RFC 9483: Lightweight Certificate Management Protocol (CMP) Profile

3.6.1. Reporting Error Conditions Upstream

An EE SHALL NOT send error messages. PKI management entities SHALL NOT send error messages in the upstream direction either.¶

In case an EE rejects a newly issued certificate contained in an ip, cp, or kup message and implicit confirmation has not been granted, the EE MUST report this using a certConf message with "rejection" status and await the pkiConf response as described in Section 4.1.1.¶

On all other error conditions regarding response messages, the EE or PKI management entity MUST regard the current PKI management operation as terminated with failure. The error conditions include:¶

Upstream PKI management entities will not receive any CMP message to learn that the PKI management operation has been terminated. In case they expect a further message from the EE, a connection interruption or timeout will occur. The value set for such timeouts will vary by use case. Then they MUST also regard the current PKI management operation as terminated with failure and MUST NOT attempt to send an error message downstream.¶

3.6.2. Reporting Error Conditions Downstream

In case the PKI management entity detects an error condition, e.g., rejecting the request due to policy decision, in the body of an ir, cr, p10cr, kur, or rr message received from downstream, it MUST report the error in the specific response message, i.e., an ip, cp, kup, or rp with "rejection" status, as described in Sections 4.1.1 and 4.2. This can also happen in case of polling.¶

In case the PKI management entity detects any other error condition on requests (including pollReq, certConf, genm, and nested messages) received from downstream and on responses received from upstream (such as invalid message header, body type, protection, or extraCerts, according to the checks described in Section 3.5), it MUST report them downstream in the form of an error message as described in Section 3.6.4.¶

3.6.3. Handling Error Conditions on Nested Messages Used for Batching

Batching of messages using nested messages as described in Section 5.2.2.2 requires special error handling.¶

If the error condition is on an upstream nested message containing batched requests, it MUST NOT attempt to respond to the individual requests included in it but to the nested message itself.¶

In case a PKI management entity receives an error message in response to a nested message, it must propagate the error by responding with an error message to each of the request messages contained in the nested message.¶

In case a PKI management entity detects an error condition on the downstream nested message received in response to a nested message sent before and the body of the received nested message still parses, it MAY ignore this error condition and handle the included responses as described in Section 5.2.2.2. Otherwise, it MUST propagate the error by responding with an error message to each of the requests contained in the nested message it sent originally.¶

3.6.4. PKIStatusInfo and Error Messages

When sending any kind of negative response, including error messages, a PKI entity MUST indicate the error condition in the PKIStatusInfo structure of the respective message as described below. Then it MUST regard the current PKI management operation as terminated with failure.¶

The PKIStatusInfo structure is used to report errors. It may be part of various message types, in particular, ip, cp, kup, certConf, and error. The PKIStatusInfo structure consists of the following fields:¶

status:

Here, the PKIStatus value "rejection" MUST be used in case an error was detected. When a PKI management entity indicates delayed delivery of a CMP response message to the EE with an error message as described in Section 4.4, the status "waiting" MUST be used there.¶

statusString:

Here, any human-readable valid value for logging or to display via a user interface should be added.¶

failInfo:

Here, the PKIFailureInfo bits MAY be used in the way explained in Appendix F of [RFC4210]. PKIFailureInfo bits regarding the validation described in Section 3.5 are referenced there. The PKIFailureInfo bits referenced in Sections 5.1 and 6 are described here:¶

badCertId:

A kur, certConf, or rr message references an unknown certificate.¶

badPOP:

An ir/cr/kur/p10cr contains an invalid proof-of-possession.¶

certRevoked:

Revocation is requested for a certificate that is already revoked.¶

badCertTemplate:

The contents of a certificate request are not accepted, e.g., a field is missing or has an unacceptable value or the given public key is already in use in some other certificate (depending on policy).¶

transactionIdInUse:

This is sent by a PKI management entity in case the received request contains a transactionID that is currently in use for another transaction. An EE receiving such an error message should resend the request in a new transaction using a different transactionID.¶

notAuthorized:

The sender of a request message is not authorized for requesting the operation.¶

systemUnavail:

This is sent by a PKI management entity in case a back-end system is not available.¶

systemFailure:

This is sent by a PKI management entity in case a back-end system is currently not functioning correctly.¶

An EE receiving a systemUnavail or systemFailure failInfo should resend the request in a new transaction after some time.¶

Detailed Message Description:¶

Error Message -- error

Field                         Value

header
    -- As described in Section 3.1

body
    -- The message indicating the error that occurred
  error                       REQUIRED
    pKIStatusInfo             REQUIRED
      status                  REQUIRED
    -- MUST have the value "rejection"
      statusString            OPTIONAL
    -- This field should contain any human-readable text for
    --   debugging, for logging, or to display in a GUI
      failInfo                OPTIONAL
    -- MAY be present and contain the relevant PKIFailureInfo bits

protection                    RECOMMENDED
    -- As described in Section 3.2

extraCerts                    RECOMMENDED
    -- As described in Section 3.3

Protecting the error message may not be technically feasible if it is not clear which credential the recipient will be able to use when validating this protection, e.g., in case the request message was fundamentally broken. In these exceptional cases, the protection of the error message MAY be omitted.¶

4.1.1. Enrolling an End Entity to a New PKI

This PKI management operation should be used by an EE to request a certificate from a new PKI using an existing certificate from an external PKI, e.g., a manufacturer-issued IDevID certificate [IEEE.802.1AR_2018], to authenticate itself to the new PKI.¶

Note: In Bootstrapping Remote Secure Key Infrastructure (BRSKI) [RFC8995] environments, "BRSKI-AE: Alternative Enrollment Protocols in BRSKI" [BRSKI-AE] describes a generalization regarding enrollment protocols alternative to EST [RFC7030]. As replacement of EST simpleenroll, BRSKI-AE uses this PKI management operation for bootstrapping LDevID certificates.¶

Specific prerequisites augmenting the prerequisites in Section 3.4 are as follows:¶

Message Flow:¶

Step# EE                                  PKI management entity
  1   format ir
  2                      ->   ir      ->
  3                                        handle or
                                             forward ir
  4                                        format or receive ip
  5                                        possibly grant
                                             implicitConfirm
  6                      <-   ip      <-
  7   handle ip

-----------------  if implicitConfirm not granted  -----------------

  8   format certConf
  9                      ->   certConf ->
 10                                        handle or
                                             forward certConf
 11                                        format or receive pkiConf
 12                      <-   pkiConf  <-
 13   handle pkiConf

For this PKI management operation, the EE MUST include a sequence of one CertReqMsg in the ir. If more certificates are required, further requests MUST be sent using separate PKI management operations.¶

The EE MUST include the generalInfo field implicitConfirm in the header of the ir message as described in Section 3.1, unless it requires certificate confirmation. This leaves the PKI management entities the choice of whether or not the EE must send a certConf message upon receiving a new certificate. Depending on the PKI policy and requirements for managing EE certificates, it can be important for PKI management entities to learn if the EE accepted the new certificate. In such cases, when responding with an ip message, the PKI management entity MUST NOT include the implicitConfirm extension. In case the EE included the generalInfo field implicitConfirm in the request message and the PKI management entity does not need any explicit confirmation from the EE, the PKI management entity MUST include the generalInfo field implicitConfirm in the response message. This prevents explicit certificate confirmation and saves the overhead of a further message round trip. Otherwise, the PKI management entity SHOULD include confirmWaitTime as described in Section 3.1.¶

If the EE did not request implicit confirmation or implicit confirmation was not granted by the PKI management entity, certificate confirmation MUST be performed as follows. If the EE successfully received the certificate, it MUST send a certConf message in due time. On receiving a valid certConf message, the PKI management entity MUST respond with a pkiConf message. If the PKI management entity does not receive the expected certConf message in time, it MUST handle this like a rejection by the EE. In case of rejection, depending on its policy, the PKI management entity MAY revoke the newly issued certificate, notify a monitoring system, or log the event internally.¶

Note: Depending on PKI policy, a new certificate may be published by a PKI management entity, and explicit confirmation may be required. In this case, it is advisable not to do the publication until a positive certificate confirmation has been received. This way, the need to revoke the certificate on negative confirmation can be avoided.¶

If the certificate request was rejected by the CA, the PKI management entity MUST return an ip message containing the status code "rejection" as described in Section 3.6, and the certifiedKeyPair field SHALL be omitted. The EE MUST NOT react to such an ip message with a certConf message, and the PKI management operation MUST be terminated.¶

Detailed Message Description:¶

Initialization Request -- ir

Field                         Value

header
    -- As described in Section 3.1

body
    -- The request of the EE for a new certificate
  ir                          REQUIRED
    -- MUST contain a sequence of one CertReqMsg
    -- If more certificates are required, further PKI management
    --   operations needs to be initiated
    certReq                   REQUIRED
      certReqId               REQUIRED
    -- MUST be 0
      certTemplate            REQUIRED
        version               OPTIONAL
    -- MUST be 2 if supplied
        subject               REQUIRED
    -- The EE's identity MUST be carried in the subject field
    --   and/or the subjectAltName extension.
    -- If subject name is present only in the subjectAltName
    --   extension, then the subject field MUST be NULL-DN
        publicKey             OPTIONAL
    -- MUST be present if local key generation is used
    -- MAY be absent if central key generation is requested
          algorithm           OPTIONAL
    -- MUST be present if local key generation is used and MUST
    --   include the subject public key algorithm identifier
    -- MAY be present if central key generation is requested and,
    --   if present, informs the KGA of algorithm and parameter
    --   preferences regarding the to-be-generated key pair
          subjectPublicKey    REQUIRED
    -- MUST contain the public key to be certified in case of local
    --   key generation
    -- MUST be a zero-length BIT STRING if central key generation
    --   is requested
        extensions            OPTIONAL
    -- MAY include end-entity-specific X.509 extensions of the
    --   requested certificate, like subject alternative name, key
    --   usage, and extended key usage
    -- The subjectAltName extension MUST be present if the EE subject
    --   name includes a subject alternative name.
    popo                      OPTIONAL
    -- MUST be present if local key generation is used
    -- MUST be absent if central key generation is requested
      signature               OPTIONAL
    -- MUST be used by an EE if the key can be used for signing, and
    --   if used, it MUST have the type POPOSigningKey
        poposkInput           PROHIBITED
    -- MUST NOT be used; it is not needed because subject and
    --   publicKey are both present in the certTemplate
        algorithmIdentifier   REQUIRED
    -- The signature algorithm MUST be consistent with the publicKey
    --   algorithm field of the certTemplate
        signature             REQUIRED
    -- MUST contain the signature value computed over the DER-encoded
    --   certReq
      raVerified              OPTIONAL
    -- MAY be used by an RA after verifying the proof-of-possession
    --   provided by the EE

protection                    REQUIRED
    -- As described in Section 3.2

extraCerts                    REQUIRED
    -- As described in Section 3.3


Initialization Response -- ip

Field                         Value

header
    -- As described in Section 3.1

body
    -- The response of the CA to the request as appropriate
  ip                          REQUIRED
    caPubs                    OPTIONAL
    -- MAY be used if the certifiedKeyPair field is present
    -- If used, it MUST contain only a trust anchor, e.g., root
    --   certificate, of the certificate contained in certOrEncCert
    response                  REQUIRED
    -- MUST contain a sequence of one CertResponse
      certReqId              REQUIRED
    -- MUST be 0
      status                  REQUIRED
    -- PKIStatusInfo structure MUST be present
        status                REQUIRED
    -- positive values allowed: "accepted", "grantedWithMods"
    -- negative values allowed: "rejection"
    -- "waiting" only allowed with a polling use case as described
    --   in Section 4.4
        statusString          OPTIONAL
    -- MAY be any human-readable text for debugging, for logging, or
    --   to display in a GUI
        failInfo              OPTIONAL
    -- MAY be present if status is "rejection"
    -- MUST be absent if status is "accepted" or "grantedWithMods"
      certifiedKeyPair        OPTIONAL
    -- MUST be present if status is "accepted" or "grantedWithMods"
    -- MUST be absent if status is "rejection"
        certOrEncCert         REQUIRED
    -- MUST be present if status is "accepted" or "grantedWithMods"
          certificate         REQUIRED
    -- MUST be present when certifiedKeyPair is present
    -- MUST contain the newly enrolled X.509 certificate
        privateKey            OPTIONAL
    -- MUST be absent in case of local key generation or "rejection"
    -- MUST contain the encrypted private key in an EnvelopedData
    --   structure as specified in Section 4.1.6 in case the
    --   private key was generated centrally

protection                    REQUIRED
    -- As described in Section 3.2

extraCerts                    REQUIRED
    -- As described in Section 3.3
    -- MUST contain the chain of the certificate present in
    --   certOrEncCert
    -- Duplicate certificates MAY be omitted


Certificate Confirmation -- certConf

Field                         Value

header
    -- As described in Section 3.1

body
    -- The message of the EE sends a confirmation to the PKI
    --   management entity to accept or reject the issued
    --   certificates
  certConf                    REQUIRED
    -- MUST contain a sequence of one CertStatus
    CertStatus                REQUIRED
      certHash                REQUIRED
    -- The hash algorithm to use MUST be the hash algorithm indicated
    --   in the below hashAlg field.  If the hashAlg field is not
    --   set, it MUST be the hash algorithm defined by the algorithm
    --   identifier of the certificate signature or the dedicated
    --   hash algorithm defined in [RFC9481] for the used certificate
    --   signature algorithm.
      certReqId               REQUIRED
    -- MUST be 0
      statusInfo              OPTIONAL
    -- PKIStatusInfo structure should be present
    -- Omission indicates acceptance of the indicated certificate
        status                REQUIRED
    -- positive values allowed: "accepted"
    -- negative values allowed: "rejection"
        statusString          OPTIONAL
    -- MAY be any human-readable text for debugging, for logging, or
    --   to display in a GUI
        failInfo              OPTIONAL
    -- MAY be present if status is "rejection"
    -- MUST be absent if status is "accepted"
      hashAlg                 OPTIONAL
    -- The hash algorithm to use for calculating the above certHash
    -- If used, the pvno field in the header MUST be cmp2021 (3).
    --   For backward compatibility, use of this field is
    --   NOT RECOMMENDED if the hash algorithm to use can be
    --   identified by other means; see above.

protection                    REQUIRED
    -- As described in Section 3.2
    -- MUST use the same credentials as in the first request message
    --   of this PKI management operation

extraCerts                    RECOMMENDED
    -- As described in Section 3.3
    -- MAY be omitted if the message size is critical and the PKI
    --   management entity caches the CMP protection certificate from
    --   the first request message of this PKI management operation


PKI Confirmation -- pkiConf

Field                         Value

header
    -- As described in Section 3.1

body
  pkiconf                     REQUIRED
    -- The content of this field MUST be NULL

protection                    REQUIRED
    -- As described in Section 3.2
    -- MUST use the same credentials as in the first response
    --   message of this PKI management operation

extraCerts                    RECOMMENDED
    -- As described in Section 3.3
    -- MAY be omitted if the message size is critical and the EE has
    --   cached the CMP protection certificate from the first
    --   response message of this PKI management operation

4.1.2. Enrolling an End Entity to a Known PKI

This PKI management operation should be used by an EE to request an additional certificate of the same PKI it already has certificates from. The EE uses one of these existing certificates to authenticate itself by signing its request messages using the respective private key.¶

Specific prerequisites augmenting the prerequisites in Section 3.4 are as follows:¶

The message sequence for this PKI management operation is identical to that given in Section 4.1.1, with the following changes:¶

4.1.3. Updating a Valid Certificate

This PKI management operation should be used by an EE to request an update for one of its certificates that is still valid. The EE uses the certificate it wishes to update as the CMP protection certificate. Both for authenticating itself and for proving ownership of the certificate to be updated, it signs the request messages with the corresponding private key.¶

Specific prerequisites augmenting the prerequisites in Section 3.4 are as follows:¶

The message sequence for this PKI management operation is identical to that given in Section 4.1.1, with the following changes:¶

As part of the certReq structure of the kur, the oldCertId control is added after the certTemplate field.¶

    controls
      type                    RECOMMENDED
    -- MUST be the value id-regCtrl-oldCertID, if present
      value
        issuer                REQUIRED
        serialNumber          REQUIRED
    -- MUST contain the issuer and serialNumber of the certificate
    --   to be updated

4.1.4. Enrolling an End Entity Using a PKCS #10 Request

This PKI management operation can be used by an EE to request a certificate using the PKCS #10 [RFC2986] format to interoperate with CAs not supporting CRMF [RFC4211]. This offers a variation of the PKI management operations specified in Sections 4.1.1 to 4.1.3.¶

In this PKI management operation, the public key and all further certificate template data MUST be contained in the subjectPKInfo and other certificationRequestInfo fields of the PKCS #10 structure.¶

The prerequisites are the same as given in Section 4.1.2.¶

The message sequence for this PKI management operation is identical to that given in Sections 4.1.1 to 4.1.3, with the following changes:¶

Detailed Message Description:¶

Certification Request -- p10cr

Field                         Value

header
    -- As described in Section 3.1

body
    -- The request of the EE for a new certificate using a PKCS #10
    --   certificate request
  p10cr                       REQUIRED
    certificationRequestInfo  REQUIRED
      version                 REQUIRED
    -- MUST be 0 to indicate PKCS #10 v1.7
      subject                 REQUIRED
    -- The EE subject name MUST be carried in the subject field
    --   and/or the subjectAltName extension.
    -- If subject name is present only in the subjectAltName
    --   extension, then the subject field MUST be NULL-DN
      subjectPKInfo           REQUIRED
        algorithm             REQUIRED
    -- MUST include the subject public key algorithm identifier
        subjectPublicKey      REQUIRED
    -- MUST include the public key to be certified
      attributes              OPTIONAL
    -- MAY include end-entity-specific X.509 extensions of the
    --   requested certificate like subject alternative name,
    --   key usage, and extended key usage
    -- The subjectAltName extension MUST be present if the EE
    --   subject name includes a subject alternative name.
    signatureAlgorithm        REQUIRED
    -- The signature algorithm MUST be consistent with the
    --   subjectPKInfo field.
    signature                 REQUIRED
    -- MUST contain the self-signature for proof-of-possession

protection                    REQUIRED
    -- As described in Section 3.2

extraCerts                    REQUIRED
    -- As described for the underlying PKI management operation

4.1.5. Using MAC-Based Protection for Enrollment

This is a variant of the PKI management operations described in Sections 4.1.1, 4.1.2, and 4.1.4. It should be used by an EE to request a certificate of a new PKI in case it does not have a certificate to prove its identity to the target PKI but has some secret information shared with the PKI management entity. Therefore, the request and response messages are MAC-protected using this shared secret information. The distribution of this shared secret is out of scope for this document. The PKI management entity checking the MAC-based protection MUST replace this protection according to Section 5.2.3, as the next hop may not know the shared secret information.¶

Note: The entropy of the shared secret information is crucial for the level of protection when using MAC-based protection. Further guidance is available in the security considerations updated by CMP Updates [RFC9480].¶

Specific prerequisites augmenting the prerequisites in Section 3.4 are as follows:¶

The message sequence for this PKI management operation is identical to that given in Sections 4.1.1, 4.1.2, and 4.1.4, with the following changes:¶

See Section 6 of CMP Algorithms [RFC9481] for details on message authentication code algorithms (MSG_MAC_ALG) to use. Typically, parameters are part of the protectionAlg field, e.g., used for key derivation, like a salt and an iteration count. Such parameters should remain constant for message protection throughout this PKI management operation to reduce the computational overhead.¶

4.1.6. Adding Central Key Pair Generation to Enrollment

This is a variant of the PKI management operations described in Sections 4.1.1 to 4.1.4 and the variant described in Section 4.1.5. It needs to be used in case an EE is not able to generate its new public-private key pair itself or central generation of the EE key material is preferred. Which PKI management entity will act as Key Generation Authority (KGA) and perform the key generation is a matter of the local implementation. This PKI management entity MUST use a certificate containing the additional extended key usage extension id-kp-cmKGA in order to be accepted by the EE as a legitimate key generation authority.¶

Note: As described in Section 5.3.1, the KGA can use the PKI management operation described in Section 4.1.2 to request the certificate for this key pair on behalf of the EE.¶

When an EE requests central key generation for a certificate update using a kur message, the KGA cannot use a kur message to request the certificate on behalf of the EE, as the old EE credential is not available to the KGA for protecting this message. Therefore, if the EE uses the PKI management operation described in Section 4.1.3, the KGA MUST act as described in Section 4.1.2 to request the certificate for the newly generated key pair on behalf of the EE from the CA.¶

Generally speaking, it is strongly preferable to generate public-private key pairs locally at the EE. This is advisable to make sure that the entity identified in the newly issued certificate is the only entity that knows the private key.¶

Reasons for central key generation may include the following:¶

Note: As mentioned in Section 2, central key generation may be required in a push model, where the certificate response message is transferred by the PKI management entity to the EE without a previous request message.¶

The EE requesting central key generation MUST omit the publicKey field from the certTemplate or, in case it has a preference on the key type to be generated, provide this preference in the algorithm sub-field and fill the subjectPublicKey sub-field with a zero-length BIT STRING. Both variants indicate to the PKI management entity that a new key pair shall be generated centrally on behalf of the EE.¶

Note: As the protection of centrally generated keys in the response message has been extended to EncryptedKey by Section 2.7 of CMP Updates [RFC9480], EnvelopedData is the preferred alternative to EncryptedValue. In CRMF [RFC4211], Section 2.1, point 9, the use of EncryptedValue has been deprecated in favor of the EnvelopedData structure. Therefore, this profile requires using EnvelopedData, as specified in Section 6 of CMS [RFC5652]. When EnvelopedData is to be used in a PKI management operation, CMP v3 MUST be indicated in the message header already for the initial request message; see Section 2.20 of CMP Updates [RFC9480].¶

+----------------------------------+
| EnvelopedData                    |
| [RFC5652], Section 6             |
| +------------------------------+ |
| | SignedData                   | |
| | [RFC5652], Section 5         | |
| | +--------------------------+ | |
| | | AsymmetricKeyPackage     | | |
| | | [RFC5958]                | | |
| | | +----------------------+ | | |
| | | | private key          | | | |
| | | +----------------------+ | | |
| | +--------------------------+ | |
| +------------------------------+ |
+----------------------------------+

The PKI management entity delivers the private key in the privateKey field in the certifiedKeyPair structure of the response message also containing the newly issued certificate.¶

The private key MUST be provided as an AsymmetricKeyPackage structure as defined in [RFC5958].¶

This AsymmetricKeyPackage structure MUST be wrapped in a SignedData structure, as specified in Section 5 of CMS [RFC5652] and [RFC8933], and signed by the KGA generating the key pair. The signature MUST be performed using a private key related to a certificate asserting the extended key usage id-kp-cmKGA, as described in Section 2.2 of CMP Updates [RFC9480], to demonstrate authorization to generate key pairs on behalf of an EE. For response messages using signature-based protection, the EE MUST validate the signer certificate contained in the SignedData structure and SHOULD authorize the KGA considering any given id-kp-cmKGA extended key usage in the signer certificate. For response messages using MAC-based protection, the EE MAY omit the validation as it may not be possible or meaningful to the EE. In this case, the EE authorizes the KGA using the shard secret information.¶

The SignedData structure MUST be wrapped in an EnvelopedData structure, as specified in Section 6 of CMS [RFC5652], encrypting it using a newly generated symmetric content-encryption key.¶

This content-encryption key MUST be securely provided as part of the EnvelopedData structure to the EE using one of three key management techniques. The choice of the key management technique to be used by the PKI management entity depends on the authentication mechanism the EE chose to protect the request message. See Section 2.7 of CMP Updates [RFC9480] for details on which key management technique to use.¶

Specific prerequisites augmenting those of the respective certificate enrollment PKI management operations are as follows:¶

Detailed Description of the privateKey Field:¶

        privateKey            REQUIRED
    -- MUST be an EnvelopedData structure, as specified in
    --   Section 6 of CMS [RFC5652]
          version             REQUIRED
    -- MUST be 2 for recipientInfo type KeyAgreeRecipientInfo and
    --   KeyTransRecipientInfo
    -- MUST be 0 for recipientInfo type PasswordRecipientInfo
          recipientInfos      REQUIRED
    -- MUST contain a sequence of one RecipientInfo, which MUST be
    --   ktri of type KeyTransRecipientInfo (see Section 4.1.6.1),
    --   kari of type KeyAgreeRecipientInfo (see Section 4.1.6.2), or
    --   pwri of type PasswordRecipientInfo (see Section 4.1.6.3)
          encryptedContentInfo
                              REQUIRED
            contentType       REQUIRED
    -- MUST be id-signedData
            contentEncryptionAlgorithm
                              REQUIRED
    -- MUST be the algorithm identifier of the algorithm used for
    --   content encryption
    -- The algorithm type MUST be PROT_SYM_ALG as specified in
    --   [RFC9481], Section 5
            encryptedContent  REQUIRED
    -- MUST be the SignedData structure, as specified in Section 5
    -- of CMS [RFC5652] and [RFC8933], in encrypted form
              version         REQUIRED
    -- MUST be 3
              digestAlgorithms
                              REQUIRED
    -- MUST contain a sequence of one AlgorithmIdentifier element
    -- MUST be the algorithm identifier of the digest algorithm
    --   used for generating the signature and match the signature
    --   algorithm specified in signatureAlgorithm; see [RFC8933]
              encapContentInfo
                              REQUIRED
    -- MUST contain the content that is to be signed
                eContentType  REQUIRED
    -- MUST be id-ct-KP-aKeyPackage as specified in [RFC5958]
                eContent      REQUIRED
    -- MUST be of type AsymmetricKeyPackage and
    -- MUST contain a sequence of one OneAsymmetricKey element
                  version     REQUIRED
    -- MUST be 1 (indicating v2)
                  privateKeyAlgorithm
                              REQUIRED
    -- The privateKeyAlgorithm field MUST contain the algorithm
    --   identifier of the asymmetric key pair algorithm
                  privateKey  REQUIRED
                  publicKey   REQUIRED
    -- MUST contain the public key corresponding to the private key
    --   for simplicity and consistency with v2 of OneAsymmetricKey
              certificates    REQUIRED
    -- MUST contain the certificate for the private key used to sign
    --   the signedData content, together with its chain
    -- The first certificate in this field MUST be the KGA
    --   certificate used for protecting this content
    -- Self-signed certificates should not be included and MUST NOT
    --   be trusted based on their inclusion in any case
                signerInfos   REQUIRED
    -- MUST contain a sequence of one SignerInfo element
                version       REQUIRED
    -- MUST be 3
                sid           REQUIRED
                  subjectKeyIdentifier
                              REQUIRED
    -- MUST be the subjectKeyIdentifier of the KGA certificate
                digestAlgorithm
                              REQUIRED
    -- MUST be the same as in the digestAlgorithms field of
    --   encryptedContent
                signedAttrs   REQUIRED
    -- MUST contain an id-contentType attribute containing the value
    --   id-ct-KP-aKeyPackage
    -- MUST contain an id-messageDigest attribute containing the
    --   message digest of eContent
    -- MAY contain an id-signingTime attribute containing the time
    --   of a signature.  It SHOULD be omitted if the transactionTime
    --   field is not present in the PKIHeader.
    -- For details on the signed attributes, see Sections 5.3 and
    --   11 of CMS [RFC5652] and [RFC8933]
                signatureAlgorithm
                              REQUIRED
    -- MUST be the algorithm identifier of the signature algorithm
    --   used for calculation of the signature bits
    -- The signature algorithm type MUST be MSG_SIG_ALG, as
    --   specified in [RFC9481], Section 3, and MUST be consistent
    --   with the subjectPublicKeyInfo field of the KGA certificate
                signature     REQUIRED
    -- MUST be the digital signature of the encapContentInfo

As stated in Section 1.8, all fields of the ASN.1 syntax that are defined in [RFC5652] but are not explicitly specified here SHOULD NOT be used.¶

            ktri              REQUIRED
    -- MUST be KeyTransRecipientInfo as specified in Section 6.2.1
    --   of CMS [RFC5652]
              version         REQUIRED
    -- MUST be 2
              rid             REQUIRED
    -- MUST contain the subjectKeyIdentifier of the CMP protection
    --   certificate, if available, in the rKeyId choice, and the
    --   subjectKeyIdentifier MUST equal the senderKID in the
    --   PKIHeader.
    -- If the CMP protection certificate does not contain a
    --   subjectKeyIdentifier, the issuerAndSerialNumber choice MUST
    --   be used.
              keyEncryptionAlgorithm
                              REQUIRED
    -- MUST be the algorithm identifier of the key transport
    --   algorithm.  The algorithm type MUST be KM_KT_ALG as
    --   specified in [RFC9481], Section 4.2
              encryptedKey    REQUIRED
    -- MUST be the encrypted content-encryption key

            kari              REQUIRED
    -- MUST be KeyAgreeRecipientInfo as specified in Section
    --   6.2.2 of CMS [RFC5652]
              version         REQUIRED
    -- MUST be 3
              originator      REQUIRED
    -- MUST contain the subjectKeyIdentifier of the CMP protection
    --   certificate, if available, in the subjectKeyIdentifier
    --   choice, and the subjectKeyIdentifier MUST equal the
    --   senderKID in the PKIHeader.
    -- If the CMP protection certificate does not contain a
    --   subjectKeyIdentifier, the issuerAndSerialNumber choice MUST
    --   be used.
              ukm             RECOMMENDED
    -- MUST be used when 1-Pass Elliptic Curve Menezes-Qu-Vanstone
    --   (ECMQV) is used; see [RFC5753]
    -- SHOULD be present to ensure uniqueness of the key
    --   encryption key
              keyEncryptionAlgorithm
                              REQUIRED
    -- MUST be the algorithm identifier of the key agreement
    --   algorithm
    -- The algorithm type MUST be KM_KA_ALG as specified in
    --   [RFC9481], Section 4.1
    -- The parameters field of the key agreement algorithm MUST
    --   contain the key wrap algorithm.  The algorithm type
    --   MUST be KM_KW_ALG as specified in [RFC9481], Section 4.3
              recipientEncryptedKeys
                              REQUIRED
    -- MUST contain a sequence of one RecipientEncryptedKey
                rid           REQUIRED
    -- MUST contain the subjectKeyIdentifier of the CMP protection
    --   certificate, if available, in the rKeyId choice, and the
    --   subjectKeyIdentifier MUST equal the senderKID in the
    --   PKIHeader.
    -- If the CMP protection certificate does not contain a
    --   subjectKeyIdentifier, the issuerAndSerialNumber choice MUST
    --   be used
                  encryptedKey
                              REQUIRED
    -- MUST be the encrypted content-encryption key

            pwri              REQUIRED
    -- MUST be PasswordRecipientInfo as specified in
    --   Section 6.2.4 of CMS [RFC5652]
              version         REQUIRED
    -- MUST be 0
              keyDerivationAlgorithm
                              REQUIRED
    -- MUST be the algorithm identifier of the key derivation
    --   algorithm
    -- The algorithm type MUST be KM_KD_ALG as specified in
    --   [RFC9481], Section 4.4
              keyEncryptionAlgorithm
                              REQUIRED
    -- MUST be the algorithm identifier of the key wrap algorithm
    -- The algorithm type MUST be KM_KW_ALG as specified in
    --   [RFC9481], Section 4.3
              encryptedKey    REQUIRED
    -- MUST be the encrypted content-encryption key

4.3.1. Get CA Certificates

This PKI management operation can be used by an EE to request CA certificates from the PKI management entity.¶

An EE requests CA certificates, e.g., for chain construction, from a PKI management entity by sending a general message with OID id-it-caCerts, as specified in Section 2.14 of CMP Updates [RFC9480]. The PKI management entity responds with a general response with the same OID that either contains a SEQUENCE of certificates populated with the available intermediate and issuing CA certificates or no content in case no CA certificate is available.¶

No specific prerequisites apply in addition to those specified in Section 3.4.¶

The message sequence for this PKI management operation is as given above, with the following specific content:¶

Detailed Description of the infoValue Field of genp:¶

      infoValue               OPTIONAL
    -- MUST be absent if no CA certificate is available
    -- MUST be present if CA certificates are available
    --   if present, MUST be a sequence of CMPCertificate

4.3.2. Get Root CA Certificate Update

This PKI management operation can be used by an EE to request an updated root CA certificate as described in Section 4.4 of [RFC4210].¶

An EE requests an update of a root CA certificate from the PKI management entity by sending a general message with OID id-it-rootCaCert. If needed for unique identification, the EE MUST include the old root CA certificate in the message body as specified in Section 2.15 of CMP Updates [RFC9480]. The PKI management entity responds with a general response with OID id-it-rootCaKeyUpdate that either contains the update of the root CA certificate consisting of up to three certificates or no content in case no update is available.¶

Note: This mechanism may also be used to update trusted non-root certificates, e.g., directly trusted intermediate or issuing CA certificates.¶

The newWithNew certificate is the new root CA certificate and is REQUIRED to be present if available. The newWithOld certificate is REQUIRED to be present in the response message because it is needed for the receiving entity trusting the old root CA certificate to gain trust in the new root CA certificate. The oldWithNew certificate is OPTIONAL because it is only needed in rare scenarios where other entities may not already trust the old root CA.¶

No specific prerequisites apply in addition to those specified in Section 3.4.¶

The message sequence for this PKI management operation is as given above, with the following specific content:¶

Detailed Description of the infoValue Field of genm:¶

      infoValue               RECOMMENDED
    -- MUST contain the root CA certificate to be updated if needed
    --   for unique identification

Detailed Description of the infoValue Field of genp:¶

      infoValue               OPTIONAL
    -- MUST be absent if no update of the root CA certificate is
    --   available
    -- MUST be present if an update of the root CA certificate
    --   is available and MUST be of type RootCaKeyUpdateContent
        newWithNew            REQUIRED
    -- MUST be present if infoValue is present
    -- MUST contain the new root CA certificate
        newWithOld            REQUIRED
    -- MUST be present if infoValue is present
    -- MUST contain a certificate containing the new public
    --   root CA key signed with the old private root CA key
        oldWithNew            OPTIONAL
    -- MAY be present if infoValue is present
    -- MUST contain a certificate containing the old public
    --   root CA key signed with the new private root CA key

4.3.3. Get Certificate Request Template

This PKI management operation can be used by an EE to request a template with parameters for future certificate requests.¶

An EE requests certificate request parameters from the PKI management entity by sending a general message with OID id-it-certReqTemplate as specified in Section 2.16 of CMP Updates [RFC9480]. The EE MAY indicate the certificate profile to use in the id-it-certProfile extension of the generalInfo field in the PKIHeader of the general message as described in Section 3.1. The PKI management entity responds with a general response with the same OID that either contains requirements on the certificate request template or no content in case no specific requirements are imposed by the PKI. The CertReqTemplateValue contains requirements on certificate fields and extensions in a certTemplate. Optionally, it contains a keySpec field containing requirements on algorithms acceptable for key pair generation.¶

The EE SHOULD follow the requirements from the received CertTemplate by including in the certificate requests all the fields requested, taking over all the field values provided and filling in any remaining fields values. The EE SHOULD NOT add further fields, name components, and extensions or their (sub)components. If deviating from the recommendations of the template, the certificate request might be rejected.¶

Note: We deliberately do not use "MUST" or "MUST NOT" here in order to allow more flexibility in case the rules given here are not sufficient for specific scenarios. The EE can populate the certificate request as wanted and ignore any of the requirements contained in the CertReqTemplateValue. On the other hand, a PKI management entity is free to ignore or replace any parts of the content of the certificate request provided by the EE. The CertReqTemplate PKI management operation offers means to ease a joint understanding of which fields and/or which field values should be used. An example is provided in Appendix A.¶

In case a field of type Name, e.g., subject, is present in the CertTemplate but has the value NULL-DN (i.e., has an empty list of relative distinguished name (RDN) components), the field SHOULD be included in the certificate request and filled with content provided by the EE. Similarly, in case an X.509v3 extension is present but its extnValue is empty, this means that the extension SHOULD be included and filled with content provided by the EE. In case a Name component, for instance, a common name or serial number, is given but has an empty string value, the EE SHOULD fill in a value. Similarly, in case an extension has subcomponents (e.g., an IP address in a SubjectAltName field) with empty values, the EE SHOULD fill in a value.¶

The EE MUST ignore (i.e., not include) empty fields, extensions, and subcomponents that it does not understand or does not know suitable values to fill in.¶

The publicKey field of type SubjectPublicKeyInfo in the CertTemplate of the CertReqTemplateValue MUST be omitted. In case the PKI management entity wishes to make a stipulation on algorithms the EE may use for key generation, this MUST be specified using the keySpec field as specified in Section 2.16 of CMP Updates [RFC9480].¶

The keySpec field, if present, specifies the public key types optionally with parameters and/or RSA key lengths for which a certificate may be requested.¶

The value of a keySpec element with the OID id-regCtrl-algId, as specified in Section 2.16 of CMP Updates [RFC9480], MUST be of type AlgorithmIdentifier and give an algorithm other than RSA. For Elliptic Curve (EC) keys, the curve information MUST be specified as described in the respective standard documents.¶

The value of a keySpec element with the OID id-regCtrl-rsaKeyLen, as specified in Section 2.16 of CMP Updates [RFC9480], MUST be a positive integer value and give an RSA key length.¶

In the CertTemplate of the CertReqTemplateValue, the serialNumber, signingAlg, issuerUID, and subjectUID fields MUST be omitted.¶

The specific prerequisites augmenting the prerequisites in Section 3.4 is as follows:¶

The message sequence for this PKI management operation is as given above, with the following specific content:¶

Detailed Description of the infoValue Field of genp:¶

      InfoValue               OPTIONAL
    -- MUST be absent if no requirements are available
    -- MUST be present if the PKI management entity has any
    --   requirements on the contents of the certificate template
        certTemplate          REQUIRED
    -- MUST be present if infoValue is present
    -- MUST contain the required CertTemplate structure elements
    -- The SubjectPublicKeyInfo field MUST be absent
        keySpec               OPTIONAL
    -- MUST be absent if no requirements on the public key are
    --   available
    -- MUST be present if the PKI management entity has any
    --   requirements on the keys generated
    -- MUST contain a sequence of one AttributeTypeAndValue per
    --   supported algorithm with attribute id-regCtrl-algId or
    --   id-regCtrl-rsaKeyLen

4.3.4. CRL Update Retrieval

This PKI management operation can be used by an EE to request a new CRL. If a CA offers methods to access a CRL, it may include CRL distribution points or authority information access extensions into the issued certificates as specified in [RFC5280]. In addition, CMP offers CRL provisioning functionality as part of the PKI management operation.¶

An EE requests a CRL update from the PKI management entity by sending a general message with OID id-it-crlStatusList. The EE MUST include the CRL source identifying the requested CRL and, if available, the thisUpdate time of the most current CRL instance it already has, as specified in Section 2.17 of CMP Updates [RFC9480]. The PKI management entity MUST respond with a general response with OID id-it-crls.¶

The EE MUST identify the requested CRL either by a CRL distribution point name or issuer name.¶

Note: CRL distribution point names can be obtained from a cRLDistributionPoints extension of a certificate to be validated or from an issuingDistributionPoint extension of the CRL to be updated. CRL issuer names can be obtained from the cRLDistributionPoints extension of a certificate, from the issuer field of the authority key identifier extension of a certificate or CRL, and from the issuer field of a certificate or CRL.¶

If a thisUpdate value was given, the PKI management entity MUST return the latest CRL available from the referenced source if this CRL is more recent than the given thisUpdate time. If no thisUpdate value was given, it MUST return the latest CRL available from the referenced source. In all other cases, the infoValue in the response message MUST be absent.¶

The PKI management entity should treat a CRL distribution point name as an internal pointer to identify a CRL that is directly available at the PKI management entity. It is not intended as a way to fetch an arbitrary CRL from an external location, as this location may be unavailable to that PKI management entity.¶

In addition to the prerequisites specified in Section 3.4, the EE MUST know which CRL to request.¶

Note: If the EE does not want to request a specific CRL, it MAY instead use a general message with OID id-it-currentCrl as specified in Section 5.3.19.6 of [RFC4210].¶

The message sequence for this PKI management operation is as given above, with the following specific content:¶

Detailed Description of the infoValue Field of genm:¶

      infoValue               REQUIRED
    -- MUST contain a sequence of one CRLStatus element
        source                REQUIRED
    -- MUST contain the dpn choice of type DistributionPointName if
    --   the CRL distribution point name is available
    -- Otherwise, MUST contain the issuer choice identifying the CA
    --   that issues the CRL.  It MUST contain the issuer DN in the
    --   directoryName field of a GeneralName element.
        thisUpdate            OPTIONAL
    -- MUST contain the thisUpdate field of the latest CRL the EE
    --   has gotten from the issuer specified in the given dpn or
    --   issuer field
    -- MUST be omitted if the EE does not have any instance of the
    --   requested CRL

Detailed Description of the infoValue Field of genp:¶

      infoValue               OPTIONAL
    -- MUST be absent if no CRL to be returned is available
    -- MUST contain a sequence of one CRL update from the referenced
    --   source if a thisUpdate value was not given or a more recent
    --   CRL is available

5.1.1. Responding to a Certificate Request

An ir/cr/kur/p10cr message is used to request a certificate as described in Section 4.1. The responding PKI management entity MUST proceed as follows unless it initiates delayed delivery as described in Section 5.1.5.¶

The PKI management entity MUST check the message body according to the applicable requirements from Section 4.1. Possible failInfo bit values used for error reporting in case a check failed include badCertId and badCertTemplate. It MUST verify the presence and value of the proof-of-possession (failInfo bit: badPOP) unless central key generation is requested. If a signature-based proof-of-possession is present, the PKI management entity MUST verify, based on local PKI policy, that the subject name in the certTemplate identifies the same entity as the subject name in the CMP protection certificate or matches the identifier used with MAC-based protection. In case this verification fails, the message MUST have been protected by an authorized PKI management entity (failInfo bit: notAuthorized). If the special POP value "raVerified" is given, the PKI management entity should check that the request message was signed using a certificate containing the cmcRA extended key usage (failInfo bit: notAuthorized). The PKI management entity should also perform any further checks on the certTemplate contents (failInfo: badCertTemplate) according to any applicable PKI policy and certificate profile.¶

If the requested certificate is available, the PKI management entity MUST respond with a positive ip/cp/kup message as described in Section 4.1.¶

Note: If central key generation is performed by the responding PKI management entity, the responding PKI management entity MUST include the private key in encrypted form in the response as specified in Section 4.1.6.¶

The prerequisites of the respective PKI management operation specified in Section 4.1 apply.¶

If the EE requested omission of the certConf message, the PKI management entity MUST handle it as described in Section 4.1.1. Therefore, it MAY grant this by including the implicitConfirm generalInfo field or including the confirmWaitTime field in the response header.¶

5.1.2. Responding to a Confirmation Message

A PKI management entity MUST handle a certConf message if it has responded before with a positive ip/cp/kup message not granting implicit confirmation. It should check the message body according to the requirements given in Section 4.1.1 (failInfo bit: badCertId) and MUST react as described there.¶

The prerequisites of the respective PKI management operation specified in Section 4.1 apply.¶

5.1.3. Responding to a Revocation Request

An rr message is used to request revocation of a certificate. The responding PKI management entity should check the message body according to the requirements in Section 4.2. It MUST make sure that the referenced certificate exists (failInfo bit: badCertId), has been issued by the addressed CA, and is not already expired or revoked (failInfo bit: certRevoked). On success, it MUST respond with a positive rp message, as described in Section 4.2.¶

No specific prerequisites apply in addition to those specified in Section 3.4.¶

5.1.4. Responding to a Support Message

A genm message is used to retrieve extra content. The responding PKI management entity should check the message body according to the applicable requirements in Section 4.3 and perform any further checks depending on the PKI policy. On success, it MUST respond with a genp message as described there.¶

Note: The responding PKI management entity may generate the response from scratch or reuse the contents of previous responses. Therefore, it may be worth caching the body of the response message as long as the contained information is valid and current, such that further requests for the same contents can be answered immediately.¶

No specific prerequisites apply in addition to those specified in Section 3.4.¶

5.1.5. Initiating Delayed Delivery

This functional extension can be used by a PKI management entity in case the response to a request takes longer than usual. In this case, the PKI management entity should completely validate the request as usual and then start processing the request itself or forward it further upstream as soon as possible. In the meantime, it MUST respond with an ip/cp/kup/error message including the status "waiting" and handle subsequent polling as described in Section 4.4.¶

Typically, as stated in Section 5.2.3, an intermediate PKI management entity should not change the sender and recipient nonces even in case it modifies a request or a response message. In the special case of delayed delivery initiated by an intermediate PKI management entity, there is an exception. Between the EE and this PKI management entity, pollReq and pollRep messages are exchanged handling the nonces as usual. Yet when the final response from upstream has arrived at the PKI management entity, this response contains the recipNonce copied (as usual) from the senderNonce in the original request message. The PKI management entity that initiated the delayed delivery MAY replace the recipNonce in the response message with the senderNonce of the last received pollReq because the downstream entities, including the EE, might expect it in this way. Yet the check specified in Section 3.5 allows alternate use of the senderNonce of the original request.¶

No specific prerequisites apply in addition to those of the respective PKI management operation.¶

5.2.1. Not Changing Protection

This variant means that a PKI management entity forwards a CMP message without changing the header, body, or protection. In this case, the PKI management entity acts more like a proxy, e.g., on a network boundary, implementing no specific RA-like security functionality that requires an authentic indication to the PKI. Still, the PKI management entity might implement checks that result in refusing to forward the request message and instead responding as specified in Section 3.6.¶

This variant of forwarding a message or the one described in Section 5.2.2.1 MUST be used for kur messages and for central key generation.¶

No specific prerequisites apply in addition to those specified in Section 3.4.¶

5.2.2. Adding Protection and Batching of Messages

This variant of forwarding a message means that a PKI management entity adds another protection to PKI management messages before forwarding them.¶

The nested message is a PKI management message containing a PKIMessages sequence as its body, containing one or more CMP messages.¶

As specified in the updated Section 5.1.3.4 of [RFC4210] (also see Section 2.6 of CMP Updates [RFC9480]), there are various use cases for adding another protection by a PKI management entity. Specific procedures are described in more detail in the following sections.¶

Detailed Message Description:¶

Nested Message - nested

Field                         Value

header
    -- As described in Section 3.1

body
    -- Container to provide additional protection to original
    --   messages and to bundle request messages or alternatively
    --   response messages
  PKIMessages                 REQUIRED
    -- MUST be a sequence of one or more CMP messages

protection                    REQUIRED
    -- As described in Section 3.2, using the CMP protection key of
    --   the PKI management entity

extraCerts                    REQUIRED
    -- As described in Section 3.3

Step# PKI management entity               PKI management entity
 1   format nested
 2                      ->  nested   ->
 3                                        handle or forward nested
 4                                        format or receive response
 5                      <-  response <-
 6   forward response

Step# PKI management entity               PKI management entity
 1   format nested
 2                      ->  nested   ->
 3                                        handle or forward nested
 4                                        format or receive nested
 5                      <-  nested   <-
 6   handle nested

5.2.3. Replacing Protection

The following two alternatives can be used by any PKI management entity forwarding a CMP message with or without changes while providing its own protection and, in this way, asserting approval of the message.¶

If retaining end-to-end message authentication is required, an additional protection SHALL be added instead of replacing the original protection.¶

By replacing the existing protection using its own CMP protection key, the PKI management entity provides a proof of verifying and approving the message as described above. Thus, the PKI management entity acts as an actual registration authority (RA), which implements important security functionality of the PKI such as verifying the proof of requester identity and authorization.¶

Note: By replacing the message protection, the binding of a signature-based proof-of-possession to the proof-of-identity given by the original message protection gets lost. To enable the CA to verify this binding, the original message can be provided in the origPKIMessage generalInfo field.¶

Before replacing the existing protection with a new protection, the PKI management entity:¶

These message adaptations MUST NOT be applied to kur messages described in Section 4.1.3 since their original protection using the key and certificate to be updated needs to be preserved.¶

These message adaptations MUST NOT be applied to certificate request messages described in Section 4.1.6 for central key generation since their original protection needs to be preserved up to the KGA, which needs to use it for encrypting the new private key for the EE.¶

In both the kur and central key generation cases, if a PKI management entity needs to state its approval of the original request message, it MUST provide this using a nested message as specified in Section 5.2.2.1.¶

When an intermediate PKI management entity modifies a message, it MUST NOT change the transactionID, the senderNonce, or the recipNonce, apart from the exception for the recipNonce given in Section 5.1.5.¶

    popo
      raVerified              REQUIRED
    -- MUST have the value NULL and indicates that the PKI
    --   management entity verified the popo of the original message

5.3.1. Requesting a Certificate

A PKI management entity may use one of the PKI management operations described in Section 4.1 to request a certificate on behalf of another PKI entity. It either generates the key pair itself and inserts the new public key in the subjectPublicKey field of the request certTemplate, or it uses a certificate request received from downstream, e.g., by means of a different protocol. In the latter case, it MUST verify the received proof-of-possession if this proof breaks, e.g., due to transformation from PKCS #10 [RFC2986] to CRMF [RFC4211]. It MUST also verify, based on local PKI policy, that the subject name in the certTemplate identifies the EE.¶

No specific prerequisites apply in addition to those specified in Section 4.1.¶

Note: An upstream PKI management entity will not be able to differentiate this PKI management operation from the one described in Section 5.2.3 because, in both cases, the message is protected by the PKI management entity.¶

The message sequence for this PKI management operation is identical to the respective PKI management operation given in Section 4.1, with the following changes:¶

5.3.2. Revoking a Certificate

A PKI management entity may use the PKI management operation described in Section 4.2 to revoke a certificate of another PKI entity. This revocation request message MUST be signed by the PKI management entity using its own CMP protection key to prove to the PKI authorization to revoke the certificate on behalf of that PKI entity.¶

No specific prerequisites apply in addition to those specified in Section 4.2.¶

Note: An upstream PKI management entity will not be able to differentiate this PKI management operation from the ones described in Section 5.2.3.¶

The message sequence for this PKI management operation is identical to that given in Section 4.2, with the following changes:¶

6.4.1. File-Based Transfer

CMP messages MAY be transferred between PKI entities using file-based mechanisms, for instance, when an EE is offline or a PKI management entity performs delayed delivery. Each file MUST contain the ASN.1 DER encoding of one CMP message only, where the message may be nested. There MUST be no extraneous header or trailer information in the file. The filename extension ".pki" MUST be used.¶

6.4.2. Other Asynchronous Transfer Protocols

Other asynchronous transfer protocols, e.g., email or website upload/download, MAY transfer CMP messages between PKI entities. A MIME wrapping is defined for those environments that are MIME-native. The MIME wrapping is specified in Section 3.1 of [RFC8551].¶

The ASN.1 DER encoding of the CMP messages MUST be transferred using the "application/pkixcmp" content type and base64-encoded content transfer encoding, as specified in Section 3.4 of CMP over HTTP [RFC6712]. A filename MUST be included either in a "content-type" or a "content-disposition" statement. The filename extension ".pki" MUST be used.¶