I want to understand how certificates add to the security of information exchange.
Suppose i have a encrypted bidirectional connection between Alice and Bob, using a public key/private key pair. As long as i confirm by secure channels that the public key actually belongs to the expected end of the tunnel, i have secured the connection from MITM.
What security do certificates bring to the table? In theory i need a certificate from a CA itself in order to be sure that further certificates from this CA are from actually the same CA
Another doubt; its stated also that SSL/TLS supports perfect forward secrecy because IKE happens at regular intervals; i don't understand how this allows perfect forward secrecy at all; it seems that if you save all the packet exchange between two endpoints and you happen to brute-force a send-receive key, this will expose all IKE happening during that session. Probably this could be alleviated by doing IKE over several sessions, that is, exchanging each key under multiple session keys, which means you need to crack more than one key to get to other keys
EDIT i've added a follow up question here.