A method for securely transferring a master key from a host to a terminal, such as an automated teller machine, is disclosed. Each of the host and terminal is initialized with a certificate, signed by a certificate authority, and containing a public key used in used in connection with public key infrastructure communication schemes. An identifier of an authorized host is stored in the terminal. Upon receiving a communication from a host including a host certificate, the terminal validates whether it is already bound to a host, if not, whether the host identifier of the remote host matches the preloaded authorized host identifier, before further communicating with the remote host, including the exchange of certificates. In this way, the terminal is protected against attacks or intruders. Following the exchange of certificates, the host may securely transfer the master key to the terminal in a message encrypted under the terminal's public key. The terminal may decrypt the message, including the master key, using its corresponding secret key.