1.3 Overview

The Windows Client Certificate Enrollment Protocol is built from two DCOM interfaces: ICertRequestD and ICertRequestD2, successive versions. The two DCOM interfaces allow a client to interact with a CA to request a certificate and to obtain certain information about the CA. This document specifies the protocol, the Windows Client Certificate Enrollment Protocol, but also specifies certain elements of the behavior of the client and the CA (the server), because those behaviors are reflected in or influence protocol behavior.

The Windows Client Certificate Enrollment Protocol occurs between one client and one server. However, the client and the server are subject to variation, so the enrollment process can appear very complex. Other machines and services can also interact with the client and/or the server during enrollment, but those interactions depend on the particular variations in use.

Two elements of a server are subject to variation. These elements are independent of each other and independent of the implementation of the Windows Client Certificate Enrollment Protocol stack. This protocol specification refers to these elements as follows:

  • CA policy algorithm

    This algorithm determines 1) whether to issue the certificate requested, and 2) how to populate the fields of a certificate that is issued.

  • CA exit algorithm

    The optional algorithm that is invoked when a certificate is issued. This algorithm might store a copy of that certificate in one or more repositories, or the algorithm might make a log entry or notify some person of the issuance of the certificate.

The variants of interest in the CA policy algorithm are as follows:

  • Hard-coded

    A policy algorithm that performs the same operation on certificate requests regardless of the information specified in the request is called a hard-coded policy algorithm. A simple, hard-coded policy algorithm might issue any certificate that is requested.

  • Manual

    A policy algorithm that requires human intervention in order to determine whether or not to issue a certificate is called a manual policy algorithm. A simple manual policy algorithm accepts the requester's choice of certificate fields, presents the requested certificate to an administrator, and asks the administrator whether or not to issue the certificate.

  • Policy-driven via certificate templates

    A policy algorithm that determines whether or not to issue certificates based on enrollment policies specified in a certificate template [MS-CRTD]. Each certificate template in a collection of certificate templates describes a kind of certificate with its fields. The security descriptor on the certificate template provides an access control list (ACL) that can include the Enroll permission for an individual or, more typically, a group of individuals. A policy algorithm that strictly implements a policy stored as certificate templates is described in section

    Note The capability to base certificate policy on user types is not available for a standalone CA since standalone CAs do not support the use of certificate templates.

One aspect of a client subject to variation is whether certificate templates are used to form certificate requests.