Blockchain Technology Cryptography in Blockchain 3

Question 1

In Bitcoin's HD wallets (BIP-32), what is the role of the chain code alongside an extended key?

Accepted Answer

It provides additional entropy to prevent child key derivation without it

Answer

The chain code is 256 bits of extra entropy combined with the key, ensuring child key derivation requires both components to proceed.

Question 2

Which hash function does Bitcoin use to produce a 256-bit block hash in Proof of Work?

Accepted Answer

SHA-256 applied twice (SHA-256d)

Answer

Bitcoin applies SHA-256 twice to block headers (SHA-256d) to produce the block hash used in Proof of Work difficulty comparison.

Question 3

What does 'hardened' child key derivation in BIP-32 prevent compared to 'normal' derivation?

Accepted Answer

Prevents leaking the parent private key if a child private key is compromised

Answer

Hardened derivation uses the parent private key (not public key) as input, so a compromised child private key cannot be used to derive the parent private key.

Question 4

Ethereum uses Keccak-256 rather than the standardized SHA-3. What is the key difference?

Accepted Answer

Ethereum's Keccak-256 uses different padding than NIST's final SHA-3 standard

Answer

Ethereum adopted Keccak before NIST finalized SHA-3 with modified padding; both are sponge constructions but produce different outputs for the same input.

Question 5

In a threshold signature scheme (e.g., t-of-n multisig via Shamir's Secret Sharing), what must be true to reconstruct the secret?

Accepted Answer

Any t shares out of n are sufficient

Answer

Shamir's Secret Sharing is designed so that any t (threshold) shares are sufficient to reconstruct the secret, while fewer than t reveal nothing.

Blockchain Practice Test

Blockchain Practice Test

Blockchain Technology Cryptography in Blockchain 3