conflict in host signature checking

Harald Dunkel harri at
Tue Jun 16 03:17:59 AEST 2020

Hi folks,

AFAICS the recent ssh versions don't support the ssh-rsa signature
algorithm for host keys anymore:

	check_host_cert: certificate signature algorithm ssh-rsa:
	signature algorithm not supported

So I refreshed the host key signatures using	

	ssh-keygen -s ~/.ssh/ca_rsa -t rsa-sha2-256 \
	  -I -h /tmp/

This went well for almost all hosts in my environment, except for an
ancient Solaris 10 host used to checkout and build some very old code
(just in case). The problem on this host is

	% ssh -V
	OpenSSH_6.2p1, OpenSSL 1.0.1r  28 Jan 2016

	% ssh -F /dev/null git
	ssh_rsa_verify: cannot handle type rsa-sha2-256
	cert_parse: Certificate signature verification failed
	key_from_blob: can't parse cert data
	cannot decode server_host_key_blob

	% echo $?

If I put the old signed key back into place on git, then Solaris is
happy, but all other hosts complain as shown above.

Using */bin/ssh -F /dev/null* (i.e. the ancient ssh provided with Solaris10)
there is no problem with an unsupported signature algorithm, so I wonder
if I missed some command line flag to skip the signature verification in
openssh 6.2, as /bin/ssh does? Of course I checked the man page. Please
excuse if I am too blind to see.

Every helpful comment is highly appreciated

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