Is there a good resource for understanding SSL extensions?

[Hubble]

I am trying to understand how the SSL extension length and extensions are set in the server hello packet but can't find a good resource for it. Any help is appreciated.

[Tommy Stallings]

Not sure if this late response will be of any value, but perhaps for future readers it will help. The server builds its hello packet much like the clients - it uses the crypto library it was built with to establish encrypted sessions. If you want to know how the hello packet is constructed, you need to review the crypto library the server uses, and how the server uses that library to ensure it doesn't request specific settings when initializing the SSL-wrapped socket. Servers like Nginx and Apache allow you to choose what extensions and ciphers you want to offer through their config files, but the actual construction of the packet would be handled by the crypto lib.