Cryptography – Communication system using cryptography – Time segment interchange
Reexamination Certificate
2005-09-06
2005-09-06
Smithers, Matthew (Department: 2137)
Cryptography
Communication system using cryptography
Time segment interchange
C380S029000
Reexamination Certificate
active
06940975
ABSTRACT:
A pair of a pattern of a mask and a mask pattern obtained by bit inversion of the mask is prepared for each round function in a data scrambler. Every time encryption is to be performed, one mask pattern of the pair is randomly selected by a switch, and an exclusive OR of an input to an S-box and the selected mask pattern is calculated. In addition, an exclusive OR of an output from the S-box and bits of inverse permutation of the mask is calculated. The exclusive ORs are calculated in advance and stored as a table in the S-box. Furthermore, an exclusive OR of the output from each round function and a mask is calculated and concealed. The influence of the mask is removed by calculating the exclusive OR with the mask again on the next round.
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Kawamura Shin'ichi
Sano Fumihiko
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