Cryptography Flashcards

Which elliptic curve is used by Bitcoin for its digital signature scheme?

Answer: secp256k1

Bitcoin uses the secp256k1 elliptic curve defined in the SEC standard for its ECDSA signature scheme.

What property ensures that a cryptographic hash function cannot be reversed to find the original input?

Answer: Pre-image resistance

Pre-image resistance means it is computationally infeasible to find an input that produces a given hash output.

In Ethereum's signature scheme, what is the purpose of the 'v' value returned alongside r and s?

Answer: It allows recovery of the public key from the signature

The 'v' recovery identifier allows the verifier to reconstruct the public key directly from the signature and message hash.

What is a Merkle proof used for in blockchain systems?

Answer: Proving a transaction is included in a block without downloading the full block

A Merkle proof provides a compact set of hashes that allows a lightweight client to verify inclusion of a transaction in a Merkle tree.

Which type of encryption scheme does Diffie-Hellman key exchange establish?

Answer: A shared symmetric key over an insecure channel

Diffie-Hellman allows two parties to derive a shared symmetric secret over a public channel without ever transmitting the secret itself.

What does 'key derivation' accomplish in the context of HD (Hierarchical Deterministic) wallets?

Answer: It generates a tree of child keys from a single master seed

HD wallets use BIP-32 key derivation to produce an unlimited tree of child key pairs from one master seed, enabling backup of all keys from a single phrase.

Why is a nonce included in a block hash computation for proof-of-work?

Answer: To provide a variable field that miners iterate to find a hash below the target difficulty

The nonce is the only field miners freely change; by iterating it, they search for a hash output that satisfies the network's difficulty target.