Digital Signature: Meaning and Verification
A cryptographic mechanism that helps verify signed data and detect changes, distinct from the broader electronic-signature concept.
- A private key signs data; the corresponding public key verifies the signature.
- Digital signatures protect integrity and authenticity, not confidentiality by themselves.
- A digital signature is not automatically an advanced or qualified electronic signature.
What is a digital signature?
A digital signature is a cryptographic result used to verify the origin and integrity of digital data. A private key creates the signature; the corresponding public key verifies it. Changes to the signed data cause verification against that original signature to fail.
NIST's digital-signature definitions distinguish these authenticity and integrity protections from confidentiality. Signing does not, by itself, encrypt a document or hide its contents.
Digital signature versus electronic signature
An electronic signature describes the broader act of signing electronically. A digital signature is a technical mechanism that can support it. A drawn or typed visible signature does not establish that cryptographic signing occurred underneath.
A certificate can connect a public key to an identified person or organization. How much that connection establishes depends on the certificate, identity checks and key protection. A mathematical verification result alone does not establish someone's authority to sign a contract.
Does a digital signature mean AES or QES?
No. EU advanced-signature requirements concern the complete signing process. QES status adds qualified credentials and creation requirements. Neither level follows automatically from the word “digital.”
For a received agreement, keep the original signed file and use the appropriate validation tools. A screenshot of the visible signature does not preserve the cryptographic information needed for that check.
A Common Case: Validating a client’s signed PDF
When a Washington consultancy receives a digitally signed client agreement, its operations team can retain the original PDF and validate the signature with suitable software. A screenshot of the visible mark would leave out the cryptographic information needed for that check.
FAQs
Does a digital signature encrypt the document?
No. Digital signing and encryption serve different purposes; signing alone does not hide the document contents.
Does a valid digital signature prove signing authority?
No. It can support verification of the data and signing key, but authority to act for an organization is a separate question.
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