Classical Ciphers (Caesar, Vigenere, Playfair, ADFGVX) ECES Practice Questions (Page 4)

Questions 16–20

1. 16expert · medium

   A historian is studying the ADFGVX cipher and wants to explain why it was considered a significant advancement over earlier field ciphers. Which statement correctly describes the ADFGVX cipher's contribution?

   • AIt combined substitution and transposition, making it resistant to simple frequency analysis
   • BIt was the first cipher to use a Polybius square
   • CIt was the first cipher to be broken by frequency analysis
   • DIt was the first cipher to use a keyword
   Reveal Solution Discussion Select an answer first
2. 17application · medium

   A student is studying the Playfair cipher and wants to understand why it was considered an improvement over simple substitution ciphers. Which of the following is the primary reason?

   • AIt uses a longer key, making brute force impossible
   • BIt is a polyalphabetic cipher, using multiple substitution alphabets
   • CIt adds a transposition step, scrambling the order of letters
   • DIt encrypts digraphs, which obscures single-letter frequency patterns
   Reveal Solution Discussion Select an answer first
4. 18application · medium

   A puzzle designer wants to create a cipher challenge for a game. He decides to use the Playfair cipher with the key square built from the keyword 'PLAYFAIR'. A player encrypts the plaintext 'HELLO WORLD' (after removing spaces). Which of the following correctly describes the first step of the encryption process?

   • AConvert all letters to numbers and apply a Caesar shift to each pair
   • BRemove spaces, split into digraphs, and insert X between repeated letters in a digraph
   • CUse a keyword to generate a 5x5 square and then apply a columnar transposition
   • DRemove spaces and split into digraphs without any further changes
   Reveal Solution Discussion Select an answer first
5. 19application · medium

   A small team uses a Caesar cipher with a shift of 3 to protect internal notes. A new member suggests switching to a Vigenere cipher with a 5-letter keyword to improve security. What is the primary security advantage of the Vigenere cipher over the Caesar cipher in this context?

   • AIt uses a longer key that is impossible to break
   • BIt adds a transposition step that scrambles letter order
   • CIt encrypts letters in pairs, hiding single-letter frequencies
   • DIt uses multiple substitution alphabets, making frequency analysis harder
   Reveal Solution Discussion Select an answer first
6. 20application · medium

   A cryptographer is implementing a Playfair cipher for a legacy system. The key square is built from the keyword 'PLAYFAIR'. The plaintext is 'HELLO WORLD'. Following the standard Playfair rules, what is the first step the cryptographer must perform before encrypting?

   • ARemove spaces and split into digraphs, inserting a filler letter (e.g., X) between repeated letters in the same digraph
   • BConvert each letter to its numeric equivalent and add the keyword values
   • CApply a fixed shift of 5 to each letter
   • DReplace each letter with a pair of coordinates from a 6x6 grid
   Reveal Solution Discussion Select an answer first