Blockchain Records as Evidence in Spanish Courts: Evidentiary Disputes, Legal Framework and Case Law

1. Short Answer

Spanish law has no dedicated statute that says "blockchain evidence is valid" or "invalid". Blockchain records are admitted through the general rules on electronic evidence in the Civil Procedure Act (Ley de Enjuiciamiento Civil, LEC) and the Criminal Procedure Act (LECrim), and the court assesses them under the rule of sana crítica (sound judgment). In practice, a blockchain record is strong proof that specific data existed in a specific form at a specific time. It is weak or contestable proof of who did it and of whether the underlying content is true.

2. Legal Framework

• LEC art. 299.2 and 299.3: allows "means of reproducing words, sounds and images" and instruments that store data relevant to the proceedings. Any other means not listed may be admitted if it can produce certainty, at the judge's discretion.
• LEC arts. 317 to 327: documentary evidence. Public documents (art. 319) prove the fact, date and the people involved. Private documents (art. 326.1) have full evidentiary force unless the other party challenges their authenticity.
• LEC art. 326.2 and 326.3: if authenticity is challenged, the party offering the document must prove it by other means. For non-qualified electronic signatures or trust services, the court assesses the evidence according to the sana crítica, and the burden of proving reliability falls on the party who relies on it.
• LEC arts. 382 to 384: reproduction instruments and data-storage media. The court may require expert opinion and sets the probative value under sana crítica.
• LEC arts. 335 to 352: expert evidence. Technical experts are normally needed to explain hashes, nodes, consensus and wallet attribution.
• LECrim art. 726: in criminal trials the court directly assesses documents and other physical evidence. Art. 11 LOPJ and art. 24 Spanish Constitution: evidence obtained in violation of fundamental rights is inadmissible, and the right to use relevant means of proof is protected.
• Regulation (EU) 910/2014 (eIDAS) art. 46: an electronic document cannot be denied legal effect or admissibility solely because it is electronic. Law 6/2020 (Spanish law on electronic trust services) implements this domestically.
• Regulation (EU) 2024/1183 (eIDAS 2): introduces qualified electronic ledgers as a trust service. Qualified ledgers benefit from a legal presumption of reliable chronological ordering and data integrity. Check the current status of the implementing acts and of the qualified providers before relying on this route.
• Law 34/2002 (LSSI) art. 24: electronic contracts are admissible as evidence of the contract.

3. How a Blockchain Record Is Classified

• As a private electronic document: this is the mainstream view. The record (a transaction, a timestamp or a hash anchor) is filed as documentary evidence under the LEC, and it counts as a private document. If the opposing party does not challenge it, it carries full force. If challenged, the proponent must prove authenticity.
• As a public document: not accepted. A blockchain is not a public registry and is not kept by a public official, so it does not carry the strong presumption of art. 319 LEC.
• As a notarised record: a notary can record in an acta what they observed on a blockchain explorer or what a hash verification showed. The acta is a public document, but only for what the notary perceived (the observation), not for the truth of the underlying content.
• As an unlisted evidentiary means (art. 299.3): used where the court needs a technical report or live demonstration, usually combined with expert evidence.

4. Main Evidentiary Disputes

• Authenticity and integrity of the capture: the opposing party typically argues that the screenshot, PDF or explorer printout was altered or incomplete. Answer: preserve the transaction hash, block number and timestamp so the court or expert can re-verify directly on the network, and obtain a notarial acta or a recognised forensic capture.
• Attribution (who controls the wallet): a blockchain proves that an address signed a transaction. It does not prove that a specific person controls that address. Attribution needs exchange KYC records, device evidence, or admissions by the other party.
• Garbage in, garbage out: anchoring a document's hash proves the document existed in that exact form by that date. It does not prove that the content is true, that the signer had authority, or that the document was lawfully obtained.
• Off-chain data: most useful files live off-chain, and only a hash is on-chain. If the original file is lost, the hash alone proves nothing.
• Technical reliability: the opposing party may question the network (private or permissioned chains, small chains vulnerable to reorganisations, centralised operators) and the provider's methodology. Public, widely used chains are easier to defend.
• Legal nature of the asset: disputes about whether crypto-assets are money or property affect remedies, not admissibility.
• Smart contracts: courts treat the code as evidence of the parties' agreement and conduct. Interpretation follows the Civil Code rules on contract interpretation, and a bug in the code does not automatically bind the parties to its outcome.
• Data protection: immutable personal data on a public chain can clash with GDPR rights of rectification and erasure, which may become a separate dispute.

5. Case Law

Important caution: Spanish case law specifically about the probative value of blockchain is thin, and there is no Supreme Court civil doctrine that settles it. Commentators often cite the decisions below, and some of them are cited for more than they actually decided. Always read the full judgment and confirm the citation (CENDOJ) before using it in a filing.

• STS (Sala Penal) 326/2019, 20 June 2019: a Supreme Court criminal ruling on a bitcoin investment fraud. It held that bitcoin is an intangible asset used as consideration, not money, so the victims could not recover bitcoins as restitution and were awarded the euro value instead. Many articles describe it as the first Supreme Court acceptance of blockchain as evidence, because the court relied on evidence of the bitcoin transfers and applied the direct assessment of documents under LECrim art. 726. Treat it as a case about the legal nature of bitcoin and as an indirect example of courts working with crypto-transaction evidence, not as a ruling that sets out standards for blockchain proof.
• SAP Álava (Vitoria-Gasteiz) 2021 (cited in secondary sources as SAP VI 1302/2021): the Provincial Court reportedly accepted that information registered on a blockchain can be filed as documentary evidence because the technology allows a minimum audit of authenticity. It is one of the few appellate decisions presented as directly addressing blockchain evidence. Verify the exact reference and reasoning in the full text.
• SAP Madrid 7/2019, 15 January 2019: listed in legal commentary on the validity of blockchain proof. Check the full text for what it actually decided before citing it.
• STS 300/2015, 19 May 2015 (Sala Penal): not a blockchain case, but the leading Supreme Court authority on electronic messages (WhatsApp, social networks). The court held that when authenticity is challenged, the party offering the evidence must prove its origin and integrity, usually with an expert report. Lower courts apply the same logic to blockchain records, and this is where most disputes about captures and printouts are decided.

Practical reading of the case law: courts accept blockchain evidence when it is explained clearly and backed by an expert or notarial verification, and they reject it when the proponent only presents an unsupported screenshot.

6. Practical Strategy for the Party Offering Blockchain Evidence

• File the transaction hash, block height, timestamp, wallet addresses and the original file whose hash was anchored.
• Capture the explorer data through a notary or a recognised forensic provider, so the capture has its own chain of custody.
• Commission an expert report that explains the technology in plain language, shows how to verify the record independently, and addresses the likely objections (integrity, network reliability, attribution).
• Offer the court a live verification at the hearing or a court-appointed expert, so authenticity does not rest on trust in your provider.
• If the data may be central to a dispute, consider a qualified trust service (qualified timestamp or, once available, a qualified electronic ledger) in addition to the blockchain anchor, because these carry statutory presumptions.
• Combine blockchain proof with other evidence on attribution and on the truth of the content.

7. Practical Strategy for the Party Challenging Blockchain Evidence

• Challenge authenticity under LEC art. 326.2 promptly, in the form and time the procedure requires, so the burden shifts to the proponent.
• Attack the link between the record and the person (wallet control) and between the hash and the claimed content.
• Question the method of capture, the network used, and the independence of the expert.
• Request your own expert report and ask for verification against the live network.

8. Conclusion

In Spain, blockchain evidence is admissible, but its weight is decided case by case under sana crítica. It works best as proof of existence, integrity and timing of data. It needs additional evidence for identity, authority and truth of content. The legal position is moving with the EU rules on electronic ledgers, so check the latest implementation status and any new appellate decisions before relying on the points above in an actual proceeding. This is general legal information and not a substitute for advice from a Spanish lawyer (abogado) on a specific case.