Apparatus and a method for ciphering messages in mobile telecommunications system user equipment are disclosed. The apparatus is arranged to receive ciphering configuration parameters in a Radio Resource Control (RRC) layer; forward ciphering configuration parameters to a Radio Link Control (RLC) or Medium Access Control (MAC) layer; and, in response to subsequent receipt of a message from the network, which message indicates that the user equipment device is to start ciphering, configuring the user equipment device to start ciphering using the ciphering configuration parameters in the RLC/MAC layer.