If you already know (or recovered) the password to iPhone/iPad/iPod or BlackBerry backup, EPPB can decrypt it, so you will be able to open [decrypted] backup file in some other software (for BlackBerry backups, we recommend to use Elcomsoft Blackberry Backup Explorer; for Apple devices, there is a lot more compatible software). It is strictly NOT recommended to restore your device from the decrypted backup, though.
Select [File] | [Decrypt Backup...] menu item, browse for backup file (both iPhone and BlackBerry backups are listed there), and supply the password when prompted.
Please note that there are two types of BlackBerry backups: *.ipd and *.bbb files. In fact, *.bbb file is a plain ZIP archive with *.ipb file inside. EPPB can work with both of them, but when you decrypt the *.bbb file, decrypted file can be saved only as *.ipd. However, only BlackBerry smartphones backups can be decrypted; backups made from PlayBook devices have different format and are not supported yet, so EPPB can only recover the passwords for such files, but cannot decrypt them.
For iPhone backups, you will also need to select the folder to put decrypted files, because iPhone backup is not a single file, but may contain hundreds or even thousands of files. This folder should be empty. During decryption process, the program shows the files that are being decrypted:
