4: Cryptography in Software
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IDEA (International Data Encryption Algorithm) started out as PES, or Proposed Encryption Cipher, in 1990, and it was modified to improve its resistance to differential cryptanalysis and its name was changed to IDEA in 1992 It is a blockmode cipher using a 64bit block size and a 128bit key The input plaintext is split into four 16bit segments, A, B, C, and D The process uses eight rounds with each round performing the following function: A * S1 = X1 B + S2 = X2 C + S3 = X3 D * S4 = X4 X1 XOR X3 = X5 X2 XOR X4 = X6 X5 * S5 = X7 X6 + X7 = X8 X8 * S6 = X9

