Exam 312-50v13 topic 1 question 262 discussion

Serpent is a 128-bit symmetric block cipher that supports key sizes of 128, 192, or 256 bits. It operates with 32 rounds of substitution-permutation operations on four 32-bit word blocks. Additionally, it uses 8-variable S-boxes with 4-bit input and output, making it a perfect match for Tony's requirements.

RC5 doesn't use fixed 32 rounds or S-boxes

The RC5 algorithm, developed by Ronald Rivest, is a symmetric-key block cipher that fits the criteria described in the question. Why RC5 is the correct choice: - 128-bit symmetric block cipher: RC5 is a block cipher, and it can operate on 128-bit blocks. - Key sizes of 128, 192, or 256 bits: RC5 supports variable key sizes, including 128, 192, and 256 bits, making it adaptable to different security requirements. - 32 rounds: RC5 uses a variable number of rounds, and it can be configured to perform 32 rounds in its computations. - Substitution and permutation operations: RC5 uses a combination of substitution and permutation (SP) operations during each round, which is in line with the question's description. - S-boxes with 4-bit entry and 4-bit exit: RC5 uses S-boxes in its round function. The S-boxes in RC5, which operate on 4 bits, fit the specified entry and exit size. - 32-bit word blocks: RC5 operates on 32-bit words, which aligns with the requirement of using 4 32-bit word blocks.