Unit 1: Introduction and mathematics of cryptography - Practice Quiz

1 Which security goal ensures that information is accessible only to authorized users?

2 Which security goal ensures that data is not altered without authorization?

3 In which attack does an attacker have access only to encrypted messages?

4 Which security service verifies the identity of a communicating entity?

5 What does the Extended Euclidean Algorithm compute in addition to ?

6 What is ?

7 Which statement correctly represents and as congruent modulo ?

8 Which type of attacker only monitors network communication without modifying it?

9 Which physical-layer attack deliberately transmits interference to disrupt wireless communication?

10 Which MAC-layer attack causes repeated collisions by intentionally disrupting frame transmissions?

11 Which network-layer attack creates a false short path between two distant network locations?

12 Which transport-layer attack sends many connection requests to exhaust a server's resources?

13 Which application-layer attack tricks users into revealing sensitive information through deceptive messages?

14 Which VANET attack involves one vehicle presenting multiple false identities?

15 Which cipher is a traditional symmetric-key cipher?

16 What is the main key characteristic of a symmetric-key cipher?

17 What is the primary purpose of cryptanalysis?

18 What happens to plaintext symbols in a substitution cipher?

19 What does a transposition cipher change in a plaintext message?

20 Which VANET attack sends previously captured valid messages again at a later time?

21 A receiver obtains a file whose hash differs from the hash published by the sender. Which security goal has most directly failed?

22 An attacker can submit selected ciphertexts to a decryption system and observe the resulting plaintexts, except for one target ciphertext. What type of attack is this?

23 Which mechanism most directly provides data-origin authentication and nonrepudiation for a transmitted message?

24 Using the Extended Euclidean Algorithm, what is the multiplicative inverse of modulo ?

25 Which pair satisfies ?

26 What is the value of ?

27 Find the smallest nonnegative integer satisfying and .

28 A vehicle silently records safety beacons exchanged by nearby nodes without modifying or blocking them. How should this attack be classified?

29 An attacker continuously transmits interference on the frequency used by an ad hoc network. Which technique most directly improves resistance to this attack?

30 A selfish wireless node repeatedly selects a much smaller contention window than other nodes to gain extra transmission opportunities. Which attack is being performed?

31 Two malicious nodes in distant parts of an ad hoc network create a fast private link and replay routing packets between their locations. Which attack does this describe?

32 An attacker predicts valid TCP sequence numbers and injects packets into an established connection between two mobile nodes. Which attack is most likely?

33 After sending an authenticated service request in a mobile network, a user falsely denies having issued it. Which application-layer attack is illustrated?

34 A malicious vehicle uses several fabricated identities to report a nonexistent traffic jam, making the reports appear to come from many vehicles. Which attack is this?

35 Using the Vigenère cipher with , what is the encryption of plaintext CAT with key DOG?

36 A bitmap encrypted with a block cipher still reveals repeated visual patterns because identical plaintext blocks produce identical ciphertext blocks. Which replacement is most appropriate?

37 A cipher has a -bit key, and a machine can test keys per second. Approximately how long is an average brute-force search?

38 For the affine cipher , where , which plaintext letter corresponds to ciphertext W?

39 The ciphertext HLOOLELWRD was produced using a two-rail rail-fence cipher. What is the plaintext?

40 Which Hill-cipher key matrix is invertible modulo and can therefore be used for encryption and decryption?

41 A message authentication code is verified successfully, but an attacker has replayed a previously valid transaction. Which security goal remains unsatisfied?

42 An attacker can submit chosen plaintexts to an encryption service and observe the resulting ciphertexts, but cannot decrypt arbitrary ciphertexts. Which attack model is this?

43 Which pairing most accurately distinguishes a security service from a security mechanism?

44 Using the extended Euclidean algorithm, determine the multiplicative inverse of modulo .

45 Find the least nonnegative residue of modulo .

46 A malicious node advertises an extremely attractive route, attracts traffic, and then selectively drops or inspects packets while forwarding the rest. How is this attack best classified?

47 A vehicle transmits high-power noise across the control channel, preventing legitimate nodes from decoding frames. Which physical-layer attack is directly represented?

48 In a carrier-sense wireless network, an attacker repeatedly transmits short frames with unusually high priority, causing other nodes to defer access. Which MAC-layer weakness is being exploited?

49 Two colluding nodes create a low-latency private link and make distant nodes believe that they are adjacent, attracting routes through the link. Which attack is this?

50 An attacker sends many spoofed TCP SYN segments and never completes the handshakes, exhausting the server's half-open connection table. Which attack is being described?

51 A compromised vehicle sends syntactically valid but false emergency-braking alerts signed with a legitimate credential. Which application-layer threat is most directly involved?

52 A vehicle uses several simultaneously valid pseudonyms to appear as multiple independent vehicles and create an artificial traffic jam in a routing or trust system. Which attack is this?

53 A classical cipher encrypts each plaintext letter by replacing it with the letter . Is this cipher invertible over the alphabet?

54 Why must a secure block-cipher mode use a unique nonce or initialization vector when encrypting distinct messages under the same key?

55 A cryptanalyst observes that a substitution-cipher ciphertext preserves repeated word patterns and has a letter-frequency profile close to natural language. Which method is most appropriate as an initial attack?

56 A monoalphabetic substitution cipher maps plaintext letters one-to-one. If the ciphertext contains the repeated pattern QXYQ, which plaintext pattern must it have?

57 Using a columnar transposition with a key of length , a plaintext has length and is written row-wise without padding. How many columns contain four characters in the final arrangement?

58 A two-round Feistel cipher uses round transformation and . Which property permits decryption with the same structure while applying keys in reverse order?

59 Which congruence has no solution?

60 For RSA-style modular arithmetic, what is the inverse of modulo ?