Advanced Electronic Signature (AES), Simple (SES) and Qualified (QES): the 3 eIDAS Levels

The electronic signature advanced (AES) is the most widely used level in B2B and the only one to offer a legal presumption of integrity without requiring the signatory to use a smart card. Alongside the simple electronic signature (SES) and the qualified electronic signature (QES), it makes up the three levels defined by the European eIDAS regulation. Here's how to choose the right level depending on the nature of your document, its expected evidential value and the level of friction acceptable to the signatory.

What is the advanced electronic signature (AES)?

The advanced electronic signature is the intermediate level defined by Article 26 of the eIDAS regulation. It must meet four cumulative conditions: (1) be uniquely linked to the signatory, (2) enable the signatory to be identified, (3) be created using data that is under the signatory's sole control, (4) enable any subsequent modification to the signed document to be detected. In practice, these conditions are met via strong authentication (email + SMS OTP), a timestamped audit trail and a cryptographic hash of the PDF.

AES benefits from a legal presumption of integrity and origin which reverses the burden of proof before the courts: it is up to the party disputing the signature to prove it is false, not up to the signatory to prove its validity. This is what fundamentally distinguishes AES from SES, where reliability is assessed case by case by the courts.

The three levels defined by eIDAS

The European eIDAS regulation (No. 910/2014) organises electronic signatures into three levels, corresponding to increasing degrees of requirement regarding signatory identification and the strength of the evidence. Understanding these levels properly allows you to choose the right signature for each document, without over-engineering the process.

Level 1: the simple electronic signature (SES)

The simple electronic signature is the basic level. It corresponds to any expression of electronic consent: clicking "I accept", ticking a box, or an initial drawn on a touchscreen.

• Requirements: clear consent, minimal identification (email)
• Evidence: low to moderate, varies depending on the provider
• Use case: quotes, purchase orders, internal agreements, terms and conditions
• Signatory friction: almost none — the signatory does not create an account

SES is sufficient for the vast majority of everyday commercial exchanges where the risk of dispute is low. It remains legally valid, with the courts assessing the reliability of the process on a case-by-case basis.

Level 2: the advanced electronic signature (AES)

The advanced signature strengthens the identification of the signatory and establishes a unique link between them and the document. It rests on four criteria set out in Article 26 of eIDAS:

1. it is uniquely linked to the signatory
2. it enables the signatory to be identified
3. it is created using means that the signatory can, with a high level of confidence, keep under their sole control
4. it is linked to the document in such a way that any subsequent modification can be detected

In practice, AES relies on two-factor authentication: a unique link sent by email + an OTP code received by SMS. The final PDF includes a timestamp and a detailed audit trail.

• Use case: employment contracts, leases, powers of attorney, high-stakes commercial contracts, NDAs
• Signatory friction: low — an SMS code to enter in addition to the email
• Evidence: strong, rebuttable presumption of validity

Level 3: the qualified electronic signature (QES)

The qualified signature is the highest level. It relies on a qualified certificate issued by a qualified trust service provider (QTSP) listed on an EU member state's trusted list, together with a secure signature creation device (e.g. YubiKey, smart card).

• Legal value: equivalent to a handwritten signature throughout the EU
• Use case: notarised deeds, public procurement contracts, certain notarial acts
• Signatory friction: high — face-to-face or video KYC identity verification
• Cost: significantly higher than SES/AES

For most businesses, QES is rarely needed on a day-to-day basis. It becomes essential when required by law (legal proceedings, certain public procurement contracts) or when the contract has exceptionally high value.

Quick comparison table

How to choose the right level

The simple rule: align the level with what's at stake in the document.

• If the document is disputed, what's at stake? A few hundred pounds, or a contract worth tens of thousands?
• Is the relationship with the signatory known (an existing customer) or unknown (first contact)?
• Does the document fall under a legal framework that requires a specific level (e.g. employment contract, lease) ?

As a general rule: SES for simple agreements, AES for anything relating to HR, property, or finance, and QES only when required by law.

Common mistakes

• Systematically choosing QES "to be on the safe side": unnecessary friction for the signatory, high cost, often over-engineered.
• Relying on SES for everything: in the event of a dispute over an employment contract, the lack of strong authentication can weaken the evidence.
• Confusing validation with signature: an acknowledgement of receipt is not a signature.

How Certyneo helps you

Certyneo natively supports the simple (SES) and advanced (AES) levels, with double OTP via email and SMS through Twilio Verify for AES. For cases requiring a QES, Certyneo interfaces with several European qualified providers (Docaposte Certigna, Universign, CertEurope) to trigger a qualified signature without having to change tools.

You can set the signature level document by document depending on what's at stake — or by template if you have industrialised a process.

Discover the Certyneo electronic signature solution

FAQ

Can I mix levels within the same envelope?

Yes. A multi-document envelope can include, for example, a quote signed using SES and a contract signed using AES. Each signatory sees the authentication method suited to the document they need to sign.

Is the advanced signature recognised internationally?

Within the EU, yes, under eIDAS's principle of mutual recognition. Outside the EU, recognition depends on local legal frameworks — this should be checked according to the jurisdiction concerned.

Do you need a personal certificate to sign using AES?

No. AES can be obtained without a prior personal certificate, thanks to the double OTP. This is what makes AES highly accessible, whereas QES requires a qualified certificate.

Is a qualified signature mandatory for an employment contract?

No. Employment contracts can be signed using the advanced electronic signature (AES), which already offers a strong presumption of validity. For more details, see electronic signature of employment contracts.

How can I check the level of a signed document?

Open the PDF in Adobe Acrobat Reader: the signature properties display the level, the signatory and the timestamp. You can also use an online verifier.

Conclusion

Choosing the right level of electronic signature means finding the right balance between evidential value and friction for the signatory. Start simple, and step it up a level when the legal stakes require it.

Try Certyneo to send, sign and track your documents online simply, quickly and securely.