Khan Academy The Internet Practice Test 2026 – Your All-in-One Guide to Mastering the Internet!

Public-key digital signatures bind the signer’s identity to a message and provide evidence that the message came from them and hasn’t been altered. You create a signature with your private key, and others verify it with your public key. Because the private key is kept secret, it’s strong evidence that you were the one who signed, so you can’t credibly deny having signed the message later. That ability to prove origin and non-denial is non-repudiation.

Availability isn’t addressed by signatures, which is about keeping a service up and accessible. Confidentiality is about keeping content secret, which signing alone doesn’t do (encryption does that). While signatures do protect integrity—the message must match the signature to verify—non-repudiation is the standout property that digital signatures primarily provide.