What Is a Digital Signature?

A digital signature uses a private key to produce a value that anyone can verify with the matching public key, proving that the holder of the key signed this exact content and that it has not changed since. It gives three things at once: authenticity, integrity, and non-repudiation — the signer cannot later deny it. It is how a verifiable credential, a signed agent action, or a sealed record proves who stands behind it.

Proves

Authenticity, integrity, non-repudiation

Made with

The signer’s private key

Checked with

The matching public key

Sign the hash, not the document

In practice a signature is computed over a hash of the content, not the content itself: the signer hashes the document and signs the hash, and a verifier re-hashes and checks. That is why a single changed byte breaks the signature — the hash no longer matches — and why signatures and hash functions are always paired.

For agents, the signature is what turns an action into an accountable one: who authorised it is not a claim in a log but a value anyone can verify against a public key held at the actor’s own domain.

Related standards

NIST FIPS 186-5 — Digital Signature Standard

Questions

Is a digital signature the same as an electronic signature?

No. An e-signature can be a typed name or an image; a digital signature is a cryptographic proof tied to a key.

What is non-repudiation?

Because only the private-key holder could have produced the signature, they cannot credibly deny having signed — the property that makes signatures accountable.