Why ssh client breaks connection in expecting SSH2_MSG_NEWKEYS state?

[Yuri]

On 12/11/2013 02:09, Darren Tucker wrote:
> That's a modified ssh server.  Can you reproduce the problem with a
> stock openssh from openssh.com?

The modification is minor, to port for FreeBSD. It did work with this 
modification on the same system.

>
> You might get some more clues if you run the server in debug mode
> (/path/to/sshd -ddde).

Unfortunately, this didn't give any new clues. No new debug messages 
around the failure.

I also looked at the server system call trace, and the first major 
difference is that in successful case one read(2) call returns 16 bytes, 
and in failed case it returns 0 bytes, which means disconnect.

What are the possible client failure points between the server events 
'expecting SSH2_MSG_NEWKEYS' and 'SSH2_MSG_NEWKEYS received'?

Yuri