function Decrypt(Src: string; Key: string): string;

var

  KeyLen, KeyPos, Offset, SrcPos, SrcAsc, TmpSrcAsc: Integer;

  Dest: string;

begin

  KeyLen := Length(Key);

  if KeyLen = 0 then

    Key := cPasswordKey;

  KeyPos := 0;

  Offset := StrToInt('$' + Copy(Src, 1, 2));

  SrcPos := 3;

  while SrcPos < Length(Src) do

  begin

    SrcAsc := StrToInt('$' + Copy(Src, SrcPos, 2));

    if KeyPos < KeyLen then

      KeyPos := KeyPos + 1

     else

      KeyPos := 1;

    TmpSrcAsc := SrcAsc xor Ord(Key[KeyPos]);

    if TmpSrcAsc <= Offset then

      TmpSrcAsc := 255 + TmpSrcAsc - Offset

    else

      TmpSrcAsc := TmpSrcAsc - Offset;

    Dest := Dest + Chr(TmpSrcAsc);

    Offset := SrcAsc;

    SrcPos := SrcPos + 2;

  end;

  Result := Dest;

end;

function Encrypt(Src: string; Key: string): string;

var

  KeyLen, KeyPos, Offset, SrcPos, SrcAsc: Integer;

  Dest: string;

begin

  KeyLen := Length(Key);

  if KeyLen = 0 then

    Key := cPasswordKey;

  KeyPos := 0;

  Randomize;

  Offset := Random(256);

  Dest := Format('%1.2x', [Offset]);

  for SrcPos := 1 to Length(Src) do

  begin

    SrcAsc := (Ord(Src[SrcPos]) + Offset) mod 255;

    if KeyPos < KeyLen then

      KeyPos:= KeyPos + 1

    else

      KeyPos:=1;

    SrcAsc := SrcAsc xor Ord(Key[KeyPos]);

    Dest := Dest + Format('%1.2x', [SrcAsc]);

    Offset := SrcAsc;

  end;

  Result := Dest;

end;