Given a credential definition identifier and a tag, return the corresponding
    revocation registry identifier, repeating the issuer DID from the
    input identifier.

    :param cd_id: credential definition identifier
    :param tag: tag to use
    :return: revocation registry identifier

def rev_reg_id(cd_id: str, tag: str) -> str:
    """
    Given a credential definition identifier and a tag, return the corresponding
    revocation registry identifier, repeating the issuer DID from the
    input identifier.

    :param cd_id: credential definition identifier
    :param tag: tag to use
    :return: revocation registry identifier
    """

    return '{}:4:{}:CL_ACCUM:{}'.format(cd_id.split(':', 1)[0], cd_id, tag)