FIELD NOTE / 01

A hash, a key,
a signature.

Hashes identify data.

A cryptographic hash turns an input into a fixed-length digest. It is deterministic: the same bytes produce the same digest. Comparing a downloaded file with a checksum from a trusted source can help detect changes.

A hash by itself does not tell you who created a file. The source of the expected checksum matters.

Keys authorize actions.

Public-key cryptography uses a related pair of keys. The public key can be shared; the private key stays with its owner. The precise role of each depends on the algorithm.

Signatures connect keys to messages.

A digital signature allows others to check that a message was signed with a particular private key and has not changed. A valid signature proves possession of that key; it does not, by itself, establish a real-world identity.

Experiment with a SHA-256 digest →

Further reading: Web Crypto digest documentation and Bitcoin signatures and transactions.