The password requirements for itunes and also app store, mac app store, Apple ID is
Passwords must be at least 8 characters, including a number, an uppercase letter, and a lowercase letter. Don't use spaces, the same character 3 times in a row, your Apple ID, or a password you've used in the last year.
Password requirements rating
Passrequirements.com has given itunes's password requirements strength a 5 out of 5 locks.