Cryptanalysis and Attacks CEH Practice Questions (Page 13)

Questions 61–63

1. 61foundation · easy

   What statistical property does frequency analysis exploit to break classical ciphers?

   • AThe randomness of the encryption algorithm
   • BThe non-uniform frequency distribution of letters in natural language
   • CThe length of the key used for encryption
   • DThe uniform distribution of characters in plaintext
   Reveal Solution Discussion Select an answer first
2. 62expert · hard

   A cryptanalyst is testing a custom encryption protocol that uses a block cipher in CBC mode. The protocol has a padding oracle vulnerability: the server returns a different error if padding is invalid. The cryptanalyst has the ability to submit arbitrary ciphertexts to the server. Which attack would be most effective to decrypt a target ciphertext without knowing the key?

   • APadding oracle attack, modifying the ciphertext byte-by-byte and observing the server's padding error responses to recover the plaintext.
   • BKnown-plaintext attack using previously captured plaintext-ciphertext pairs.
   • CMeet-in-the-middle attack on the CBC mode.
   • DBrute-force attack on the block cipher key.
   Reveal Solution Discussion Select an answer first
3. 63application · medium

   A forensic analyst is trying to decrypt a file that was encrypted with a 40-bit key. The analyst has access to a high-performance computing cluster. Which attack would be the most practical to recover the key?

   • ASide-channel attack to measure power consumption during decryption.
   • BDictionary attack using a list of common keys.
   • CRainbow table attack on the encryption algorithm.
   • DBrute-force attack, systematically trying all 2^40 possible keys.
   Reveal Solution Discussion Select an answer first