Tamper-Evident Seal

A tamper-evident seal is a cryptographic lock placed on a document the moment signing is complete. It works by calculating a hash, a unique fingerprint of the file's exact contents, and binding that fingerprint to the finished record. If even a single character changes afterward, a price, a date, a clause, or a swapped page, the fingerprint no longer matches and the alteration becomes detectable. The seal does not prevent someone from editing a copy of the file; what it does is make any edit impossible to hide. That is the difference between tamper-proof, which no digital file truly is, and tamper-evident, which is what actually holds up under scrutiny.

The seal is the integrity layer of a signed document. A signature establishes that a specific person agreed to something, but on its own it says nothing about whether the document you are holding is the document they actually signed. The tamper-evident seal closes that gap. It is one of the core elements recorded in an audit trail, alongside timestamps, IP addresses, and email verification, and it is what lets the trail answer the question every court and counterparty eventually asks: can you prove this file was not changed after the fact? Without the seal, a signature on a document you cannot verify carries little weight in a dispute.

Legally, the seal supports the integrity requirement that gives an electronic signature evidentiary weight. The federal ESIGN Act of 2000 and the Uniform Electronic Transactions Act of 1999, adopted by 49 states plus the District of Columbia (New York instead relies on its Electronic Signatures and Records Act), establish that electronic signatures are valid in the United States. In the European Union, eIDAS, Regulation (EU) No 910/2014, does the same and defines three signature levels: simple, advanced, and qualified. Validity still has to be proven when challenged, and a tamper-evident seal is precisely the kind of supporting evidence that helps a document satisfy authentication standards such as US Federal Rules of Evidence 901 and 902. It is also what makes a signed record difficult to repudiate later, because the signer cannot credibly claim the terms were different when the sealed fingerprint shows otherwise.

At sign.pink, every completed document carries a tamper-evident seal as part of its audit trail, with no extra setup and no account required for the people you send documents to. Skipping the signer account does not mean skipping the evidence. The seal is applied automatically at completion, and the resulting certificate is something you can download, store, and produce on demand, readable by a lawyer or auditor without special software.

Examples

• A signed contract is sealed at completion. Months later, someone edits the price on a copy. The hash no longer matches the sealed original, so the change is immediately detectable.
• An audit trail lists a tamper-evident seal alongside timestamps and IP addresses, giving a complete who, when, and proof-nothing-changed record.
• In a dispute, the seal lets you show a court the file is identical to the one that was signed, supporting authentication under Federal Rules of Evidence 901 and 902.
• Tamper-evident is not the same as tamper-proof: the seal does not block edits, it makes any edit impossible to hide.