Method of executing an irregular permutation of data protected by encryption
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United States of America Patent
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-
Dec 1, 1992
Grant Date -
N/A
app pub date -
Jul 24, 1990
filing date -
Jul 25, 1989
priority date (Note) -
Expired
status (Latency Note)
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Abstract
This method of processing data protected by encryption is particularly suitable for smart cards utilizing the DES system. The method enables the execution of the irregular permutation of the key on the basis of a correspondence table, which operation is most costly as regards processing time and code length in the cited system. The method involves the decomposition of the initial permutation into a plurality of elementary permutations so that the majority thereof is performed on at least two bits, the bits of the various octets of the key being marked, a masking system being applied in order to extract the appropriate bits for their permutation in the positions predetermined by the correspondence table.
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