Here is a list of all related documentation pages:

Data channel key generation	This section describes how OpenVPN peers generate and exchange key material necessary for the security operations performed on data channel packets
OpenVPN's memory management strategies	This section describes several implementation details relating to OpenVPN's memory management strategies
OpenVPN's network protocol	Description of packet structure in OpenVPN's network protocol
Structure of the VPN tunnel state storage	This section describes how OpenVPN stores its VPN tunnel state during operation