How to sign an NDA you can prove

What makes an NDA provable

If a nondisclosure agreement is ever tested, four questions come up: whether both parties signed it, which version they signed, when, and whether it has changed since. An Attest signature answers each one with evidence anyone can check.

• Each party signs with their own key. Each signer approves with a passkey, a cryptographic key only the signer controls, unlocked with Face ID, Touch ID, Windows Hello or the device PIN. The passkey signs a statement that names the NDA's fingerprint (a SHA-256 hash, a short code calculated from the file's contents) and everything that signer entered.
• The time is part of the record. The signing time is in the statement each passkey signs, and the completed agreement is anchored on Horizen, a public blockchain, whose block time shows when.
• Nothing can change unnoticed. Change one byte of the NDA, of any signer's entries or of the signed pages, and verification fails.
• Every party holds the same proof. Each party downloads the same sealed PDF: the signed pages, with a "Signed with Attest" stamp on each signature and a seal line at the foot of every page, a certificate of completion, an audit trail of every step up to completion and a "Verify it yourself, without us" page, with the original document, the evidence and a standalone verifier attached inside.

Anyone can verify the signed copy for free at attest.datahubz.com/verify, with no account. The open-source verifier inside the PDF runs in any browser, even if Attest no longer exists, and checks each signer's passkey signature, the original document, the pages you see and Attest's anchored record on Horizen.

Why an NDA should be signed privately

An NDA often reveals what it protects: the project's name, the parties, what will be disclosed and why. Most e-signature services describe their protection as encryption in transit and at rest, and describe no end-to-end mechanism, so their systems can decrypt the documents they store. We compared 21 e-signature services in October 2026, Attest and 20 others, and Attest was the only one that end-to-end encrypts every document, for every signer, by default.

End-to-end encryption means a document is encrypted on your device and decrypted only by the people it is meant for. With Attest:

1. Your browser encrypts the NDA before upload, with a new key for that document.
2. That key is locked separately to each party's own key, so only the parties' browsers can open the NDA.
3. What each signer fills in, such as their signature, name and date, is encrypted in their browser too.
4. Before your browser encrypts anything to someone, it checks their key against Attest's public key directory, so not even a key swapped in by Attest would be used.

Attest stores the NDA only as ciphertext it can't read, so the terms of your confidentiality agreement stay confidential from the service that delivers it.

Attest does see the information around the document: its title, file name, size and type, your note, the email addresses of your account and of the signers, the signers' names, where fields are placed and when each step happened. Give the NDA a plain title, such as "Mutual NDA", rather than one that names the project.

Keep the certificate private

Every agreement has a certificate of who signed and when. By default it is public: anyone with its link, its code or the document's fingerprint sees the title, the file name, the verification code, the fingerprints of the document, the signed copy and the signed state, each signer's name and signing time, the blockchain anchor and each signature's evidence. It never shows the document, and it shows signers' email addresses only to the parties. Certificate pages are marked so that search engines don't list them.

An NDA's title and the names of the people who signed it can say more than you want, so choose Private when you send it. Only the parties then see the certificate; anyone else who looks it up is told the agreement is private. If you sent the agreement, you can also switch it later with Make private on its row. That stops the public link working for anyone who isn't a party, though it can't recall copies already downloaded.

Prove the NDA exists without revealing it

Sometimes someone needs to know an NDA is in place, without reading it. A client may ask you to confirm that a subcontractor signed an agreement with you before you share the client's files. A partner may ask whether you and a supplier are under contract.

On a completed agreement you signed, Share proof creates a zero-knowledge proof: a proof that a statement is true which reveals nothing beyond the statement. You choose one of two statements:

• That you signed it, on its completion date.
• That you and another signer signed it, on its completion date.

The recipient sees	Never shown
Your email address	The NDA and its terms
The other signer's email address (second kind only)	Its title
The completion date, as a calendar day (UTC)	Any other signer
That the proof is valid, and where its record is anchored

Each proof is submitted to zkVerify for independent verification, and anyone can check it for free, without an account, at attest.datahubz.com/verify or from its link. A proof is made for each signer automatically when the agreement completes, and Share proof is on every plan, Free included.

Be precise about what a proof covers. It shows that your email address, or yours and the other party's, signed an agreement completed on a given day. Because the title stays hidden, it doesn't say the agreement is an NDA: you tell the recipient what it is, and the proof backs the facts it states.

How to send a mutual NDA

1. Open Documents in the menu (it reads Agreements on accounts that use every Attest tool) and click New agreement.
2. Give it a plain Title, such as "Mutual NDA".
3. Click Attach the document to be signed and choose the NDA as a PDF of up to 8 MB.
4. Under Signers, type the other party's email address, and check Add me as a signer (sign in-app, no email).
5. Under Verification, choose Private.
6. Click Next: place the fields and place a signature field for each party, plus a date or full name field where the NDA asks for one.
7. Click Create and send.
8. If the other party is new to Attest, Attest emails you when they are ready. Click Unlock it for … in that email (or open the agreement in Attest), confirm, and approve with your passkey: your browser releases it to them, never Attest.
9. When it's your turn, click Sign on the document's row and approve with your passkey.
10. When both of you have signed, click View the signed copy and download the sealed PDF.

If the other party sent you their NDA

When a client or partner emails you their own NDA as a PDF, click Sign a document yourself. Attach the PDF, choose Private if you don't want its certificate online, click Next: place your signature and click where you sign. Then click Continue to sign and sign with your passkey. Download the signed copy and send it back: it carries a Signed with Attest stamp, and they can check it for free with the verifier attached inside the PDF. This uses one of your documents, because it creates a document in your account. If they send the NDA to you through Attest instead, signing it is free.