Part 3. LDES (3 marks) The figure below describes a block cipher LDES (“linear” DES) M (4 bits) f(X,Y)-Z rotate left 2-bit 3-bit 1 I2 Is Ji I2 +1 linear rotate left rotate right LDES is a mini example of a block cipher that has 2 rounds in the Feistel structure. It operates on 4-bit block and 2-bit key. The important feature of LDES is that the S-box has been replaced with a linear operation,
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