This document presents semi-formal specifications of the security protocol SSH, more specifically the transport layer protocol, and describes a source code review of OpenSSH, the leading implementation of SSH, using these specifications.
You can download it from the following link: https://packetstormsecurity.com/files/download/159101/ssh-specifications.pdf
Source: https://packetstormsecurity.com/files/159101/Rigorous-Specifications-Of-The-SSH-Transport-Layer.html