The current Nostr DM (NIP4) integrates four capabilities into a single Nostr key—it serves as an ID, an encryption key, a receiving address, and a sending address.
In Keychat, the ID, encryption key, receiving address, sending address are separated, allowing the encryption key , the receiving and sending addresses to be updated continually. This achieves better encryption security (forward secrecy and backward secrecy) and metadata privacy.