The Certificate Management Protocol (CMP) is an Internet protocol used for obtaining X.509 digital certificates in a public key infrastructure (PKI). It is described in RFC 4210 and is one of two protocols so far to use the Certificate Request Message Format (CRMF), described in RFC 4211, with the other protocol being Certificate Management over CMS (CMC), described in RFC 5273. An obsolete version of CMP is described in RFC 2510, the respective CRMF version in RFC 2511.
Contents
CMP messages are encoded in ASN.1, using the DER method and usually transported over HTTP.
PKI Entities
A certificate authority (CA), issuing the certificates, acts as the server in a PKI using CMP. One of the clients, obtaining their digital certificates by means of this protocol is called end entity (EE). None or any number of registration authorities (RA), can be used to mediate between the EEs and the CA.
Features
An EE can utilize CMP to obtain certificates from the CA. This can be done through an "initial registration/certification", a "key pair update" or a "certificate update" message sequence. By means of a revocation request it can also get one of its own certificates revoked. Using a "cross-certification request" a CA can get a certificate signed by another CA. In case an EE has lost its private key and it is stored by the CA, it might be recovered by requesting a "key pair recovery".
Transport
Several means of transportation are foreseen for conveying CMP messages:
The Content-Type used is application/pkixcmp; older versions of the draft used application/pkixcmp-poll, application/x-pkixcmp or application/x-pkixcmp-poll.