The Certificate Management Protocol (CMP) is an Internet protocol standardized by the IETF used for obtaining X.509 digital certificates in a public key infrastructure (PKI). CMP is a very feature-rich and flexible protocol, supporting any types of cryptography. CMP messages are self-contained, which, as opposed to EST, makes the protocol independent of the transport mechanism and provides end-to-end security. CMP messages are encoded in ASN.1, using the DER method. CMP is described in . Enrollment request messages employ the Certificate Request Message Format (CRMF), described in . The only other protocol so far using CRMF is Certificate Management over CMS (CMC), described in . History An obsolete version of CMP is described in , the respective CRMF version in . A CMP Update is in preparation as well as a Lightweight CMP Profile focusing on industrial use. PKI Entities In a public key infrastructure (PKI), so-called end entities (EEs) act as CMP client, requesting one or more certificates for themselves from a certificate authority (CA), which issues the legal certificates and acts as a CMP server. None or any number of registration authorities (RA), can be used to mediate between the EEs and CAs, having both a downstream CMP server interface and an upstream CMP client interface. Using a "cross-certification request" a CA can get a certificate signed by another CA. Features Self-contained messages with protection independent of transfer mechanism - as opposed to related protocols EST and SCEP, this supports end-to-end security. Full certificate life-cycle support: an end entity can utilize CMP to obtain certificates from a CA, request updates for them, and also get them revoked. Key pair generation is usually done by the client side, but can also be requested from the server side. Proof-of-possession is usually done by a self-signature of the requested certificate contents, but CMP supports also other methods. CMP supports the very important aspect of proof-of-origin in two formats: based on a shared secret (used initially) and signature-based (using pre-existing certificates). In case an end entity has lost its private key and it is stored by the CA, it might be recovered by requesting a "key pair recovery". There are various further types of requests possible, for instance to retrieve CA certificates and to obtain PKI parameters and preferences of the server side. Transport CMP messages are usually transferred using HTTP, but any reliable means of transportation can be used. Encapsulated in HTTP