An open grading scale for signed documents
How strongly this file proves, on its own, who signed it and that it has not changed — and how long it will keep proving it, without the signing platform.
Version 0.3.1 · pre-release, open for comment · published 2026-09-28Three questions in strict order: integrity (has it changed?), then trust (does the identity chain to a recognised trust regime?), then durability (will it still verify years from now without anyone's help?). This is a ladder of necessary conditions, not a points total — a file receives the highest grade whose conditions it meets in full, and one failed gate caps it regardless of everything else.
The file proves who signed it and that nothing has changed, on its own, and the proof can be kept alive for decades. Embedded evidence packages and similar additions are shown alongside the grade; they do not change the letter.
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This is what a properly signed document looks like. It proves who signed it, when, and that nothing has changed — on its own, offline, without the platform that made it.
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An independent third party has proven when this was signed, and it will keep verifying for years.
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Verifies today. There is no independent proof of when it was signed, and once the signing certificate expires or its revocation data goes offline, it may stop verifying entirely.
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You can prove this file has not changed. You cannot prove who signed it. The result also states the grade the file’s own construction would reach with a certificate from a recognised provider — B or C — so a well-built document on a private root is not confused with a self-signed PDF.
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Something was signed. This file cannot prove it. The proof sits with the signing platform, not with you. Nothing here is wrong — it is simply not self-proving.
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This document does not prove what it claims. Do not rely on it without going back to the source.
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No letter is issued when there is no signature and no evidence package to assess, or the file cannot be read. This is never shown as F. F means the document was checked and failed; absence of proof is a different statement from disproof.
A validator applying the scale checks every trust source it carries and names the one that vouched for the document, rather than refusing documents outside a preferred list. What differs between regimes is what a positive result legally means — and that sets the highest grade the document can reach.
| Regime | What it is | Legal weight | Ceiling |
|---|---|---|---|
| EU/EEA qualified | Member-state trusted lists under eIDAS Article 22, where the service is granted for qualified certificates. Published by each member state, aggregated by the European Commission. | Qualified signatures have the legal effect of a handwritten signature (eIDAS Article 25(2)); qualified seals carry a presumption of integrity and origin (Article 35(2)). Advanced signatures and seals — including on qualified certificates — carry neither. | A+ |
| Recognised third country | Trusted lists of countries holding an eIDAS Article 14 mutual-recognition agreement — currently Ukraine and Moldova. | Legally equivalent to EU-qualified, by agreement. | A+ |
| EU/EEA non-qualified | On a member-state trusted list, but the service is not granted for qualified certificates. | Supervised; no presumption. | B |
| National regulated | A national trusted list operating outside eIDAS recognition — the Swiss list (ZertES, Swiss Accreditation Service) and the UK list (Information Commissioner's Office). Real supervision, real audit, no EU mutual recognition. | Regulated nationally; no eIDAS presumption. | B |
| Commercial programme | The Adobe Approved Trust List — around 300 certificate authorities admitted under Adobe's published technical requirements and independent audit. This is what makes Adobe Acrobat show a green tick. | Contractual, not statutory; no presumption. | B |
| Not recognised | Chains to none of the lists above: self-signed, a private certificate authority, or an unknown issuer. | None. | D |
A document's grade is the lowest of its signatures' grades — a contract is only as good as its weakest party's proof. Each signature also carries its own grade, so the roll-up is never opaque.
A grade is never shown as a bare letter. It always appears with the assurance level, the ETSI form, and the trust regime that vouched for it — the letter carries the legibility, the rest carries the defensibility.
A PDF sealed by an e-signing platform, validated by Tindom. It clears every gate up to the top of the ladder and is then held at B by two separate things — which is the ordinary case, not a failure.
Grade B. Trusted and time-anchored, and it will keep verifying for years — but two separate things stand between it and A, and either one alone would be enough to hold it there. Both are configuration changes on the signing platform's side, not re-architecture.
The scale is only useful if it says what to change. Each entry below is a ceiling a document can hit, what it means, and what would move it up.
Timestamped, but the file does not carry what is needed to verify it on its own later (B-T).
Embed the certificate chain and revocation data at signing time — B-T becomes B-LT. Usually a setting in the signing platform.
The signature alone, with no independent proof of when it was made (B-B).
Add a timestamp from a trusted timestamping authority at signing — B-B becomes B-T, and the document stops depending on a claimed signing time.
An advanced signature or seal, possibly on a qualified certificate, but not a qualified signature or seal in the eIDAS sense.
Issue on a qualified certificate held on a qualified signature creation device (QSCD). This is a change of product with the trust service provider, not a file-format change.
Self-contained, but without archive timestamps the proof cannot be refreshed as cryptographic algorithms age (B-LT).
Apply an archive timestamp from a qualified timestamp service — B-LT becomes B-LTA, and the evidence outlives both the certificate and the algorithms in use today.
The certificate chains to none of the recognised trust regimes — self-signed, a private authority, or an unknown issuer.
Sign with a certificate from a provider on one of the trust lists above. An internal certificate authority cannot reach beyond D, however well run.
The file records that signing happened, but carries no cryptographic signature that can be checked.
Embed a real signature in the document itself (PAdES for PDFs) rather than keeping the proof on the platform. This is the single largest step available — it moves a document from E to a graded rung.
Something was added to the file after signing that changes what the document shows, or that the validation engine cannot classify — or the signature covers only part of the content.
Sign the whole document, and make any later change as a new signed revision. Adding validation data, timestamps or further signatures is fine; editing content after signing is not.
The certificate chains to a list whose ceiling is B — a non-qualified EU/EEA service, a national list outside eIDAS recognition, or the Adobe Approved Trust List.
Sign with a qualified certificate from a provider on an EU/EEA Trusted List. The file format is not the limit here; the trust regime is.
The signature is intact and trusted, but the validation engine could not reach a definitive pass — for example because revocation status or a certificate in the chain could not be confirmed.
Embed the full certificate chain and revocation data at signing (B-LT), so the result does not depend on what can be fetched at validation time.
A trusted signature in a form outside the ETSI baseline profiles, so its long-term durability cannot be assessed against them.
Produce signatures to an ETSI baseline profile — PAdES for PDFs, XAdES, CAdES or JAdES otherwise.
A signature is present, but whether the signed content is intact could not be determined.
Check that the file is the original signed version and has not been converted or re-saved after signing.
Meets the ETSI standard in full, but something added after signing changes what the document shows or cannot be classified.
Make later changes as new signed revisions rather than edits to a signed file.
B-LTA, but the archive timestamp that renews the proof is not a qualified time stamp, or it does not validate.
Take the archive timestamp from a qualified timestamp service on an EU/EEA Trusted List. Usually a setting in the signing platform — the same kind of service many already use for the signature timestamp.
Wording only. The text now reads as a standard rather than as one validator’s documentation: criteria refer to the trust regimes the scale recognises instead of “we”; the validation status is defined by ETSI EN 319 102-1 (TOTAL-PASSED) rather than by the constant of one validation library; and the note on qualified validation applies to any validator instead of naming Tindom. The eIDAS Article 25 note is shown once, next to how the scale works, instead of twice.