$xmlResult = file_get_contents("php://input");//获取微信的数据
$result = $this->xmlToArray($xmlResult);//将xml转成数组

// 将加密的数据解密,方法在下面
$reqInfo = $this->refund_decrypt($result['req_info']);

/*
 * 退款通知解密
 * @Author WangZhaoBo
 * @param $str 微信同步的加密串req_info
 * @param $key 商户key
 */
public function refund_decrypt($str) {
    $key = md5($this->appSecret);
    $str = base64_decode($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);
}