Which statement defines Non-repudiation?

• A. Verifying the identity of a user or system.
• B. Granting permissions after authentication.
• C. Preventing a sender from denying an action.
• D. Ensuring data is not altered without authorization.

Answer: (C)

Non-repudiation means that once a message is sent or an action is performed, the originator cannot deny having done it. In practice, this is achieved through mechanisms like digital signatures and tamper-evident logs, which bind the sender to the content and make it verifiable by others. The option that describes preventing a sender from denying an action directly captures this idea, because it emphasizes accountability and the ability to prove who performed the action. The other statements refer to authentication (verifying identity), authorization (granting permissions after identity is proven), and data integrity (ensuring data isn’t altered), which are important security concepts but do not define non-repudiation.