Cryptography and Hashing Flashcards

What is the output size of the SHA-256 hash function?

Answer: 256 bits

SHA-256 always produces a fixed 256-bit (32-byte) digest regardless of input size.

Which attack attempts to find any second input that hashes to the same value as a given first input?

Answer: Second preimage attack

A second preimage attack tries to find m2 ≠ m1 such that H(m2) = H(m1), given a known message m1 and its hash.

What advantage does Schnorr signature aggregation offer over ECDSA in blockchain systems?

Answer: Multiple signatures can be combined into one, reducing data size

Schnorr signatures support linear aggregation, allowing multiple signers' signatures to be merged into a single compact signature, improving scalability.

Which property ensures that even a one-bit change in input causes roughly half the output bits to flip in a hash function?

Answer: Avalanche effect

The avalanche effect means tiny input changes cause drastically different hash outputs, preventing any correlation between similar inputs and outputs.

In Ethereum, which hashing algorithm is used natively for account addresses and state trees?

Answer: Keccak-256 (SHA-3 variant)

Ethereum uses Keccak-256 (the original SHA-3 submission, not the finalized NIST SHA-3 standard) for hashing throughout its protocol.

What is a rainbow table attack, and how does salting defend against it?

Answer: A precomputed hash-to-plaintext lookup attack; salting adds a unique random value to each input before hashing

Salting prepends or appends a unique random value to each password before hashing, making precomputed rainbow tables useless since each salt produces different hashes.

Which cryptographic concept underlies the generation of a Bitcoin address from a public key?

Answer: One-way hash chaining (SHA-256 then RIPEMD-160)

A Bitcoin address is derived by applying SHA-256 and then RIPEMD-160 to the public key, producing a shorter, one-way-derived identifier.