Which of the following provides the best protection against a man-in-the-middle attack?

A man-in-the-middle attack relies on an attacker intercepting and reading or modifying communications between two parties. Strong encryption, such as TLS, ensures that even if the attacker captures the traffic, they cannot decrypt or alter the payload without the cryptographic keys. This directly neutralizes the core capability the attacker relies on in a MITM attack.

Fiber-optic cable is more difficult to physically tap than copper, but it is not impossible, and does not protect against logical MITM attacks on the network layer.

A firewall controls traffic at network boundaries but does not encrypt data in transit and cannot prevent an attacker who is already positioned between the communicating parties.

A strong password protects authentication credentials but does not protect the confidentiality or integrity of data transmitted over the network during a session.