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Security Fundamentals & Crypto · Foundational

Non-repudiation

Assurance that a party cannot credibly deny having performed an action, such as sending a message or signing a document.

Definition

Non-repudiation binds an action to a specific identity in a way that can be proven to a third party. In cryptography it is provided by digital signatures created with a private key that only the signer controls; audit logs and timestamps support it operationally. Symmetric MACs cannot provide non-repudiation because both parties share the key.

Example

A contract signed with the sender's private key can be verified by anyone with the public key, so the sender cannot deny signing it.

Exam tip

If asked which control provides non-repudiation, choose digital signatures, not hashing, HMAC, or symmetric encryption.

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