ARRANGEMENT FOR THE ENCRYPTION AND DECRYPTION OF A DIGITAL SIGNAL

摘要

The arrangement comprises the encryption of a digital signal of n-bit words Ni into an encrypted signal of n-bit words Ri. In the encryption device (1), a logic circuit (11) generates each encrypted word Ri from a logic operation g effected on the word Ni and on a stored word Pi-1 having n bits. An addressing circuit (13) elaborates an a-bit address word Ai-1 belonging completely or partially at least to the preceding encrypted word Ri-1. A store (12) of predetermined 2 words Pi-1 is read out for each address word Ai-1 to provide a corresponding word Pi-1 to the logic circuit (11) so as to carry out the operation g so that Ri = g (N , Pi-1). The decryption device receives the encrypted words Ri to elaborate the address words Ai controlling the reading of the corresponding words Pi among 2 stored words. Each decrypted word Ni is obtained by a logic operation h which is opposite to g and which is effected on the encrypted Ri and on the stored word Pi-1, so that Ni = h (Ri, Pi-1). The stores (12) may be programmed by computers (15) which compute according to a predetermined algorithm a table of words Pi for a given key (C). Application particularly to the encryption and decryption of teletexts.