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 [ Evidence ](https://sendnda.com/docs/evidence)     

The signing record
==================

The chained log of every step, and what each entry holds.

 03

Evidence
--------

Article 1 of 3

 Every NDA on Send NDA carries its own log. Each step, from the moment the agreement is saved to the moment its PDF is sealed, is written as an event. Nothing in the log is edited later: a new fact is a new event at the end.

The events are chained. Each one's hash covers the event before it, so taking an event out, changing one, or putting them in another order breaks every hash after it. That's what lets anyone check the record later instead of taking our word for it.

What gets recorded
------------------

These are the events an NDA can collect, in the order they usually happen:

 | Event | When | What it holds |
|---|---|---|
| `created` | The NDA is saved | Both names and email addresses, who discloses, the AI tools level, the purpose, the four optional clauses, and both durations. |
| `sent` | The signing emails go out | Nothing beyond the time. |
| `resent` | The sender resends the recipient's link | Nothing beyond the time. |
| `viewed` | The recipient first opens their link | The IP address and which signing link was used. |
| `signed` | A party signs | Which party, the signature (the party's name as entered on the NDA), the IP address, the signing link, the browser's user agent, that consent was given, the template version, and the SHA-256 of the agreement as that party saw it. |
| `completed` | The second signature lands | Nothing beyond the time. |
| `frozen` | The sealed PDF is stored | The template version and the SHA-256 of both the PDF and the HTML it was printed from. |

Two more kinds of event can appear. `amended` records a change the sender made before anyone signed: which fields, the values before and after, and whether the old signing links were withdrawn. And the email provider reports back when a signing email was delivered, bounced or opened, as `resend.email.delivered`, `resend.email.bounced` and `resend.email.opened`, with the provider's own message id and timestamp.

How the chain works
-------------------

Every event is first written out as one fixed piece of text, the canonical payload. It has a version line, the NDA's id, the event's sequence number, its type, the time in UTC, and then every field sorted by name. Each field carries its length in bytes, so a value that contains a line break can't pass itself off as a second field.

The event's hash is the SHA-256 of the previous event's hash, a line break, and that canonical payload. The first event has no previous hash. Sequence numbers start at 1 and have no gaps, and the database refuses two events with the same number for one NDA.

```
hash = sha256(previous_hash + "\n" + canonical_payload)
```

The canonical payload is stored exactly as it was hashed, next to the fields it came from. A check hashes the stored text, and also rebuilds it from the stored fields to see that the two still agree.

How it's checked
----------------

A check walks the events in order and stops at the first one that fails. An event passes when:

- its sequence number is the next one, with no gap;
- it points at the hash of the event before it;
- its stored canonical payload is what its stored fields produce, so changing a field alone is caught;
- its hash is what the previous hash and its canonical payload produce.

This check runs every time someone verifies a PDF. A PDF only counts as a match when its NDA's chain passes. See [Verify a copy](https://sendnda.com/docs/evidence/verify-a-copy).

Who sees what
-------------

Both parties get the result in the sealed PDF: each signature with its date, time in UTC and IP address. As the sender, your signing page also shows an audit trail of when the recipient viewed the NDA and when each of you signed. The full chain stays on Send NDA's side, and the [Privacy Policy](https://sendnda.com/legal/privacy) says how long it's kept.

 Checked against the code on 21 September 2026.

 [ The sealed PDF   ](https://sendnda.com/docs/evidence/the-sealed-pdf)