A digital signature proves two things: a message came from a specific person (authenticity) and wasn't altered (integrity). It's asymmetric crypto run in reverse.
How it works
Sign: hash the message → encrypt the hash with your PRIVATE key → signature
Verify: decrypt the signature with the sender's PUBLIC key → compare to a fresh hashBecause only you hold your private key, only you could have produced a signature your public key verifies — and because it covers a hash of the content, any tampering breaks it.
Where you rely on it daily
| Use | Signs what |
|---|---|
| HTTPS certificates | CA signs your cert |
| Software updates | Vendor signs the package |
| Git commits / SSH | Prove authorship |
| Documents, crypto | Legal e-signatures, transactions |
| Media provenance | C2PA-signed photos vs deepfakes |
A handwritten signature proves little and is trivial to forge. A digital signature is mathematically bound to both the signer and the exact content.
Related: Public Key Infrastructure · Hashing Explained · Symmetric vs Asymmetric Encryption