Block cipher system for data security

Details Block cipher system for data security Block cipher system for data security

H - Electricity

04

K

340/70

H04K 1/00 (2006.01) H04L 9/00 (2006.01) H04L 9/06 (2006.01)

Patent

CA 1048935

BLOCK CIPHER SYSTEM FOR DATA SECURITY Abstract A device for ciphering message blocks of data bits under con- trol of a cipher key. The cipher device performs a ciphering pro- cess for the first half of the message block of data bits from a first store by carrying out an operation in which the block of data bits is expanded by duplicating predetermined ones of the data bits of the first half of the message block. The data bits of the ex- panded first half of said message block are combined by modulo-2 addition with an equal number of cipher key bits, selected in accor- dance with an arbitrary but fixed permutation, to produce a plurality of multi-bit segments forming the arguments for a plurality of dif- ferent non-linear substitution function boxes. The substitution boxes perform a plurality of nonlinear transformation functions to produce a substitution set of bits which are equal in number to the number of data bits in the first half of the message block. The substitution of data bits is then subjected to a linear transformation in accor- dance with an arbitrary but fixed permutation. The combined non-linear transformation and linear transformation results in a product block cipher for the first half of the said message block. Then the second half of the message block from a second store is subjected to a linear transformation in accordance with the product block cipher to produce a set of bits representing a modified second half of said message block. Finally said modified second half of said message block is loaded into the first store and the first half of the message block from the first store is loaded into the second store concurrently with the modified second half of the message block being loaded into the first store to complete a first iteration operation of the cipher device. -1-

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