Passless ssh

First log in on A as user a and generate a pair of authentication keys. Do not enter a passphrase:

a@A:~> ssh-keygen -t rsa

Finally append a's new public key to b@B:.ssh/authorized_keys and enter b's password one last 

time:

a@A:~> cat .ssh/id_rsa.pub | ssh b@B 'cat >> .ssh/authorized_keys'
b@B's password: 

From now on you can log into B as b from A as a without password.

http://www.linuxproblem.org/art_9.html