<?php
// $key是将一个base64_encode过的字符串去掉“=”获得的
$key = 'dGhpcyBpcyBhIGV4YW1wbGU';
$appid = "wxb11529c136998cb6";

$pc = new Prpcrypt($key);
$enStr = $pc->encrypt('123',$appid);
echo '加密后：'.$enStr."\n";
echo '解密后:'.$pc->decrypt($enStr,$appid);

/**
* 由微信消息加密，解密修改而来
*
* @package aes
*/
class Prpcrypt
{
    public $key;
    public static $block_size = 32;

    function __construct($k)
    {
        $this->key = base64_decode($k . "=");
    }

    /**
     * 对明文进行加密
     * @param string $text 需要加密的明文
     * @return string 加密后的密文
     */
    public function encrypt($text, $appid)
    {
        try {
            //获得16位随机字符串，填充到明文之前
            $random = $this->getRandomStr();
            $text = $random . pack("N", strlen($text)) . $text . $appid;
            // 网络字节序
            $size = mcrypt_get_block_size(MCRYPT_RIJNDAEL_128, MCRYPT_MODE_CBC);
            $module = mcrypt_module_open(MCRYPT_RIJNDAEL_128, '', MCRYPT_MODE_CBC, '');
            $iv = substr($this->key, 0, 16);
            //使用自定义的填充方式对明文进行补位填充
            $text = $this->encode($text);
            mcrypt_generic_init($module, $this->key, $iv);
            //加密
            $encrypted = mcrypt_generic($module, $text);
            mcrypt_generic_deinit($module);
            mcrypt_module_close($module);

            //print(base64_encode($encrypted));
            //使用BASE64对加密后的字符串进行编码
            return base64_encode($encrypted);
        } catch (Exception $e) {
            //print $e;
            return null;
        }
    }

    /**
     * 对密文进行解密
     * @param string $encrypted 需要解密的密文
     * @return string 解密得到的明文
     */
    public function decrypt($encrypted, $appid)
    {

        try {
            //使用BASE64对需要解密的字符串进行解码
            $ciphertext_dec = base64_decode($encrypted);
            $module = mcrypt_module_open(MCRYPT_RIJNDAEL_128, '', MCRYPT_MODE_CBC, '');
            $iv = substr($this->key, 0, 16);
            mcrypt_generic_init($module, $this->key, $iv);

            //解密
            $decrypted = mdecrypt_generic($module, $ciphertext_dec);
            mcrypt_generic_deinit($module);
            mcrypt_module_close($module);
        } catch (Exception $e) {
            return null;
        }


        try {
            //去除补位字符
            $result = $this->decode($decrypted);
            //去除16位随机字符串,网络字节序和AppId
            if (strlen($result) < 16)
                return "";
            $content = substr($result, 16, strlen($result));
            $len_list = unpack("N", substr($content, 0, 4));
            $xml_len = $len_list[1];
            $xml_content = substr($content, 4, $xml_len);
            $from_appid = substr($content, $xml_len + 4);
        } catch (Exception $e) {
            //print $e;
            return null;
        }
        if ($from_appid != $appid)
            return null;
        return $xml_content;

    }


    /**
     * 随机生成16位字符串
     * @return string 生成的字符串
     */
    function getRandomStr()
    {

        $str = "";
        $str_pol = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789abcdefghijklmnopqrstuvwxyz";
        $max = strlen($str_pol) - 1;
        for ($i = 0; $i < 16; $i++) {
            $str .= $str_pol[mt_rand(0, $max)];
        }
        return $str;
    }

    /**
     * 对需要加密的明文进行填充补位
     * @param $text 需要进行填充补位操作的明文
     * @return 补齐明文字符串
     */
    function encode($text)
    {
        $block_size = self::$block_size;
        $text_length = strlen($text);
        //计算需要填充的位数
        $amount_to_pad = self::$block_size - ($text_length % self::$block_size);
        if ($amount_to_pad == 0) {
            $amount_to_pad = self::block_size;
        }
        //获得补位所用的字符
        $pad_chr = chr($amount_to_pad);
        $tmp = "";
        for ($index = 0; $index < $amount_to_pad; $index++) {
            $tmp .= $pad_chr;
        }
        return $text . $tmp;
    }

    /**
     * 对解密后的明文进行补位删除
     * @param decrypted 解密后的明文
     * @return 删除填充补位后的明文
     */
    function decode($text)
    {

        $pad = ord(substr($text, -1));
        if ($pad < 1 || $pad > 32) {
            $pad = 0;
        }
        return substr($text, 0, (strlen($text) - $pad));
    }

}