Non-repudiation is a security property that providesverifiable evidenceof an action or communication so that the parties involved cannot credibly deny their participation later. In web security, it most commonly means being able to provewho sent a message or performed a transactionand, in many cases, that the message was received and recorded. This is why option D is correct: it captures the idea of giving the receiver proof of the sender’s identity and giving the sender evidence that the message or transaction was delivered or accepted.
Cybersecurity guidance typically associates non-repudiation withdigital signatures, strong identity binding, and protected audit evidence. A digital signature uses asymmetric cryptography so that only the holder of a private key can sign, while anyone with the public key can verify the signature. When combined with trusted certificates, accurate time sources, and protected logs, this creates strong accountability. Non-repudiation also depends on maintaining the integrity of supporting evidence, such as tamper-resistant audit logs, secure log retention, and controlled access to signing keys.
It is different from confidentiality (encryption of traffic), and different from integrity alone (preventing unauthorized modification). It is also different from authorization and auditing, which support accountability but do not, by themselves, provide cryptographic-grade proof that a specific entity performed a specific action. Non-repudiation is especially important for high-trust transactions such as approvals, payments, and legally binding communications.
