Blockchain Cryptography Fundamentals Flashcards

Schnorr signatures offer which advantage over ECDSA that is particularly valuable for multi-signature schemes on blockchains?

Answer: Multiple signatures can be aggregated into a single compact signature

Schnorr signatures support linear aggregation, allowing multiple signers to combine their signatures into one, reducing on-chain storage and improving privacy in multi-sig schemes.

In the context of blockchain key management, a BIP-39 mnemonic phrase encodes entropy as:

Answer: A list of 12–24 words derived from a standardized wordlist that encodes the wallet seed

BIP-39 converts entropy (128–256 bits) into 12–24 human-readable words from a 2048-word list, making wallet backup more reliable and user-friendly.

Which cryptographic technique underpins Confidential Transactions in blockchains like Monero, hiding transaction amounts while still allowing miners to verify no coins are created from nothing?

Answer: Pedersen commitments

Pedersen commitments are homomorphic, allowing miners to verify that inputs equal outputs without knowing the actual values, hiding transaction amounts cryptographically.

An attacker performs a 51% attack and attempts to double-spend. Which cryptographic property of SHA-256 makes rewriting deep blockchain history computationally prohibitive even with majority hash power?

Answer: Pre-image resistance forces the attacker to redo all proof-of-work for every block in the rewritten chain

Pre-image resistance means there is no shortcut to find a nonce satisfying the target — the attacker must brute-force redo every block's proof-of-work for the rewritten chain.

What is the primary cryptographic security concern with using the same public/private key pair for both signing and encryption operations?

Answer: Cross-protocol attacks can use ciphertexts to forge signatures or vice versa

Using the same key for signing and encryption can enable cross-protocol attacks where an adversary submits crafted ciphertexts as signing inputs to extract key material.

In Ethereum's Keccak-256 implementation, how does it differ from the NIST standardized SHA-3?

Answer: Ethereum uses a different padding scheme than the NIST finalized SHA-3 standard

Ethereum adopted Keccak-256 before NIST finalized SHA-3 and applied a different padding rule; NIST's SHA-3 uses a different domain separation suffix, making them produce different outputs.

Ring signatures, as used in Monero, allow a signer to:

Answer: Sign a transaction with a group of possible signers such that verifiers cannot identify the actual signer

Ring signatures allow the actual signer to produce a signature that could have been made by any member of a specified ring of public keys, providing sender anonymity.