The invention relates to a method of ciphering data transmission in a radio system, and to a user equipment using the method, and to a radio network subsystem using the method. The method includes the steps of: (602) generating a ciphering key; (604A) producing a ciphering mask in a ciphering algorithm using the ciphering key as an input parameter; (604B) using a logical channel specific parameter or a transport channel specific parameter as an additional input parameter to the ciphering algorithm; and (606) producing ciphered data by applying the ciphering mask to plain data.