iTunes asking a password for encrypted iPad/iPhone Backup you did not set

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Here's my experience when trying to restore a backup to a new iPad. I broke my iPad and needed a new one so I took a Genius Bar appointement. The night before I did a backup on both my Mac and my PC just in case something goes wrong. So the next day, got my new iPad, went home and started the restoration. Suddenly iTunes asked me for a password. I did not set any. Tried on both computers, same thing. I tried every current password I use, none of them worked. Somehow the password happen to be an old 4 unlock screen digits I have used a while ago.

Hopefully my story will help you find your lost password or 4 digits.

Pascal