oy --- option encrYption 

        default range                                   syntax
           1,$                                            oy[key]
        
        This option allows you to edit encrypted files. oy followed by a key
        will cause e, r, and w, commands to encrypt  and decrypt files using
        crypt(1).  oy will toggle the current  encryption setting.  If there
        is  no current key, se will ask you for one. If encryption is turned
        on, it will be  turned off.   Encryption in indicated by the message
        "ENCRYPT" in the status line. The key is never shown on your screen.

        Type "ho" for help on the option command.
        Type "hdir" to go back to the general help directory.