Practical Aspects of Electronic Signature
How it works technically, its legal standing, and how to verify it: everything you need to know to use electronic signatures with confidence.
What problem does electronic signature actually solve?
Electronic signature guarantees that a document has not been modified since it was signed, and that the signer's identity is traceable. Unlike paper, any alteration — even a single space or digit — is automatically detectable.
With a paper contract, several parties each hold a copy that is supposed to be identical. But nothing proves that one copy hasn't been quietly altered after the fact. A handwritten date proves nothing either: anyone can write whatever they want. Electronic signature eliminates this uncertainty at a structural level. If any element of the document changes, the signature becomes invalid.
How does an electronic signature work?
It relies on two complementary mechanisms: a fingerprint calculation that detects any modification, and a cryptographic signature that authenticates the operation.
The fingerprint calculation (or hash) produces a unique value derived from the exact content of the document. Think of it as adding up the value of every character in the text: the result changes as soon as a single letter is modified. In practice, the algorithm used (SHA-256) is far more sophisticated, but the principle is the same. And this calculation is one-way: it is impossible to reconstruct the document from its fingerprint.
The cryptographic signature is applied by the trusted service provider using a secured private key. It seals the document's fingerprint and guarantees that the operation was supervised by an identified third party. The signer's identity is established by the proof file assembled at the time of signing: email address, explicit consent, IP address, and timestamp.
Does an electronic signature carry the same weight as a handwritten one?
Yes. European law (the eIDAS regulation) and US law (the eSign Act) both guarantee that a judge cannot reject an electronic signature solely on the grounds that it is digital. Its admissibility is established.
A simple electronic signature (SES) is actually more evidentially robust than a scanned signature. A scanned signature simply proves that someone signed something, at some point. An electronic signature proves who signed, exactly when, and that the document has not been altered since. Any modification is detectable — which is not the case with paper.
This evidentiary value is further strengthened by two elements. The proof file consolidates all traces of the operation: the signer's identity, a timestamp for each action, IP address, and explicit consent. The qualified timestamp (in PAdES B-LTA format) certifies the date through an audited and qualified external provider — this is not a simple notation on the document, but a legally enforceable guarantee.
When is a simple electronic signature not enough?
A simple signature covers the vast majority of professional needs, but certain legal acts require a qualified signature or the involvement of a public official.
These include, in particular:
- Notarized deeds
- Real estate transactions
- Family law documents
- Certain public procurement contracts
- Certain administrative procedures that explicitly require a qualified signature (for example, in France: filings with the INPI)
For these cases, a qualified signature is required. It involves in-person identity verification and the use of a physical device (a cryptographic USB key), making it more cumbersome and more expensive. For the remaining 95% — commercial contracts, quotes, purchase orders, non-disclosure agreements — a simple signature is legally valid and more than sufficient.
Is electronic signature recognized internationally?
Yes. The eIDAS regulation covers the entire European Union, and the eSign Act applies in the United States. Both frameworks guarantee legal recognition of electronically signed documents.
Other countries have compatible frameworks: the United Kingdom retained a regime similar to eIDAS after Brexit, and Switzerland has its own legislation. In practice, electronic signatures are accepted in most international commercial contexts.
What are the concrete day-to-day benefits?
The full cycle — sending, signing, and retrieving the signed document — takes minutes, not days. The signer doesn't need to install anything: they receive a link and sign directly from their browser.
Electronic signature also eliminates the constraints of paper. No more printing, initialing every page, scanning, or mailing. In fact, initialing page by page no longer serves any purpose: the cryptographic fingerprint covers the entire document, and every page is implicitly protected. The signed PDF is the original — and a more reliable original than paper, since any alteration is detectable.
Finally, going paperless mechanically reduces printing, postage, and shipping costs, as well as the associated carbon footprint.
Is the cryptography behind it truly reliable?
Yes. The cryptographic functions that underpin electronic signature have never been compromised. They are built on decades of mathematical research and have been proven at massive scale.
Skepticism is understandable: the news regularly reports cyberattacks. But what gets hacked are poorly configured systems, weak passwords, and human behavior. The cryptographic algorithms themselves hold firm. The same principles are used every day in contexts where the question never even arises: every credit card payment, every online banking session, every online tax filing relies on these same mathematical building blocks — not out of hope that they'll hold, but because decades of intensive use have proven that they do.
How do you verify that a document has been properly signed?
The simplest way is to open the PDF in Adobe Acrobat Reader. A banner at the top of the document displays the status of the signatures and confirms their validity.
For a deeper check, the signatures panel in Acrobat lets you verify that the signature is in LTV (Long Term Validation) or LTA format. This ensures the signature will remain verifiable over time, even after the certificate used has expired.
The proof file is also accessible in the signature properties: it details how the signer was identified (email, consent, IP address, timestamp).
For professionals or disputed cases, the European Commission provides an official validator (the DSS Validation Tool) that enables a thorough and independent technical verification of the signature's compliance.
Key takeaways
- Electronic signature guarantees document integrity and signer traceability — something paper cannot offer
- Its legal validity is recognized in Europe (eIDAS) and the United States (eSign Act)
- A simple signature covers the vast majority of everyday professional needs
- The cryptography used is the same as that behind banking payments and online government services
- Verifying a signature is as simple as opening the PDF in Adobe Acrobat Reader
- The entire process takes just a few minutes, with nothing to install on the signer's end