SSH without password

sometimes it become bored when you need to key in the password each time you want to login to the server by using ssh..so how to login through ssh without a password?

this step need to be once only and it done from client side only:

#ssh-keygen -t rsa

Generating public/private rsa key pair.
Enter file in which to save the key (/root/.ssh/id_rsa):
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /root/.ssh/id_rsa.
Your public key has been saved in /root/.ssh/id_rsa.pub.
The key fingerprint is:
c1:7b:fe:cc:32:9f:51:6b:0d:be:5c:6d:b0:94:b9:fc root@bordersmart

#scp /root/.ssh/id_rsa.pub user@targetserver.com:/root/.ssh/authorized_keys

Now try login to targetserver.com

#ssh targetserver.com

It will not prompt a password. Done. Anyway, try google about DSA vs RSA. There are differents, but it depend how the usage.