Patent ID: 6301362
Filing Date: 2001-10-09
Classification: H04L

Abstract:
A method of transforming an input block into an output block using a cryptographic procedure, one of sad blocks comprising a plaintext block and the other of said blocks comprising a ciphertext block, the input block having a first block size and being partitionable into a plurality of input subblocks having a second block size, the method comprising the steps of:passing the input subblocks through respective first substitution functions to generate a first plurality of modified subblocks, each of said first substitution functions comprising a plurality of keyed cryptographic operations performed in succession using a plurality of different keys of predetermined length for an effective key length that is greater than said predetermined length, each of said first plurality of modified subblocks corresponding to one of said input subblocks and being generated as a function of only that one of said input subblocks independently of any other of said input subblocks;passing the first plurality of modified subblocks through a keyless mixing function to generate a second plurality of modified subblocks, each of the second plurality of modified subblocks depending on each of the first plurality of modified subblocks; andpassing the second plurality of modified subblocks through respective second substitution functions to generate a plurality of output subblocks that are combinable into an output block, each of said second substitution functions comprising a plurality of keyed cryptographic operations performed in succession using a plurality of different keys of predetermined length for an effective key length that is greater than said predetermined length, each of said plurality of output subblocks corresponding to one of said second plurality of modified subblocks and being generated as a function of only that one of said second plurality of modified subblocks independently of any other of said second plurality of modified subblocks.