Electronic signatures in Spain

The laws

Five texts work together in Spain:

• eIDAS, Regulation (EU) No 910/2014, as amended by Regulation (EU) 2024/1183. It applies directly in Spain and defines the three signature tiers. It leaves national rules on contracts and form untouched (Article 2(3)); the EU guide covers the EU-wide rules.
• Ley 6/2020, de 11 de noviembre, on electronic trust services, in force since November 13, 2020. It replaced the old Ley 59/2003 de firma electrónica and sends the proof of electronic documents to the civil procedure code: LEC article 326.3 for documents that used a non-qualified trust service, and 326.4 for qualified ones (article 3.2).
• The LSSI (Ley 34/2002), on electronic commerce, whose article 23 governs contracts concluded electronically.
• The Código Civil and the Ley de Enjuiciamiento Civil (LEC, Ley 1/2000), for form and for evidence.

Contracts bind whatever their form

Spanish contract law starts from consent, not paper. A contract exists once the parties consent to be bound (Código Civil article 1254), it is perfected by mere consent (article 1258), and contracts "serán obligatorios, cualquiera que sea la forma en que se hayan celebrado" (are binding whatever the form in which they were concluded) when the essential conditions for validity are present (article 1278).

LSSI article 23 applies this to electronic contracts:

1. A contract concluded electronically produces all the effects the law provides when consent and the other validity requirements are present (23.1).
2. The parties don't need a prior agreement to use electronic means (23.2).
3. Where the law requires a contract to be in writing, an electronic medium satisfies it (23.3).

The three tiers under eIDAS

Tier	What it requires	Legal effect in Spain
Electronic signature (firma electrónica, Article 3(10))	"data in electronic form which is attached to or logically associated with other data in electronic form and which is used by the signatory to sign"	Can't be refused legal effect or admissibility as evidence solely because it is electronic or not qualified (Article 25(1)). If challenged, it is proved under LEC article 326.3
Advanced (firma electrónica avanzada, Article 26)	Uniquely linked to and capable of identifying the signatory, created with data the signatory can use under their sole control with a high level of confidence, and linked to the data so that any later change is detectable	The same as above: Spanish law gives it no presumption, so it is also proved under article 326.3
Qualified (firma electrónica cualificada, Article 3(12))	An advanced signature created with a qualified signature creation device and based on a qualified certificate. Ley 6/2020 article 7 sets how the applicant's identity is checked, in person as a rule	The equivalent legal effect of a handwritten signature (Article 25(2)), and a presumption in court (LEC article 326.4)

What happens when a signature is challenged

The LEC sets out three cases:

• Not challenged. A private document makes full proof when the party it harms doesn't challenge its authenticity (article 326.1).
• Challenged, non-qualified signature. When the authenticity, integrity, date and time or other features of an electronic document are challenged, the party that presented it may ask for an expert comparison or propose any other useful evidence; if authenticity can't be established, the court weighs the document under the rules of "sana crítica", its reasoned judgment (articles 326.2 and 326.3).
• Challenged, qualified signature. The document is presumed to have the challenged feature, and the service to have been provided correctly, if the provider was on the trusted list at the time. The person challenging it bears the burden of the check, and its costs only if the check comes out against them, and a reckless challenge can be fined €300 to €1,200 (article 326.4).

The electronic medium holding a contract concluded electronically is admissible in court as documentary evidence (LSSI article 24.2). In practice, a simple signature is valid, and its strength is the evidence behind it.

Documents excluded or with their own rules

• Family law and succession. The LSSI's electronic-contracting rules don't apply to contracts relating to family law and succession (article 23.4).
• Public documents and official intervention. Contracts and acts that by law need a public document, or the intervention of courts, notaries, property or commercial registrars or public authorities, are governed by their own legislation (article 23.4).
• Real estate. Acts that create, transfer, modify or extinguish real rights in immovable property, and leases of six years or more that are to affect third parties, must be recorded in a public document (Código Civil article 1280); once the parties have agreed, either can compel the other to complete that form (article 1279). Registration in the Land Registry needs a public deed or an authentic judicial or administrative document (Ley Hipotecaria article 3), and a voluntary mortgage is validly created only by public deed registered in the Land Registry (article 145).
• Gifts of real estate and marital property agreements are valid only in a public deed (Código Civil articles 633 and 1327).
• Wills. A holographic will must be entirely written and signed by the testator (article 688), and an open will is executed before a notary (article 694).
• Remote notarial acts. Since November 9, 2023, a notary can authorize certain acts by videoconference through the notarial e-office (Ley del Notariado article 17 ter), such as commercial policies (pólizas mercantiles), company formation with cash contributions, powers for specific acts, payment receipts and signature authentications. That is a notarial act, not a private electronic signature.

How to make an electronic signature hold up

1. Check the form. If the document needs a public deed, a notary or a registry, use that route.
2. Plan for article 326.3. If the other party disputes the signature, you will prove its authenticity, integrity and date, so choose a method that leaves that evidence.
3. Keep the electronic original that every party can reproduce, since it is admissible as documentary evidence (LSSI article 24.2).

How Attest fits ordinary business agreements

Attest signatures are electronic signatures, the base tier of eIDAS (Article 3(10)), which Spanish law recognizes for most agreements. They are not qualified electronic signatures: Attest is not a qualified trust service provider and issues no qualified certificates. Attest doesn't claim the advanced tier either. In a dispute, that puts them under LEC article 326.3, and Attest's evidence speaks to the features that article names:

What article 326.3 asks about	What Attest records
Authenticity (who signed)	Each signature is made with a passkey registered to the signer's email address. A passkey is a cryptographic key only the signer controls, unlocked with Face ID, Touch ID, Windows Hello or the device PIN, and it must confirm the signer is present and verified. Attest checks each signature against the passkey's public key. Attest confirms control of the email address and the passkey, not a government ID
Integrity (what was signed)	The passkey signs a statement that begins "I have reviewed and I sign", with the SHA-256 fingerprint of the exact document and of the signer's entries. Change one byte and verification fails
Date and time	The signing time in each statement is set by Attest's server and signed by the passkey, and the signed state is anchored on the Horizen public blockchain, whose block time shows when it was anchored. This is evidence for the court to weigh, not a qualified electronic time stamp
The original	Every party downloads the same sealed PDF: the signed pages, with a "Signed with Attest" stamp on each signature and a seal line at the foot of every page, a certificate of completion, the audit trail up to completion and a "Verify it yourself, without us" page, with the full evidence, the original document and a standalone verifier attached inside

A fingerprint (SHA-256 hash) is a short code calculated from a file's contents that changes if a single byte changes. An expert, or the court, can run the open-source verifier inside the copy in any browser without any Attest service: it checks each signer's passkey signature, the original document, the pages you see and Attest's anchored record on Horizen.

Attest is built for everyday business agreements such as client contracts, statements of work, NDAs and supplier agreements. For a document that needs a public deed, a notary or a registry, or a qualified signature, use that route.

Every document is end-to-end encrypted, so Attest can't read it. Signers need no account and never pay, and anyone can verify a signed copy for free at attest.datahubz.com/verify. Your first 2 documents are free, in total, then the Signing plan is $5 a month for 20 documents.