Key agreement for wireless communication

A wireless network operator system comprising:

• a communication interface operable to receive an identifier of a mobile device;
• data processing apparatus operable to:
• access, based on the identifier, a secret key associated with the mobile device;
• evaluate a message authentication code function based on the secret key to produce an output value;
• and
• obtain a session key based on the output value.

A method performed by a mobile device, the method comprising:

• accessing a secret key in response to receiving a challenge value from a wireless network operator system;
• evaluating a message authentication code function based on the secret key to produce an output value;
• obtaining a response value and a session key based on the output value;
• and
• transmitting the response value to the wireless network operator system.

A mobile device comprising:

• a communication interface operable to receive a challenge value from a wireless network operator system;
• data processing apparatus operable to:
• access a secret key in response to receiving the challenge value;
• evaluate a message authentication code function, based on the secret key, to produce an output value;
• obtain a response value and a session key based on the output value;
• and
• transmit the response value to the wireless network operator system.