Playfair Cipher Overview and Key Construction Answers 1. What is a significant advantage of the Playfair cipher over simple substitution ciphers? A. It uses a larger key size. B. It reduces the effectiveness of frequency analysis. C. It employs frequency analysis techniques. D. It encrypts individual letters. Answer: It reduces the effectiveness of frequency analysis. (B) The use of digraphs in the Playfair cipher significantly reduces the effectiveness of frequency analysis compared to simple substitution ciphers. 2. What is one major weakness of the Playfair cipher? A. It is immune to modern cryptanalysis. B. It relies on a strong key for security. C. Its structure makes it complex for attackers. D. It encrypts plaintext using a one-time pad. Answer: It relies on a strong key for security. (B) The security of the Playfair cipher is heavily reliant on the strength of its key; if the key is compromised, the cipher's security is significantly weakened. 3. Which technique can still decipher the Playfair cipher despite its complexity? A. Frequency analysis with digraphs. B. Brute force attacks. C. Symmetrical key analysis. D. Transposition cipher attacks. Answer: Frequency analysis with digraphs. (A) Frequency analysis can still be effectively applied to digraphs in the Playfair cipher to break it, although the calculations are more complex. 4. What aspect of the Playfair cipher makes it more challenging to break than the Caesar cipher? A. The key length and matrix size. B. The reliance on single letters. C. The static substitution of letters. D. The use of encryption algorithms. Answer: The key length and matrix size. (A) The Playfair cipher's longer key length and matrix size contribute to its increased difficulty in being deciphered compared to the simpler Caesar cipher. 5. How does the Playfair cipher compare to modern cryptanalytic techniques? A. It remains secure against all types of analysis. B. It uses advanced mathematics to secure data. C. It is significantly stronger than modern methods. D. It is easily broken by modern techniques. Answer: It is easily broken by modern techniques. (D) Modern cryptanalytic techniques can easily break the Playfair cipher, revealing its vulnerabilities despite its complexity.