SSH – How to Change a SSH Host Key on Debian

It's impossible that ssh-keygen would interpret a key as the wrong type, since the type is encoded in two places of the file; also RSA and DSA keys use different internal structures, so you would get an error message.

• It could be that there is a ssh_host_dsa_key and you're just missing its .pub counterpart.

• It could be that sshd is configured to look for keys elsewhere. Check sshd_config:

  grep -i ^hostkey /etc/ssh/sshd_config
  

• ...or that someone removed the DSA key file but didn't restart sshd.

• It could be that the server is using a different SSH daemon, not OpenSSH.

• As a last resort, you can use ssh-keyscan -t dsa localhost > hostkey-dsa.pub and run ssh-keygen -lf on the output file.

1. get the rsa key of your server, where server_ip is your server's IP address, such as 192.168.2.1:

   $ ssh-keyscan -t rsa server_ip
   

   Sample response:

   # server_ip SSH-2.0-OpenSSH_4.3
   server_ip ssh-rsa AAAAB3NzaC1yc2EAAAABIwAAAQEAwH5EXZG...
   

2. and on the client, copy the entire response line server_ip ssh-rsa AAAAB3NzaC1yc2EAAAABIwAAAQEAwH5EXZG..., and add this key to the bottom of your ~/.ssh/known_hosts file:

   server_ip ssh-rsa AAAAB3NzaC1yc2EAAAABIwAAAQEAqx9m529...(the offending key, and/or the very bottom of the `known_hosts` file)
   server_ip ssh-rsa AAAAB3NzaC1yc2EAAAABIwAAAQEAwH5EXZG... (line you're adding, copied and pasted from above)