Security/Server Side TLS: Difference between revisions

With Forward Secrecy, if an attacker gets a hold of the server's private key, it will not be able to decrypt past communications. The private key is only used to sign the DH handshake, which does not reveal the pre-master key. Diffie-Hellman ensures that the pre-master keys never leave the client and the server, and cannot be intercepted by a MITM.

When an ephemeral Diffie-Hellman cipher is used, the server and the client negotiate a pre-master key using the Diffie-Hellman algorithm. This algorithm requires that the server sends the client a prime number and a generator. Neither are confidential, and are sent in clear text. However, they must be signed, such that a MITM cannot hijack the handshake.