There’s a new version of OpenSSH out there recently.
In this new version, 7.0, the installation has deprecated ssh-dss and diffie-hellman-group1-sha1 key exchange method for security enforcement.
So, the best fix if you face issues would be updating your OpenSSH Servers to the most recent versions.
However, if you don’t have access to the servers configuration, there’s a temporary workaround for keep using the legacy implementations.
For the ssh-dss error, create an entry in your ~/.ssh/config with the following content:
Host somehost.example.org PubkeyAcceptedKeyTypes +ssh-dss
And, for the diffie-hellman-group1-sha1 error, the following entry:
Host somehost.example.org KexAlgorithms +diffie-hellman-group1-sha1
You could also add other hosts, followed by comma:
Host somehost.example.org, otherhost.example.org
Or even regular expressions and IP addresses:
Host app*.example.org, *.example.com, 192.168.0.1
That’s all, folks.