Decrypting an ssh session knowing the private key?

[Jeff Sadowski]

I would like to write a program that could deycrypt ssh communication
by using the private key of the server computer. This should be
possable right? And I should be able to use libraries the openssh has
already writen. In fact the majority of the code should already be
writen right? I should just need to send a packet with the private key
to a function right?