An agreement signed today may be challenged years from now. The dispute could involve the signing date, the document's contents, or the sequence of events recorded during signing. If that evidence exists only in the signing platform's database, anyone reviewing it must rely on records maintained by the same platform.
Signater now anchors envelope evidence to the Bitcoin blockchain. Every 10 minutes, we group cryptographic digests of envelope events into a batch and anchor its root to the network. Once the transaction is confirmed, anyone with the corresponding receipt can independently verify the cryptographic proof using open tools.
The documents themselves and the signers' personal information are not published to Bitcoin. The blockchain record contains cryptographic data used to verify the evidence.
When evidence needs to stand the test of time
Anchoring can be useful when someone needs to check a document long after it was signed.
Consider a business reviewing a lease after the tenancy ends, or retrieving the history of an agreement during an audit. If a question arises about the file or its recorded history, the available evidence can be compared with a cryptographic proof anchored to the blockchain.
This adds an external reference to the records maintained by Signater. Rather than relying solely on the platform's stored history, anyone with the receipt can independently verify the cryptographic proof.
What gets recorded
A hash is a digest calculated from the contents of a file or event. A small change to the input normally produces a different hash, making it possible to detect differences between files.
When blockchain anchoring is enabled, Signater creates cryptographic digests for envelope events, including:
- envelope events such as creation, editing, scheduling, publishing, pausing, cancellation, expiration, and completion;
- signer events such as views, signatures, rejections, and verification-code requests by email, SMS, WhatsApp, and PIX.
The record also includes the hash of each uploaded document and each signed PDF. This covers both the envelope's event history and the files associated with the signing process.
Each digest is combined with a random value, which is stored in the envelope receipt. This helps make it harder to associate a public record with a specific envelope without access to the receipt. Names, email addresses, national ID numbers, and document contents remain off the blockchain.
Every 10 minutes, Signater organizes the digests from that period into a Merkle tree. The result, called the Merkle root, represents the batch of evidence and is the data anchored to Bitcoin. Each event receipt contains the proof that links the event to that root, without having to record every event individually on the blockchain.
Signater handles batch submission. You don't need a cryptocurrency wallet or pay Bitcoin network fees directly to use the feature.
What blockchain adds to an electronic signature
Signater envelopes already include a PAdES digital signature, a seal using an Adobe Approved Trust List (AATL) certificate or an ICP-Brasil certificate, and a timestamp. A timestamp authority issues a timestamp attesting that specific data existed at a particular date and time.
Blockchain anchoring adds an external reference for checking the evidence. If someone later claims that a record was changed after signing, the proof can be used to check whether the corresponding digest was already committed to a root recorded on Bitcoin.
Each batch root also receives an RFC 3161 timestamp. The batch therefore has both a blockchain record and a timestamp issued by a timestamp authority. These are different mechanisms that can be used together to verify the evidence.
How to verify the evidence
Using the document's QR code
The QR code on the document opens the public verification page. Once Bitcoin confirms the batch, the page displays “Evidence anchored on a public blockchain” and the block number. Until confirmation, it displays “Anchoring in progress.” The envelope certificate also includes a reference to the anchoring, with links to the receipt and verification page.
Using the receipt and open tools
On the envelope page, Download blockchain receipt generates a ZIP file containing the material needed for verification:
- manifest.json, listing the events, batch, root, and status of each event;
- the events folder, with one JSON file per event and its corresponding OTS proof;
- the tsa folder, containing the timestamp for each batch.
Visit opentimestamps.org, an open and independent tool, and provide the JSON file and OTS proof for the same event. The tool verifies the proof against the Bitcoin record and reports the available confirmation details. You can also verify from a terminal with the ots verify command from the same project.
Checking the signed PDF
To check the file, calculate the SHA-256 hash of the signed PDF and compare it with the sha256Signed field in the document.signed event in the receipt.
On a Mac, run:
shasum -a 256 agreement.pdfOn Windows, run:
certutil -hashfile agreement.pdf SHA256If the calculated hash matches the value in the receipt, the PDF corresponds to the file identified by that record.
A new event joins the next batch, which is submitted at 10-minute intervals. Confirmation on Bitcoin may take a few hours. Until confirmation, the receipt marks the event as pending. Download the receipt again later to get the updated proof.
Integrating with another blockchain
Some companies maintain their own records on public or private networks. For these organizations, Signater sends the envelope.anchored webhook for each batch. The notification includes the batch root, which the company's system can record on its chosen network using the organization's own credentials and procedures.
The webhook is configured alongside the other Signater webhooks, with authentication, delivery history, and reporting.
Monitor your account's records
Under Reports → Envelopes → Blockchain, you can see how many events Bitcoin has confirmed, how many are awaiting confirmation, how many envelopes have a record, and the median time between an event and its confirmation. The list shows each envelope's status, supports filtering by vault and status, and exports to a spreadsheet.
The feature settings also show when the next batch will be submitted, how many events are awaiting confirmation, the latest recorded block, and which webhooks receive anchoring notifications.
How to enable blockchain anchoring
- Go to Settings → Account → Blockchain.
- Enable Anchor evidence on a public blockchain.
- Click Save changes.
From then on, new actions in your envelopes are included in subsequent batches. Blockchain anchoring is part of the Enterprise plan. Technical details, including receipt and webhook formats, are available in the API documentation. You can also read the Signater security overview.
New to Signater? Create a free account and send up to three envelopes per month on the Free plan, with no credit card required.
