What does non-repudiation mean?

• A. To prove data was never created.
• B. To ensure data is always available.
• C. Assurance that origin or authorship of a message cannot be denied.
• D. To prevent data from being modified.

Answer: (C)

Non-repudiation means you have verifiable proof that the origin or authorship of a message cannot be denied. In practice, this is achieved with mechanisms like digital signatures: a signer uses a private key to sign a message, and anyone can verify the signature with the signer’s public key. This binding of the signer to the exact content creates evidence that the message came from that signer and hasn’t been altered since it was signed. Auditable logs, timestamps, and trusted authorities (certificates) often accompany signatures to provide a durable trail that can be presented in disputes. This concept is about accountability for who sent or initiated something, not about proving the data was never created, guaranteeing always-available data, or preventing all changes to the data.