my question from stackoverflow: http://stackoverflow.com/questions/11374592/why-do-we-need-diffie-hellman
Diffie–Hellman offers secure key exchange only if sides are authenticated. for authentication, sides are using public/private key. so if side A knows the public key of the side B, then A can simply use that key to encrypt the message (or the new session key). why bother to use separate key exchange algorithm?