What technical evidence enforces an advanced signature (hash, timestamps, and logs)

Beyond the click: why an advanced signature is robust

An advanced electronic signature is not a button, a stroke on screen, or an OTP via SMS. The legal value of an advanced signature is not in the “act of signing,” but in the technical evidence that allows demonstrating:

• who signed,
• what document was signed,
• how the signer was identified,
• when the signature was performed,
• and that the document has not been altered afterwards.

Article 26 of the eIDAS Regulation establishes these requirements, but does not describe the technology necessary to fulfill them. That responsibility falls on the signature service provider.

In this article, we explain the technical evidence that makes an advanced signature truly advanced.

1. Cryptographic hash: the document’s digital fingerprint

The hash is a cryptographic function that generates a unique fingerprint of any set of data, such as a document. If the document changes by a single comma, the hash obtained from it changes completely.

Example (abbreviated):

What it contributes to the advanced signature:

• Guarantees that the signed document has not been modified.
• Links the signature to a specific document.
• Allows verifying integrity even years later.

2. Signer identification and exclusive control

eIDAS requires linking the signature to the signer through “creation data under their exclusive control.”

This is achieved through evidence such as:

• Request sent via certified email, which links identity and channel.
• OTP via certified SMS, which demonstrates possession of the number.
• Unique secure link (single-use token).

The more independent evidence converges, the more unequivocal the identification is.

3. Detailed logs of the signing process

Logs document everything that occurred during the signature:

• Sends, openings, and attempts.
• IP address and device.
• Identity validations.
• Final signature result.

Example:

To be valid, logs must be:

• signed,
• immutable,
• and preserved with technical custody.

4. Evidence of process integrity

An advanced signature protects not only the document, but the entire flow:

• Records (logs) of each step.
• Links with expiration and secure tokens.
• Integrity verification of the final PDF.

This demonstrates that the signature could not be intercepted or altered.

5. The evidence package (audit trail)

The result of an advanced signature is not simply a signed PDF. An evidence package must be generated that is verifiable:

• Signed document.
• Hashes and metadata.
• Timestamp.
• Complete logs.
• Digital signature of the provider.

In eEvidSign, this set forms an Evidence Audit ready for litigation or audits.

How it differs from a simple signature

Both are valid, but they are used in different contexts according to legal risk.

When all these proofs are necessary

• Commercial contracts.
• HR (contracts, annexes, authorizations).
• Regulated sectors.
• Processes susceptible to challenge.

Conclusion

Advanced signature does not consist of “drawing” a signature on a document. It is a system of hashes, timestamps, logs, and evidence that demonstrates:

• who signed,
• what was signed,
• how they were identified,
• and that the document did not change.

Without these proofs, an advanced signature is not truly advanced.

With solutions like eEvidSign from eEvidence, companies obtain complete technical evidence, ready for audits or litigation.