Cryptography questions

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Cryptography question collection

Review Cryptography questions for Computer Science, with correct answers shown and coverage across encryption and decryption; ciphers and keys; secure communication.

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Question 1

What is cryptography?
  1. Encoding information securely
  2. Building computer hardware
  3. Creating spreadsheet formulas
  4. Connecting network cables

Question 2

What is plaintext?
  1. The readable message
  2. A public key
  3. A compressed file
  4. A binary image

Question 3

What is ciphertext?
  1. The encrypted message
  2. The unencrypted message
  3. A network address
  4. A chart label

Question 4

What does encryption convert?
  1. Plaintext to ciphertext
  2. Ciphertext to plaintext
  3. Text to image
  4. Binary to decimal

Question 5

What does decryption convert?
  1. Ciphertext to plaintext
  2. Plaintext to ciphertext
  3. Image to audio
  4. Data to formulas

Question 6

What is a key in cryptography?
  1. A value used to encrypt or decrypt data
  2. A value used to identify a database record
  3. A value used to count loop repetitions
  4. A value used to locate a network device

Question 7

With a Caesar shift of 1, what does A become?
  1. B
  2. Z
  3. C
  4. 1

Question 8

What does frequency analysis compare?
  1. How often symbols occur in ciphertext
  2. How long encryption takes to run
  3. How many messages use the same key
  4. How large the encrypted file becomes

Question 9

The Enigma machine was used in which war?
  1. World War II
  2. The 1990s web era
  3. The first smartphone launch
  4. Victorian schools

Question 10

Where was Enigma cracked?
  1. Bletchley Park
  2. Silicon Valley
  3. NASA Houston
  4. MIT Lab

Question 11

What is Alan Turing best known for?
  1. Helping to break Enigma
  2. Helping to invent the World Wide Web
  3. Helping to design the first mechanical computer
  4. Helping to write the first computer algorithm

Question 12

Which process describes a rail fence cipher?
  1. Writing in a zigzag, then reading rows
  2. Shifting letters by a fixed amount
  3. Replacing letters with one fixed mapping
  4. Hashing the message to a fixed length

Question 13

What happens to letter frequencies in a transposition cipher?
  1. They stay the same
  2. Common letters become rare
  3. All letters become equally frequent
  4. The first letter becomes most frequent

Question 14

How does HTTPS protect web traffic?
  1. By encrypting it
  2. By compressing images
  3. By adding extra RAM
  4. By using local caching

Question 15

What is phishing?
  1. Deceptive messages that steal information
  2. Malware that encrypts files for ransom
  3. Repeated guesses at a password
  4. Traffic that overwhelms a service

Question 16

What does ransomware do?
  1. Locks files, demanding payment
  2. Speeds up quizzes
  3. Improves Wi-Fi signal
  4. Adds spreadsheet charts

Question 17

What is a brute-force attack?
  1. Trying many possible keys until one works
  2. Replacing each letter with a symbol once
  3. Sending plaintext with no key
  4. Sharing a private key publicly

Question 18

What does a hash function produce?
  1. A fixed-length hash value
  2. A reversible encrypted message
  3. A public/private key pair
  4. A compressed image file

Question 19

What does a transposition cipher do?
  1. Rearranges the plaintext symbols
  2. Replaces each plaintext symbol
  3. Converts plaintext into a hash
  4. Compresses repeated plaintext symbols

Question 20

In frequency analysis, what might the most common ciphertext symbol represent?
  1. A common plaintext letter
  2. The letter shifted furthest
  3. The first plaintext letter
  4. The final letter of the key

Question 21

With a Caesar shift of 3, what does X become?
  1. A
  2. U
  3. Y
  4. Z

Question 22

What is the key for a Caesar cipher?
  1. The number of alphabet positions shifted
  2. The first letter in the message
  3. The total number of message letters
  4. The number of symbols in the alphabet

Question 23

Why should a password not be stored as plaintext?
  1. A data leak could reveal the original password
  2. It makes password recovery impossible
  3. It stops users choosing passwords
  4. It prevents encryption being used

Question 24

What best protects an online account?
  1. A long, unique password
  2. A short password used elsewhere
  3. Your date of birth
  4. Your first name

Question 25

What should you do about inappropriate content online?
  1. Report it
  2. Share it with others
  3. Reply to the sender
  4. Delete your own account

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Review Cryptography questions for Computer Science, with correct answers shown and coverage across encryption and decryption; ciphers and keys; secure communication.

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