解决php中字符串输出一样但比较不相等（编码不同导致长度不一样）

问题：在phpstorm中用AES产生的一段加密代码，发现解密的过程中字符串的长度和编码方式都不一样了。代码如下：

header("Content-type:text/html;charset=utf-8");
$secret1 = "rZa9GneIzd9MNyoTv/Ghpk2V6ZHD0KeQC7t0ymEH7cI=";
$secret2 = 'rZa9GneIzd9MNyoTv/Ghpk2V6ZHD0KeQC7t0ymEH7cI=';
$secret3 = 'rZa9GneIzd9MNyoTv/Ghpk2V6ZHD0KeQC7t0ymEH7cI=';

var_dump(trim($secret1));
echo "
";
var_dump(trim($secret2));
echo "
";
var_dump($secret3);
echo "
";
echo mb_detect_encoding($secret1, array("ASCII", "UTF-8", "GB2312", "GBK", "BIG5"));
echo "
";
echo mb_detect_encoding($secret2, array("ASCII", "UTF-8", "GB2312", "GBK", "BIG5"));
echo "
";
echo mb_detect_encoding($secret3, array("ASCII", "UTF-8", "GB2312", "GBK", "BIG5"));

通过CSDN问答，知道BOM问题，解决方案如下：

function removeBom($string)//去除BOM
{
	if (substr($string, 0, 3) == pack("CCC", 0xef, 0xbb, 0xbf)) {
		return substr($string, 3);
	}
	return $string;
}

function ConvertUTF8ToGB2312($str)//转化为统一编码;
{
	return iconv("UTF-8", "GB2312//IGNORE", $str);
}