Feistel Networks, DES, 3DES, and AES ECES Practice Questions (Page 10)

Questions 46–50

1. 46foundation · easy

   What is the primary purpose of the S-boxes in the DES round function?

   • ATo mix the key with the data using XOR
   • BTo provide nonlinearity, which is essential for cryptographic strength
   • CTo permute the bits according to a fixed table
   • DTo expand the data from 32 bits to 48 bits
   Reveal Solution Discussion Select an answer first
2. 47foundation · easy

   Why is 3DES considered slow compared to AES?

   • AIt uses a more complex key schedule than AES
   • BIt requires hardware acceleration to run at all
   • CIt performs three DES operations for each block of data
   • DIt uses a larger block size, requiring more processing
   Reveal Solution Discussion Select an answer first
4. 48expert · hard

   A cryptanalyst is analyzing a custom block cipher that uses a Feistel network with a 64-bit block and 16 rounds. They notice that the round function is very simple and does not provide good diffusion. Which property of the cipher is most likely to be weakened?

   • AThe cipher's block size.
   • BThe cipher's invertibility.
   • CThe cipher's resistance to differential cryptanalysis.
   • DThe cipher's key schedule.
   Reveal Solution Discussion Select an answer first
5. 49application · medium

   A company is using 3DES in EDE mode with two keys (K1 = K3, K2 different) to encrypt sensitive data. A security consultant recommends migrating to AES-256. What is the effective key length of the current 2-key 3DES configuration?

   • A56 bits
   • B80 bits
   • C112 bits
   • D168 bits
   Reveal Solution Discussion Select an answer first
6. 50application · medium

   A software engineer is selecting a symmetric cipher for a new high-throughput application that will run on both 8-bit microcontrollers and 64-bit servers. The application requires strong security and must be efficient in both hardware and software. Which cipher should they choose?

   • ADES with a 56-bit key and 16 rounds.
   • BAES with a 128-bit key and 10 rounds.
   • C3DES with three independent keys.
   • DA custom Feistel cipher with a 64-bit block and 8 rounds.
   Reveal Solution Discussion Select an answer first