简化PHP代码：$mystr = $operation == DECODE base64_decodesubstr$mystr $ckey_length sprintf010d $expiry $expiry + time 0substrmd5$mystr$keyb 0 16$mystr;

if ($operation == 'DECODE') { $mystr = base64_decode(substr($mystr, $ckey_length)); } else { $expiry_time = $expiry ? $expiry + time() : 0; $md5_str = substr(md5($mystr.$keyb), 0, 16); $mystr = sprintf('%010d', $expiry_time) . $md5_str . $mystr; }