Lesson 1.3.1

1.3.1 Compression, encryption and hashing Quiz: OCR Computer Science, Unit 3

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 1.3.1, Compression, encryption and hashing: 20 multiple choice questions for the OCR Computer Science (H446), Unit 3: Exchanging data, written with Revision Ninja.

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The 20 questions

  1. Which type of compression permanently removes data to reduce file size?

    • Run length encoding
    • Dictionary coding
    • Lossless compression
    • Lossy compression

  2. Which compression method allows the original file to be reconstructed perfectly?

    • Symmetric encryption
    • Asymmetric encryption
    • Lossy compression
    • Lossless compression

  3. Which file type typically uses lossy compression to reduce file size?

    • Executable file
    • JPEG image
    • Text document
    • Source code

  4. What does run length encoding replace repeated sequences of data with?

    • Dictionary keys
    • Hash digests
    • Frequency-value pairs
    • Public keys

  5. What is the run length encoding output for the string AAAAABBB?

    • A5B3
    • 8AB
    • 5A8B
    • 5A3B

  6. What replaces recurring words or phrases when using dictionary compression?

    • Run counts
    • Short index tokens
    • Hash digests
    • Private keys

  7. What must be transmitted alongside the compressed data in dictionary coding?

    • The private key
    • The hash function
    • The original file
    • The dictionary table

  8. Which key structure is used to encrypt and decrypt in symmetric encryption?

    • Two public keys
    • Hash digest key
    • Public-private pair
    • Single shared key

  9. What is the main security challenge associated with using symmetric encryption?

    • Data corruption
    • Irreversible hashing
    • Key distribution
    • Slow processing speed

  10. How many keys are used in an asymmetric encryption key pair?

    • Three separate keys
    • Two different keys
    • One shared key
    • No keys

  11. Which key decrypts a message that was encrypted using asymmetric encryption?

    • Recipient's public key
    • Sender's public key
    • Sender's private key
    • Recipient's private key

  12. Which key does a sender use to encrypt a private message for a recipient?

    • Sender's private key
    • Recipient's public key
    • Recipient's private key
    • Sender's public key

  13. Which fundamental property distinguishes a hash function from an encryption algorithm?

    • It is one-way
    • It requires passwords
    • It uses keys
    • It is reversible

  14. Which application relies on hashing rather than encryption for data security?

    • Compressing text files
    • Sending private emails
    • Storing user passwords
    • Establishing VPN tunnels

  15. What happens to the hash digest if a single input character is changed?

    • Output remains identical
    • Output length doubles
    • One character changes
    • Output changes completely

  16. What is a hash value called when used to verify data integrity during transfer?

    • Ciphertext
    • Checksum digest
    • Symmetric key
    • Dictionary index

  17. What term describes unreadable encrypted data before it has been decrypted?

    • Plaintext
    • Ciphertext
    • Hash digest
    • Dictionary token

  18. Which key does a sender use to create a valid digital signature?

    • Recipient's public key
    • Sender's public key
    • Sender's private key
    • Recipient's private key

  19. What term describes the event when two different inputs produce identical hash outputs?

    • Key exchange error
    • Encryption failure
    • Hash collision
    • Dictionary overflow

  20. Why is symmetric encryption generally preferred over asymmetric encryption for large files?

    • One-way transformation
    • Faster processing speed
    • Higher key secrecy
    • No key distribution

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