macbook time machine

I'm trying to go back to find a version of iTunes that has a non-encrypted iPhone back-up. I was not clever when I backed up my iPhone before I factory reset it in order to gift it to my son. Unfortunately i didn't notice that the backup was encrypted. I do not remember adding encryption passwords. I have backed it up every time i have a software update available. I have tried over 100 possible passwords. I have tried to restore iTunes from time machine, but keeps giving error msg:-

"ITunes.app" can't be modified or deleted because it's

required by OS X.

Can anyone advise me?

Thanks