uRC4.pas

unit uRC4;

interface

uses
  SysUtils;

type
  RC4 = class
  protected
  private
  public
    class function Encrypt(Key, Text: string): string;
    class function Decrypt(Key, Text: string): string;
  end;

implementation

{ RC4 }

class function RC4.Encrypt(Key, Text: string): string;
var
  i, j, x, y: Integer;
  s: array[0..255] of Integer;
  charCode: Integer;
  ct: string;
  ctInt: Integer;
begin
  for i := 0 to 255 do
  begin
    s[i] := i;
  end;

  j := 0;

  for i := 0 to 255 do
  begin
    charCode := Ord(Char(Key[(i mod Length(Key)) + 1]));
    j := (j + s[i] + charCode) mod 256;

    x := s[i];
    s[i] := s[j];
    s[j] := x;
  end;

  // Reset variables
  i := 0;
  j := 0;

  ct := '';

  for y := 0 to (Length(Text) - 1) do
  begin
    i := (i + 1) mod 256;
    j := (j + s[i]) mod 256;
    x := s[i];

    s[i] := s[j];
    s[j] := x;

    ctInt := Ord(Char(Text[y + 1])) xor (s[((s[i] + s[j]) mod 256)]);

    ct := concat(ct, IntToHex(ctInt, 2));
  end;

  Result := UpperCase(ct);
end;

class function RC4.Decrypt(Key, Text: string): string;
var
  c, i, j, x, y: Integer;
  s: array[0..255] of Integer;
  copyText: string;
  charCode: Integer;
  ct: string;
begin
  for i := 0 to 255 do
  begin
    s[i] := i;
  end;

  j := 0;

  for i := 0 to 255 do
  begin
    charCode := Ord(Char(Key[(i mod Length(Key)) + 1]));
    j := (j + s[i] + charCode) mod 256;

    x := s[i];
    s[i] := s[j];
    s[j] := x;
  end;

  // Reset variables
  i := 0;
  j := 0;

  ct := '';

  if (0 = (Length(Text) and 1)) and (Length(Text) > 0) then
  begin
    c := 0;
    y := 0;

    while y < (Length(Text)) do
    begin
      i := (i + 1) mod 256;
      j := (j + s[i]) mod 256;
      x := s[i];

      s[i] := s[j];
      s[j] := x;

      copyText := Copy(Text, c, 2);

      // Convert previous text
      charCode := StrToInt('$' + copyText) xor (s[((s[i] + s[j]) mod 256)]);

      ct := concat(ct, string(Chr(charCode)));

      // Increasing loop counter
      y := y + 2;
      // Increasing copy counter
      c := y + 1;
    end;
  end;

  Result := ct;
end;

end.