Blockchain Technology Cryptographic Principles 4

Question 1

What is a 'replay attack' in the context of blockchain transactions, and which cryptographic element prevents it?

Accepted Answer

Broadcasting a valid signed transaction on another chain; prevented by chain ID in signatures

Answer

A replay attack reuses a signed transaction on a different chain; including the chain ID in the signed data (EIP-155) binds the signature to one specific chain.

Question 2

Which concept describes the property that a signed blockchain transaction cannot be denied by the sender after the fact?

Accepted Answer

Non-repudiation

Answer

Non-repudiation means the signer cannot later deny having signed the transaction, because the signature is mathematically tied to their private key.

Question 3

In Hierarchical Deterministic (HD) wallets, what cryptographic function derives child keys from a parent key?

Accepted Answer

HMAC-SHA512

Answer

HD wallets use HMAC-SHA512 with the parent key and chain code to derive child private and public keys deterministically (BIP-32).

Question 4

What is the role of a 'commitment scheme' in a blockchain smart contract auction?

Accepted Answer

Allowing bidders to commit to a hidden bid, revealed only after the bidding phase ends

Answer

A commit-reveal scheme lets bidders submit a hash of their bid first, then reveal the actual value later, preventing other bidders from seeing bids before committing.

Question 5

Which term describes a cryptographic proof system where the verifier learns nothing about the witness beyond the truth of the statement?

Accepted Answer

Zero-knowledge proof

Answer

A zero-knowledge proof allows a prover to convince a verifier that a statement is true without revealing any information about the underlying secret (witness).

Blockchain Practice Test

Blockchain Practice Test

Blockchain Technology Cryptographic Principles 4