[SOLVED] XOREncode and XORDecode files using TFileStream

[Gizmo]

Hi

Am trying to write a simple XOREncode and XORDecode of files, using FileStreams.

The following almost works, in that it compiles and the XOREncode seems to work (the output looks like a valid XOR'd text file). But the decode fails to successfully decode.

When I run through it with the debugger, the variable XORData seems to jump between legible decoded text first pass, illegible second pass, legible third pass, illegible forth pass, and so on. I can't see where I am going wrong? Can anyone direct me? I am suspecting it has something to do with unprintable characters, but given that I am feeding the program text files, I'm not sure why this would be happening.

Thanks

Code: Pascal  [Select][+][-]

1. // Encode a plain text file
2. procedure TForm1.btnInputFileClick(Sender: TObject);
3. var
4.   FileToEncode : string;
5.   OutputFile   : string;
6.   Key          : string;
7.   XORData      : string;
8.   fIn, fOut    : TFileStream;
9.   Buffer       : array [0..65534] of char;
10.   TotalBytesRead : Int64;
11.   BinaryBytesRead : integer;
12. begin
13.   TotalBytesRead := 0;
14.   BinaryBytesRead := 0;
15.   Label2.Caption:= ' Encoding...';
16.   Key := ledtPasswordFile.Text;  // takes the password key from the user input field
17.   FillChar(Buffer,SizeOf(Buffer),0);
18.  
19.   if odInputFile.Execute then
20.   begin
21.   // Get inputfile
22.   FileToEncode := odInputFile.FileName;
23.   // Get output file
24.   if sdOutFile.Execute then
25.     begin
26.     OutputFile := sdOutFile.FileName;
27.     // Read input file in buffers
28.       try
29.         fIn := TFileStream.Create(FileToEncode, fmOpenRead);
30.         fIn.Position := 0;
31.         try
32.           // Encode and write out Output file in buffers
33.           fOut := TFileStream.create(OutputFile, fmCreate);
34.           fOut.Position := 0;
35.           while (TotalBytesRead < fIn.Size) do
36.             begin
37.               BinaryBytesRead := fIn.Read(Buffer[0], SizeOf(Buffer));
38.               if BinaryBytesRead > -1 then
39.                 begin
40.                   XORData := XorEncode(Key, Buffer);
41.                   fOut.Write(XORData[1], Length(XORData));
42.                 end;
43.               inc(TotalBytesRead, BinaryBytesRead);
44.             end;
45.         finally
46.           fOut.Free;
47.         end;
48.       finally
49.         fIn.Free;
50.       end;
51.     end;
52.   end;
53.   Label2.Caption:= ' Finished.';
54. end;
55.  
56. // Decode an XOREncoded file
57. procedure TForm1.btnDecodeFileClick(Sender: TObject);
58. var
59.   FileToDecode : string;
60.   OutputFile   : string;
61.   Key          : string;
62.   XORData      : string;
63.   fIn, fOut    : TFileStream;
64.   Buffer       : array [0..65534] of char;
65.   TotalBytesRead : Int64;
66.   BinaryBytesRead : integer;
67. begin
68.   TotalBytesRead := 0;
69.   BinaryBytesRead := 0;
70.   Label2.Caption:= ' Decoding...';
71.   Key := ledtPasswordFile.Text;   // takes the password key from the user input field
72.   FillChar(Buffer,SizeOf(Buffer),0);
73.  
74.   if odInputFile.Execute then
75.   begin
76.   // Get inputfile
77.   FileToDecode := odInputFile.FileName;
78.   // Get output file
79.   if sdOutFile.Execute then
80.     begin
81.     OutputFile := sdOutFile.FileName;
82.     // Read input file in buffers
83.       try
84.         fIn := TFileStream.Create(FileToDecode, fmOpenRead);
85.         fIn.Position := 0;
86.         try
87.           // Encode and write out Output file in buffers
88.           fOut := TFileStream.create(OutputFile, fmCreate);
89.           fOut.Position := 0;
90.           while (TotalBytesRead < fIn.Size) do
91.             begin
92.               BinaryBytesRead := fIn.Read(Buffer[0], SizeOf(Buffer));
93.               if BinaryBytesRead > -1 then
94.                 begin
95.                   XORData := XorDecode(Key, Buffer);
96.                   fOut.Write(XORData[1], Length(XORData));
97.                 end;
98.               inc(TotalBytesRead, BinaryBytesRead);
99.             end;
100.         finally
101.           fOut.Free;
102.         end;
103.       finally
104.         fIn.Free;
105.       end;
106.     end;
107.   end;
108.   Label2.Caption:= ' Finished.';
109. end;
110.  

[Thaddy]

That is terribly over-complex code.
Try string.ToCharArray, then do xor on the array. (sysutils)
If you can not figure it out, I will post a small example (less than 20 lines)

[Gizmo]

I can't use ToCharArray with the Buffer I have as its an array of char and not a string. If I change buffer to type string, then I'm not sure how I can use FileStream.Read when the size will not be known? FS.ReadAnsiString might be btter but then what about non-ASCII chars?

Your example might be helpful if you have the time to share? I'd appreciate it.   

UPDATE : Resolved with following code (assumes the input files are not too big and small enough for memory I accept but gets over the streaming difficulty and it works). If anyone has a stream method that will work, I'd still welcome the example.

Code: Pascal  [Select][+][-]

1. procedure TForm1.btnInputFileClick(Sender: TObject);
2. var
3.   FileToEncode, OutputFile, Key, XORData, Buffer : string;
4.   fIn, fOut    : TFileStream;
5. begin
6.   Label2.Caption := ' Encoding...';
7.   Key            := ledtPasswordFile.Text;
8.   Buffer         := '';
9.  
10.   if odInputFile.Execute then
11.   begin
12.   // Get inputfile
13.   FileToEncode := odInputFile.FileName;
14.   // Get output file
15.   if sdOutFile.Execute then
16.     begin
17.     OutputFile := sdOutFile.FileName;
18.     // Read input file in buffers
19.       try
20.         fIn := TFileStream.Create(FileToEncode, fmOpenRead);
21.         fIn.Position := 0;
22.         try
23.           // Encode and write out Output file in buffers
24.           fOut := TFileStream.create(OutputFile, fmCreate);
25.           fOut.Position := 0;
26.           try
27.             SetLength(Buffer, fIn.Size);
28.             fIn.Read(Buffer[1], fIn.Size);
29.             XORData := XorEncode(Key, Buffer);
30.             fOut.Write(XORData[1], Length(XORData));
31.           finally
32.           end;
33.         finally
34.          fOut.free;
35.         end;
36.       finally
37.         fIn.Free;
38.       end;
39.     end;
40.   end;
41.   Label2.Caption:= ' Finished.';
42. end;
43.  
44. procedure TForm1.btnDecodeFileClick(Sender: TObject);
45. var
46.   FileToDecode, OutputFile, Key, XORData, Buffer : string;
47.   fIn, fOut    : TFileStream;
48. begin
49.   Label2.Caption := ' Decoding...';
50.   Key            := ledtPasswordFile.Text;
51.   Buffer         := '';
52.  
53.   if odInputFile.Execute then
54.   begin
55.   // Get inputfile
56.   FileToDecode := odInputFile.FileName;
57.   // Get output file
58.   if sdOutFile.Execute then
59.     begin
60.     OutputFile := sdOutFile.FileName;
61.     // Read input file in buffers
62.       try
63.         fIn := TFileStream.Create(FileToDecode, fmOpenRead);
64.         fIn.Position := 0;
65.         try
66.           // Encode and write out Output file in buffers
67.           fOut := TFileStream.create(OutputFile, fmCreate);
68.           fOut.Position := 0;
69.           try
70.             SetLength(Buffer, fIn.Size);
71.             fIn.Read(Buffer[1], fIn.Size);
72.             XORData := XorDecode(Key, Buffer);
73.             fOut.Write(XORData[1], Length(XORData));
74.           finally
75.           end;
76.         finally
77.          fOut.free;
78.         end;
79.       finally
80.         fIn.Free;
81.       end;
82.     end;
83.   end;
84.   Label2.Caption:= ' Finished.';
85. end;
86.                  
87.