Follow the following steps in order to login between the Debian machines without giving the password each time: 

• login to a Linux machine
• issue

ssh-keygen -t rsa

and press Enter until you return to the prompt.

• issue

cp ~/.ssh/id_rsa.pub ~/.ssh/authorized_keys

After this, you will login with ssh without password. First time you login to a host, you will be asked to answer "yes" to connect.