Q1. What is the core purpose of a cryptographic hash function?

1. To encrypt user data securely.
2. To produce a fixed-length digest representing arbitrary input.
3. To speed up network communication.
4. To store private keys safely.

Select one:

Q2. The avalanche effect means that:

1. Hashes become easier to reverse over time.
2. A small input change results in a drastically different hash.
3. Private keys cannot be stored securely.
4. Data is encrypted by default.

Select one:

Q3. Which of the following properties makes hashes essential for blockchain?

1. They allow nodes to communicate without latency.
2. They enable tamper detection through hash chaining.
3. They create private keys.
4. They reduce energy expenditure.

Select one:

Q4. (Short answer) Describe why one-wayness (preimage resistance) is crucial for blockchain security.

Q5. What does a hash pointer store?

1. A pointer to memory only.
2. A hash of the entire blockchain.
3. A pointer + the hash of the data being pointed to.
4. A private key for verification.

Select one:

Q6. The Merkle root in a block represents:

1. The hash of the previous block.
2. The hash of the miner’s private key.
3. A commitment to all transactions in the block.
4. A random nonce used for difficulty adjustment.

Select one:

Q7. What is a key benefit of Merkle proofs?

1. They allow verification using only a small subset of hashes.
2. They eliminate mining completely.
3. They allow centralised validation.
4. They replace cryptographic signatures.

Select one:

Q8. (Short answer) Explain why Merkle trees allow blockchains to scale light clients efficiently.

Q9. A private key must remain secret because:

1. It increases mining efficiency.
2. It is required to generate block headers.
3. It grants full control over a blockchain identity.
4. It cannot be backed up.

Select one:

Q10. Digital signatures provide:

1. Confidentiality only.
2. Authentication and integrity.
3. Mining difficulty adjustment.
4. Network compression.

Select one:

Q11. Blockchain identity is fundamentally based on:

1. Domain registration.
2. Centralised databases.
3. Control of a private key.
4. Government-issued certificates.

Select one:

Q12. (Short answer) Explain why losing the private key means losing access to all associated blockchain assets permanently.

Q13. The Byzantine Generals Problem illustrates:

1. How to compress blockchain data.
2. The difficulty of achieving agreement in the presence of malicious actors.
3. How to generate private keys.
4. Why networks must use central servers.

Select one:

Q14. The central idea behind Nakamoto Consensus is that:

1. The longest valid chain represents the canonical blockchain.
2. Nodes vote manually on each block.
3. All nodes must be known beforehand.
4. Consensus is achieved instantly.

Q15. In Proof of Work, the mining puzzle is designed to be:

1. Easy to compute and easy to verify.
2. Hard to compute and hard to verify.
3. Hard to compute but easy to verify.
4. Easy to compute but impossible to verify.

Q16. (Short answer) Why is finality in Nakamoto Consensus considered probabilistic rather than absolute?

Q17. Which of the following is included in a block header?

1. The miner’s private key.
2. Pending mempool transactions.
3. The parent hash and Merkle root.
4. The full world state.

Q18. A full node is best described as a node that:

1. Stores only block headers.
2. Stores and verifies the entire blockchain history.
3. Mines blocks without verification.
4. Only forwards gossip messages.

Q19. Mempool transactions are:

1. Expired data discarded by the network.
2. Unsigned messages awaiting hashing.
3. Pending transactions waiting to be included in a block.
4. Mining difficulty records.

Q20. (Short answer) Explain why light clients do not need the full blockchain to validate transactions.