of the following two places:¶

• The attributes field in a CertificationRequest.¶

• The controls field of a CertRequest for a CRMF certification request.¶

The control is identified by the Object Identifier id-cmc-changeSubjectName.¶

The ASN.1 type associated with control is ChangeSubjectName. The fields of the structure are configured as follows:¶

• • subject contains the requested subject name for the new certificate.¶

• • subjectAlt contains the requested subject alternative name for the new certificate.¶

At least one of the fields in the sequence MUST be present when encoding the structure.¶

When the CA processes this attribute in a certification request, it will do the following:¶

1. If present, the subject field is copied to the name field of the template. If the subject field is absent, the name field of the template will be set to a empty sequence.¶

2. If present, the subjectAlt field is used as the content of a SubjectAltName extension in the certificate. If the subjectAlt field is absent, the subjectAltName extension is removed from the certificate template.¶

8.1. Encryption Removal

There are two cases that require an RA to remove or change encryption in a PKI Request. In the first case, the encryption was applied for the purposes of protecting the entire PKI Request from unauthorized entities. If the CA does not have a Recipient Info entry in the encryption layer, the RA MUST remove the encryption layer. The RA MAY add a new encryption layer with or without adding a new signing layer.¶

The second change of encryption that may be required is to change the encryption inside of a signing layer. In this case, the RA MUST remove all signing layers containing the encryption. All control statements MUST be merged according to local policy rules as each signing layer is removed and the resulting merged controls MUST be placed in a new signing layer provided by the RA. If the signing layer provided by the EE needs to also be removed, the RA can also remove this layer.¶

8.2. Signature Layer Removal

Only two instances exist where an RA should remove a signature layer on a Full PKI Request: if an encryption layer needs to be modified within the request, or if a CA will not accept secondary delegation (i.e., multiple RA signatures). In all other situations, RAs SHOULD NOT remove a signing layer from a PKI Request.¶

If an RA removes a signing layer from a PKI Request, all control statements MUST be merged according to local policy rules. The resulting merged control statements MUST be placed in a new signing layer provided by the RA.¶

9.1. Extended Key Usage

The Extended Key Usage (EKU) extension is used to restrict the use of a certificate to specific applications. We define three different EKUs in this document. The ASN.1 to define these EKUs is:¶

  id-kp-cmcCA      OBJECT IDENTIFIER ::= { id-kp 27 }
  id-kp-cmcRA      OBJECT IDENTIFIER ::= { id-kp 28 }
  id-kp-cmcArchive OBJECT IDENTIFIER ::= { id-kp 29 }

The usage description for each of the EKUs is as follows:¶

• • CMC Certification Authorities are identified by the id-kp-cmcCA extended key usage. The certificate may be the same as or different than the CA certificate. If a different certificate is used, the certificates containing the id-kp-cmcCA extended key usage SHOULD have the same name as the certificate used for issuing the certificates. (Using a separate key pair for CMC protocol operations and for issuing certificates and CRLs decreases the number of operations for which the private key used to sign certificates and CRLs would be used.)¶

• • CMC Registration Authorities are identified by the id-kp-cmcRA extended key usage. This usage is placed into RA certificates.¶

• • CMC Archive Servers are identified by the id-kp-cmcArchive extended key usage. CMC Archive Servers and the associated protocol are to be defined in a future document.¶

9.2. Subject Information Access

The subject information access extension indicates how to access information and services for the subject of the certificate. We define a new value for use in this extension, to identify the different locations that CMC services will be available. If this value is placed in a certificate, an appropriate extended key usage defined in Section 9.1 MUST be included in the certificate as well.¶

The id-ad-cmc OID is used when the subject offers certification services using the CMC protocol. If the CMC services are available via HTTP or FTP, accessLocation MUST be a uniformResourceIdentifier. If the CMC services are available via electronic mail, accessLocation MUST be an rfc822Name. If CMC services are available using TCP/IP, the dNSName or iPAddress name forms MUST be used. Since the GeneralName data structure does not permit the inclusion of a port number, in the absence of other external configuration information, the value of 5318 should be used. (The port registration is in Section 3.2) The semantics of other name forms of accessLocation (when accessMethod is id-ad-cmc) are not defined by this specification.¶

The ASN.1 type for this extension is GeneralName see Section 4.2.1.8 of [PKIXCERT].¶

  id-ad-cmc OBJECT IDENTIFIER ::= { id-ad 12 }

B.1. Request of a Signing Certificate

This section looks at the messages that would flow in the event that an enrollment is occurring for a signing-only key. If the certificate was designed for both signing and encryption, the only difference would be the key usage extension in the certification request.¶

Message #2 from client to server:¶

   ContentInfo.contentType = id-signedData
   ContentInfo.content
     SignedData.encapContentInfo
       eContentType = id-cct-PKIData
       eContent
         controlSequence
           {102, id-cmc-identityProof, computed value}
           {103, id-cmc-senderNonce, 10001}
         reqSequence
           certRequest
             certReqId = 201
             certTemplate
               subject = My Proposed DN
               publicKey = My Public Key
               extensions
                 {id-ce-subjectPublicKeyIdentifier, 1000}
                 {id-ce-keyUsage, digitalSignature}
     SignedData.SignerInfos
       SignerInfo
         sid.subjectKeyIdentifier = 1000

Response from server to client:¶

   ContentInfo.contentType = id-signedData
   ContentInfo.content
     SignedData.encapContentInfo
       eContentType = id-cct-PKIResponse
       eContent
         controlSequence
           {102, id-cmc-statusInfoV2, {success, 201}}
           {103, id-cmc-senderNonce, 10005}
           {104, id-cmc-recipientNonce, 10001}
     certificates
       Newly issued certificate
       Other certificates
     SignedData.SignerInfos
       Signed by CA

B.2. Single Certification Request, But Modified by RA

This section looks at the messages that would flow in the event that an enrollment has one RA in the middle of the data flow. That RA will modify the certification request before passing it on to the CA.¶

Message from client to RA:¶

   ContentInfo.contentType = id-signedData
   ContentInfo.content
     SignedData.encapContentInfo
       eContentType = id-cct-PKIData
       eContent
         controlSequence
           {102, id-cmc-identityProof, computed value}
           {103, id-cmc-senderNonce, 10001}
         reqSequence
           certRequest
             certReqId = 201
             certTemplate
               subject = My Proposed DN
               publicKey = My Public Key
               extensions
                 {id-ce-subjectPublicKeyIdentifier, 1000}
                 {id-ce-keyUsage, digitalSignature}
     SignedData.SignerInfos
       SignerInfo
         sid.subjectKeyIdentifier = 1000

Message from RA to CA:¶

   ContentInfo.contentType = id-signedData
   ContentInfo.content
     SignedData.encapContentInfo
       eContentType = id-cct-PKIData
       eContent
         controlSequence
           { 102, id-cmc-batchRequests, { 1, 2} }
           { 103, id-cmc-addExtensions,
             { {1, 201, {id-ce-certificatePolicies, anyPolicy}}
               {1, 201, {id-ce-subjectAltName, {extension data}}
               {2, XXX, {id-ce-subjectAltName, {extension data}}}
                     The Value XXX is not known here; it would
                     reference into the second client request,
                     which is not displayed above.
         cmsSequence
           { 1, <Message from client to RA #1> }
           { 2, <Message from client to RA #2> }
     SignedData.SignerInfos
       SignerInfo
         sid = RA key.

Response from CA to RA:¶

   ContentInfo.contentType = id-signedData
   ContentInfo.content
     SignedData.encapContentInfo
       eContentType = id-cct-PKIResponse
       eContent
         controlSequence
           {102, id-cmc-BatchResponse, {999, 998}}

           {103, id-cmc-statusInfoV2, {failed, 2, badIdentity}}
         cmsSequence
           { bodyPartID = 999
             contentInfo
               ContentInfo.contentType = id-signedData
               ContentInfo.content
                 SignedData.encapContentInfo
                   eContentType = id-cct-PKIResponse
                   eContent
                     controlSequence
                      {102, id-cmc-statusInfoV2, {success, 201}}
                 certificates
                   Newly issued certificate
                   Other certificates
                 SignedData.SignerInfos
                   Signed by CA
           }
           { bodyPartID = 998,
             contentInfo
               ContentInfo.contentType = id-signedData
               ContentInfo.content
                 SignedData.encapContentInfo
                   eContentType = id-cct-PKIResponse
                   eContent
                     controlSequence
                       {102, id-cmc-statusInfoV2, {failure, badAlg}}
                 certificates
                   Newly issued certificate
                   Other certificates
                 SignedData.SignerInfos
                   Signed by CA
           }
         SignedData.SignerInfos
           Signed by CA

Response from RA to client:¶

   ContentInfo.contentType = id-signedData
   ContentInfo.content
     SignedData.encapContentInfo
       eContentType = id-cct-PKIResponse
       eContent
         controlSequence
           {102, id-cmc-statusInfoV2, {success, 201}}
     certificates
       Newly issued certificate
       Other certificates
     SignedData.SignerInfos
       Signed by CA

B.3. Direct POP for an RSA Certificate

This section looks at the messages that would flow in the event that an enrollment is done for an encryption only certificate using an direct POP method. For simplicity, it is assumed that the certification requester already has a signing-only certificate.¶

The fact that a second round-trip is required is implicit rather than explicit. The server determines this based on the fact that no other POP exists for the certification request.¶

Message #1 from client to server:¶

   ContentInfo.contentType = id-signedData
   ContentInfo.content
     SignedData.encapContentInfo
       eContentType = id-cct-PKIData
       eContent
         controlSequence
           {102, id-cmc-transactionId, 10132985123483401}
           {103, id-cmc-senderNonce, 10001}
           {104, id-cmc-dataReturn, <packet of binary data identifying
                                     where the key in question is.>}
         reqSequence
           certRequest
             certReqId = 201
             certTemplate
               subject = <My DN from my signing cert>
               publicKey = My Public Key
               extensions
                 {id-ce-keyUsage, keyEncipherment}
             popo
               keyEncipherment
                 subsequentMessage
     SignedData.SignerInfos
       SignerInfo
         Signed by requester's signing cert

Response #1 from server to client:¶

   ContentInfo.contentType = id-signedData
   ContentInfo.content
     SignedData.encapContentInfo
       eContentType = id-cct-PKIResponse
       eContent
         controlSequence
           {101, id-cmc-statusInfoV2, {failed, 201, popRequired}}
           {102, id-cmc-transactionId, 10132985123483401}
           {103, id-cmc-senderNonce, 10005}
           {104, id-cmc-recipientNonce, 10001}
           {105, id-cmc-encryptedPOP, {
              request {
                certRequest
                  certReqId = 201
                   certTemplate
                     subject = <My DN from my signing cert>
                     publicKey = My Public Key
                     extensions
                       {id-ce-keyUsage, keyEncipherment}
                   popo
                     keyEncipherment
                     subsequentMessage
              }
              cms
                contentType = id-envelopedData
                content
                  recipientInfos.riid.issuerSerialNumber = <NULL, 201>
                  encryptedContentInfo
                    eContentType = id-data
                    eContent = <Encrypted value of 'y'>
              thePOPAlgID = HMAC-SHA256
              witnessAlgID = SHA-256
              witness <hashed value of 'y'>}}
           {106, id-cmc-dataReturn, <packet of binary data identifying
                                     where the key in question is.>}
     certificates
       Other certificates (optional)
     SignedData.SignerInfos
       Signed by CA

   ContentInfo.contentType = id-signedData
   ContentInfo.content
     SignedData.encapContentInfo
       eContentType = id-cct-PKIData
       eContent
         controlSequence
           {102, id-cmc-transactionId, 10132985123483401}
           {103, id-cmc-senderNonce, 100101}
           {104, id-cmc-dataReturn, <packet of binary data identifying
                                     where the key in question is.>}
           {105, id-cmc-recipientNonce, 10005}
           {107, id-cmc-decryptedPOP, {
             bodyPartID 201,
             thePOPAlgID HMAC-SHA256,
             thePOP <HMAC computed value goes here>}}
         reqSequence
           certRequest
             certReqId = 201
             certTemplate
               subject = <My DN from my signing cert>
               publicKey = My Public Key
               extensions
                 {id-ce-keyUsage, keyEncipherment}
             popo
               keyEncipherment
                 subsequentMessage
     SignedData.SignerInfos
       SignerInfo
         Signed by requester's signing cert

Response #2 from server to client:¶

   ContentInfo.contentType = id-signedData
   ContentInfo.content
     SignedData.encapContentInfo
       eContentType = id-cct-PKIResponse
       eContent
         controlSequence
           {101, id-cmc-transactionId, 10132985123483401}
           {102, id-cmc-statusInfoV2, {success, 201}}
           {103, id-cmc-senderNonce, 10019}
           {104, id-cmc-recipientNonce, 100101}
           {105, id-cmc-dataReturn, <packet of binary data identifying
                                     where the key in question is.>}
     certificates
       Newly issued certificate
       Other certificates
     SignedData.SignerInfos
       Signed by CA

C.1. No-Signature Signature Mechanism

Key management (encryption/decryption) private keys cannot always be used to produce some type of signature value as they can be in a decrypt-only device. Certification requests require that the signature field be populated. This section provides a signature algorithm specifically for that purposes. The following object identifier and signature value are used to identify this signature type:¶

  id-alg-noSignature OBJECT IDENTIFIER ::= { id-pkix id-alg(6) 2 }

  NoSignatureValue ::= OCTET STRING

The parameters for id-alg-noSignature MUST be present and MUST be encoded as NULL. NoSignatureValue contains the hash of the certification request. It is important to realize that there is no security associated with this signature type. If this signature type is on a certification request and the Certification Authority policy requires proof-of-possession of the private key, the POP mechanism defined in Section 6.7 MUST be used.¶