Certificate Revocation List

The certificate revocation list (CRL) consists of certificate serial numbers of issued certificates that are no longer valid. It is used by nodes when they establish a TLS connection between each other and need to ensure on certificate validity. In order to add entries to the certificate revocation list there is the certificate revocation process that resembles the one from the certificate signing request (CSR).

Note: For context on how the certificate revocation list fits into the wider context, see Certificate Hierarchy Guide. Once added, the entries cannot be removed from the certificate revocation list.

As with CSR, the approval workflow for revocation requests is integrated with the Jira tool by default, and the submitted requests follow the same lifecycle. To support the above functionality, there are two externally available REST endpoints:

• one for certificate revocation request submission
• one for certificate revocation list retrieval

Since the certificate revocation list needs to be signed, the revocation process integrates with the HSM Signing Service.

The certificate revocation list signing process requires human interaction for which there is a separate tool. Once signed, the certificate revocation list will replace the current one.

HTTP certificate revocation protocol

The set of REST endpoints for the revocation service are determined by the CRL file names provided in the PKI tool configuration. The example below shows the relevant part of such a PKI configuration along with the respective endpoints.

certificates = {
    "::CORDA_TLS_CRL_SIGNER" = {
        crl = {
          crlDistributionUrl = "http://identitymanager:10000/certificate-revocation-list/tls"
          indirectIssuer = true
          issuer = "CN=Corda TLS Signer Certificate, OU=Corda, O=R3 HoldCo LLC, L=New York, C=US"
          file = "/etc/corda/crl-files/tls.crl"
        }
    },
    "::CORDA_ROOT" = {
        crl = {
          crlDistributionUrl = "http://identitymanager:10000/certificate-revocation-list/root"
          file = "/etc/corda/crl-files/root.crl"
        }
    },
    "::CORDA_SUBORDINATE" = {
        crl = {
          crlDistributionUrl = "http://identitymanager:10000/certificate-revocation-list/subordinate"
          file = "/etc/corda/crl-files/subordinate.crl"
        }
    }
)

Empty Certificate Revocation List

The TLS-level certificate revocation check validates the entire certificate chain. For each certificate in the certificate path, the corresponding CRL will be downloaded and the certificate will be checked against that CRL. However, this requires each Certificate Authority, including the Node CA, to provide a CRL for the certificates it issues. Since this requirement cannot always be met, especially by the Node CA, the alternative is to use a CRL signed by the trusted CA. As each Corda node trusts the Root CA, an additional empty CRL signed by the Root CA is provided on one of the revocation service endpoints and can be used for any certificate issued by the Node CA.

Certificate Revocation Request submission

When you submit the certification revocation requests, the following fields should be present in the request payload:

• certificateSerialNumber: Serial number of the certificate that is to be revoked.

• csrRequestId: Certificate signing request identifier associated with the certificate that is to be revoked.

• legalName: Legal name associated with the certificate that is to be revoked.

• reason: Revocation reason (as specified in the java.security.cert.CRLReason). The following values are allowed:

  • KEY_COMPROMISE: Known or suspected that the certificate subject’s private key has been compromised. It applies to end-entity certificates only.

  • CA_COMPROMISE: Known or suspected that the certificate subject’s private key has been compromised. It applies to certificate authority (CA) certificates only.

  • AFFILIATION_CHANGED: The subject’s name or other information has changed.

  • SUPERSEDED: The certificate has been superseded.

  • CESSATION_OF_OPERATION: The certificate is no longer needed.

  • PRIVILEGE_WITHDRAWN: The privileges granted to the subject of the certificate have been withdrawn.

• reporter: Issuer of this certificate revocation request.

Corda AMQP serialization framework is used as the serialization framework.

Internal protocol

There is an internal communication protocol between the Signing Service and the HSM Signing Service for producing the signed CRLs. This does not use HTTP to avoid exposing any web vulnerabilities to the signing process.

Lifecycle

CRLs contain a field called “next update”, after which the CRL is no longer valid. This is to ensure that an up-to-date CRL is distributed in the network before the previous one expires. Conventionally, they have a lifecycle of 6 months and are manually signed every 3 months. This kind of scheduling allows plenty of time to resolve any signing issues.