Keep an agreement confidential and prove it exists

Confidential has more than one layer

An agreement can be seen in more places than the PDF itself. Before you decide what to keep quiet, it helps to know each layer, who can see it and what controls it.

Layer	Who can see it	What it shows	What controls it
The document, and what each signer entered	Only the parties, in their own browsers	The whole document and every entry	Always end-to-end encrypted on Attest, which stores it only as ciphertext it can't read
Attest's own records	Attest	The title, file name, size and type, your note to the signers, account and signer email addresses, the signers' names, where fields are placed and when each step happened	What you write as the title, file name and note
The certificate	Public by default: anyone with its link, ID, stamp code or the document's fingerprint. Private: the parties only	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. Never the document, and email addresses only to the parties	The sender: Private when sending, or Make private later
The public blockchain	Anyone	Fingerprints only (SHA-256 hashes and Merkle roots), never content, titles or email addresses. The number and timing of the anchors sent from each account's wallet are public	Nothing to set: nothing readable is written
What the parties share	Whoever they send it to	A signed copy shows the whole document with every signer's entries, a certificate of completion, the audit trail up to completion and a "Verify it yourself, without us" page; a proof shows only its statement	Each party

The first and fourth layers protect themselves. The second, third and fifth depend on choices, and the rest of this page is about those choices.

Before you send: four settings

• A plain title: it appears in the signing email, on a public certificate and in Attest's records.
• A plain file name: rename the PDF before you attach it, because the file name shows on a public certificate too.
• Private, under Verification: "Only the parties see the certificate. Others verify through zero-knowledge proofs you create."
• Add me as a signer, if you will ever need to prove the agreement yourself: proofs are made by signers, and you sign in the dashboard, with no email.

Keep the message to your signers neutral too, since Attest can read it. How to sign a confidential agreement privately goes through each step of sending one.

Already sent? Make it private now

The sender can switch a public certificate to private at any time: click Make private on the document's row and confirm. From then on, its public link stops working for anyone who isn't a party, and the agreement stays verifiable through zero-knowledge proofs. Making it private doesn't recall copies already downloaded, and only the sender can change the setting.

What an outsider can learn about a private agreement

• With its ID or a stamp's verification code, for example from a printed page: that the agreement exists and is private. The verify page says: "This agreement is private. Its parties chose not to publish a certificate; they can share zero-knowledge proofs about it instead."
• With the original document's file: nothing about the agreement. The original document of a private agreement isn't found by its fingerprint.
• With a signed copy: that it is the exact file recorded and anchored, as "Sealed signed copy of a private agreement" (or "Signed pages of a private agreement"), without its title. Whoever holds the copy can read it, so share it only with people who should.
• From the blockchain: fingerprints and the timing of anchors, never the agreement, its title or anyone's email address. The record a proof is checked against is anchored from Attest's own wallet, never from a party's, so a proof you share doesn't point to your wallet or the other party's.
• From search engines: nothing. Certificate pages are marked noindex, so search engines don't list them.

Prove it exists, and nothing else

When a lender, an auditor, a partner or a new client needs to know the agreement is in place, you don't have to change any setting. Each signer can share a zero-knowledge proof: a piece of cryptography that proves a statement is true while revealing nothing beyond it. Attest's Share proof offers two statements about a completed agreement: that you signed it, or that you and a named co-signer both signed it, with the day it was completed. How to share proof that you signed shows every step.

Share the least that answers the question:

What they need to learn	What to share	What they see
That you are a party to a signed agreement, and since when	A proof that you signed it	Your email address, the completion day (UTC), and that the proof is valid and where its record is anchored
The same, and who it is with	A proof that you and another signer signed it	The same, plus that signer's email address
Its title, every signer's name and their exact signing times	The certificate of completion PDF	The title, the completion time (UTC), the number of parties, the verification code, the fingerprints of the document and the signed state, the Horizen anchor transaction, and each signer's name and signing time, with no document, entries or audit trail
The terms	The signed copy	The whole document, with every signer's entries, the stamps and the seal line, plus the certificate of completion, the audit trail up to completion, the "Verify it yourself, without us" page and the three attached files

A proof doesn't reveal the title, so it doesn't say what the agreement is: you tell the recipient, and the proof confirms the people and the day. Anyone can check a proof at attest.datahubz.com/verify, free and with no account, and every proof is verified independently on zkVerify. A party signed in to Attest can download the certificate of completion PDF from the agreement's certificate, even when the certificate is private.

Agree it with the other parties

Every signer can make proofs about an agreement they signed, and a proof that names a co-signer shows that co-signer's email address. Some confidentiality clauses cover the existence of the agreement itself, not only its terms. If yours does, or if the relationship is sensitive, agree before signing how each party may confirm the agreement exists, for example only through a proof that names the two signers involved. The guide to proving a partnership confidentially has sample wording.

What it costs

End-to-end encryption, the Private option and Share proof are on every plan, Free included. Proofs come with the document and use none of your documents or records. Your first 2 documents are free, in total; after that, the Signing plan is $5 a month for 20 documents. The people who sign never pay.