Cryptographic Principles (Diffusion, Confusion, Kerckhoff Principle) ECES Practice Questions (Page 4)

Questions 16–20

1. 16expert · hard

   A security architect is choosing between two encryption algorithms for a public-key infrastructure. Algorithm A is open-source and widely analyzed. Algorithm B is proprietary and its design is kept secret. Both have similar performance and key lengths. Which choice best aligns with Kerckhoffs's principle?

   • AChoose either algorithm because Kerckhoffs's principle only applies to symmetric ciphers.
   • BChoose Algorithm B because its secrecy provides an additional layer of security.
   • CChoose Algorithm B because it is less likely to be attacked by hackers who don't know its design.
   • DChoose Algorithm A because its security is based on the key, not on the secrecy of the algorithm.
   Reveal Solution Discussion Select an answer first
2. 17application · medium

   A network engineer is troubleshooting an encryption implementation that is leaking information about the plaintext through statistical patterns in the ciphertext. The engineer suspects that the cipher does not sufficiently hide the plaintext's structure. Which principle is most likely being violated?

   • AThe key schedule, because it generates weak subkeys.
   • BConfusion, because the key relationship is too simple.
   • CDiffusion, because the influence of plaintext bits is not spread enough across the ciphertext.
   • DKerckhoffs's principle, because the algorithm is public.
   Reveal Solution Discussion Select an answer first
4. 18expert · hard

   A cryptanalyst is analyzing a new cipher. The cipher uses a linear feedback shift register (LFSR) to generate a keystream. The analyst discovers that the keystream is a linear function of the key and the initial state. This allows the analyst to recover the key with a known-plaintext attack. Which principle is the cipher lacking, and what is the most effective countermeasure?

   • ADiffusion; increase the length of the LFSR to spread the key bits more.
   • BConfusion; introduce a nonlinear combining function, such as a Boolean function with high nonlinearity, to obscure the key-keystream relationship.
   • CConfusion; use a longer key to make brute-force infeasible.
   • DKerckhoffs's principle; keep the LFSR structure secret.
   Reveal Solution Discussion Select an answer first
5. 19application · medium

   A cryptographer is designing a new symmetric cipher. The cipher uses a substitution box (S-box) that is carefully designed to be nonlinear. The goal is to make it difficult for an attacker who knows many plaintext-ciphertext pairs to deduce the secret key. Which cryptographic principle is the S-box primarily intended to achieve?

   • ADiffusion, by spreading the influence of each plaintext bit across many ciphertext bits.
   • BKerckhoffs's principle, by ensuring the algorithm can be publicly disclosed.
   • CConfusion, by making the relationship between the key and ciphertext complex and nonlinear.
   • DAvalanche effect, by ensuring that a one-bit key change produces a completely different ciphertext.
   Reveal Solution Discussion Select an answer first
6. 20application · medium

   A company is designing a proprietary encryption protocol. The design team wants to keep the algorithm secret to protect against attackers. A security consultant advises against this, citing Kerckhoffs's principle. What is the best justification for the consultant's advice?

   • APublic algorithms are always more secure than proprietary ones.
   • BPublic algorithms undergo extensive review, and security should rely on the key, not obscurity.
   • CKerckhoffs's principle requires that the key be public.
   • DKeeping the algorithm secret makes it harder for attackers to find vulnerabilities.
   Reveal Solution Discussion Select an answer first