stage 04 · fingerprint: Hash without mystery
A hash is the fingerprint of a piece of content. Same text, same mark. One different comma, a completely different mark.
- sha-256
- hash
- integrity
Change the last letter of this sentence and its hash changes completely. That's the behavior that matters here.
What it does
A hash takes any content — a word, a file, a photo, a contract — and returns a code of fixed size. Same content, same code. Different content, different code.
It's for checking, not for hiding. A hash doesn't encrypt: you can't get back to the original text from it. Whoever has the content recalculates and compares. NIST publishes the standard behind SHA-256.
Where beginners get lost
A hash carries two families of promise, and confusing the two is the classic mistake. First: "the bytes are the same as the ones I saw before" — checkable by anyone, and that's all. Second: "such-and-such a person wrote this on that date" — no hash proves that.
Storing a document's hash on the blockchain doesn't turn the document into truth, nor into an official record. What gets recorded is that a key published that code in that transaction. Nothing more.
Mission
Open the Hash Notary and calculate the SHA-256 of two nearly identical sentences, changing just one comma. See with your own eyes that the results don't look remotely alike. The calculation runs in your browser; the text isn't sent anywhere.
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