SES, AES and QES: choosing the right electronic signature level

The legal framework

eIDAS applies directly in every EU member state and defines the three levels in Article 3. National law adds form requirements. In Germany, for example, where the law requires written form (§ 126 BGB), it can only be replaced electronically by a QES (§ 126a BGB). Other member states have similar rules for specific documents.

The basic rule is simple: check the form requirement first, then assess the risk.

Simple electronic signature (SES)

The SES is the basic level. It includes a scanned signature, a typed name or clicking “Sign” in a signing platform. There are no specific identification requirements, so its evidential value depends on how well the process is recorded – email verification, time stamps and a complete audit trail.

Typical uses are internal approvals, order confirmations, delivery notes, quote acceptances and acknowledgements. For these documents, SES is fast, cost-effective and easy for signatories.

Advanced electronic signature (AES)

Under Article 26 eIDAS, an AES must be uniquely linked to the signatory, capable of identifying them, created using data under their sole control, and linked to the document so that any subsequent change is detectable.

In practice this usually means stronger authentication, such as an SMS code or app approval. AES suits higher-value or higher-risk contracts: service agreements, framework and supply contracts, NDAs and employment documents without a written-form requirement.

Qualified electronic signature (QES)

A QES is an AES based on a qualified certificate and created with a qualified signature creation device. A qualified trust service provider (QTSP) issues the certificate after verifying identity. Under Article 25(2) eIDAS, a QES has the same legal effect as a handwritten signature, and under Article 25(3) it is recognised in all member states.

Signature cards and readers used to be required. Today remote signing is standard: the certificate is held securely by the provider and you approve on your smartphone. Note that some declarations cannot be made electronically under national law – in Germany, for example, guarantees (§ 766 BGB) and the termination of employment (§ 623 BGB).

Common mistakes to avoid

Organisations often default to the highest level for everything. That adds identification effort for external signatories and can lower completion rates without adding legal value for formless documents. The opposite mistake is using a simple signature where national law requires written form – the document may then be formally invalid.

Document the chosen level per document type and review it when laws or processes change.

Choosing in four steps

1. Check form requirements: does a law, statute or contract require written form? Then only QES works – or paper, where electronic form is excluded.

2. Assess risk: how high is the value, how likely is a dispute? The higher the risk, the more AES or QES makes sense.

3. Consider signatories: external customers need a simple flow; experts and managing directors sign frequently and benefit from a one-time QES identification.

4. Set a standard: define a level for each document type and save it as a template to avoid case-by-case decisions.

Frequently asked questions