Cryptography – Communication system using cryptography – Data stream/substitution enciphering
Patent
1988-05-02
1990-01-30
Cangialosi, Salvatore
Cryptography
Communication system using cryptography
Data stream/substitution enciphering
380 44, H04L 900
Patent
active
048978760
ABSTRACT:
An improved arrangement for digital signal encrytion using a cipher algorithm in which a multi-bit key signal is used to produce a first keystream signal of coding bytes which are used in an exclusive-OR logical operation with data bytes of a received digital data signal to produce an enciphered/deciphered output digital data signal. Hitherto, the keysteam signal was also fed back into the algorithm for processing with the key signal, but this was found to result in an insecure arrangement because the keystream signal can be found by exclusive-ORing the received digital data signal with only a few bytes of the output data signal that are already known, following which the key signal itself can be deduced by a fairly simple trial-and-error computing procedure. The improvement consists in feeding back into the algorithm a keystream signal which is not the same as that used for the exclusive-OR logical operation. This different keystream signal can be produced either directly or indirectly from the keystream signal used for the exclusive-OR logical operation. FIGS. 3 and 7 show these two possible ways of producing the different keystream signal.
REFERENCES:
patent: 3984668 (1976-10-01), Zetterberg et al.
patent: 4447672 (1984-05-01), Nakamora
patent: 4634808 (1987-01-01), Moerder
patent: 4712238 (1987-12-01), Gilhousen et al.
patent: 4760600 (1988-07-01), Nakai
patent: 4802217 (1989-01-01), Michner
Cangialosi Salvatore
Lobato Emmanuel J.
U.S. Philips Corp.
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