PHP加密方法

//字符串解密加密
function authcode($string, $operation = 'DECODE', $key = '', $expiry = 0) {

	$ckey_length = 8; // 随机密钥长度 取值 0-32;
	// 加入随机密钥，可以令密文无任何规律，即便是原文和密钥完全相同，加密结果也会每次不同，增大破解难度。
	// 取值越大，密文变动规律越大，密文变化 = 16 的 $ckey_length 次方
	// 当此值为 0 时，则不产生随机密钥

	$CI = &get_instance();
	$key = md5($key ? $key : $CI->config->item('encryption_key'));
	$keya = md5(substr($key, 0, 16));
	$keyb = md5(substr($key, 16, 16));
	$keyc = $ckey_length ? ($operation == 'DECODE' ? substr($string, 0, $ckey_length) : substr(md5(microtime()), -$ckey_length)):'';

	$cryptkey = $keya . md5($keya . $keyc);
	$key_length = strlen($cryptkey);

	$string = $operation == 'DECODE' ? base64_decode(substr($string, $ckey_length)) : sprintf('%010d', $expiry ? $expiry + time() : 0) . substr(md5($string . $keyb), 0, 16) . $string;
	$string_length = strlen($string);

	$result = '';
	$box = range(0, 255);

	$rndkey = array();
	for ($i = 0; $i <= 255; $i++) {
		$rndkey[$i] = ord($cryptkey[$i % $key_length]);
	}

	for ($j = $i = 0; $i < 256; $i++) {
		$j = ($j + $box[$i] + $rndkey[$i]) % 256;
		$tmp = $box[$i];
		$box[$i] = $box[$j];
		$box[$j] = $tmp;
	}

	for ($a = $j = $i = 0; $i < $string_length; $i++) {
		$a = ($a + 1) % 256;
		$j = ($j + $box[$a]) % 256;
		$tmp = $box[$a];
		$box[$a] = $box[$j];
		$box[$j] = $tmp;
		$result .= chr(ord($string[$i]) ^ ($box[($box[$a] + $box[$j]) % 256]));
	}

	if ($operation == 'DECODE') {
		if ((substr($result, 0, 10) == 0 || substr($result, 0, 10) - time() > 0) && substr($result, 10, 16) == substr(md5(substr($result, 26) . $keyb), 0, 16)) {
			return substr($result, 26);
		} else {
			return '';
		}
	} else {
		return $keyc . str_replace('=', '', base64_encode($result));
	}
}