The guarantee that a sender cannot later deny having sent a message is…

Concept: Network and information security is commonly described through a set of goals: confidentiality (keeping data private), integrity (keeping data unaltered), authentication (verifying identity), availability (ensuring access), and non-repudiation — the guarantee that a party cannot later deny having sent or received a communication, usually enforced through digital signatures or other proof-of-origin mechanisms.

Application: The stem describes exactly this guarantee: once the sender has transmitted a message, the sender must not be able to deny, at a later date, having sent it. This matches the definition of Non-Repudiability, confirmed by NIST’s security glossary and IETF RFC 4949, both of which define non-repudiation as protection against a party falsely denying having sent or received data.

Cross-check: Contrasting with the other options confirms the choice:

• Authenticity verifies that a message or its sender is genuinely who or what it claims to be at the time of communication — it does not by itself stop a later denial.

• Auditability is the broader ability to record and trace system actions for review, not specifically a proof-of-origin guarantee against denial.

• Repudiability is the inverse notion — the ability of a party to deny an action — the opposite of what the stem describes.

So the property described in the stem is Non-Repudiability.