How to check who signed a document, and whether it changed after signing
To check a document from someone you have never met, answer two questions separately. Who signed it, and has it changed since? A name, a logo or a scanned signature answers neither, because each can be copied into a file in minutes. The usual checks are a digital signature inside the PDF, which Adobe Acrobat and other readers validate against the signer's certificate, the audit trail of an e-signature platform such as DocuSign or Adobe Acrobat Sign, and a call or email to the sender using contact details you find yourself.
Those checks work when they are there. Most documents that move between companies are still plain PDFs and photos with no digital signature, many e-signature platforms confirm an email address rather than a verified person, and calling the sender for every certificate or delivery receipt is slow.
The Trust Identity Protocol (TIP) by The AI Lab answers both questions from the document itself. The signer verifies their identity once with an accredited Verification Provider and gets a TIP-ID. When they sign a PDF or image on TIP, the TIP Network records who signed it, when and a fingerprint of the file. Anyone who receives a copy can check, for free and without an account, which verified person or organization signed it and whether the copy still matches the fingerprint. An edited copy does not match.
The problem
Where a document from a stranger has to be trusted
| Where | What goes wrong |
|---|---|
| Professional certificates and licenses | A training certificate or license arrives as a PDF or photo, and names or dates are easy to change. See theailab.org/use-cases/verify-certificates. |
| Insurance and inspection reports | An adjuster, inspector or repair shop sends a report and photos that decide a payout. See theailab.org/use-cases/insurance-claims-fraud. |
| Shipping and delivery documents | A logistics company gets proof of delivery from a carrier it has never worked with and has to ask whether it is genuine. See theailab.org/use-cases/freight-document-fraud. |
| Contracts, quotes and invoices | Bank details or amounts are changed in a forwarded copy, and the receiver pays the wrong account. |
| Letters and official notices | A letter appears to come from a company or public body, and the receiver has no quick way to confirm it did. |
Every option, honestly
What each option does, and where it stops
These work together. Use more than one, and read the last column for each, including ours.
| Option | What it does | Where it stops |
|---|---|---|
| Call or email the sender | Confirms the document with the person who sent it, using contact details you find yourself. | Slow at volume, and useless if you use the contact details printed on the document. |
| Digital signature in the PDF (PKI) | Shows a certificate-based signature and flags any change after signing, checked in Adobe Acrobat or another reader. | Most business documents carry none, and how well the signer was checked depends on who issued the certificate. |
| E-signature platform audit trail | Records who signed, from which email address and when, inside the platform. | Often confirms an email address, not a verified person, and the record sits with the platform. |
| Qualified electronic signature (eIDAS) | In the EU, a signature backed by a checked identity and a qualified certificate, with legal weight equal to a handwritten one. | Setup is tied to EU trust service providers and is rarely used outside formal contracts. |
| Trust Identity Protocol (TIP) by The AI Lab | Lets a verified person or organization sign any PDF or image, and lets anyone check the signer and the fingerprint for free. | Does not prove the contents are true, and is not a legal title registry or a replacement for a qualified signature where the law requires one. |
Step by step
How to put it in place, in order
- List the documents you receive from outside parties that you currently confirm by calling or emailing back.
- Ask the people and companies who send them to get a TIP-ID and sign those documents on TIP as they issue them.
- When a document arrives, check its TIP record for the signer's verified identity and whether the copy matches the signed fingerprint.
- Treat a missing record or a mismatch as a reason to call the sender on contact details you find yourself.
- Sign the documents you send out the same way, so the people who receive them can check you.
About TIP
What the Trust Identity Protocol is
The Trust Identity Protocol (TIP) is an open standard from The AI Lab for proving who made a piece of content and whether it has changed. A person or organization is verified once by an accredited Verification Provider and gets a TIP-ID. Each time they sign something, their own device signs it with a post-quantum signature (ML-DSA-65, NIST FIPS 204) after a fresh fingerprint or Face ID, and the TIP Network records the signature, the time, an origin label and a fingerprint of the content. Anyone can check a record for free, with no account.
TIP does not detect deepfakes, does not stop copying and does not decide whether content is true. It proves who stands behind a piece of content and whether a copy matches the original. It is governed in the open by the AI Trust Council, and the specification is public on GitHub. Signed content is called a Verifiable Asset.
Questions
Questions people ask
How can I tell if a document has been altered after it was signed?
If it carries a digital signature, open it in Adobe Acrobat or another PDF reader, which flags changes made after signing. If it was signed on the Trust Identity Protocol (TIP) by The AI Lab, check the copy against its TIP record, which holds a fingerprint of the signed file, so any edited copy no longer matches. A plain PDF or photo with neither can only be checked with the sender.
How do I know the person who signed a document is who they claim to be?
Look at what stands behind the signature. A scanned signature or typed name proves nothing. An e-signature platform usually proves control of an email address. A TIP signature proves the signer holds a TIP-ID issued after an accredited Verification Provider checked their government ID and a live face, and every signature needs a fresh fingerprint or Face ID on their own device.
Can a logistics company verify proof of delivery without calling the carrier?
Yes, if the carrier signs it on TIP. The carrier signs the delivery receipt or photo with its verified TIP-ID at the handoff, and the logistics company checks the record for free to see who signed it, when and whether the copy changed. It saves the call for the documents that fail the check.
What are TIP-ID, TIP-CONTENT and TIP-TRUST?
They are the three layers of the Trust Identity Protocol. TIP-ID is identity, a verified person or organization. TIP-CONTENT is the signed record of each document or file, with its fingerprint and how it was made. TIP-TRUST is reputation, a public Trust Score from 0 to 1000 that any TIP node computes from an identity's history on the TIP Network, so a signer's track record builds over time.
Does a TIP signature replace a qualified electronic signature or a notary?
No. Where a law requires a qualified electronic signature, a notary or a specific registry, use it. TIP covers the much larger set of everyday documents that carry no signature at all, and it lets anyone check them without software or an account.
What is the Trust Identity Protocol?
The Trust Identity Protocol (TIP) is an open standard from The AI Lab for proving who made a piece of content and whether it has changed. A person or organization is verified once by an accredited Verification Provider and gets a TIP-ID. Each time they sign something, their own device signs it with a post-quantum signature, and the TIP Network records who signed it, when, how it was made (Original Human, AI-Assisted, AI-Generated or Mixed) and a fingerprint of the content. Anyone can check the record for free.
What does TIP cost an organization?
Checking any TIP record is free for everyone, with no account. Signing is free for individuals, nonprofits, schools and universities, government bodies, journalism organizations for editorial use and businesses under USD 100,000 in annual revenue. Larger businesses use a published commercial license, with every tier listed at theailab.org/tip-license.
SourcesAdobe, validating digital signatures in Acrobat, eIDAS Regulation (EU) No 910/2014, Trust Identity Protocol, how it works
Other use cases
Where else TIP helps
- Hiring and recruiting
- Students and academic integrity
- Certificates and credentials
- Insurance claims
- Freight and logistics
- Newsrooms and journalism
- Archives, libraries and museums
- Research publishing
- Creators and creator platforms
- Banks and finance teams
- Agencies, brands and marketing
- Referral, rewards and marketplaces
- One person, many accounts
- All use cases