PHP aes （ecb）解密后乱码问题

function apiDataDecrypt($data, $key='') {
$data = base64_decode($data);
$pad = 16 - (strlen($data) % 16);
$padData = $data . str_repeat(chr($pad), $pad);
return mcrypt_decrypt(MCRYPT_RIJNDAEL_128, $key,$padData, MCRYPT_MODE_ECB);
}
}

$key = '1234567890123456';
$content = 'T7UT2NQ1AFvR9unjA0wKWA==';
$desStr = decryptString($content,$key);
echo($desStr);
 
function decryptString($str,$key) {
$str = base64_decode($str);
$str = mcrypt_decrypt(MCRYPT_RIJNDAEL_128, $key, $str, MCRYPT_MODE_ECB);
$block = mcrypt_get_block_size('rijndael_128', 'ecb');
$pad = ord($str[($len = strlen($str)) - 1]);
$len = strlen($str);
$pad = ord($str[$len-1]);
return substr($str, 0, strlen($str) - $pad);
}