Cryptographic Principles (Diffusion, Confusion, Kerckhoff Principle) ECES Practice Questions (Page 5)

Questions 21–25

1. 21expert · hard

   A company is deploying a new encryption system. The CEO suggests keeping the algorithm secret to gain a competitive advantage. The CISO argues that this violates Kerckhoffs's principle and could weaken security. However, the CEO is concerned that a public algorithm would allow attackers to find vulnerabilities. Which argument best supports the CISO's position?

   • AKeeping the algorithm secret makes it harder for attackers to find vulnerabilities.
   • BPublic algorithms are always more secure than proprietary ones.
   • CKerckhoffs's principle requires that the key be public.
   • DPublic algorithms benefit from widespread cryptanalysis, and security should rely on the key, not obscurity.
   Reveal Solution Discussion Select an answer first
2. 22foundation · easy

   What is the primary purpose of diffusion in a cryptographic algorithm?

   • ATo make the ciphertext the same length as the plaintext regardless of the algorithm
   • BTo spread the influence of each plaintext bit over many ciphertext bits so that statistical patterns in the plaintext are hidden
   • CTo obscure the relationship between the ciphertext and the encryption key so that the key cannot be derived
   • DTo ensure that every plaintext bit appears exactly once in the ciphertext
   Reveal Solution Discussion Select an answer first
4. 23application · medium

   A security architect is evaluating a new block cipher for encrypting database backups. The cipher will be used with a fixed key for a long period, and the plaintext often contains repetitive headers. The architect wants to ensure that two nearly identical plaintext blocks produce completely different ciphertext blocks, so that an attacker cannot infer the structure of the data. Which property of the cipher should the architect prioritize?

   • AA large key space, so that brute-force attacks are infeasible.
   • BAdherence to Kerckhoffs's principle, so that the algorithm can be public.
   • CHigh diffusion, so that changing one plaintext bit changes many ciphertext bits.
   • DHigh confusion, so that the relationship between the key and ciphertext is complex.
   Reveal Solution Discussion Select an answer first
5. 24application · medium

   A startup is developing a new encryption product. The team is debating whether to use a well-known, publicly reviewed algorithm or a proprietary algorithm developed in-house. The team's security advisor recommends the public algorithm. Which reasoning best aligns with Kerckhoffs's principle?

   • AThe proprietary algorithm is more secure because it is unique.
   • BThe public algorithm is faster because it is optimized by the community.
   • CThe proprietary algorithm is more secure because attackers cannot analyze it.
   • DThe public algorithm has been analyzed by many experts, and security relies on the key, not the algorithm's secrecy.
   Reveal Solution Discussion Select an answer first
6. 25foundation · easy

   Which technique is commonly used to achieve confusion in a block cipher?

   • AAdding a fixed padding scheme to the plaintext
   • BPermutation of bits across rounds
   • CUsing a longer key without any substitution
   • DSubstitution using a non-linear S-box
   Reveal Solution Discussion Select an answer first