What is electronic signature? Complete guide 2026

A electronic signature is a set of data in electronic form which are attached to or logically associated with other data in electronic form and which the signatory uses to sign. This definition, taken from eIDAS regulation (regulation (EU) No. 910/2014), covers a wide spectrum of technical mechanisms, from the simplest (ticking a box, typing your name) to the most sophisticated (qualified cryptographic certificate).

Under French law, article 1367 of the Civil Code provides that "the signature necessary for the completion of a legal act identifies the person who apposes it" and that, when it is electronic, it "consists in the use of a reliable identification procedure guaranteeing its link with the act to which it attaches". The reliability of the procedure is presumed for signatures qualified within the meaning of eIDAS.

Concretely, an electronic signature fulfils three functions: it identifies the signatory, it expresses their consent to the content of the document, and it guarantees the integrity of the document (any modification after signature is detectable).

The mechanism rests on two pillars: the authentication of the signer and the integrity of the document.

To authenticate the signatory, one or more identification factors are used: trusted email address (single-use link), OTP code received by SMS, personal cryptographic certificate, etc. To guarantee integrity, a fingerprint (hash) of the document is calculated at the time of signature. If the document is subsequently modified, the fingerprint no longer matches — the signature is then invalidated.

In solutions like Certyneo, the process relies on PDF processing libraries that integrate these cryptographic metadata directly into the file. A timestamped audit trail (action log) completes the system by recording each step: sending, opening, OTP validated, signature, etc.

On the technical side, several security mechanisms reinforce the inviolability of the process: qualified timestamping (RFC 3161) applies certified time proof to each signature; TLS 1.3 encryption protects data in transit; the signatory's geolocation and IP address are recorded for traceability; finally, in certain flows (AES/QES), behavioural biometric data (typing speed, pressure) complements the identity fingerprint.

The concept of non-repudiation is central: thanks to the timestamped and cryptographically signed audit trail, it is technically impossible for a signatory to deny signing a document without falsifying the chain of evidence. For archiving purposes, French regulation (Decree 2016-1673) requires a retention period of 10 years for most business documents — Certyneo ensures this archiving with probative value in sovereign hosting (EU).

In France, electronic signature has been recognised since law No. 2000-230 of 13 March 2000, which amended the Civil Code to establish electronic writing and electronic signature as equivalent to their paper counterparts. Article 1366 specifies that electronic writing "has the same probative force as writing on paper support".

At European level, the eIDAS regulation (EU) No. 910/2014 creates a unified legal framework for electronic signatures. Its article 25 establishes the principle of non-discrimination: "electronic signature shall not be refused legal effect and admissibility as evidence in legal proceedings on the sole ground that it is in electronic form". Qualified signatures (QES) also benefit from a legal presumption equivalent to a handwritten signature in all 27 Member States.

For standard documents (commercial contracts, employment contracts, quotations, NDA, mandates), an advanced signature (AES) offers an excellent balance between ease of use and legal certainty. Qualified signature (QES) is reserved for high-value acts or situations where sectoral regulation explicitly requires it.