John works as a professional Ethical Hacker. He has been assigned the project of testing the to a man-inthe-middle attack since the key exchange process of the cryptographic algorithm it is using…

RSA incorporates digital signatures and certificate-based authentication through PKI, which allows parties to verify each other's identities and prevents a straightforward MITM substitution of keys.

Diffie-Hellman allows two parties to derive a shared secret over an untrusted channel, but the protocol contains no mechanism to verify that the party you are exchanging keys with is who they claim to be. An attacker positioned between the two endpoints can intercept the exchange, substitute their own public key values, and independently complete key exchanges with each party - transparently reading and relaying all traffic. This unauthenticated key exchange is the textbook scenario for a Diffie-Hellman MITM attack.

Twofish is a symmetric block cipher used to encrypt data after a key has already been established; it is not a key exchange protocol and therefore not vulnerable to the MITM key substitution attack described.

Blowfish is a symmetric block cipher used for bulk data encryption, not a key exchange algorithm, so it does not involve the participant authentication gap that enables a man-in-the-middle attack.