You can login with password or with certificates. To generate certificates use these commands and accept all questions with enter:

ssh-keygen -t rsa
ssh-keygen -t dsa

This will generate a public and private certificate pair under ~/.ssh/ 

Now you can authorize a user with the gernated public certificates on other machines. You only need to copy the content from the public certificates to the other remote systems in this file~/.ssh/authorized_keys

For this purpose there is a special ssh tool:

ssh-copy-id -i ~/.ssh/ user@remote-system
ssh-copy-id -i ~/.ssh/ user@remote-system

Without that tool you can do it this way:

cat ~/.ssh/*.pub | ssh user@remote-system 'umask 077; cat >>.ssh/authorized_keys'