Man-in-the-middle attacks are a real threat to what type of communication?

A.
Communication based on random challenge.

B.
Communication based on face to face contact.

C.
Communication based on token.

D.
Communication based on asymmetric encryption.

Explanation:
The weakest point in the communication based on asymmetric encryption is the knowledge about
the real owners of keys. Somebody evil could generate a key pair, give the public key away and tell
everybody, that it belongs to somebody else. Now, everyone believing it will use this key for
encryption, resulting in the evil man being able to read the messages. If he encrypts the messages
again with the public key of the real recipient, he will not be easily recognized. This sort of attack is
called “man-in-the-middle” attack and can only be prevented by making sure, public keys really
belong to the one being designated as owner.