Cryptographic Principles (Diffusion, Confusion, Kerckhoff Principle) ECES Practice Questions (Page 8)

Questions 36–37

1. 36application · medium

   A software developer is implementing a block cipher and wants to test whether it has good diffusion. Which test would directly measure diffusion?

   • ACheck if the ciphertext length is the same as the plaintext length.
   • BEncrypt the same plaintext with two keys that differ by one bit and compare the ciphertexts.
   • CEncrypt two plaintexts that differ by one bit with the same key and compare the percentage of ciphertext bits that differ.
   • DDecrypt a ciphertext with the wrong key and see if the output looks random.
   Reveal Solution Discussion Select an answer first
2. 37application · medium

   A cryptographer is designing a new block cipher and wants to ensure that even if an attacker collects many plaintext-ciphertext pairs, they cannot deduce the secret key. Which design goal is most directly aligned with this requirement?

   • AMaximize confusion so that the statistical relationship between the ciphertext and the key is complex and non-linear.
   • BUse a simple linear transformation to speed up encryption.
   • CMaximize diffusion so that each plaintext bit affects many ciphertext bits.
   • DIncrease the block size to 256 bits to provide more possible plaintext mappings.
   Reveal Solution Discussion Select an answer first