Bumped against similar issues with ssh servers (also dropbear) and the problem turned out to be a "lack of entropy".

It takes the ssh server up to several minutes to initialize on an embedded system, because there's no source of randomness and /dev/random just blocks.

When you connect to such a system with SSH, everything is fine, no errors, but the connection won't show any activity for a long time.


You can speed it up by writing some random strings to /dev/random.

A quick workaround is to just add "haveged" to your image. That creates an entropy source based on CPU characteristics, which is questionable from a security point of view. A secure workaround would be to have an actual hardware random number generator on board somewhere.

--
M.



Met vriendelijke groet / kind regards,

Mike Looijmans
System Expert


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