如何实现下面的md5算法的解密啊

procedure TForm1.Button1Click(Sender: TObject);
var
  MyMD5: TIdHashMessageDigest5;
  Digest: T4x4LongWordRecord;
begin
  MyMD5 := TIdHashMessageDigest5.Create;
  Digest := MyMD5.HashValue('');
  ShowMessage('32: ' + MyMD5.AsHex(Digest));  //显示32个字符长度的MD5签名结果
  ShowMessage('16: ' + Copy(MyMD5.AsHex(Digest), 9, 16));   //显示16个字符长度的MD5签名结果
end;