Initializing secure environment…
Initializing secure environment…
Hash a PDF and get a fingerprint that identifies it exactly. SHA-256, SHA-1 and MD5 are all computed, so you have the modern hash and the one a legacy system will ask for. Hash a file before you send it and re-hash the copy that comes back: identical SHA-256 means the bytes have not changed, which is how you prove a document arrived as it was sent and detect a substitution in transit. Nothing is uploaded — the file is read locally and never transmitted.
To fingerprint a PDF free, add the file and its SHA-256, SHA-1 and MD5 hashes are computed in your browser. Hash the file again later and identical SHA-256 means the bytes are unchanged. Nothing is uploaded.
Fingerprint before sending, send the SHA-256 through a different channel, and re-fingerprint on arrival. A match proves the file was not modified in transit. This is the practical alternative to a signing certificate when the concern is alteration rather than identity.
Keep the hash of the file you sent. When a copy turns up publicly, hash it. A match proves it is your file, not a lookalike someone reconstructed from a printout — which is a different and much weaker claim, and one people often make without checking.
Fingerprint an entire production set before it goes out and keep a manifest of hashes. Integrity checks on forty documents become one comparison per file, and a missing or altered file is identified by name rather than by eye.
Because a re-save changes the bytes without changing what you see. A tracked change accepted, metadata stripped, or a page deleted and re-added all produce a different file that renders identically. If the question is whether the file is the one you sent, only a hash answers it.
That the bytes are identical. A cryptographic hash of the same bytes is always the same value, and finding a second file with the same SHA-256 is computationally infeasible. So an identical hash proves the file you have is the file you were sent — it does not prove the content is truthful, only that it is unchanged.
Because the file is genuinely different. Re-saving rewrites the document structure, and the timestamp in the metadata changes even if no visible content does. This is why a fingerprint has to be taken on the exact file you sent, and why 'the document looks the same' is not evidence of anything.
SHA-256. MD5 and SHA-1 are shown for compatibility with older systems, and both have practical collision attacks — two different documents can be made to share a hash. For proving that a file is unchanged, use SHA-256 and ignore the other two.
Only by producing a collision, which for SHA-256 is not currently feasible. The practical attack is not mathematics: it is getting the recipient to accept a hash sent by the same person who supplied the file. Send the hash over a channel the sender does not control, and the check becomes meaningful.
No. The bytes are read in this tab and hashed with the browser's crypto implementation. Nothing is transmitted, which is what makes this usable on a document that must not leave the machine.
Yes. Any file you can add can be hashed — a Word document, a ZIP, an image. Useful when you are sending a bundle and want to prove each part arrived intact.
Fingerprint the file before you send it, and keep the hash. If a copy appears somewhere you did not put it, hash that copy. If the hash matches, it is your file, and the fact that it is the same bytes tells you it was copied rather than reconstructed from a printout.
Yes. Free, no account, no watermark, and no upload. Hashing is the clearest example of a job that has no reason to involve a server.
More security & privacy — all free, no upload.