[squid-users] sftp through Squid: sftp error with proxy: command-line line 0 bad protocol 2 host key algorithms +ssh-dss

[Roberto Carna]

Dear all, I have an Ubuntu 22.04 with Squid package, and I've
configured it in order to let pass ssh protocol to Internet.

>From the own proxy, if I execute:

$ sftp -v -oConnectTimeout=20 -oPoxyCommand='nc -X connect -x
10.12.1.1:8080 %h %p' -oPort 60000 user at x.x.x.x

I can login successfully.

But if I try to connect with sftp from a host behind the proxy 10.12.1.1:8080:

$ sftp -v -oHostKeyAlgorithms=+ssh-dss -oConnectTimeout=20
-oPoxyCommand='nc -X connect -x 10.12.1.1:8080 %h %p' -oPort 60000
user at x.x.x.x

I get this error:

command-line line 0: Bad protocol 2 host key algorithms '+ssh-dss'.
Couldn't read packet: connection reset by peer.

What can be the cause of this error, trying to use sftp from a host
behind my Squid proxy?

Thanks a lot and regards!!!