Cryptographic Principles (Diffusion, Confusion, Kerckhoff Principle) ECES Practice Questions (Page 3)

Questions 11–15

1. 11foundation · easy

   Why do modern cryptographic algorithms follow Kerckhoffs's principle?

   • ABecause it makes the algorithm impossible to reverse-engineer
   • BBecause it eliminates the need for key management
   • CBecause it allows the algorithm to be publicly reviewed and tested without compromising security
   • DBecause it guarantees that the ciphertext cannot be decrypted without the key
   Reveal Solution Discussion Select an answer first
2. 12expert · hard

   A government agency is considering two encryption algorithms. Algorithm X is proprietary and kept secret. Algorithm Y is publicly documented and has undergone extensive cryptanalysis. Both algorithms have similar performance. The agency's policy requires that security not depend on the secrecy of the algorithm. Which algorithm should the agency choose, and why?

   • AAlgorithm Y, because public algorithms are always faster.
   • BAlgorithm Y, because it adheres to Kerckhoffs's principle and has been publicly vetted.
   • CAlgorithm X, because keeping the algorithm secret provides an additional layer of security.
   • DAlgorithm X, because proprietary algorithms are less likely to be targeted by attackers.
   Reveal Solution Discussion Select an answer first
4. 13application · medium

   A security analyst is testing a new block cipher. The analyst encrypts a plaintext block and then changes one bit in the plaintext. The resulting ciphertext has only one bit different from the original ciphertext. What does this indicate about the cipher?

   • AThe cipher has poor diffusion, as a single plaintext bit change should affect many ciphertext bits.
   • BThe cipher has strong confusion, as the key relationship is complex.
   • CThe cipher has a weak key schedule.
   • DThe cipher adheres to Kerckhoffs's principle.
   Reveal Solution Discussion Select an answer first
5. 14foundation · easy

   Which effect best illustrates diffusion in a block cipher?

   • AThe key schedule generates different round keys from the original key
   • BThe same plaintext block always produces the same ciphertext block
   • CThe ciphertext is padded to a multiple of the block size
   • DChanging one bit of the plaintext changes roughly half of the ciphertext bits
   Reveal Solution Discussion Select an answer first
6. 15application · medium

   A network administrator notices that encrypted traffic from a legacy device always starts with the same 16-byte pattern. The device encrypts fixed-size blocks with a block cipher in ECB mode. The administrator wants to recommend a change that will hide this pattern. Which approach directly addresses the lack of diffusion across blocks?

   • AApply a substitution cipher to the plaintext before encryption.
   • BKeep the algorithm secret to prevent attackers from knowing the block size.
   • CUse a stronger key by increasing the key length from 128 to 256 bits.
   • DSwitch to a mode like CBC or CTR that uses an initialization vector to randomize identical plaintext blocks.
   Reveal Solution Discussion Select an answer first