What does non-repudiation (Verbindlichkeit / Nicht-Abstreitbarkeit) guarantee?

That someone cannot later deny an action — it legally binds an authenticated identity to integrity-checked content.

Non-repudiation creates a provable, legally binding link between who did something (authenticated identity) and what they did (integrity-verified content).

Everyday example: when you order a product in an online shop, the order is binding — you can't later claim "I never ordered that" and refuse to pay once it's delivered.

How it's achieved: digital signatures. Because only the signer holds the private key, only they could have produced the signature — so they can't credibly deny it. (A shared-secret MAC can't do this: either party could have made the tag.)

Tip: Non-repudiation is the top of the integrity ladder — it requires authenticity plus the asymmetry that ties it to one and only one identity.