i Spring and Autumn Fuzzing

First check the source code. . . No thing, Ethereal

Found nothing, but on the right there is a hint hint: ip, Large Internal Network (the largest network ip )

We may need to fake code access, this is not a simple, direct request to join in

X-Forwarded-For: 10.0.0.0

To forge ip

Go about the discovery request bar there is a new file

Copy the file name, the right to create a new repeater access to Try

Change the GET url bar to access the file

弹出show me your key

Conventional thinking is a direct GET bar incoming

Go look no reaction. . . . Try POST Incoming

Right- request column select mode change request

Directly into the POST pass, GO look

Prompted

Our key is incorrect, the correct key is md5 Yes. . . . . And this key form is ichunqiu *** ( * range in ...)

Here you can write a script blasting (keep trying *** combinations) can also go directly to see if you can translate

To get back to the incoming

Tips to get the next step

Is a php file, try to directly access

The next step tips given

This encryption source is x0.txt then that have been encrypted flag Yes. . . . .

We directly access this x0.txt

Really is a encryption process

According to him the encryption process is then reversed to write the script decrypted

<?php
function authcode($string, $operation = 'DECODE', $key = '', $expiry = 0) {
    $ckey_length = 4;

    $key = md5($key ? $key : UC_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));
    }

}

echo authcode($string = '5f04rJx7uHz25mDp4vUfC0JB4Nx5nMvyQzHwjRb6kN88N+T9RRipbwbHDIcRWtqXjemcJit26oE1Vu6lpdQPZ6St/obCAEc', $operation = 'DECODE', $key = 'ichunqiu105');
?>

( Back contact ciphertext string )

Local running to get flag

i Spring and Autumn Fuzzing

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