Public blockchain anchoring technology—of which OpenTimestamps is one of the finest examples—has now fully entered the legal arena. [1, 2]
While open-source protocols such as OpenTimestamps are widely used upstream by NGOs, investigative journalists (such as the Starling Lab consortium to document war crimes), and companies to preserve evidence of automation, their admissibility in a sovereign court is subject to specific rules. [3, 4]
An analysis of the current state of case law and arbitration practices highlights the following points:
Key Case Law: The AZ Factory Case (March 2025)
In France, the historic turning point occurred before the Marseille Judicial Court (March 20, 2025, AZ Factory v. Valeria Moda). [1, 2]
- The Dispute: A case of counterfeiting and copyright infringement in the fashion industry. [5, 6]
- Use of Evidence: To prove the prior existence of his sketches and visuals, the designer had anchored the cryptographic fingerprints (SHA-256 hashes) of his digital files in a public blockchain. [2, 6]
- The judge’s ruling: The court formally validated the probative value of blockchain timestamping. It characterized it as prima facie evidence in writing (within the meaning of Article 1362 of the Civil Code), sufficient to establish beyond doubt that the file existed in that precise form on that date. [1, 2, 7]
How is an OpenTimestamps receipt (.ots) used in court?
In civil law (particularly French or European law), the prevailing principle is that of freedom to present evidence by any means, provided it is fair. An OpenTimestamps receipt (.ots) is not a standalone “magical” piece of evidence, but it acts as a perfect mathematical witness. [3, 8]
In a dispute, the presentation of evidence generally takes place in three stages:
The report by a bailiff (judicial officer) or expert: The attorney does not simply present the .ots file to the judge. An expert or judicial officer verifies the source file, calculates its hash, and uses an independent OpenTimestamps client to verify the Merkle tree all the way back to the Bitcoin block. [3, 7]
Demonstration of non-retroactivity: The expert demonstrates to the court that to falsify this evidence, the history of the Bitcoin blockchain would have had to be rewritten (which is mathematically and financially impossible), guaranteeing that no retroactive modifications could have taken place. [9, 10]
The body of evidence: The judge combines this mathematical anchor with other evidence (emails, contracts) to establish ownership of the right. [11]
Arbitration Tribunals and International Compliance
In the context of international commercial arbitration (often more flexible and technical than state courts), the use of OpenTimestamps and blockchain hashes has become standard practice, particularly for:
- Intellectual property and trade secret disputes: Proving that a chemical formula or source code existed confidentially within the company on a specific date (T) prior to a leak or a competing patent filing.
- Strengthening evidence: An increasing number of legaltech companies are integrating OpenTimestamps to supplement traditional timestamps (such as the eIDAS standards in Europe) to ensure absolute cross-border validity in the event of a failure by a central certification authority. [12, 13]
Case court of Nancy (France) 1st april 2002.
Certisio increases the likelihood of legal success by drawing on established case law regarding the “presumption of evidence.” In its ruling of November 29, 2001, the Nancy Court of Appeals (BICC No. 553 of April 1, 2002) held that a party’s refusal to cooperate in the presentation of evidence could be viewed as a presumption that it had acknowledged the validity of its opponent’s claim.
This amounts to nothing less than a reversal of the burden of proof by the party challenging the technical tools used to establish the chain of custody. In the absence of such a challenge, the evidence provided by CERTISIO renders the proof irrefutable.
CERTISIO RESPONSE transforms a simple field recording into a secure and traceable piece of documentary evidence. The solution establishes a robust chain of custody that includes:
• photo capture via a secure app,
• automatic timestamping,
• geolocation,
• generation of a PDF certificate,
• electronic signature,
• recording of the digital fingerprint on the blockchain,
• archiving that can be utilized in operational processes.
[2] https://www.village-justice.com
[5] https://www.village-justice.com
[7] https://cmc-avocats-bordeaux.fr
