Abstract: A cipher for enciphering and deciphering a signal includes a plurality of sequentially coupled cipher units, each cipher unit being operable to carry out a reversible operation on the signal. The couplings between cipher units can be randomly configured using a cipher code. The cipher code can be secretly shared between the encipher and decipher. A signal which is enciphered using this technique is thus deciphered using a randomly selected cipher circuit as described by the cipher code.

Abstract: An apparatus is provided for use in supplying personalised information for users of an information or similar system. In particular, an apparatus is provided with capability to access to one or more suppliers of information, the apparatus including a facility for allocating a common reference for a particular user for use in communications between the apparatus and a particular information supplier. The apparatus is also provided with means for inviting a selected information supplier to supply personalised information for presentation to that user, identifying the user with the respectively allocated common reference. The common reference enables a particular user to be consistently identified so that user profile information held independently by two or more entities may contribute to the selection and generation of personalised information for that user or group of users.