Patent ID: 6769063
Filing Date: 2004-07-27
Classification: H04L

Abstract:
A data transformation device which has key storage means for storing plural pieces of key data and a plurality of cascade-connected round processing parts each composed of a nonlinear function part supplied with said plural pieces of key data to perform key-dependent nonlinear transformation, whereby input data is transformed to different data in dependence on key data, said nonlinear function part of each of said round processing parts comprising:first key-dependent linear transformation means for linearly transforming input data to said round processing part based on first key data stored in said key storage means; splitting means for splitting the output data from said first key-dependent linear transformation means to n pieces of subdata, said n being an integer equal to or larger than 4; first nonlinear transformation means for nonlinearly transforming each of said n pieces of subdata; second key-dependent linear transformation means for linearly transforming the output subdata from each of said first nonlinear transformation means based on second key data stored in said key storage means; second nonlinear transformation means for nonlinearly transforming n pieces of output subdata from said second key-dependent linear transformation means; and combining means for combining n pieces of output subdata from said second nonlinear transformation means to provide the output from said nonlinear function means; wherein said second key-dependent linear transformation means contains a linear transformation layer wherein the input thereto is transformed linearly using XORs defined by an nÃ—n matrix.