Exam 312-50v13 topic 1 question 262 discussion

D. Serpent Block & Key Sizes: 128-bit block cipher with key sizes of 128, 192, or 256 bits. Rounds & Structure: 32 rounds, each involving substitution (S-boxes) and permutation (P-boxes). Processes data as four 32-bit words, aligning with the requirement. S-box Characteristics: Uses 8-variable S-boxes (8 input bits) with 4-bit outputs, though each S-box is defined as 4x4 (4-bit in, 4-bit out). This matches the description (note: 8-variable likely refers to the number of S-boxes, not input bits—Serpent uses 8 distinct S-boxes, each with 4-bit input/output).

Ciphers - Serpent Serpent uses a 128-bit symmetric block cipher with key sizes of 128, 192, or 256 bits. It can be integrated into software or hardware programs without any restrictions. Serpent involves 32 rounds of computational operations that include substitution and permutation operations on four 32-bit word blocks using 8-variable S-boxes with 4-bit entry and 4-bit exit. (P.3033/3017)

D is correct

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.