Digital signature
Also known as: Ed25519 · cryptographic signature · electronic signature
A digital signature lets anyone verify that a document genuinely comes from its issuer and has not been altered since, without having to trust whoever presents it.
The mechanism rests on a key pair: a private key only the issuer holds, which signs, and a public key anyone can obtain, which verifies. Verifying therefore requires no shared secret.
What gets signed is usually a digest of the document rather than the document itself — a fixed-size fingerprint that changes entirely if a single character moves.
One important and little-seen practice is domain separation: the same key must not be able to sign two different kinds of object, otherwise a signature valid for one could be replayed as valid for the other.
What it means for a small business
For a small business the value is not technical: it is that the customer does not have to take your word for it, and does not have to come back to you to check either.
So what actually applies to you?
A definition tells you what a term means, not what your organization must do. The assessment answers the second question — free, no credit card.
Updated September 1, 2026 · Educational definition; not legal advice.