Which scenario best illustrates non-repudiation?

• A. A digital signature proving the origin of a message
• B. A password reset
• C. A backup procedure
• D. A system outage notification

Answer: (A)

Non-repudiation means there is undeniable proof of who sent or created something and that it hasn’t been tampered with. A digital signature attaches to a message a verifiable link to the signer; using the signer’s private key to sign and the public key to verify, anyone can confirm both the origin and the integrity of the message. Because the private key is controlled by the signer, they cannot later deny having sent it, assuming the key remains secure. This is exactly what non-repudiation aims to provide: a reliable, auditable link between the author and the message.

A password reset is about proving identity to change credentials, not establishing a verifiable link between a message and its true sender. A backup procedure focuses on data protection and recovery, not proving who created or sent content. A system outage notification communicates status but does not offer verifiable proof of origin for a message or action.