Authentication of data transmission devices

Abstract

An intermediate data transmission device arranges for mutual authentication between itself and a remote terminal to allow data to be exchanged between the remote terminal and a server through the device. The server sends first and second key codes to the intermediate device, the key codes both being derived from a shared secret known to the server and remote terminal but not to the intermediate device. In response to a challenge from the intermediate device the remote terminal uses the shared secret to generate a duplicate of the first key code and transmits the duplicate to the intermediate device. The intermediate device compares the first key code and the duplicate of the first key code received respectively from the server and the remote terminal to verify the authenticity of the remote terminal. The intermediate device then transmits the second key code to the remote terminal, to be compared by the remote terminal with a duplicate of the second key code to verify the authenticity of the intermediate device. This process allows the intermediate device to be used without itself having the shared secret. The codes generated by the server may be encoded with a network identity of the intermediate device using the shared secret, such that the remote terminal can only respond to the same intermediate device that transmitted the codes. This prevents a 'man-in-the middle' attack by another intermediate device, as without the shared secret no intermediate device can modify the codes to include a different network identity.