SES vs AES: what’s the difference?
The EU’s eIDAS regulation recognises several tiers of electronic signature, each with its own requirements and evidentiary weight. The two that everyday business runs on are the Simple Electronic Signature (SES) and the Advanced Electronic Signature (AES). Here is how they differ, what each is good for, and what the law says.
What is a Simple Electronic Signature (SES)?
An SES is the broadest category: any data in electronic form that is attached to, or logically associated with, other electronic data and used by the signer to sign. A typed name under an email, a drawn signature on a screen, or a click on an “I agree” button can all qualify.
An SES is quick and frictionless, which makes it well suited to low-risk agreements: internal sign-offs, consents, acknowledgements, and everyday paperwork where the parties already trust each other. Its limitation is evidentiary: an SES does not by itself prove who signed or that the document is unchanged.
What is an Advanced Electronic Signature (AES)?
An AES must meet four requirements set out in eIDAS. It must be:
- uniquely linked to the signer,
- capable of identifying the signer,
- created using electronic signature creation data that the signer can, with a high level of confidence, use under their sole control, and
- linked to the signed data so that any subsequent change is detectable.
In practice this means the signer verifies their identity with an electronic ID - on Kaddye, MitID or MitID Erhverv - and the signature is cryptographically bound to the document’s contents. Alter so much as a character afterwards and the signature breaks, exposing the change. This makes an AES suitable for higher-value contracts and most everyday business documents.
Side by side
| SES | AES | |
|---|---|---|
| How you sign | Draw, type, or upload a signature | Verify identity with MitID / MitID Erhverv |
| Proves who signed | Not by itself | Yes - uniquely linked to the signer |
| Tamper-evident | Not required | Yes - any change breaks the signature |
| Legally binding in the EU | Yes (eIDAS) | Yes, with stronger evidentiary weight |
| Typical use | Consents, low-risk agreements | Contracts, leases, employment, B2B |
Frequently asked questions
Is an SES legally binding?
Yes. Under eIDAS, an electronic signature cannot be denied legal effect solely because it is electronic. An SES is admissible as evidence in EU courts; it simply carries less evidentiary weight than an AES because it does not by itself prove who signed.
When should I use an AES instead of an SES?
Use an AES whenever it matters that you can prove who signed and that the document was not changed afterwards: employment contracts, supplier and customer agreements, loans, leases, and board documents. Use an SES for low-risk, everyday consents where convenience matters more than evidentiary weight.
What is a QES, and do I need one?
A Qualified Electronic Signature (QES) is the third eIDAS tier: an AES created with a qualified signature-creation device and a qualified certificate. It is legally equivalent to a handwritten signature across the EU, but most everyday business documents do not require it - an AES is sufficient for the vast majority of B2B agreements.
How do I create an AES with Kaddye?
Signers verify their identity with MitID or MitID Erhverv (Denmark). Kaddye then seals the document with a qualified certificate from a trust service provider on the EU Trusted Lists using the PAdES standard, with PAdES-LTA archive timestamps for long-term validity.
Sign with SES and AES on every Kaddye plan
Kaddye includes both signature types on every plan - no tier upgrades, no per-envelope surcharges. Pay per document from 30 kr., or 130 kr./month for unlimited sending. See pricing or get started.