Bye-bye Three-way Handshake, and Hello to 0-RTT

And, so, today, OpenSSL 3.5.0 was released, and which supports a range of PQC methods and 0-RTT [here]:

Overall, we have stuck with the 3-way handshake for many decades, and it is now seen as too slow in a modern “always-on, always-connected” world. In a normal Web connection, the client sends a SYN TCP request, the server then replies with a TCP SYN/ACK, and then the client sends back an ACK. This obviously slows down the connection, and where we might close a connection, and want it opened up again in a short interval. In fact, HTTP was meant to be stateless, and where we disconnect after a connection is made. Most browsers overcome this with a keep-alive packet.

But all of this will change with 0-RTT (Zero Round Trip Time) and which is integrated into TLS 1.3. This will allow a client to immediately reconnect without the requirement for the three-way handshake. Basically, it allows data to be sent by a client without…