The "Register-Registrar/Registrant" protocol is developed by Register.BG to provide access to the BG domain name registration system by the Registrars or the Registrants. For brevity the protocol will be referred to as REGRR.

Similar to the EPP protocol [RFC5730], REGRR is based on exchange of XML messages via Internet transport and permits computer to computer communication on client-server principles. The server is hosted by the Registry and the client by the Registrar or the Registrant. The REGRR protocol is designed to provide high reliability and security of the communication, by using digital signature certificates for encrypting the connection and signing the messages.

Specification of the protocol REGRR
Version	Validity date	Cancellation date	Active	Download
2.0, redaction 4	12.11.2019		Yes
2.0, redaction 3	03.10.2019	12.11.2019	No
2.0, redaction 2	29.08.2019	03.10.2019	No
2.0, redaction 1	10.04.2019	29.08.2019	No
2.0	25.11.2018	10.04.2019	No
2.0, preliminary	30.04.2017	25.11.2018	No