PURPOSE: A fast block encryption method guaranteeing security for differential cryptanalysis and linear cryptanalysis is provided to simplify realization and realize a fast process by forming a rotation function with four S-boxes. CONSTITUTION: A data stream to be encrypted is divided into each 64-bit block, and the 64-bit block is divided into 32-bit left/right block. An OR operation for the left block and a 32-bit rotation key is performed by 8-bit sub-block unit. The first block from the 8-bit sub-blocks is inputted to the first S-box, and the OR operation of the rest sub-blocks with the previous output value of the S-box are respectively performed/inputted to the S-box in order. The output value of the S-boxes is moved to right 8 bits and rotated. After the OR operation of the rotated values and the right block, the data is set to the left block for a next round. The left block is set to the right block for the next round. After iteratively performing the previous steps to the last round by using the newly set left/right block, the left/right block set by an iteration result is output as the encrypted left/right block.
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