From: "Filsinger, Andreas (Softwareentwicklung)" <andreas@filsinger.de>
To: "Filsinger, Andreas (Softwareentwicklung)" <andreas@filsinger.de>; <efg2@efg2.com>
Subject: Re: Computer Lab Feedback, "Image Encryption"
Date: Saturday, December 01, 2001 18:55

Earl,

sorry, but take "Rev 1.001":
------------------------------------------------------------------------


var
 BMPScrambleSeed: integer;

procedure BMPScramble(const b: TBitMap; Key: integer);

//
// (c)'01 by http://www.efg2.com/Lab
//
// scrambles (encrypt) a bitmap before you save it to
// disk (for example) or before post it to a database-field.
// Scramble it again before you want to view it.
// Ensure to use the same key-value, for each pic, but
// different key-values for different pictures.
//
//
// Rev. 1.001 (2001-12-02) Andreas Filsinger, www.cargobay.de
//            new: "global" var "BMPScrambleSeed"
//            fix: NextModulu Bug
// Rev. 1.000 (2001-12-02) Andreas Filsinger, www.cargobay.de
//            info: This is my delphi 6.01 Version: There where two reasons
//            because i rewrite the code.
//             1) In the Delphi Help there is a hint, that you should NOT
//                use "random" to encrypt data, because implementations may
//                change in future releases.
//             2) after "dormat" i accessed the Rows: That caused an Exception
//            new: only one ScanLine[n]
//            new: NO random()-call
//

var
  i, j: integer;
  Row: PWordArray;
  ScanlineBytes: integer;
  _ScanlineOp: word;

  function NextModulu : word;
  asm
   PUSH    EBX
   XOR     EBX, EBX
   MOV     EAX,10000H
   IMUL    EDX,[EBX].BMPScrambleSeed,08088405H
   INC     EDX
   MOV     [EBX].BMPScrambleSeed,EDX
   MUL     EDX
   MOV     EAX,EDX
   POP     EBX
  end;

begin
  BMPScrambleSeed := Key;
  with b do
  begin
    // Ensure, this is a device independent Bitmap
    HandleType := bmDIB;
    // Get the Adress of the first Pixel-Data-Row
    Row := ScanLine[0];
    // Obtain Lenght of one ROW
    ScanlineBytes := Integer(ScanLine[1]) - Integer(Row);
    // Obtain Lenght of one, ignore direction, "Count of words" is OK
    _ScanlineOp := abs(ScanlineBytes) div 2;
    // for each line
    for j := 0 to pred(Height) do
    begin
      // for each pixel-data-word
      for i := 0 to pred(_ScanlineOp) do
       Row[i] := Row[i] xor NextModulu;
      // theres no need to call ScanLine[] again
      inc(Integer(Row), ScanlineBytes);
    end;
  end;
end;



...


  -----------------------------------------------------------------
  Thanks.
  Andreas Filsinger
   _______________________________________________________
  / Tel. +49 7251 966100        | Andreas Filsinger       \
  | Mob. +49 175 5913758        | Softwareentwicklung     |
  | Fax. +49 7251 966101        | Stettfelder Strasse 44  |
  | mailto:Andreas@Filsinger.de | 76698 Ubstadt           |
  | http://www.CargoBay.de      | GERMANY                 |
  \_______________________________________________________/