以下代码来自微信sdk里面

/**

* Prpcrypt class

*

* 提供接收和推送给公众平台消息的加解密接口.

*/

class Prpcrypt

{

public $key;

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();//"aaaabbbbccccdddd";

$text = $random . pack("N", strlen($text)) . $text . $appid;

$iv = substr($this->key, 0, 16);

$pkc_encoder = new \PKCS7Encoder;

$text = $pkc_encoder->encode($text);

$encrypted = openssl_encrypt($text, 'AES-256-CBC', substr($this->key, 0, 32), OPENSSL_ZERO_PADDING, $iv);

return array(ErrorCode::$OK, $encrypted);

} catch (Exception $e) {

//print $e;

return array(ErrorCode::$EncryptAESError, 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 {

$iv = substr($this->key, 0, 16);

$decrypted = openssl_decrypt($encrypted, 'AES-256-CBC', substr($this->key, 0, 32), OPENSSL_ZERO_PADDING, $iv);

} catch (Exception $e) {

return array(ErrorCode::$DecryptAESError, null);

}

try {

//去除补位字符

$pkc_encoder = new PKCS7Encoder;

$result = $pkc_encoder->decode($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);

if (!$appid)

$appid = $from_appid;

//如果传入的appid是空的，则认为是订阅号，使用数据中提取出来的appid

} catch (Exception $e) {

//print $e;

return array(ErrorCode::$IllegalBuffer, null);

}

if ($from_appid != $appid) {

return array(ErrorCode::$ValidateAppidError, null);

}

//不注释上边两行，避免传入appid是错误的情况

return array(0, $xml_content, $from_appid);

//增加appid，为了解决后面加密回复消息的时候没有appid的订阅号会无法回复

}

/**

* 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;

}

/**

* PKCS7Encoder class

*

* 提供基于PKCS7算法的加解密接口.

*/

class PKCS7Encoder

{

public static $block_size = 32;

/**

* 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)

{

$block_size = PKCS7Encoder::$block_size;

$text_length = strlen($text);

//计算需要填充的位数

$amount_to_pad = PKCS7Encoder::$block_size - ($text_length % PKCS7Encoder::$block_size);

if ($amount_to_pad == 0) {

$amount_to_pad = PKCS7Encoder::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));

}

}