How to stop the event chain?

I've add an event to ckeditor:

CKEDITOR.instances['edit-user-name'].on('instanceReady', function(){
this.document.on('keypress', function(event){
event.cancel();
event.stop();
});
});

As the above, I try to stop the event chain. Unfornately, neither cancel() or stop() can prevent it. I intend to prevent the letter I'm pressing from showing on the screen. How can I do it?

Thanks in advance.