Navicat client can’t connect to the MySQL server via SSH tunnel. This happens on the Navicat 8. Possible it’s true for all old versions.

Error: Server does not support diffie-hellman-group1-sha1 for keyexchange.

Add new algorithms to config file /etc/ssh/sshd_config.

KexAlgorithms diffie-hellman-group1-sha1,curve25519-sha256@libssh.org,ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group-exchange-sha256,diffie-hellman-group14-sha1
Ciphers 3des-cbc,blowfish-cbc,aes128-cbc,aes128-ctr,aes256-ctr

Rebuild all keys by command:

ssh-keygen -A

Restart SSH service by command:

service ssh restart

Profit. I recommend to use the latest Navicat version.