Data transmission links

A method of establishing a secure communications link between a server and a terminal, the method comprising:

• assembling a message comprising a secret number and a digital signature for the secret number, the digital signature being generated using a private key for the terminal;
• encrypting the message at the terminal end of the communications link using a public key for the server;
• sending said encrypted message from the terminal to the server;
• decrypting said encrypted message at the server using a private key for the server;
• validating the message by checking the digital signature using a public key for the terminal;
• and
• establishing said secure communications link using said secret number;
• wherein the public and private keys for the server and terminal are public and private keys of an asymmetric cryptographic technique.

A method of establishing a secure communications link between a terminal and a server, the method comprising:

• performing, at the server-end of the communications link, a signing operation on a message comprising a secret number, using a private key for the server, to generate a digital signature, the message being recoverable from the digital signature;
• sending a message comprising the digital signature from the server to the terminal;
• extracting the secret number from the digital signature at the terminal and
• establishing said secure communications links using the secret number.

A method of establishing a secure communications link between a server and a terminal, the method comprising:

• performing, at the terminal-end of the communications link, a signing operation on a message comprising a secret number using a private key for the terminal to generate a digital signature, the message being recoverable from the digital signature;
• sending a message comprising the digital signature from the terminal to the server;
• extracting the secret number from the digital signature at the server and
• establishing said secure communications links using the secret number.

A method of establishing a secure communications link between a mobile terminal and a server, of a mobile communications system, one of the terminal and server being an originator and the other a recipient, the method comprising:

• sending a first message from the originator to the recipient, the first message comprising:
• an identity certificate for the originator, the certificate including a public key for the originator,
• a first data block, and
• a signature of the originator generated by operating on the first data block,
• the first data block comprising at least an identifier for the originator and a secret number encrypted using a public key of the recipient;
• and
• authenticating the first message at the recipient using the originator identifier.