Delphi RC4 Encryption Source Code

Post date: Mar 13, 2010 5:21:52 PM

{

Unit: uRC4 // RC4 Encryption

Author: Andreas J”nsson

Original: freevbcode.com/ShowCode.asp?ID=4398

Ported by: steve10120

Website: hackhound.org

}

This unit should be used in place of TheRogue's unit, since there existed a bug in:

Result := Result + ...

because the result was never nulled. This wouldn't be a problem with a byte array - which is used in this unit.

unit uRC4;

interface

uses Windows;

function RC4(Expression, Password:string):string;

type

  TByteArray = array of Byte;

implementation

procedure Move(Destination, Source: Pointer; dLength:Cardinal);

begin

  CopyMemory(Destination, Source, dLength);

end;

function RC4(Expression, Password:string):string;

var

  RB:         array[0..255] of integer;

  X, Y, Z:    LongInt;

  Key:        TByteArray;

  ByteArray:  TByteArray;

  Temp:       Byte;

begin

  if Length(Password) = 0 then

    Exit;

  if Length(Expression) = 0 then

    Exit;

  if Length(Password) > 256 then

  begin

    SetLength(Key, 256);

    Move(@Key[0], @Password[1], 256)

end

  else

  begin

    SetLength(Key, Length(Password));

    Move(@Key[0], @Password[1], Length(Password));

  end;

  for X := 0 to 255 do

    RB[X] := X;

  X := 0;

  Y := 0;

  Z := 0;

  for X := 0 to 255 do

  begin

    Y := (Y + RB[X] + Key[X mod Length(Password)]) mod 256;

    Temp := RB[X];

    RB[X] := RB[Y];

    RB[Y] := Temp;

  end;

  X := 0;

  Y := 0;

  Z := 0;

  SetLength(ByteArray, Length(Expression));

  Move(@ByteArray[0], @Expression[1], Length(Expression));

  for X := 0 to Length(Expression) - 1 do

  begin

    Y := (Y + 1) mod 256;

    Z := (Z + RB[Y]) mod 256;

    Temp := RB[Y];

    RB[Y] := RB[Z];

    RB[Z] := Temp;

    ByteArray[X] := ByteArray[X] xor (RB[(RB[Y] + RB[Z]) mod 256]);

  end;

  SetLength(Result, Length(Expression));

  Move(@Result[1], @ByteArray[0], Length(Expression));

end;

end.