Cryptographic Principles Flashcards
7 cards from real Blockchain Technology practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Cryptographic Principles flashcards as text
What is a 'replay attack' in the context of blockchain transactions, and which cryptographic element prevents it?
Answer: Broadcasting a valid signed transaction on another chain; prevented by chain ID in signatures
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.
Which concept describes the property that a signed blockchain transaction cannot be denied by the sender after the fact?
Answer: Non-repudiation
Non-repudiation means the signer cannot later deny having signed the transaction, because the signature is mathematically tied to their private key.
In Hierarchical Deterministic (HD) wallets, what cryptographic function derives child keys from a parent key?
Answer: HMAC-SHA512
HD wallets use HMAC-SHA512 with the parent key and chain code to derive child private and public keys deterministically (BIP-32).
What is the role of a 'commitment scheme' in a blockchain smart contract auction?
Answer: Allowing bidders to commit to a hidden bid, revealed only after the bidding phase ends
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.
Which term describes a cryptographic proof system where the verifier learns nothing about the witness beyond the truth of the statement?
Answer: Zero-knowledge proof
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).
What is the significance of the 'difficulty target' in Bitcoin's proof-of-work, expressed as a hash output constraint?
Answer: It requires the block hash to be numerically less than a target value (i.e., begin with enough leading zeros)
Miners must find a nonce such that the block header's SHA-256d hash is below the network's target value, effectively requiring a certain number of leading zero bits.
In multi-signature (multisig) wallets, which cryptographic scheme is commonly used to allow M-of-N signers to authorize a transaction without revealing individual private keys using threshold signatures?
Answer: Shamir's Secret Sharing combined with threshold ECDSA
Threshold ECDSA, often built on Shamir's Secret Sharing, lets M of N parties collaboratively sign without any single party exposing their private key share.