Can't back up to my iPhone. Asking for password for the back up file. I don't know it. Options?

i Did the latest update for my iPhone 5 and lost everything. I tried to restore through ITunes a resent back up.

ITunes es keeps asking me for a password to use the restore file. I don't know the password. I don't remember using one. What are my options to get the restore file back on my iPhone?