Point of Diffie-Hellman key exchange when public keys are known Since the basic version of Diffie-Hellman key exchange protocol is vulnerable to Man In The Middle Attack, some sort of authentication is needed. It was mentioned that RSA digital signature can be used to handle this case. However, I don't understand that if the public keys of the two parties are known to each other, what would be the point of using DH at all? One of them can just propose a shared key k, compute its hash value and send the (k, h(k)) encrypted with the other one's public key. I appreciate if anyone can clarify the benefit of using DH in case of known public keys.
Diffie-Hellman allows for forward secrecy. In the protocol you describe, if the private key is ever leaked all previously exchanged keys are leaked.

If we only use RSA to authenticate keys created with Diffie-Hellman, past keys are safe even if you lose control over your private key in the future.