var
  s: string;
 //Шифрование
procedure Code(var text: string; password: string;
  decode: boolean);
var
  i, PasswordLength: integer;
  sign: shortint;
begin
  PasswordLength := length(password);
  if PasswordLength = 0 then
    Exit;
  if decode then
    sign := -1
  else
    sign := 1;
  for i := 1 to Length(text) do
    text[i] := chr(ord(text[i]) + sign *
      ord(password[i mod PasswordLength + 1]));
end;
{Пример использования:} 

procedure TForm1.Button1Click(Sender: TObject);
begin
  s := Memo1.Text;
  code(s, Edit1.Text, false);
  Memo1.Text := s;
end;

procedure TForm1.Button2Click(Sender: TObject);
begin
  code(s, Edit1.Text, true);
  Memo1.Text := s;
end;