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Creating and signing

Creating a proof

Text or a file, how the fingerprint is made, what happens to your content, drafts and publishing, and the limits.

Text or a file

Text is for words you type or paste: an idea, a statement, a short agreement. Only its fingerprint is kept, unless you choose to store the text too. See Text.
A file is for a document, photo or other file. Only its name and fingerprint are kept, not the file.

The fingerprint

The fingerprint is the SHA-256 hash of your content: of the text as UTF-8 bytes, or of the file’s bytes exactly as they are. It is 64 characters long, the same content always gives the same fingerprint, and you cannot work the content out from it.

While you type or choose a file, your browser works out the fingerprint on your device and shows it under the form, before anything is sent. When you create the proof, the server works it out again from what you submitted, and that is the fingerprint the proof records. The two always agree.

What happens to your text or file

When you choose Create proof, your text or file is sent to DigiStamp so the server can compute the fingerprint. What happens next depends on the kind of proof:

A file: It is read in memory to compute the fingerprint and is not saved. Proof keeps the file's name, size and fingerprint.
Text: Only the fingerprint is kept, unless you tick "Also store this text". Stored text is shown on the public certificate once you publish.

Checking a proof is different: the Verify page and the check on a certificate work out the fingerprint in your browser, so the content you check is not sent anywhere.

Title and description

Title and Description are optional. Once the proof is published they are shown on its certificate and in the downloads, so do not put anything there you would not want the people you share the link with to read.

They are not part of the fingerprint, and they are never written to the blockchain. Only the content is fingerprinted.

Limits and file types

Text: Up to 50,000 characters.
File size: Up to 5 MB.
File types: PDF, plain text, CSV, JSON, JPEG, PNG, GIF, WebP, SVG, ZIP, and Word, Excel and PowerPoint files (.docx, .xlsx, .pptx).
Title: Up to 200 characters.
Description: Up to 2,000 characters.

To prove a file of another type, put it in a ZIP file first. The proof is then a proof of that ZIP file, so keep the ZIP file itself.

Drafts and publishing

A new proof is a private draft: only you can see it, on its page under My proofs. The fingerprint and its date are recorded from the moment you create it.

Choose Publish proof to give it a public certificate at a permanent link, which anyone you share it with can open without signing in. Only a published proof can be saved to the blockchain. You can sign a proof before or after publishing it.

Keep your original

A proof is only useful with the original. To show that a file matches, you need a copy with exactly the same bytes. A copy that has been re-saved, converted, compressed, resized or edited, even without visible changes, has a different fingerprint and will not match.

For text, every character counts, including spaces, line breaks and punctuation.

Example (illustrative)

You prove a signed contract as a PDF, then later print it and scan it back in. The scan is a different file with a different fingerprint, so it will not match. The PDF you proved still will.

DigiStamp cannot recover a lost file

Only the fingerprint is kept, and a file cannot be rebuilt from it. Store the original where you keep other important records.