Patent ID: 7356145

Claim:
A method for arranging data ciphering in a telecommunication system having one wireless terminal, a wireless local area network and a public land mobile network, the method comprising: offering an identifier for the at least one wireless terminal and a specific secret key for the identifier, the secret key also being stored in the mobile network, arranging data transmission between the mobile network and the at least one wireless terminal through the wireless local area network, sending the terminal identifier from the at least one wireless terminal to the mobile network via the wireless local area network, calculating in the mobile network at least one first ciphering key using the secret key specific for the identifier and a challenge code selected for the first ciphering key, sending at least one challenge code to the at least one wireless via the wireless local area network, calculating in the at least one wireless terminal at least one first ciphering key using the secret key and at least one challenge code, calculating a second ciphering key in the at least one terminal and in the mobile network using said at least one first ciphering key, sending said second ciphering key from the mobile network to the wireless local area network, and ciphering the data between the at least one wireless terminal and mobile network in the at least one wireless terminal and in the wireless local area network using said second ciphering key, wherein the terminal comprises a subscriber identity module SIM of the GSM system, the wireless local area network supports IEEE802.11 standard, and the mobile network supports GSM standard.