Generate ssh keys

Setting up SSH public/private keys

There are two types of keys in ssh :

a) Public keys &
b) Private keys

RSA & DSA are two most popular public key cryptography algorithm.
RSA was named after the initials of its co-founders, Rivest, Shamir and Adleman.
DSA is Digital Signature Algorithm.

Difference between DSA & RSA :
DSA is faster in signing, but slower in verifying. A DSA key of the same strength as RSA (1024 bits) generates a smaller signature. An RSA 512 bit key has been cracked, but only a 280 DSA key.

Path of Public & Private keys file :
If you are root
Public key file :  /root/.ssh/id_dsa.pub or /root/.ssh/id_rsa.pub
Private key file : /root/.ssh/id_dsa or /root/.ssh/id_rsa

If you are user
Public key file :  /home/user/.ssh/id_dsa.pub or /home/user/.ssh/id_rsa.pub
Private key file : /home/user/.ssh/id_dsa or /home/user/.ssh/id_rsa

Generate Public keys : dsa

# ssh-keygen -t dsa

Generating public/private dsa key pair.
Enter file in which to save the key (/root/.ssh/id_dsa): 
Enter passphrase (empty for no passphrase): 
Enter same passphrase again: 
Your identification has been saved in /root/.ssh/id_dsa.
Your public key has been saved in /root/.ssh/id_dsa.pub.
The key fingerprint is:
c9:a7:51:72:2b:e1:58:be:2a:12:53:41:28:03:e2:3e root@user-To-be-filled-by-O-E-M
The key's randomart image is:
+--[ DSA 1024]----+
|+  o.            |
|= . .            |
| +   .  + o      |
|.   .  * * .     |
| E .  . S o      |
|  +      *       |
|   o    o        |
|  . .  .         |
|   . ..          |

+-----------------+

In your .ssh directory

id_dsa.pub is public key file & id_dsa is private key file.

Generate Public keys : rsa

# 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:
44:ba:dc:d2:e1:f8:27:27:db:c0:e8:e5:21:31:43:2d root@user-To-be-filled-by-O-E-M
The key's randomart image is:
+--[ RSA 2048]----+
|        .        |
|       +         |
|      E +        |
|     o O .       |
|      O S        |
|       O         |
|      o O o      |
|     . + X       |
|      . o .      |
+-----------------+

In your .ssh directory

id_rsa.pub is public key file & id_rsa is private key file

NOTE :
You need either RSA or DSA key. You do not need to generate both.