Authentication: ssh + key

IMPORTANT : please choose a good password

$ ssh-keygen -b 4096
Generating public/private rsa key pair.
Enter file in which to save the key (/home/username/.ssh/id_rsa): 
Created directory '/home/username/.ssh'.
Enter passphrase (empty for no passphrase):           
Enter same passphrase again:                          
Your identification has been saved in /home/username/.ssh/id_rsa.
Your public key has been saved in /home/username/.ssh/id_rsa.pub.
The key fingerprint is:
a8:60:b3:73:aa:ed:7f:bf:88:32:7a:fc:9d:00:1d:1d username@mydesktop
The key's randomart image is:
+--[ RSA 2048]----+
|      E          |
|     . .         |
|    . .          |
|   . . .         |
|  = . . S        |
| . = .           |
| .o +            |
| .=+ +.o         |
|o=+=+.+.o.       |
+-----------------+

cd 
ls -l ~/.ssh/
total 8
-rw------- 1 username group 1743 Feb 19 10:52 id_rsa
-rw-r--r-- 1 username group  404 Feb 19 10:52 id_rsa.pub