Halo Reach GPD Hash / Checksum

        public void FixHash()//game be expe's api xdbf
        {
            System.Security.Cryptography.SHA1 SHA1 = new System.Security.Cryptography.SHA1CryptoServiceProvider();

            Game.xIO_TitleSpecific1.Stream.Position = 0;
            SHA1.TransformBlock(Game.xIO_TitleSpecific1.Reader.ReadBytes((System.Int32)Game.xIO_TitleSpecific1.Stream.Length), 0, (System.Int32)Game.xIO_TitleSpecific1.Stream.Length, new byte[(System.Int32)Game.xIO_TitleSpecific1.Stream.Length], 0);
            Game.xIO_TitleSpecific2.Stream.Position = 0;
            SHA1.TransformBlock(Game.xIO_TitleSpecific2.Reader.ReadBytes((System.Int32)Game.xIO_TitleSpecific2.Stream.Length), 0, (System.Int32)Game.xIO_TitleSpecific2.Stream.Length, new byte[(System.Int32)Game.xIO_TitleSpecific2.Stream.Length], 0);

            Game.xIO_TitleSpecific3.Stream.Position = 744;
            for (int i = 0; i < 20; i++)//write the old hash to 0x99's(153)
            {
                Game.xIO_TitleSpecific3.Writer.Write((System.Byte)153);
            }

            Game.xIO_TitleSpecific3.Stream.Position = 0;
            SHA1.TransformBlock(Game.xIO_TitleSpecific3.Reader.ReadBytes((System.Int32)Game.xIO_TitleSpecific3.Stream.Length), 0, (System.Int32)Game.xIO_TitleSpecific3.Stream.Length, new byte[(System.Int32)Game.xIO_TitleSpecific3.Stream.Length], 0);

            Game.xIO_TitleSpecific3.Stream.Position = 744;
            Game.xIO_TitleSpecific3.Writer.Write(SHA1.Hash);
        }