# Advanced electronic signature (AES)

> AES under Art. 26 eIDAS: the four requirements, evidential value, typical documents, limits, the SMS code flow and costs at SmartDocs.

Source: https://smartdocs.de/en/advanced-electronic-signature/

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The advanced electronic signature (AES, in German FES) is the middle of the three levels in the eIDAS Regulation. It is uniquely linked to the signer, makes it possible to identify them, is created under their sole control and makes any later change to the document detectable. At SmartDocs, the signer confirms the signature with a six-digit code by SMS, with no app and no account.

## Key facts

- Legal basis: Art. 26 of the eIDAS Regulation (EU) No 910/2014
- Attribution: personal signing link plus a one-time code by SMS
- Written form: AES does not satisfy it; that is what QES is for (§ 126a BGB, German Civil Code)
- At SmartDocs: from the Pro plan, 15 SMS per seat per month included

## The four requirements under Art. 26 eIDAS

1. Uniquely linked: each signer receives their own signing link. The signature belongs to exactly this link and exactly this person.
2. Capable of identifying the signer: name, email address and mobile number are recorded with the signature and appear in the completion certificate, with the number shortened to its last digits.
3. Under sole control: the signature is only completed with the six-digit code that only the signer's mobile phone receives. It is valid for 10 minutes, and a new code invalidates the old one.
4. Changes detectable: the SHA-256 hash of the final document appears in the completion certificate, and every event is part of the audit trail's hash chain.

## Evidential value

No electronic signature may be denied admissibility as evidence solely because it is electronic (Art. 25 (1) eIDAS). A statutory presumption of authenticity exists only for QES (§ 371a ZPO, German Code of Civil Procedure). For AES, the court assesses the evidence freely (§ 286 ZPO). In a dispute, you present the completion certificate, the audit trail with the SMS code confirmation and the signed document, whose hash matches the certificate.

## Documents where AES pays off

| Document | Why AES |
| --- | --- |
| Permanent employment contract | no form requirement, strong need for evidence over many years |
| Residential lease | no form requirement if open-ended; AES proves who entered into the contract |
| Brokerage agreement | for apartments and single-family homes, text form is sufficient (§ 656a BGB); AES additionally secures the commission claim |
| Vehicle purchase contract | large sums and warranty questions |
| Maintenance and framework agreement | ongoing obligations over years |
| Banquet and conference contract | large sums and tiered cancellation fees |
| Amendment with a written form clause | for a contractually agreed written form, electronic transmission is sufficient in case of doubt (§ 127 (2) BGB) |

## Where AES is not enough

- Statutory written form, which requires QES: fixed-term employment contracts (§ 14 (4) TzBfG, Part-Time and Fixed-Term Employment Act), real estate consumer credit agreements (§ 492 BGB), fixed-term residential leases over one year (§ 550 BGB), electronic employment references with the employee's consent (§ 109 (3) GewO).
- Not electronic at all: real estate purchase contracts (§ 311b BGB), wills and inheritance contracts, marriage contracts, GmbH formations and share transfers, terminations of employment and termination agreements (§ 623 BGB).

## How it works in SmartDocs

1. Create a request with AES: upload a document or choose a template, set the level to AES and enter the signer's mobile number.
2. Link by email: the signer opens the document in the browser, with no app and no account, and adds their signature.
3. Complete with the SMS code: SmartDocs sends a six-digit code to the number on file. Once it is entered, the signature is complete and recorded in the audit trail.

## Costs

AES is included from the Pro plan. Pro costs €25 per seat per month with 15 SMS per seat per month included, Enterprise €40 per seat per month with 30 SMS. Each additional SMS costs €0.15. AES is not included in the Free plan. All prices plus VAT, cancel monthly.

Example: a team with 3 seats on the Pro plan (€75) has 45 SMS included. If it has 60 contracts signed with AES in one month, that adds 15 SMS at €0.15 each, so €2.25. Total: €77.25 plus VAT.

More on the [Signature levels](/en/signature-levels/), [Qualified electronic signature](/en/qualified-electronic-signature/) and [Pricing](/en/pricing/) pages.