What characterizes a man-in-the-middle attack?

A man-in-the-middle attack is fundamentally characterized by the interception and relaying of messages between two parties who believe they are communicating directly with each other. In this type of attack, the attacker positions themselves between the two parties, capturing and potentially altering the communications without the knowledge of either party. This ability to intercept messages can lead to unauthorized access to sensitive information, data tampering, or even full control over the session.

The nature of this attack is particularly deceptive because both communicating parties are often unaware that their communications are being monitored or manipulated. This distinguishes it from other types of attacks, such as blocking access to a network, which involves preventing connections rather than silently intercepting and altering data.

Thus, the core characteristic of a man-in-the-middle attack is its ability to facilitate communication interception, making option C the correct answer.