The following command changes the authentication mechanism for the private key, the passphrase, and not the actual private key. For more information, see the ssh-keygen (1) man page.
Type the ssh-keygen command with the –p option, and answer the prompts.
mySystem$ ssh-keygen -p Enter file which contains the private key (/home/username/.ssh/id_rsa):<Press Return> Enter passphrase (empty for no passphrase): passphrase Enter same passphrase again: passphrase
where –p requests changing the passphrase of a private key file.