Hash Function (Cryptographic)

A one-way mathematical function that maps arbitrary-length input to a fixed-size output (digest). Properties: deterministic, fast to compute, infeasible to reverse, collision-resistant. SHA-256 (used in Bitcoin, Solana PoH) produces 256-bit hashes. Keccak-256 is used in Ethereum. Hashes are used for block linking, Merkle trees, and data integrity.