SES vs AES vs QES: eIDAS Signature Levels Explained

eIDAS Regulation (EU) 910/2014 defines three tiers of electronic signature: Simple (SES), Advanced (AES), and Qualified (QES). They differ in how strongly they bind a signer to a document, and consequently in their legal weight and cost. Most businesses use SES for daily contracts and reserve QES for statutory-form documents. Here's how to tell which one you need.

The three tiers at a glance

Simple Electronic Signature (SES)

SES is the baseline eIDAS tier. The regulation defines it as "data in electronic form which is attached to or logically associated with other data in electronic form and which is used by the signatory to sign" (Article 3(10)). That's deliberately broad — a typed name, a scanned handwritten signature, or a cryptographic PAdES signature all qualify.

Legally, SES cannot be denied admissibility or legal effect solely because it's electronic (Article 25(1)). In practice, courts across the EU treat SES as valid evidence of agreement, weighing it alongside other proof (email correspondence, IP logs, timestamp).

Where SES works well: NDAs, statements of work, consulting and freelance agreements, vendor contracts, purchase orders, quotes, most B2B commercial documents. Anything where both parties are cooperating in good faith and neither is likely to deny they signed.

Where SES falls short: if a signer might later claim "that wasn't me" and there's real money at stake, SES puts the burden of proof on the party asserting the signature. Stronger identity binding — AES or QES — is worth the cost.

Advanced Electronic Signature (AES)

AES adds four requirements over SES (Article 26):

• Uniquely linked to the signatory
• Capable of identifying the signatory
• Created using data the signatory can, with high confidence, use under their sole control
• Any subsequent change to the data is detectable

In practice this means a certificate issued to the individual signer, held in something they alone control (a device or a server-based signing key protected by strong authentication). The signature is cryptographic and tamper-evident.

When to use AES: higher-value B2B contracts, financial agreements, regulated industries (insurance, some banking), HR contracts where signer identity really matters. Some sectors mandate AES minimum via regulation (e.g. some banking / trading confirmations).

Qualified Electronic Signature (QES)

QES is AES plus two extra requirements:

• Created using a qualified signature creation device (QSCD) — typically a smartcard, secure USB token, or a certified remote signing server
• Backed by a qualified certificate issued by a Qualified Trust Service Provider (QTSP) listed on the EU Trust List (EUTL)

Under Article 25(2) of eIDAS, a QES has the equivalent legal effect of a handwritten signature. Under Article 25(3), a QES issued in any member state must be recognised in all others without additional legalisation.

When QES is required: notarial acts, real estate purchase agreements, wills, powers of attorney, some employment contracts with statutory-form requirements, government-facing documents. If a national law says "handwritten signature required," QES is what makes an electronic version equivalent.

Which one do you need?

Start with the question: what does the contract itself, or the law governing it, require?

• No form requirement in law + counterparty cooperative → SES is fine
• Regulated sector or high-value with disputed-identity risk → AES
• Statutory "written form" or "handwritten signature" requirement → QES mandatory

The vast majority of everyday commercial signing — probably 90%+ of contracts a typical business signs — falls in the SES category. QES is expensive and slow (each signer needs a QTSP account and a QSCD), so it's overkill for an NDA or a consulting agreement.

eSeal's tier

eSeal produces SES-tier PAdES B-T signatures: cryptographically embedded in the PDF, RFC 3161-timestamped, verifiable with the ETSI PAdES conformance checker. That's the right tier for standard B2B commercial contracts. AES and QES tiers are planned; for now, if you need those, use a QTSP.

For more on the underlying regulation, see our eIDAS guide. For the PDF signature format specifically, see PAdES explained.