In-Browser SHA-256 Integrity Demonstration

Calculate a local file digest and test a published synthetic fixture, without transferring the file to a server.

Your selected file is read by this page inside your browser. The demonstration performs no upload. SHA-256 can establish a digest equality for identical bytes, not identity, authorship, event truth, acquisition legitimacy, or legal chain of custody.

Choose a local file (up to 20 MiB for this browser demonstration)Optional expected SHA-256 digest, 64 hexadecimal characters

No file selected. Download and select the fixture below.

Known-answer test

Download the original synthetic text fixture. Its expected SHA-256 is:

9c0834a05c1ee3c693784e1c9aecacb416623cbe36b3ab34b5192d0410b3a92c

Hash the downloaded file and compare. Edit one byte and save a copy; the new file should produce a different digest. The original plain-text fixture and this script are included in the GitHub source package.

Security limits

Use a trusted acquisition utility and documented handling procedures in real casework. For files larger than 20 MiB, this example refuses processing instead of silently reading an arbitrarily large object into memory. Modern browsers require a secure context for Web Crypto; use HTTPS or local development on localhost.