Digital signature: definition, how it works and difference from electronic signature
Many people confuse "digital signature" and "electronic signature". However, the two terms do not refer to the same thing. Here is a clear explanation, without jargon, to understand the difference and choose the right solution.
In brief
A digital signature is a precise cryptographic mechanism (private key + certificate + document fingerprint) that proves the signer''s identity and the document''s integrity. An electronic signature is a broader, legal term that refers to any device allowing a document to be signed in dematerialized form — digital signature is an advanced form of it. In practice, when a site like Certyneo talks about "electronic signature", it is almost always a digital signature in the technical sense.
What is a digital signature?
A digital signature is cryptographic data attached to an electronic document. It is created from the document''s fingerprint (hash) and a private key belonging to the signer. Anyone with the corresponding public key can then verify two things: that the document has not been modified after signing, and that the signature was indeed affixed by the holder of the private key. Digital signature is used in the majority of electronic signature solutions compliant with the eIDAS regulation.
Digital signature vs electronic signature
The two terms are often used interchangeably, but they do not refer to exactly the same thing.
| Criterion | Digital signature | Electronic signature |
|---|---|---|
| Nature | Technical mechanism (cryptography) | Legal concept (eIDAS) |
| Scope | Restricted: a precise method | Broad: any dematerialized signature device |
| Guarantees | Identity + integrity mathematically proven | Variable depending on level (SES, AES, QES) |
| Example | PAdES signature of a PDF with an X.509 certificate | "I accept" checkbox, mouse signature, digital signature with certificate |
| Legal value | Strong (equivalent to handwritten signature at AES/QES level) | Variable depending on the level chosen |
How does a digital signature work?
The 4-step process — simplified.
- 1
Document fingerprint calculation
The document is passed through a hash function (SHA-256). The result is a unique fingerprint of a few bytes that changes radically if a single character of the document is modified.
- 2
Fingerprint encryption with the private key
The fingerprint is encrypted with the signer''s private key, stored on a secure medium (HSM, smart card, or eIDAS-compliant server for remote signature).
- 3
Signature and certificate application
The encrypted fingerprint is attached to the document, accompanied by the signer''s digital certificate (which contains their public key and identity verified by a certification authority).
- 4
Verification by the recipient
The recipient uses the certificate''s public key to decrypt the signed fingerprint, then compares it to the recalculated fingerprint of the document. If the two match, the document is authentic and has not been modified.
When is digital signature used?
- Signing a remote employment contract
- Validation of a compliant electronic invoice
- Signing a dematerialized notarial deed
- Authentication of banking documents
- Signing a remote commercial contract
- Validation of a quote or purchase order
- Signing a lease or real estate contract
- Medical documents and patient consents
Do you want to digitally sign your documents?
Certyneo offers eIDAS-compliant electronic signature (using digital signature under the hood) — free up to 5 envelopes per month, no credit card required.
Frequently asked questions
Digital signature and electronic signature, are they the same thing?
No, but they are closely related. Electronic signature is the legal concept defined by the eIDAS regulation — it designates any dematerialized signature device. Digital signature is the cryptographic technology that makes most compliant electronic signatures possible (notably the AES and QES levels).
Does digital signature have legal value?
Yes, when it is used as part of an advanced electronic signature (AES) or qualified signature (QES) under eIDAS, its legal value is equivalent to that of a handwritten signature. The simple level (SES) — often a checkbox — does not have the same probative force.
How to verify the authenticity of a digital signature?
Most PDF readers (Adobe Acrobat Reader, Foxit) display a signature status when a signed document is opened. You can also use the validation service from the National Agency for Information Systems Security (ANSSI) for European qualified signatures.
Do you need special software to make a digital signature?
No, not for the signer. A platform like Certyneo handles the technical part: certificate generation, fingerprint calculation, cryptographic signature, timestamping. The signer only has to click the "Sign" button in their browser.