Check ssh public key
dennis@lightning:~$ ssh-keygen -l -f .ssh/id_rsa.pub 2048 68:df:b2:22:d8:43:5d:36:75:c1:d8:59:c0:8c:22:e8 Dennis Kaarsemaker (RSA) dennis@lightning:~$ ssh-keygen -l -f foo.txt foo.txt is not a public key file.