How To Use SSH Keys

Description:

SSH is an encrypted protocol that is often used for remote management in Linux and networking devices. Windows will probably implement SSH natively in the next few years as well.

To Resolve:

1. Generate a keypair on Box1.

   ssh-keygen -t dsa
   

2. Now, you can put the public half of the key pair into the “authorized_keys” file in your account on another box, and after you do so, you’ll use the key to log in, not your password.

   • Your key:

   cat ~/.ssh/id_dsa.pub
   

   • That’s your public key.

   • You can copy it to Box2:

   cat ~/.ssh/id_dsa.pub | ssh you@box2 'cat >> ~/.ssh/authorized_keys'
   

   • You can just copy and paste it from the shell into a text editor like nano.

   ssh Box2  
   password:  
   vi ~/.ssh/authorized_keys
   # Paste in your copied password and save it, then exit the session.
   

   • The next time you ssh into Box2, it won’t ask you for a password at all because it’s using your ssh key pair for authentication:

   ssh Box2  
   you@Box2:~$
   

3. You can use the same key you generated on Box1 to get you into Box3, as well => even if your user account on box3 is under an entirely different name:

   you@box1:~$ cat ~/.ssh/id_dsa.pub | ssh me@box3 'cat >> ~/.ssh/authorized_keys
   me@box3's password:
   you@box1:~$ ssh me@box3
   me@box3:~$
   

4. Add the following to your .ssh/config:

   Host *+*
   ProxyCommand ssh $(echo %h | sed 's/+[^+]*$//;s/([^+%%]*)%%([^+]*)$/2 -l 1/;s/:/ -p /') nc -q0 $(echo %h | sed 's/^.*+//;/:/!s/$/ %p/;s/:/ /')
   
   # It lets you ssh directly along a chain of hosts, for example:
   ssh jumphost1+jumphost2+destination