There is disclosed a method of authenticating a client computing device to a server, the client computing device and the server both parties to a common authentication approach, the client computing device including an encrypted identifier containing a secret, in which the client computing device cannot decrypt the encrypted identifier, in which the client computing device encrypts the encrypted identifier using the common authentication approach and sends the encrypted encrypted identifier to the server, and in which the server decrypts the encrypted encrypted identifier, using the common authentication approach and a server secret, so as to determine the secret. Related systems, servers, client computing devices, pairs of computer program products comprising a server program product and a client computing device program product, the server program product, or the client computing program product, are disclosed.