NIST's SHA-3 standard was developed from the Keccak family, but the standardized SHA3-256 function and Ethereum's Keccak-256 use different conventions and produce different digests for the same input. Solidity documents its keccak256 function explicitly. An older alias named sha3 contributed to confusion and was removed from Solidity. A software library exposing a function called SHA3 should therefore not be assumed to produce the digest expected by an Ethereum application.

Ethereum tooling uses Keccak-256 in contexts including function selectors, event topics, and address-related calculations. If an application hashes a function signature using the wrong algorithm, it can produce the wrong selector even though the result still looks like a valid hexadecimal value. This illustrates why output length alone does not identify a hash function. Cross-language integrations should use known test vectors and explicitly name the intended algorithm rather than relying on a loosely named helper.

A hash is a deterministic fingerprint, not a reversible ciphertext and not evidence that the input is truthful. Two systems also need to agree on the exact input bytes, including encoding and structure, before comparing digests. EIP-712's structured hashing rules show why concatenating vaguely described fields can be insufficient. A correct algorithm with an incorrect encoding still produces an unusable result. Keep the algorithm, byte encoding, and application-specific signing or verification rule distinct when explaining a cryptographic workflow.