CBCP Cryptography and Security 3 — Questions and Answers
Question 1: What is the role of a nonce in blockchain proof-of-work mining?
- It encrypts the block header
- It is a number miners vary to find a hash meeting the difficulty target (Correct answer)
- It serves as the miner's private key
- It uniquely identifies each transaction in the mempool
Correct answer: It is a number miners vary to find a hash meeting the difficulty target
Miners repeatedly change the nonce (number used once) until the resulting block hash falls below the network's difficulty target.
Question 2: Which property of a cryptographic hash function means that finding the input from a given output is computationally infeasible?
- Collision resistance
- Second preimage resistance
- Preimage resistance (Correct answer)
- Avalanche effect
Correct answer: Preimage resistance
Preimage resistance means that given a hash output H, it is computationally infeasible to find any input m such that hash(m) = H.
Question 3: In zero-knowledge proofs used in blockchain privacy, what does the 'completeness' property guarantee?
- A cheating prover can always fool the verifier
- If the statement is true, an honest prover will always convince an honest verifier (Correct answer)
- The proof leaks no information to the verifier
- The verifier can reconstruct the secret from the proof
Correct answer: If the statement is true, an honest prover will always convince an honest verifier
Completeness in ZKP means that if the statement is true and both parties are honest, the verifier will accept the proof with high probability.
Question 4: What distinguishes a deterministic wallet from a non-deterministic wallet?
- Deterministic wallets use quantum-safe algorithms
- Deterministic wallets generate all keys from a single seed, enabling full backup from one phrase (Correct answer)
- Non-deterministic wallets are faster at signing transactions
- Deterministic wallets store keys on a hardware security module
Correct answer: Deterministic wallets generate all keys from a single seed, enabling full backup from one phrase
Deterministic wallets derive all private keys from a single seed, so one backup phrase recovers all addresses, unlike non-deterministic wallets which require backing up each key.
Question 5: What is the main security concern with reusing a nonce in the ECDSA signing algorithm?
- It causes double-spending on the blockchain
- It allows recovery of the private key from two signatures sharing the same nonce (Correct answer)
- It makes the transaction unverifiable by nodes
- It exposes the receiver's address
Correct answer: It allows recovery of the private key from two signatures sharing the same nonce
If two ECDSA signatures use the same nonce k, an attacker can algebraically solve for and recover the signer's private key.
Question 6: Which consensus mechanism relies on cryptographic Verifiable Random Functions (VRF) to select block producers?
- Bitcoin's Proof of Work
- Algorand's Pure Proof of Stake (Correct answer)
- Ethereum's Proof of Authority
- Hyperledger's PBFT
Correct answer: Algorand's Pure Proof of Stake
Algorand uses VRFs to cryptographically and randomly select validators for each round in an unpredictable, verifiable way.
Question 7: What is the purpose of a commitment scheme in blockchain protocols?
- To permanently lock funds in a smart contract
- To allow a party to commit to a value while keeping it hidden, then reveal it later verifiably (Correct answer)
- To commit validator nodes to a specific shard
- To lock the block difficulty for an epoch
Correct answer: To allow a party to commit to a value while keeping it hidden, then reveal it later verifiably
Commitment schemes let a party bind to a secret value (hiding property) and later reveal it in a way that cannot be changed (binding property).
CBCP Cryptography and Security 3
What is the role of a nonce in blockchain proof-of-work mining?