Which of the following security services protects against repudiation?

Security services are the specific protections a system is expected to provide against distinct classes of threats. The standard set (from the ITU-T X.800 model) includes confidentiality, integrity, authentication, access control, availability, and non-repudiation — each one is designed to counter a different kind of attack.

Repudiation is the threat of a party later denying that they carried out an action — for example, denying that they sent a message or authorized a transaction. Non-repudiation is the service built specifically to counter this threat: it attaches undeniable proof of origin and delivery to the action (for instance, via a digital signature or a verifiable log), so neither the sender nor the receiver can later deny that the action took place.

This rules out the other options:

• Access control restricts who is permitted to use a resource or perform an action in the first place; it says nothing about proving, after the fact, that an already-authorized action really happened.

• Authentication verifies an identity claim at the moment of interaction; it does not by itself create lasting proof that the verified party carried out a specific later-disputed action.

• Data integrity confirms that data was not altered in transit or storage; it says nothing about who originated an action or whether they can deny performing it.

Only non-repudiation directly targets the threat of denying that an action occurred, which is why it is the correct service here.