Detail the process of key exchange in end-to-end encryption, including the steps and security considerations involved to prevent man-in-the-middle attacks.

Key exchange is a crucial process in end-to-end encryption (E2EE), as it establishes a shared secret key between communicating parties over an insecure channel, which is then used for encrypting the actual message content. The primary goal is to achieve this without exposing the shared secret key to eavesdroppers, especially those who might be conducting a man-in-the-middle (MitM) attack. While there are various methods for key exchange, the Diffie-Hellman (DH) key exchange, and its variants, are most commonly used in modern E2EE systems. Let’s outline a general process and the related security considerations. The traditional DH key exchange can be described with two participants, Alice and Bob. First, both Alice and Bob agree on a publicly known large prime number ‘p’ and a generator ‘g’, often predetermined by the underlying protocol, such as the Signal Protocol. These values are public and can be known by an attacker without impacting security. Next, both generate random private keys; Alice generates a private key ‘a’, and Bob generates a private key ‘b’. These keys are kept secret. Alice computes her public key ‘A’ by raising the generator to the power of her private key mod ‘p’, represented as ‘A = g^a mod p’. Similarly, Bob calculates his public key ‘B’ as ‘B = g^b mod p’. Crucially, both parties use their private key in this calculation. Then they exchange their public keys with each other over the insecure channel. Alice sends her public key ‘A’ to Bob and Bob sends his public key ‘B’ to Alice. Although these keys travel through an unsecure medium where a MitM attacker might int....