Electronic signature as evidence in courts: admissibility criteria and regulatory framework in Spain

Electronic signature has been fully recognized in Spain and throughout the European Union as a valid mechanism for signing documents with legal effect and as evidence in judicial proceedings. Its legal framework is supported by two pillars:

• Regulation (EU) 910/2014 – eIDAS, directly applicable in Spain.
• Law 6/2020, which regulates complementary aspects related to electronic trust services (liability, supervision, sanctioning regime).

Likewise, Law 34/2002 on Information Society Services and Electronic Commerce establishes conditions for the validity of electronic contracts.

This regulatory framework defines the probative scope of electronic signature and establishes the criteria under which courts assess its authenticity and integrity.

Electronic signature levels and their legal value

The eIDAS Regulation distinguishes three levels of electronic signature, each with its own technical and legal characteristics:

1. Simple electronic signature
   Electronic data associated with the signer that express their intention to sign (art. 3.10 eIDAS).

2. Advanced electronic signature (AES)
   Requires additional guarantees: unambiguous identification of the signer, exclusive control over signature data, and detection of any subsequent modification.

3. Qualified electronic signature (QES)
   An advanced signature backed by a qualified device and a qualified certificate issued by a provider included in the EU trust list.

Regarding QES, despite the European legislator clearly distinguishing it:

Qualified electronic signature is the only one that has the same legal effect as a handwritten signature. (Article 25.2 of eIDAS)

this does not imply at all that simple or advanced signatures lack probative validity. Their strength will depend on the set of evidence accompanying the document.

Admissibility of non-qualified signatures: the principle of non-discrimination

eIDAS incorporates a fundamental principle:

A non-qualified electronic signature cannot be rejected as evidence solely for being in electronic format or for not being qualified.

In practice, this means:

• Private contracts can be validly signed with simple or advanced signature.
• Courts must admit them as evidence, assessing their authenticity case by case.
• Only certain procedures before Spanish public administrations may necessarily require qualified signature.

Therefore, the key for a non-qualified signature to be convincing before a judge is not its category, but the robustness of the technical evidence accompanying it. In fact, given the high complexity and friction of QES, the predominant types of electronic signature in business environments are and will continue to be simple signature and advanced signature.

How to strengthen the probative value of an electronic signature

In litigation, the validity of the signature depends on the ability to demonstrate:

• Who signed.
• How they were identified.
• What document they signed exactly.
• What happened during the signing process.
• Whether the document has remained intact since then.

Below are the mechanisms that allow strengthening a non-qualified signature for its defense in court:

1. Reinforced authentication of the signer

Methods such as:

• Tokenized access links.
• OTP codes sent via certified SMS.
• Multi-factor validations.

These elements accredit that the signer was who they claimed to be and that they acted voluntarily.

2. Audit trail and technical evidence

The provider must generate an audit trail that includes:

• IP addresses.
• Access and signature events.
• Cryptographic fingerprint of the document.

This record accredits the complete process and allows demonstrating the absence of manipulation.

3. Integrity and authenticity guarantee

The evidence document can be electronically signed using qualified signature, ensuring its immutability over time. This allows using it as robust expert evidence before any court.

4. Associated certified communications

Making the document available, reminders, or notification of completed signature must be sent via:

• registered email, or
• certified SMS.

These communications accredit sending, content, and delivery, complementing the process traceability.

Conclusion

European and Spanish law recognize that non-qualified signatures —simple and advanced— are fully admissible as evidence.

Their legal effectiveness depends on the technical and documentary strength of the signing process:

• signer authentication,
• certified traceability,
• cryptographic integrity,
• irrefutable communications,
• and verifiable evidence.

In short, if QES is the master key of the eIDAS ecosystem, non-qualified signatures can be equally valid keys, as long as they are accompanied by the appropriate “digital notarial record”: strong authentication, certified audit, and total integrity guarantee.