PHP 加密/解密函数 dencrypt(动态密文，带压缩功能，支持中文)

// +----------------------------------------------------------------------+
// | Willko Framework                                                     |
// +----------------------------------------------------------------------+
// | Copyright (c) 2008-2009 Willko Cheng                                 |
// +----------------------------------------------------------------------+
// | Authors: Willko Cheng <[e-mail]>                           |
// +----------------------------------------------------------------------+
// $string 明文 或 密文
// $isEncrypt 是否加密
// $key 密匙
// 采用SHA1生成密匙簿，超过300个字符使用ZLIB压缩
function dencrypt($string, $isEncrypt = true, $key = KEY_SPACE) {
	if (!isset($string{0}) || !isset($key{0})) {
		return false;
	}
	
	$dynKey = $isEncrypt ? hash('sha1', microtime(true)) : substr($string, 0, 40);
	$fixedKey = hash('sha1', $key);
	
	$dynKeyPart1 = substr($dynKey, 0, 20);
	$dynKeyPart2 = substr($dynKey, 20);
	$fixedKeyPart1 = substr($fixedKey, 0, 20);
	$fixedKeyPart2 = substr($fixedKey, 20);
	$key = hash('sha1', $dynKeyPart1 . $fixedKeyPart1 . $dynKeyPart2 . $fixedKeyPart2);
	
	$string = $isEncrypt ? $fixedKeyPart1 . $string . $dynKeyPart2 : (isset($string{339}) ? gzuncompress(base64_decode(substr($string, 40))) : base64_decode(substr($string, 40)));
	
	$n = 0;
	$result = '';
	$len = strlen($string);
	
	for ($n = 0; $n < $len; $n++) {
		$result .= chr(ord($string{$n}) ^ ord($key{$n % 40}));
	}
	return $isEncrypt ? $dynKey . str_replace('=', '', base64_encode($n > 299 ? gzcompress($result) : $result)) : substr($result, 20, -20);
}