What is the term for the concept that a message or piece of information is genuine?

The term that signifies a message or piece of information is genuine is best captured by the concept of authentication. Authentication refers to the process of verifying the identity of a user, device, or entity, ensuring that the parties involved in communication are who they claim to be. This notion is crucial in cybersecurity, as it establishes trust in digital transactions and communications.

Nonrepudiation, while closely related, specifically involves the assurance that someone cannot deny the validity of their actions. It ensures that a sender of a message cannot later claim they did not send it, but it does not directly imply that the message itself is genuine.

Integrity involves the protection of information from being altered in an unauthorized manner. It ensures that data remains accurate and trustworthy throughout its lifecycle. However, it does not explicitly address the authenticity or the source of the information.

Verification, similarly, asserts that something is true or real, but it is often used in contexts such as checking the accuracy of data or results, rather than affirming the authenticity of the information's origin.

Thus, while nonrepudiation does connect to the legitimacy of a transaction, authentication is the more fitting term when specifically considering the genuineness of a message or information.