6.5 TLS version 1.2
While we are largely focusing on TLS version 1.3 in this book, it is also instructive to take a look at version 1.2. Firstly, there are still many TLS servers that do not support version 1.3. Secondly, and more importantly, TLS version 1.2 and TLS version 1.3 share the same basic architecture. In particular, the basic steps in the so-called handshake protocol are the same but can be better explained in the context of TLS version 1.2, which is a bit less dense than the TLS version 1.3 handshake.
6.5.1 Subprotocols in TLS version 1.2
TLS version 1.2 consists of several subprotocols. Their location within the internet protocol stack and their relation to each other are shown in Figure 6.4.
Figure 6.4: TLS subprotocols
Handshake protocol: This protocol is invoked when the client and server meet for the first time or if they want to resume an earlier session. In the former case, they need to agree on a set of algorithms that protect the channel between them...