Sometimes we have some old servers that should be connected to new clients. Then those clients would require some encryption modes that are not available in the client.

$ ssh luighi@10.10.20.31 -p 22
Unable to negotiate with 10.10.20.31 port 22: no matching host key type found. Their offer: ssh-rsa,ssh-dss

Connecting via ssh client

One way to specify those options are directly in the command line:

$ ssh -o HostKeyAlgorithms=ssh-rsa,ssh-dss -o KexAlgorithms=diffie-hellman-group14-sha1 -p 22 luighi@10.10.20.31

Copying files

To copy files we can use an script that could insert the corresponding options into the rsync tool that is able to synchronize the files.

#!/bin/bash

LOCAL_FOLDER="/mnt/data/project/"
VM_FOLDER="~/project/"
VM_USER="luighi"
VM_HOST=10.10.20.31
VM_PORT=22

rsync -Pav --delete -e "ssh -o HostKeyAlgorithms=ssh-rsa,ssh-dss -o KexAlgorithms=diffie-hellman-group14-sha1 -p ${VM_PORT}" ${VM_USER}@${VM_HOST}:${VM_FOLDER} ${LOCAL_FOLDER}

In the case from the local to the server:

#!/bin/bash

LOCAL_FOLDER="/mnt/data/project/"
VM_FOLDER="~/project/"
VM_USER="luighi"
VM_HOST=10.10.20.31
VM_PORT=22

rsync -Pav -e "ssh -o HostKeyAlgorithms=ssh-rsa,ssh-dss -o KexAlgorithms=diffie-hellman-group14-sha1 -p ${VM_PORT}" ${LOCAL_FOLDER} ${VM_USER}@${VM_HOST}:${VM_FOLDER}

Using with X2Go

Using with X2go however, it rises errors related to the encryption mode:

X2Go key error

To solve it we use the configuration inside the ~/.ssh/config

Host 10.10.20.31
  HostName 10.10.20.31
  User luighi
  HostKeyAlgorithms=ssh-rsa,ssh-dss
  KexAlgorithms=diffie-hellman-group14-sha1
  Port 22

After that we can connect normally via X2Go. We can also connect via the command line just specifying the server host to enable connect to it without any option:

$ ssh 10.10.20.31