Note: It is recommended to make a backup of all important files before using the decrypter.
Link to decrypter download page. <- The decrypter will tell you if your files are decryptable, whether you're dealing with an "old" or "new" variant of STOP/Djvu, and whether your ID is online or offline.
Link to instructions for using the decrypter (PDF).
Link to "file pair" submission form.
Link to more information about the decrypter. <- Article at BleepingComputer.co