Feistel Networks, DES, 3DES, and AES ECES Practice Questions (Page 5)

Questions 21–25

1. 21expert · medium

   You are reviewing an AES-256 implementation and notice that the key expansion routine generates round keys that are each 128 bits long. The implementation is configured for AES-256. How many round keys are generated in total?

   • A14 round keys
   • B13 round keys
   • C15 round keys
   • D16 round keys
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2. 22foundation · easy

   In the DES key schedule, what is the effective key length after the parity bits are removed?

   • A56 bits
   • B128 bits
   • C48 bits
   • D64 bits
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4. 23foundation · easy

   Which of the following is a reason AES is considered secure against known attacks?

   • AIts large key sizes and strong resistance to differential and linear cryptanalysis
   • BIts use of a Feistel network, which is inherently secure
   • CIts use of a 64-bit block size, which prevents birthday attacks
   • DIts reliance on secret S-boxes that are not published
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5. 24foundation · easy

   Which of the following is a known weakness of DES besides its short key length?

   • AIt uses a 128-bit block size, which is too large for some applications
   • BIt has no key schedule, making related-key attacks trivial
   • CIt is a stream cipher and is prone to bit-flipping attacks
   • DIt is susceptible to differential cryptanalysis, though it was designed to resist it
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6. 25application · medium

   A security engineer is analyzing a DES implementation and wants to understand the key schedule. They know that the original key is 64 bits, but the effective key length is 56 bits. Why is the effective key length 56 bits?

   • AThe key schedule only uses 56 bits because the remaining 8 bits are discarded during the key schedule.
   • BThe key is XORed with a constant to reduce it to 56 bits.
   • CThe key is compressed to 56 bits by the initial permutation.
   • DEight bits are used as parity bits and are not used in the key schedule.
   Reveal Solution Discussion Select an answer first