Which principle prevents a sender from denying an action?

• A. Authentication
• B. Integrity
• C. Non-repudiation
• D. Authorization

Answer: (C)

Non-repudiation is the guarantee that a sender cannot convincingly deny having sent a message or performed a transaction. This is achieved by binding the action to the sender through cryptographic signatures, certificates, and tamper-evident logs. For example, signing a message with a private key allows others to verify the signature with the sender’s public key, proving both who originated the data and that it hasn’t been altered; timestamps or trusted logs can further show when the action occurred. This combination creates evidence strong enough to deter denial of involvement.

Authentication, by contrast, is about proving identity at the moment of access, not about preventing later denial of an action. Integrity focuses on ensuring the data isn’t changed, but doesn’t link the action to a specific individual. Authorization deals with what a user is allowed to do, not whether they can later repudiate having done it.