QTDecode is used to decrypt files which have been encrypted with QTEncode. QTDecode uses the same key files used by QTEncode to encrypt a file, to decrypt the file. QTDecode first decrypts the file, computing the message digest as the file is decrypted. It then decrypts the message digest computed and encrypted by QTEncode and compares the two message digests. Since the message digest is unique for every file, if the encrypted message has been changed in any way, the message digest computed by QTDecode will differ from the message digest computed by QTEncode. If the message digests are equal, then the decrypted file must be the same is the file encrypted by QTEncode, and thus the file decrypted by QTDecode has been "verified".