I forget my login password ! but i don't...

This is a user-to-user technical support forum, you are not talking to Apple.

It sounds like your backup is encrypted; you will have to enter the encryption password that you used when you first checked "Encrypt backup" in iTunes. That password never changes, even if you make later backups; they are all encrypted with the same password. So start guessing; it's a password that you have used in the past most likely. To save time uncheck "Encrypt backup" in iTunes and you will be prompted immediately.

Note also that if your phone has a company MS Exchange email account on it your IT department may have forced the backup to be encrypted. If this is a possibility try your domain passwords from the past.

There is one other thing to try: Sometimes iTunes "thinks" a backup is encrypted when it really isn't. So if the box is not checked in iTunes try rebooting your computer.

Connect the phone to your computer. Click on its icon in iTunes. You will find the checkbox displayed on the screen.