Monoalphabetic Substitution Cipher Overview Answers 1. What does a monoalphabetic substitution cipher primarily rely on for encryption? A. Variable letter mapping B. One-to-one mapping between letters C. Transposition of characters D. Symbolic representation of words Answer: One-to-one mapping between letters (B) A monoalphabetic substitution cipher uses a consistent one-to-one mapping between plaintext and ciphertext letters. 2. Which of the following best describes the key in a monoalphabetic substitution cipher? A. A substitution table mapping plaintext letters to ciphertext letters B. A fixed transposition of the alphabet C. An interchangeable alphabet D. A random sequence of letters Answer: A substitution table mapping plaintext letters to ciphertext letters (A) The key in a monoalphabetic substitution cipher is a substitution table that consistently maps plaintext letters to ciphertext letters. 3. What is a major limitation of the monoalphabetic substitution cipher? A. It encrypts data quickly B. It allows for complex encryption C. It is difficult to set up D. It can be easily broken with frequency analysis Answer: It can be easily broken with frequency analysis (D) The major limitation of the monoalphabetic substitution cipher is its vulnerability to frequency analysis, which exploits the predictable patterns in ciphertext. 4. In the decryption process of a monoalphabetic substitution cipher, what is required to successfully recover the plaintext? A. A frequency distribution chart B. A second key for verification C. The original alphabet D. The key (cipher alphabet) Answer: The key (cipher alphabet) (D) To decrypt the ciphertext, one needs to know the key, which is the cipher alphabet used during encryption. 5. What is one practical application of a monoalphabetic substitution cipher? A. Short messages where high security is not needed B. Long-term secure communications C. Secure financial transactions D. Complex data encryption for databases Answer: Short messages where high security is not needed (A) Monoalphabetic substitution ciphers can be used for short messages where high security is not a primary concern. 6. Why is the key space for a monoalphabetic substitution cipher considered limited? A. The alphabet permutations are manageable in number B. The keys are always repeated C. It requires a complex key management system D. There are only 10 possible keys Answer: The alphabet permutations are manageable in number (A) The limited key space is because the number of possible keys is relatively small, making it feasible to attempt brute-force attacks. 7. Which of the following is NOT a characteristic of a monoalphabetic substitution cipher? A. Cipher alphabet may not be an exact transposition B. Fixed mapping for a given message C. One-to-one mapping between letters D. Same plaintext letter mapped to different ciphertext letters Answer: Same plaintext letter mapped to different ciphertext letters (D) In a monoalphabetic substitution cipher, each plaintext letter is consistently mapped to the same ciphertext letter, not to different letters. 8. What is frequency analysis in the context of a monoalphabetic substitution cipher? A. Counting the number of letters used in the encryption B. Analyzing the ciphertext to find patterns based on the plaintext C. Changing the key after each letter D. Using advanced algorithms for encryption Answer: Analyzing the ciphertext to find patterns based on the plaintext (B) Frequency analysis involves analyzing the frequency distribution of letters in the ciphertext to uncover patterns that reflect the plaintext.