I have a backup of my device stored in iTunes. iTunes created a folder for my device. Now I have *.mddata and *.mdinfo files. The problem is that I accidentally told it to encrypt these files so now they are not viewable. I’m wondering what the best way to decrypt these files is, without losing this encrypted copy.
Why do you need to decrypt the backup? Do you still have the iPod? Do you have the password? If you do a restore from backup it will ask you for the password and it will restore the iPod with the information from the encrypted backup:
This guide has a tip on how to decrypt the backup file. It only works on the Mac though.
If you encrypt an iPhone backup in iTunes and then forget your password, you will not be able to restore iPhone from backup. However, you can continue to do backups and use the device, because you do not need to enter the password for your backup each time you back up or sync.
If you cannot remember the password and want to start again, you will have to do a full software restore. Search in Google with “windowspasswordsrecovery iPhone backup unlocker”, you may get the right and efficient solution.