Enrollment Methods

The core challenge when enrolling certificates is how to authenticate the device or user requesting the certificate. With the certificate, the CA confirms that the certificate owner has specific properties and that it has checked their authenticity.

Therefore, one core property of certificate enrollment protocols is how they authenticate the certificate requester. Depending on what the certificate is used for, one or the other protocol is more advantageous.

One additional important property is its practical adoption. The enrollment method or protocol must be supported by both the CA and on the client side for the intended use case.

The most popular enrollment protocols are:

• SCEP

• ACME

• EST

• Microsoft's RPC/DCOM

• Microsoft's SOAP

• Manual enrollment on the CA's web page

• Other proprietary protocols

	Microsoft proprietary DCOM and RPC	WS-Trust Enrollment Extension SOAP Enrollment	Automatic Certificate Management Environment (ACME)	Simple Certificate Enrollment Protocol (SCEP)	Enrollment over Secure Transport (EST)
Specifications	Microsoft OpenSpec1	Microsoft OpenSpec2	RFC 8555	Informal, now RFC 8894	RFC 7030 (+ …)
Implementation	Server side: Active Directory CS Client side: Windows	Server side: ADCS, others? Client side: Windows	Server side: Let’s Encrypt Client side: Many	Many server and client implementations	Poor adoption
Authentication	AD Authentication	AD Authentication* (formally, username/password might not be in AD)	DNS Authentication	“SCEP Challenge”	CBA or HTTP Basic/Digest Authentication