Certificate Management Protocol
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. Transport. CMP messages are usually transferred using HTTP, but any reliable means of transportation can be used. The Content-Type used is "application/pkixcmp"; older versions of the draft used "application/pkixcmp-poll", "application/x-pkixcmp" or "application/x-pkixcmp-poll".