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MANUAL INTRODUCTION TO CRYPTOGRAPHY
WITH CODING THEORY ,3RD EDITION QUESTIONS
AND CORRECT ANSWERS (VERIFIED ANSWERS Q&A
2026 |INSTANT DOWNLOAD PDF
1. What is the primary goal of cryptography? A. Data compression B. Secure communication C. File formatting D. Network routing Rationale: Cryptography focuses on protecting information from unauthorized access. Correct Answer: B 2. Which of the following is NOT a cryptographic objective? A. Confidentiality B. Integrity C. Availability D. Authentication Rationale: Availability is a system objective, not a core cryptographic property. Correct Answer: C
3. In symmetric encryption, the key is: A. Public only B. Private only C. Same for encryption and decryption D. Generated by attacker Rationale: Symmetric systems use one shared secret key. Correct Answer: C 4. Which algorithm is a symmetric cipher? A. RSA B. AES C. ECC D. DSA Rationale: AES is a widely used symmetric encryption standard. Correct Answer: B 5. Public key cryptography uses: A. One shared key B. Two keys (public and private) C. No keys D. Session-only keys Rationale: Asymmetric cryptography uses key pairs. Correct Answer: B
9. What is ciphertext? A. Original message B. Encrypted message C. Decryption key D. Hash output Rationale: Ciphertext is the encrypted form of plaintext. Correct Answer: B 10. Plaintext refers to: A. Encrypted data B. Original readable message C. Key stream D. Hash output Rationale: Plaintext is the original message before encryption. Correct Answer: B 11. In cryptography, confusion refers to: A. Making encryption slow B. Obscuring relationship between key and ciphertext C. Data compression D. Network routing Rationale: Confusion hides key-ciphertext relationships. Correct Answer: B
12. Diffusion ensures: A. Key secrecy B. Statistical structure of plaintext is spread in ciphertext C. Faster encryption D. Smaller keys Rationale: Diffusion spreads plaintext influence across ciphertext. Correct Answer: B 13. Caesar cipher is an example of: A. Modern encryption B. Symmetric substitution cipher C. Hash function D. Asymmetric cipher Rationale: Caesar shifts letters by fixed amount. Correct Answer: B 14. In Caesar cipher with shift 3, 'A' becomes: A. A B. B C. D D. Z Rationale: Shift of 3 moves A → D. Correct Answer: C
randomness. Correct Answer: B
18. Condition for OTP security is: A. Key reused B. Key shorter than message C. Key is truly random and used once D. Key stored online Rationale: OTP requires random one-time keys. Correct Answer: C 19. Block cipher encrypts: A. One bit at a time B. Fixed-size blocks C. Entire file only D. Hashes Rationale: Block ciphers operate on fixed-length blocks. Correct Answer: B 20. Stream cipher encrypts: A. Fixed blocks B. Bit/byte stream continuously C. Only files D. Only keys
Rationale: Stream ciphers process data sequentially. Correct Answer: B
21. AES operates on block size of: A. 32 bits B. 64 bits C. 128 bits D. 256 bits Rationale: AES uses 128-bit blocks. Correct Answer: C 22. DES key size is: A. 56 bits B. 64 bits C. 128 bits D. 256 bits Rationale: DES uses a 56-bit effective key. Correct Answer: A 23. Main weakness of DES is: A. Too slow B. Short key length C. No encryption D. Asymmetric design
Rationale: CBC uses IV for randomness. Correct Answer: B
27. A digital signature ensures: A. Compression B. Authentication and integrity C. Encryption only D. Data storage Rationale: Signatures verify sender and data integrity. Correct Answer: B 28. Hashing is used in digital signatures to: A. Encrypt message B. Reduce message size before signing C. Store keys D. Compress network traffic Rationale: Hash ensures fixed-size input for signing. Correct Answer: B 29. ECC stands for: A. Error Correction Code B. Elliptic Curve Cryptography C. Electronic Code Cipher D. Extended Cryptographic Code
Rationale: ECC uses elliptic curves in cryptography. Correct Answer: B
30. Advantage of ECC is: A. Larger keys B. Smaller keys with same security C. No encryption D. Faster hardware only Rationale: ECC is efficient with smaller key sizes. Correct Answer: B 31. In coding theory, error detection aims to: A. Encrypt messages B. Identify transmission errors C. Compress data D. Hash data Rationale: Detect errors in communication channels. Correct Answer: B 32. Error correction allows: A. Encryption B. Recovery of original message C. Hashing D. Compression
Rationale: Parity checks simple error detection. Correct Answer: B
36. Even parity means: A. Odd number of 1s B. Even number of 1s C. No 1s D. Random bits Rationale: Total 1s must be even. Correct Answer: B 37. Hamming distance measures: A. Encryption strength B. Number of differing bits C. Key size D. Compression ratio Rationale: It counts bit differences between codewords. Correct Answer: B 38. Minimum Hamming distance determines: A. Key length B. Error detection capability C. Hash speed D. Compression ratio
Rationale: Larger distance improves error detection. Correct Answer: B
39. Linear block codes are: A. Random codes B. Codes with linear structure C. Hash functions D. Encryption algorithms Rationale: They obey linear algebra properties. Correct Answer: B 40. Generator matrix is used to: A. Encrypt data B. Generate codewords C. Hash messages D. Compress files Rationale: It produces encoded vectors. Correct Answer: B 41. Syndrome decoding is used for: A. Encryption B. Error detection/correction C. Compression D. Key generation
Rationale: Cyclic Redundancy Check detects errors. Correct Answer: B
45. In cryptography, key exchange is for: A. Hashing B. Securely sharing secret keys C. Compression D. Encoding Rationale: Enables secure key distribution. Correct Answer: B 46. Diffie-Hellman is used for: A. Encryption B. Key exchange C. Hashing D. Compression Rationale: It establishes shared secret keys. Correct Answer: B 47. In Diffie-Hellman, security depends on: A. Sorting problem B. Discrete logarithm problem C. Compression ratio D. Hash collisions
Rationale: Discrete log is computationally hard. Correct Answer: B
48. Cryptanalysis is: A. Building encryption B. Breaking cryptographic systems C. Data compression D. Encoding data Rationale: It studies breaking secure systems. Correct Answer: B 49. Brute force attack involves: A. Mathematical shortcuts B. Trying all possible keys C. Compression D. Hashing Rationale: Exhaustive key search method. Correct Answer: B 50. Security of encryption depends on: A. Algorithm secrecy B. Key secrecy C. File size D. Network speed
A. AES
B. RSA
C. Caesar cipher D. DES Rationale: RSA supports signing and verification. Correct Answer: B
54. A cryptographic key is best defined as: A. Plaintext data B. Secret value controlling encryption C. Network address D. Hash output Rationale: Keys control encryption/decryption operations. Correct Answer: B 55. Which of the following is NOT a block cipher mode? A. CBC B. ECB C. OFB D. RSA Rationale: RSA is asymmetric, not a block cipher mode. Correct Answer: D 56. OFB mode converts a block cipher into a:
A. Hash function B. Stream cipher C. Compression tool D. Key generator Rationale: OFB generates keystream for stream encryption. Correct Answer: B
57. A cryptographic system is considered secure if: A. Algorithm is secret B. Key is secret C. Ciphertext is short D. Plaintext is public Rationale: Security relies on key secrecy, not algorithm secrecy. Correct Answer: B 58. Kerckhoffs’ principle states that: A. Keys should be public B. System should be secure even if algorithm is known C. Encryption must be reversible D. Hash functions are reversible Rationale: Only the key must remain secret. Correct Answer: B 59. Frequency analysis is used to break:
