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. Protecting information by encoding it
  2. Building computer hardware
  3. Creating spreadsheet formulas
  4. Connecting network cables

Question 2

What is plaintext?
  1. The original 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 original 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

How does a Caesar cipher work?
  1. By shifting letters by a fixed amount
  2. By sorting letters alphabetically
  3. By deleting every vowel
  4. By converting words to numbers

Question 8

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

Question 9

What does a substitution cipher do?
  1. Replaces plaintext symbols using a mapping
  2. Rearranges plaintext symbols without replacing them
  3. Converts the whole message to a fixed-length value
  4. Deletes repeated symbols from the message

Question 10

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 11

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 12

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

Question 13

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 14

What does a Vigenere cipher use?
  1. A keyword that changes the shift by position
  2. One fixed shift for the whole message
  3. One replacement alphabet with no repeating keyword
  4. A grid that only rearranges the letters

Question 15

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 16

Why might spaces be removed before a simple cipher is applied?
  1. To hide word boundaries
  2. To make the key longer
  3. To reverse every letter
  4. To sort the words alphabetically

Question 17

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 18

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 19

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 20

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

Question 21

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 22

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 23

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 24

Why is a Caesar cipher easy to brute-force?
  1. It has few possible shifts
  2. It uses a different key for every letter
  3. It removes repeated letters from ciphertext
  4. It creates a one-way hash of the message

Question 25

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 26

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

Question 27

Why is a short encryption key less secure?
  1. It is easier to guess by trying possibilities
  2. It uses a different encryption algorithm
  3. It makes the original message longer
  4. It prevents the use of letters

Question 28

Why does a larger key space improve security?
  1. More possible keys must be tried
  2. Each key makes the message shorter
  3. The algorithm stops using ciphertext
  4. The key is stored inside the ciphertext

Question 29

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 30

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

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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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