Advanced Electronic Signature (AES)

What is Advanced Electronic Signature (AES)?

An Advanced Electronic Signature (AES) is defined by the eIDAS Regulation as an electronic signature that meets four specific requirements: it must be uniquely linked to the signatory, it must be capable of identifying the signatory, it must be created using electronic signature creation data that the signatory can use under their sole control, and it must be linked to the data signed in such a way that any subsequent change in the data is detectable.

AES provides a middle ground between simple electronic signatures and qualified electronic signatures. It offers stronger identity assurance and tamper detection than a simple e-signature, without requiring the full qualification process of a QES. This makes it suitable for a wide range of business and legal contexts.

In practice, an AES is typically implemented using digital signature technology — PKI-based cryptographic methods that bind the signer's identity to the document. The signature creation data (usually a private key) must be under the signer's sole control, which can be achieved through hardware tokens, secure mobile apps, or cloud-based signing services with strong authentication.

Many business-to-business contracts, employment agreements, and financial documents use advanced electronic signatures to balance legal assurance with ease of signing. They are widely accepted across the EU, though their precise legal effect in court may depend on how convincingly the four requirements can be demonstrated.