Add a password to an ssh key

If you would like to change the password of an ssh private key, or add a password after the fact.

$ ssh-keygen -p -f id_dsa
Enter old passphrase:
Key has comment 'id_dsa'
Enter new passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved with the new passphrase.
$