MCQs

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1. In a known-plaintext attack, what does the attacker have access to?
   a. Only ciphertexts
   b. Plaintext-ciphertext pairs
   c. Only plaintext
   d. Encrypted keys
   Answer: b. Plaintext-ciphertext pairssciencedirect​
2. Which type of attack allows an adversary to choose arbitrary plaintexts for encryption?
   a. Known-plaintext attack
   b. Brute force attack
   c. Chosen-plaintext attack
   d. Replay attack
   Answer: c. Chosen-plaintext attacksciencedirect​
3. In a chosen-plaintext attack, what is the primary objective of the attacker?
   a. To determine the encryption key
   b. To steal plaintexts
   c. To alter ciphertext directly
   d. To decode padding values
   Answer: a. To determine the encryption keywikipedia​
4. Which variation of the chosen-plaintext attack allows iterative choice of plaintexts based on prior encryptions?
   a. Adaptive chosen-plaintext attack
   b. Batch chosen-plaintext attack
   c. Known-ciphertext attack
   d. Replay plaintext attack
   Answer: a. Adaptive chosen-plaintext attacksciencedirect​
5. What type of attack is harder than a known-plaintext attack?
   a. Ciphertext-only attack
   b. Brute force attack
   c. Adaptive plaintext attack
   d. Replay attack
   Answer: a. Ciphertext-only attackgeeksforgeeks​
6. Which cryptographic principle guarantees that a ciphertext reveals no information about plaintext?
   a. Semantic security
   b. Redundancy control
   c. Key rotation
   d. Stream cipher masking
   Answer: a. Semantic securitysciencedirect​
7. What does “semantic security” protect against?
   a. Replay attacks
   b. Chosen-plaintext attacks
   c. Phishing attacks
   d. SQL injections
   Answer: b. Chosen-plaintext attackssciencedirect​
8. The Goldwasser–Micali cryptosystem is proven secure against which attack?
   a. Known-plaintext attack
   b. Adaptive plaintext attack
   c. Chosen-plaintext attack
   d. Ciphertext-only attack
   Answer: c. Chosen-plaintext attacksciencedirect​
9. The adaptive chosen-plaintext attack increases success probabilities by:
   a. Iterative feedback
   b. Random plaintexts
   c. Encrypted backups
   d. Network flooding
   Answer: a. Iterative feedbacksciencedirect​
10. Which classic cipher could be easily broken by chosen-plaintext attacks?
    a. Caesar cipher
    b. AES
    c. RSA
    d. Diffie-Hellman
    Answer: a. Caesar cipherwikipedia​
11. What is the main limitation of a ciphertext-only attack compared to plaintext-based attacks?
    a. Lack of plaintext reference
    b. High cost of encryption oracle
    c. Key reuse restriction
    d. Computational similarity
    Answer: a. Lack of plaintext referencegeeksforgeeks​
12. The one-time pad becomes insecure under what condition?
    a. If key reuse occurs
    b. If short keys are used
    c. If padding is applied
    d. If random numbers are used
    Answer: a. If key reuse occurswikipedia​
13. What historical example represents a known-plaintext attack?
    a. The breaking of the Enigma machine
    b. The Caesar cipher
    c. The cracking of MD5 hashes
    d. Heartbleed vulnerability
    Answer: a. The breaking of the Enigma machinestartupdefense​
14. Which algorithm is considered highly resistant to plaintext attacks?
    a. AES
    b. DES
    c. RC4
    d. MD5
    Answer: a. AESsciencedirect​
15. Which cryptographic scheme uses padding like PKCS#1 to resist plaintext attacks?
    a. RSA
    b. SHA-256
    c. DES
    d. MD5
    Answer: a. RSAsciencedirect​
16. The main defense against known-plaintext attacks is:
    a. Using semantically secure encryption
    b. Reusing encryption keys
    c. Rotating ciphertext outputs
    d. Disabling padding
    Answer: a. Using semantically secure encryptionsciencedirect​
17. Chosen-ciphertext attacks differ from chosen-plaintext attacks by:
    a. Selecting ciphertexts instead of plaintexts
    b. Using brute-force techniques
    c. Encrypting hashes
    d. Randomizing inputs
    Answer: a. Selecting ciphertexts instead of plaintextsreddit​
18. What does an initialization vector (IV) prevent?
    a. Duplicate ciphertext from identical plaintext
    b. Brute-force attacks
    c. Hash collisions
    d. Replay attacks
    Answer: a. Duplicate ciphertext from identical plaintextstartupdefense​
19. What cryptographic mode uses IVs for resistance to plaintext attacks?
    a. CBC
    b. ECB
    c. SHA
    d. OTP
    Answer: a. CBCstartupdefense​
20. Chosen-plaintext attacks exploit the relationship between:
    a. Input plaintext and output ciphertext
    b. Encryption keys and signature hashes
    c. Hash functions and salts
    d. Firewalls and IDS
    Answer: a. Input plaintext and output ciphertextsciencedirect​
21. The attacker in a chosen-plaintext attack interacts with what component?
    a. Encryption oracle
    b. Decryption machine
    c. Network IDS
    d. Key vault
    Answer: a. Encryption oraclewikipedia​
22. Which attack is most realistic in modern cryptanalysis?
    a. Known-plaintext attack
    b. Differential cryptanalysis
    c. SQL injection
    d. Social engineering
    Answer: a. Known-plaintext attacksciencedirect​
23. Which encryption mode is vulnerable to identical plaintext blocks producing identical ciphertext blocks?
    a. ECB
    b. CBC
    c. OFB
    d. CFB
    Answer: a. ECBstartupdefense​
24. What does differential cryptanalysis study?
    a. Pairs of plaintext and ciphertext
    b. Network delay variations
    c. Fault-tolerant hashing
    d. IV entropy
    Answer: a. Pairs of plaintext and ciphertextgeeksforgeeks​
25. The main goal of a known-plaintext attacker is to:
    a. Recover the encryption key
    b. Steal plaintext files
    c. Destroy padding
    d. Create hash collisions
    Answer: a. Recover the encryption keysciencedirect​
26. Batch chosen-plaintext attack implies:
    a. Predefined sets of plaintexts analyzed in one phase
    b. Random decryption sequences
    c. Reverse-engineering ciphertexts
    d. Key mapping by brute force
    Answer: a. Predefined sets of plaintexts analyzed in one phaselinkedin​
27. Adaptive chosen-plaintext attacks are more efficient than:
    a. Batch chosen-plaintext attacks
    b. Hash-based methods
    c. Semantic secure models
    d. Known-ciphertext scenarios
    Answer: a. Batch chosen-plaintext attackslinkedin​
28. AES encryption incorporates diffusion to:
    a. Spread plaintext influence across ciphertext
    b. Limit key exposure
    c. Add hash complexity
    d. Prevent chosen ciphertext
    Answer: a. Spread plaintext influence across ciphertextsciencedirect​
29. Why are deprecated algorithms like DES discouraged?
    a. Vulnerable to plaintext attacks
    b. Incompatible with TLS
    c. Non-standard padding
    d. Missing semaphores
    Answer: a. Vulnerable to plaintext attacksstartupdefense​
30. What mechanism improves resistance by mixing plaintext bits thoroughly?
    a. Diffusion
    b. Confusion
    c. Precomputation
    d. Hashing
    Answer: a. Diffusionsciencedirect​
31. Semantic security ensures no adversary can:
    a. Gain information about plaintext from ciphertext
    b. Modify hashes easily
    c. Reverse padding
    d. Alter encryption rounds
    Answer: a. Gain information about plaintext from ciphertextsciencedirect​
32. Known-plaintext attack success increases if:
    a. More plaintext-ciphertext pairs are known
    b. Ciphertext-only is used
    c. Hashing is frequent
    d. IVs are reused
    Answer: a. More plaintext-ciphertext pairs are knownsciencedirect​
33. A practical mitigation to chosen-plaintext attacks is:
    a. Using probabilistic encryption
    b. Increasing key reuse
    c. Removing IVs
    d. Shortening block sizes
    Answer: a. Using probabilistic encryptionsciencedirect​
34. The adaptive approach in CPA allows what?
    a. Continuous refinement after each test
    b. Parallel key cracking
    c. Decryption guessing
    d. Static IV usage
    Answer: a. Continuous refinement after each testsciencedirect​
35. A system with indistinguishable encryptions under CPA means:
    a. The adversary cannot differentiate between ciphertexts
    b. Hash collisions are prevented
    c. Keys are rotated hourly
    d. Salt randomness fails
    Answer: a. The adversary cannot differentiate between ciphertextswikipedia​
36. Padding schemes prevent which issue in plaintext attacks?
    a. Decryption malleability
    b. IV entropy loss
    c. Key misuse
    d. Ciphertext overflow
    Answer: a. Decryption malleabilitysciencedirect​
37. Chosen-plaintext model assumes availability of:
    a. Encryption oracle access
    b. Decryption servers
    c. Random key selection
    d. Unused hashes
    Answer: a. Encryption oracle accesswikipedia​
38. The Enigma machine was cracked by leveraging:
    a. Predictable message headers
    b. Faulty padding
    c. Weak IVs
    d. Diffusion loss
    Answer: a. Predictable message headersstartupdefense​
39. Role-based access control helps mitigate plaintext attacks by:
    a. Restricting plaintext exposure
    b. Encrypting IVs
    c. Randomizing keys
    d. Masking ciphertext
    Answer: a. Restricting plaintext exposurestartupdefense​
40. NIST recommends AES because it:
    a. Is semantically secure
    b. Uses single-layer padding
    c. Disables feedback loops
    d. Uses weak IVs
    Answer: a. Is semantically securestartupdefense​
41. Chosen-plaintext attacks may be simplified if:
    a. The algorithm is deterministic
    b. Keys rotate dynamically
    c. Salts are random
    d. Block sizes vary
    Answer: a. The algorithm is deterministicsciencedirect​
42. Known-plaintext analysis maps:
    a. Relationships between texts and ciphertexts
    b. File hashes
    c. Compression ratios
    d. Random salts
    Answer: a. Relationships between texts and ciphertextsgeeksforgeeks​
43. A successful plaintext attack compromises:
    a. Encryption key
    b. Hash seed
    c. IV Alone
    d. Ciphertext padding
    Answer: a. Encryption keysciencedirect​
44. Differential cryptanalysis is aided by:
    a. Known plaintext samples
    b. Random IVs
    c. Short hash values
    d. Dynamic padding
    Answer: a. Known plaintext samplesgeeksforgeeks​
45. AES resists plaintext attacks because of:
    a. High key length and non-linearity
    b. Simple S-boxes
    c. Static key reuse
    d. Stream mode
    Answer: a. High key length and non-linearitysciencedirect​
46. What is a major weakness in ECB mode of encryption?
    a. Identical plaintext yields identical ciphertext
    b. Large block sizes
    c. Random initialization
    d. Over-padded data
    Answer: a. Identical plaintext yields identical ciphertextstartupdefense​
47. In chosen-plaintext attacks, a simple XOR cipher is:
    a. Easy to break
    b. Resistant to CPA
    c. Hash-dependent
    d. IV reliant
    Answer: a. Easy to breakgeeksforgeeks​
48. One preventive step against adaptive CPAs is:
    a. Strict key management
    b. Removing random salts
    c. Allowing oracle feedback
    d. Using the same seed
    Answer: a. Strict key managementsciencedirect​
49. The difference between batch and adaptive CPA lies in:
    a. Interactivity of plaintext choice
    b. Cipher text length
    c. Padding format
    d. Hash computation
    Answer: a. Interactivity of plaintext choicelinkedin​
50. Randomized encryption improves security by:
    a. Making ciphertexts unique even for same plaintext
    b. Reducing padding
    c. Reusing initialization vectors
    d. Compressing messages
    Answer: a. Making ciphertexts unique even for same plaintextsciencedirect​

1. https://www.sciencedirect.com/topics/computer-science/plaintext-attack
2. https://en.wikipedia.org/wiki/Chosen-plaintext_attack
3. https://www.geeksforgeeks.org/computer-networks/cryptanalysis-and-types-of-attacks/
4. https://www.startupdefense.io/cyberattacks/known-plaintext-attack
5. https://www.reddit.com/r/CEH/comments/i5tjml/exam_tommorow_which_is_the_best_way_to/
6. https://www.linkedin.com/advice/0/what-common-types-methods-chosen-plaintext-attacks-how
7. https://byjus.com/gate/cyber-security-mcqs/
8. https://www.interviewbit.com/cyber-security-mcq/
9. https://www.sanfoundry.com/cyber-security-problems/
10. https://testbook.com/objective-questions/mcq-on-cyber-security-and-emerging-technologies–5eea6a0d39140f30f369e309
11. https://www.scribd.com/document/660905820/Mcq-Quations-of-Cyber-Sequrity-Pdf00
12. https://www.balbix.com/insights/attack-vectors-and-breach-methods/
13. https://interviewkickstart.com/blogs/articles/cyber-security-mcqs-answers
14. https://www.baeldung.com/cs/cryptography-known-plaintext-attack-vs-chosen-plaintext-attack
15. https://www.tutorialspoint.com/what-is-plaintext-examples-plaintext-attack-is-it-a-lapse-in-security
16. https://www.fortinet.com/resources/cyberglossary/what-is-cyber-attack
17. https://examradar.com/cyber-security-mcqs-set-7/
18. https://www.youtube.com/watch?v=BdjGRCpYOrA
19. https://www.slideshare.net/slideshow/cryptographyknown-plain-text-attack/58897084
20. https://www.sanfoundry.com/1000-cyber-security-questions-answers/