Encrypt.php

<?php

/***
 * 加密函数（密文具有有效期,可逆,根据时间生成不同的密文）
 * @param        $string
 * @param string $operation
 * @param string $key
 * @param int    $expiry
 * @return string
 */
function authcode ($string, $operation = 'DECODE', $key = '', $expiry = 0) {
    $ckey_length = 4;
    $key  = $key != '' ? $key : 'RXAcX7sfwDba3uDucENuCMufftLdBmmrX/4a56aNqXlRC/EhLPY3mRg/+w7Dl6BbLgm+WZZrSXh1vsdyls4LqyH4i81KLNbNPFT0fwxTA29d9qSv50weGKoEgV0o';
    $keya = md5 (substr ($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));
    }
}

$code = authcode ('aaabbbcccddd','encode');
$raw = authcode ('afddxchxZAyAsJY2PRPuSGzHqOs6RYO3U0UbnrIgxXMpLFCUYBift5I');
var_dump ($code,$raw);
//string(55) "63a84lry1/uEnnB/adbrlK0z99AEjSmaQuFrMCZ/5IaGvLiW9Rxv4XA"
//string(12) "aaabbbcccddd"