<?php
	class AuthCode {
		public static function encode($str, $key) {
			return self::_auth_code($str, 'ENCODE', $key, 0);
		}
	 
		public static function decode($str, $key) {
			return self::_auth_code($str, 'DECODE', $key, 0);
		}
	 
		public static function _auth_code($string, $operation = 'DECODE', $key = '', $expiry = 3600) {
			/***
			 * 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
			 */
			$ckey_length = 4;
			
			$key = md5($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 $keyc.base64_encode($result);
			}
		}
	 
	}
?>