On 2021/09/07 14:40, Martijn van Duren wrote:
> On Mon, 2021-08-30 at 10:08 +1000, Damien Miller wrote:
> > Hi,
> > 
> > RSA/SHA1, a.k.a the "ssh-rsa" signature type is now disabled by default
> > in OpenSSH.
> > 
> > While The SSH protocol confusingly uses overlapping names for key and
> > signature algorithms, this does not stop the use of RSA keys and there
> > is no need to regenerate "ssh-rsa" keys - most servers released in the
> > last five years will automatically negotiate the use of RSA/SHA-256/512
> > signatures.
> > 
> > This has been coming for a long time, but I do expect it will be
> > distruptive for some people as there are likely to be some devices
> > out there that cannot be upgraded to support the safer algorithms.
> > 
> > In these cases, it is possible to selectively re-enable RSA/SHA1
> > support by specifying PubkeyAcceptedAlgorithms=+ssh-rsa in the
> > ssh_config(5) or sshd_config(5) for the endpoint.
> > 
> > Please report any problems here, to bugs@ or to openssh@
> > 
> > Thanks,
> > Damien
> > 
> Just did an update to the latest snapshot and this breaks connection
> to one of the older hosts I still need to connect to from time to time.
> 
> Reverting this diff fixes the issue for me.
> 
> According to -G it should work:
> 
> $ ssh -G -oPubkeyAcceptedAlgorithms=ssh-rsa 10.255.3.242 | grep -i 
> PubkeyAcceptedAlgorithms    
> pubkeyacceptedalgorithms ssh-rsa

-oHostKeyAlgorithms=+ssh-rsa

It works, I have disabled ssh-rsa by default for ages and have set that for
various cisco/procurve switches that I need to connect to.

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