Hash
cryptography · security
A fixed-size digest produced by a one-way function, used for data integrity, identifiers, signatures, and proof-of-work.
- Also known as
- cryptographic hash, digest, message digest
A cryptographic hash function maps any input to a fixed-size output called a hash or digest. The same input always produces the same hash, while a tiny input change should produce an unrelated-looking result.
Useful hash functions are preimage-resistant, second-preimage-resistant, collision-resistant, fast to verify, and well distributed. Hashing is not encryption: a hash is designed for verification, not recovery of the original message.
Blockchains use hashes to link blocks, summarize transaction sets, derive identifiers, and define proof-of-work targets. Wallet software also hashes transaction data before signing it.
The SHA-256 definition explains the hash function used by Bitcoin and Bitcoin Cash. You can also change a message and compare its fingerprint in the homepage hash playground.
Related terms
Proof of Work (PoW)
→A consensus mechanism that makes block production require verifiable computational work.
mining · blockchain · consensus
Hash rate
→The number of proof-of-work hash attempts performed per second by mining hardware or an entire network.
mining · security
Entropy
→Entropy is the randomness used to generate secure wallet seeds, private keys, and nonces in cryptographic systems.
cryptography · security