SHA-256 (Secure Hash Algorithm 256-bit) was developed by the NSA and adopted by NIST as a federal information processing standard. It is used in military and intelligence communications, underpins the TLS certificates that secure every HTTPS connection on the web, and is the algorithm at the heart of Bitcoin’s proof-of-work mechanism — the same process that makes its ledger computationally tamper-evident. It is not an emerging standard. It is the standard.

It works by computing a unique 64-character fingerprint from the complete binary content of a file. Identical files always produce identical fingerprints, without exception. Any modification to the document — a single character added, removed, or changed — produces a completely different hash. This is not an approximation or a probabilistic test. It is a binary determination: your copy either matches the registered hash or it does not. If it does, the document you hold is identical to the one published.