假設變量$a,$b,$c=$a^$b(變量a異或變量b),
所以我們有$a=$b^$c , $b=$a^$c
以上是異或邏輯的應用,(題外話：如何在不使用第3個變量的情況下，交換變量$a,$b的值呢?)
正題：
可以把變量$a看成是明文(需加密的字符串),變量$b看成是密鑰(自己定義),變量$c看成是密文(發(fā)送到客戶端在網(wǎng)上傳輸?shù)?。
當然上面只是基本原理，加密絕不是就簡單的異或字符串就行。
為了使算法更不易破解sys_auth函數(shù)對密鑰進行了一個加密：
$key_length = 4;
$key = md5($key);
$fixedkey = md5($key);
$egiskeys = md5(substr($fixedkey, 16, 16));
$runtokey = $key_length ? ($operation == 'ENCODE' ? substr(md5(microtime(true)), -$key_length) : substr($string, 0, $key_length)) : '';
$keys = md5(substr($runtokey, 0, 16) . substr($fixedkey, 0, 16) . substr($runtokey, 16) . substr($fixedkey, 16));
對明文也插入一些片段，并用base64進行了編碼。
function sys_auth($string, $operation = 'ENCODE', $key = 'hi', $expiry = 0) {$key_length = 4;$key = md5($key);$fixedkey = md5($key);$egiskeys = md5(substr($fixedkey, 16,
16));$runtokey = $key_length ? ($operation == 'ENCODE' ? substr(md5(microtime(true)), -$key_length) : substr($string, 0, $key_length)) : '';$keys = md5(substr($runtokey, 0, 16) . substr($fixedkey, 0, 16) . substr($runtokey, 16) . substr($fixedkey, 16));$string
= $operation == 'ENCODE' ? sprintf('%010d', $expiry ? $expiry + time() : 0).substr(md5($string.$egiskeys), 0, 16) . $string : base64_decode(substr($string, $key_length));//10位密文過期信息+16位明文和密鑰生成的密文驗證信息+明文$i = 0; $result = '';$string_length = strlen($string);for
($i = 0; $i < $string_length; $i++){$result .= chr(ord($string{$i}) ^ ord($keys{$i % 32}));}if($operation == 'ENCODE') {return $runtokey . str_replace('=', '', base64_encode($result));} else {if((substr($result, 0, 10) == 0 || substr($result, 0, 10) - time()
> 0) && substr($result, 10, 16) == substr(md5(substr($result, 26).$egiskeys), 0, 16)) {return substr($result, 26);} else {return '';}}}
function sys_auth($string, $operation = 'ENCODE', $key = 'hi', $expiry = 0) {$key_length = 4;$key = md5($key);$fixedkey = md5($key);$egiskeys = md5(substr($fixedkey,
16, 16));$runtokey = $key_length ? ($operation == 'ENCODE' ? substr(md5(microtime(true)), -$key_length) : substr($string, 0, $key_length)) : '';$keys = md5(substr($runtokey, 0, 16) . substr($fixedkey, 0, 16) . substr($runtokey, 16) . substr($fixedkey, 16));$string
= $operation == 'ENCODE' ? sprintf('%010d', $expiry ? $expiry + time() : 0).substr(md5($string.$egiskeys), 0, 16) . $string : base64_decode(substr($string, $key_length));//10位密文過期信息+16位明文和密鑰生成的密文驗證信息+明文$i = 0; $result = '';$string_length = strlen($string);for
($i = 0; $i < $string_length; $i++){$result .= chr(ord($string{$i}) ^ ord($keys{$i % 32}));}if($operation == 'ENCODE') {return $runtokey . str_replace('=', '', base64_encode($result));} else {if((substr($result, 0, 10) == 0 || substr($result, 0, 10) - time()
> 0) && substr($result, 10, 16) == substr(md5(substr($result, 26).$egiskeys), 0, 16)) {return substr($result, 26);} else {return '';}}}