2D-Doc: the only check that proves something

Updated 2 August 2026

Every check described in the other guides is circumstantial — it makes fraud more or less likely, never certain. 2D-Doc is different: it rests on cryptography, and allows a clear-cut answer.

Contents

1. What a 2D-Doc is
2. Why it beats everything else
3. Where TrustyFile stands
4. Check with the issuer in parallel

What a 2D-Doc is

2D-Doc is a two-dimensional DataMatrix barcode specified by the French ANTS (national agency for secure documents). It appears on tax notices, pay slips, social security certificates, proof-of-address bills from some suppliers, and assorted administrative documents.

It holds two things: the document's key data in clear text (name, amount, date, reference), and a cryptographic signature of that data, produced with the issuer's private key.

Why it beats everything else

Metadata can be rewritten, fonts can be imitated, a scan erases the traces. A cryptographic signature cannot: without the issuer's private key you cannot produce a valid signature over modified data.

That yields two distinct checks, and the difference between them matters:

• Is the code readable and consistent? Does the encoded data match the text printed on the document? If the PDF shows one amount and the code holds another, somebody edited the visual without being able to touch the code.
• Is the signature valid? This requires the issuer's certificate and an ECDSA verification. It is the only check that can assert a document is genuine, rather than merely "no anomaly detected".

Where TrustyFile stands

TrustyFile currently decodes the 2D-Doc and compares the encoded data against the visible text. That is the first check, and it already catches visual edits.

Signature verification itself is not implemented yet. We would rather write that here than imply a guarantee that does not exist: today, no TrustyFile result proves a document is genuine. The tool reports anomalies; it does not issue certificates.

Check with the issuer in parallel

For a French tax notice, the tax administration runs an online verification service (SVAIR) where you enter the tax number and the notice reference. The answer comes from the source itself, which beats any file analysis.

General rule: when the issuer offers a way to verify directly with them, that is always the route to take first.