0xfat

These CTF write-ups contain spoilers

Written: 2021/10/10 // Updated: 2021/10/15

0xf.at is a hackit style password-riddle site. The GitHub Project has setup instructions to configure it locally using Docker. The framework also allows a user to create their own levels and add them to the overall project.

The challenges primarily take up a similar format, some challenge notes along with an input box to provide the answer in. At the time of writing all the solitions have been in the page’s source code.

Level 1

Challenge notes

Easy beginnings

<!-- :::::::::::::::::==== GAME STARTS HERE ====::::::::::::::::: -->
    <h1>Level 1</h1>
    <div>Easy beginnings</div>
    <input id="pw" type="password" />
    <br/><input type="button" value="OK" onClick="checkPW()"/>
    <script type="text/javascript">
        function checkPW()
        {
            var el = document.getElementById('pw');
            if(el.value=="tooeasy")
                document.location.href="?pw="+el.value;
            else alert("Wrong password!");
        }
    </script>
<!-- ::::::::::::::::::==== GAME ENDS HERE ====:::::::::::::::::: -->

The above is pretty straight forward. The if statement checks whether the value of the el variable is a certain string and verifies whether it’s the password.

Flag

tooeasy

Level 2

Challenge notes

Not that hard either..

<!-- :::::::::::::::::==== GAME STARTS HERE ====::::::::::::::::: -->
    <h1>Level 2</h1>
                <div>Not that hard either..</div>
    <input id="pw" type="password" />
    <br/><input type="button" value="OK" onClick="checkPW()"/>
    <script type="text/javascript">
        function checkPW()
        {
            var pw = "%39%32%31%61%61";
            var el = document.getElementById('pw');
            if(el.value==unescape(pw))
                window.location.href="?pw="+el.value;
            else alert("Wrong password");
        }
    </script>
<!-- ::::::::::::::::::==== GAME ENDS HERE ====:::::::::::::::::: -->

In this scenario it looks like we are given the password as a variable (pw) and checking the if statement, we are having to unescape it. A method to do this would be to fire up the browser’s Console window and go through the steps:

var pw = "%39%32%31%61%61";
unescape(pw)

Flag

921aa

Level 3

Challenge notes

How about: No sourcecode?

<!-- :::::::::::::::::==== GAME STARTS HERE ====::::::::::::::::: -->
    <h1>Level 3</h1>

    <!--
Source code disabled

....4000 lines later....

Did I fool you?
-->
<div>How about: No sourcecode?</div>
<input id="pw" type="password" />
<br/><input type="button" value="OK" onClick="checkPW()"/>
<script type="text/javascript">
    function checkPW()
    {
        var el = document.getElementById("pw");
        if(el.value==unescape("r%20i%20g%20h%20t%20")+""+"p"+"w"+""+"6943ad11f")
            window.location.href="?pw="+el.value;
        else alert("Wrong password");
    }
</script>
<!-- ::::::::::::::::::==== GAME ENDS HERE ====:::::::::::::::::: -->

This challenge tried to trick us as if there was no source code. Instead we had to scroll down around 4400 lines to the bottom. The challenge itself is similar as before. We are this time putting together the password from a few different elements:

if(el.value==unescape("r%20i%20g%20h%20t%20")+""+"p"+"w"+""+"6943ad11f")

We first want to figure out the value of the unescape("r%20i%20g%20h%20t%20") element:

After that there was a bit of a trick by adding two empty strings to the pattern: +""+ adds nothing and can in a sense be ingored.

Flag

r i g h t pw6943ad11f

Level 4

Challenge notes

What does .length mean?

<!-- :::::::::::::::::==== GAME STARTS HERE ====::::::::::::::::: -->
    <h1>Level 4</h1>
    <div>What does .length mean?</div>
    <input id="pw" type="password" />
    <br/><input type="button" value="OK" onClick="checkPW()"/>
     <script type="text/javascript">
        function checkPW()
        {
            var el = document.getElementById("pw");
            var pwinfo = "3523 f1b04eb e2ddc14 f50 fe 1135d3a55400c503ae  1120c 51404eba50a5b45ea3d";
            if(el.value==pwinfo.length)
                window.location.href="?pw="+el.value;
            else alert("Wrong password");
        }
    </script>
<!-- ::::::::::::::::::==== GAME ENDS HERE ====:::::::::::::::::: -->

Analyzing the code, we are presented with a variable, var pwinfo = "3523 f1b04eb e2ddc14 f50 fe 1135d3a55400c503ae 1120c 51404eba50a5b45ea3d";. Looking at if statement that checks the input validity, the password matches the length of this variable. We can again solve this using the Browser Console.

Flag

var pwinfo = "3523 f1b04eb e2ddc14 f50 fe 1135d3a55400c503ae  1120c 51404eba50a5b45ea3d";
pwinfo.length;
73

Level 5

Challenge notes

Have you heard of ASCII?

<!-- :::::::::::::::::==== GAME STARTS HERE ====::::::::::::::::: -->
    <h1>Level 5</h1>
    <div>Have you heard of ASCII?</div>
    <input id="pw" type="password" />
    <br/><input type="button" value="OK" onClick="checkPW()"/>
    <script type="text/javascript">
        function checkPW()
        {
            var el = document.getElementById("pw");
            if(el.value==(atoi("o")+73))
                window.location.href="?pw="+el.value;
            else alert("Falsches Passwort");
        }

        // converts a character to its ASCII number
        function atoi(a)
        {
           return a.charCodeAt();
        }
    </script>
<!-- ::::::::::::::::::==== GAME ENDS HERE ====:::::::::::::::::: -->

We can see that the input value is compared to the following: (atoi("o")+73). Further along in the code, we see a function called atoi which takes the argument a. The function returns the charCodeAt() JavaScript method, which in a nutshell gives us the unicode value of a string. Additional information and context can be found on the w3schools.com website.

We can rely on our trusty Console to solve this challenge again, pasting in the atoi() function and calling it to find the value of the letter o.

Flag

atoi("o") + 73;
184

Level 6

Challenge notes

<!-- :::::::::::::::::==== GAME STARTS HERE ====::::::::::::::::: -->
    <h1>Level 6</h1>
    <div><span id="nice" style="color:#cc3333">Nice</span> <span id="though" style="color:#99ff33">colors</span> <span id="colors" style="color:#33ffff">though</span></div>
    <input id="pw" type="password" />
    <br/><input type="button" value="OK" onClick="checkPW()"/>
    <script type="text/javascript">
        function checkPW()
        {
            var el = document.getElementById("pw");
            if(el.value==rgb2hex(document.getElementById("though").style.color))
                window.location.href="?pw="+escape(el.value);
            else window.location.href="?pw="+escape(el.value);
        }

        function rgb2hex(rgb) {
            rgb = rgb.match(/^rgb\((\d+),\s*(\d+),\s*(\d+)\)$/);
            function hex(x) {
                return ("0" + parseInt(x).toString(16)).slice(-2);
            }
            return "#" + hex(rgb[1]) + hex(rgb[2]) + hex(rgb[3]);
        }

    </script>
<!-- ::::::::::::::::::==== GAME ENDS HERE ====:::::::::::::::::: -->

For this challenge I included a screenshot of the challenge notes as this will be key. The source code has two functions in there. checkPW(), which will verify our input is correct as well as rgb2hex() which takes the argument rgb. This function essentially returns a hex string generated from the RGB colors of our input.

Looking at the checkPW() function, the if statement is gathering the word from the page “though”, which on our screenshot is green (rgb(153, 255, 51)). The check also gathers the color style that the word is using. Our trusty Console helps us out to get the answer.

Flag

rgb2hex(document.getElementById("though").style.color)
"#99ff33"

Level 7

Challenge notes

Jerry fcked up, he forgot the password for this level but he mumbled something about a robots.txt file and something about a hint..

<!-- :::::::::::::::::==== GAME STARTS HERE ====::::::::::::::::: -->
    <h1>Level 7</h1>
    <p>Jerry f*cked up, he forgot the password for this level but he mumbled something about a robots.txt file and something about a hint..</p>
<input id="pw" type="password" />
<br/><input type="button" value="OK" onClick="checkPW()"/>
<script type="text/javascript">
    function checkPW()
    {
        var el = document.getElementById("pw");
        window.location.href="?pw="+el.value;
    }
</script>
<!-- ::::::::::::::::::==== GAME ENDS HERE ====:::::::::::::::::: -->

The challenge notes indicate that we should be looking in a file called robots.txt for a hint to our next level. Checking the file, we find the following information:

User-agent: *
Allow: /

Disallow: /play/solutionforlevel7 #don't allow google to find the solution for level 7

The key here is the Disallow line, whereby it asks crawlers not to index the page which is the solution to our current level. Visiting the page yields us the flag.

Flag

I don't know how you found it but you've found it! The password for level 7 is:
jerryIsDaBoss5c

Level 8

Challenge notes

Nice, someone already entered the password but they made a small mistake. The FIRST occurring 0 (zero) should actually be a small “o”. Can you fix it?

<!-- :::::::::::::::::==== GAME STARTS HERE ====::::::::::::::::: -->
    <h1>Level 8</h1>
    <p>Nice, someone already entered the password but they made a small mistake.<br/>The FIRST occurring 0 (zero) should actually be a small "o". Can you fix it?</p>
    <input id="pw" type="password" />
    <br/><input type="button" value="OK" onClick="checkPW()"/>
    <script type="text/javascript">
        function checkPW()
        {
            var el = document.getElementById("pw");
            window.location.href="?pw="+el.value;
        }
    </script>
<script type="text/javascript">
var _0x6a7e=["\x2F\x62\x61\x63\x6B\x65\x6E\x64\x2E\x70\x68\x70\x3F\x61\x3D\x73\x26\x6C\x3D\x38","\x70\x61\x72\x73\x65","\x72\x65\x73\x75\x6C\x74","\x76\x61\x6C","\x23\x70\x77","\x67\x65\x74","\x72\x65\x61\x64\x79"];$(document)[_0x6a7e[6]](function(){$[_0x6a7e[5]](_0x6a7e[0],function(_0xa388x1){var _0xa388x2=JSON[_0x6a7e[1]](_0xa388x1);$(_0x6a7e[4])[_0x6a7e[3]](_0xa388x2[_0x6a7e[2]]);})});
</script>
<!-- ::::::::::::::::::==== GAME ENDS HERE ====:::::::::::::::::: -->

On this challenge, the password is already given to us within the input box, however it’s obfuscated. Selecting to Inspect the page, we can modify the behavior of the input box from type password to text:

The instructions tell us to grab the already existing password and convert the first occurring zero (0) to a lowercase “o”.

Flag

635egxjz4v26ghxtzb4ouwh52pbpness

Level 9

Challenge notes

Let’s think this through

<!-- :::::::::::::::::==== GAME STARTS HERE ====::::::::::::::::: -->
    <h1>Level 9</h1>
    <p>Let's think this through</p>
    <input id="pw" type="password" />
    <br/><input type="button" value="OK" onClick="checkPW()"/>
    <script type="text/javascript">
        function checkPW()
        {
            var foo = 5 + 6 * 7;
            var bar = foo % 8; //modulo.. look it up if you don't know what it does
            var moo = bar + 1;
            var rar = moo / 3;
            var el = document.getElementById("pw");
            if(el.value.length == moo)
                window.location.href="?pw="+el.value;
            else alert("Wrong password");
        }
    </script>
<!-- ::::::::::::::::::==== GAME ENDS HERE ====:::::::::::::::::: -->

This is a pretty straight forward challenge, however as the notes suggest we just need to think it through. The first part is solving the equations. There is a little trick in there, since we have four variables: foo, bar, moo and rar, however as we can see within the challenge password verifying if statement, we actually need the value of moo.

We can step through these easily using the console:

var foo = 5 + 6 * 7;
var bar = foo % 8;
var moo = bar + 1;
moo;
8

We now know that the value of the moo variable is 8. The verification step checks whether our input’s lenght is equal to the value of the moo variable: ` if(el.value.length == moo)`. Since it’s checking the length of the input, we can use any string that matches the length criteria.

Flag

password

Level 10

Challenge notes

Try not to be fooled

<!-- :::::::::::::::::==== GAME STARTS HERE ====::::::::::::::::: -->
    <h1>Level 10</h1>
    <p>Try not to be fooled</p>
    <input id="pw" type="password" />
    <br/><input type="button" value="OK" onClick="checkPW()"/>
    <script type="text/javascript">var CodeCode = "moo451";

        function checkPW()
        {
            "+CodeCode+" == "0xf.at_hackit";
            var el = document.getElementById("pw");
            if(el.value == ""+CodeCode+"")
                document.location.href="?pw="+el.value;
            else alert("Wrong password");
        }

    </script>
<!-- ::::::::::::::::::==== GAME ENDS HERE ====:::::::::::::::::: -->

This one is more of a tricky one than a complicated challenge. Within the checkPW() function we are given a variable "+CodeCode+" and further along in the code, when checking if the input value matches our password, we can see the comparison: if(el.value == ""+CodeCode+"").

One might be fooled into thinking we are trying to compare to the value of the "+CodeCode+" variable, however if we take a look at the behavior, we are actually searching for the variable CodeCode. The "" add an empty string and the + in this case works to concatenate the empty strings with the word CodeCode. Searching the code, outside of the checkPW() function we can find this variable.

Flag

<prevar CodeCode = "moo451";</pre>

Level 11

Challenge notes

The password of this level is calculated by the following function

function pwCheck($password)
{
    if($password==date("d.m.Y")) //GMT +1
        return true;
    else return false;
}

<!-- :::::::::::::::::==== GAME STARTS HERE ====::::::::::::::::: -->
    <h1>Level 11</h1>
    <p>The password of this level is calculated by the following function</p>
    <pre><code class="language-php">function pwCheck($password)
{
if($password==date("d.m.Y")) //GMT +1
return true;
else return false;
}</code></pre><br/>
    <input id="pw" type="password" />
    <br/><input type="button" value="OK" onClick="checkPW()"/>
    <script type="text/javascript">

        function checkPW()
        {
            var el = document.getElementById("pw");
            document.location.href="?pw="+el.value;
        }

    </script>
<!-- ::::::::::::::::::==== GAME ENDS HERE ====:::::::::::::::::: -->

This one gives us a simple PHP script that checks whether the password provided is equal to date("d.m.Y"). Since PHP is installed by default on OSX, I was able to fire it up and run that method to get the flag.

php -a
echo date("d.m.Y");

Flag

10.10.2021

Level 12

Challenge notes

The password is the sum of all numbers from 1 to 477

<!-- :::::::::::::::::==== GAME STARTS HERE ====::::::::::::::::: -->
    <h1>Level 12</h1>
    <p>The password is the sum of all numbers from 1 to 477</p>
    <br/>
    <input id="pw" type="password" />
    <br/><input type="button" value="OK" onClick="checkPW()"/>
    <script type="text/javascript">

        function checkPW()
        {
            var el = document.getElementById("pw");
            document.location.href="?pw="+el.value;
        }

    </script>
<!-- ::::::::::::::::::==== GAME ENDS HERE ====:::::::::::::::::: -->

For this challenge we are asked to calculate the sum of all numbers between 1 and 477. A friend of mine and I came up with a solution each when solving this challenge.

Solution 1

I went down the route of a loop to calculate the sum, whereby i is our sum and x is our iterator, which tracks where in the loop we are as well as adding the value of that number to i:

>>> i = 0
>>> x = 1
>>> while x < 478:
...     i += x
...     x += 1

To get the flag, we just need to print the value of i.

Solution 2

On a similar note, my friend used Python along with the mathematical formula for the sum of the first n natural numbers:

python -c "n=477; print((n*(n+1))/2)"

Flag

Level 13

Challenge notes

The password of this level is calculated by the following function

function pwCheck($username,$password)
{
    if(!$username || !$password) return false;
    if(strlen($username)==$password)
        return true;
    else return false;
}

<!-- :::::::::::::::::==== GAME STARTS HERE ====::::::::::::::::: -->
    <h1>Level 13</h1>
    <p>The password of this level is calculated by the following function</p>
    <pre><code class="language-php">function pwCheck($username,$password)
{
if(!$username || !$password) return false;
if(strlen($username)==$password)
return true;
else return false;
}</code></pre><br/>
    Username
    <input id="user" name="user" type="text" />
    <br/>
    Password
    <input id ="pw" name="pw" type="password" /><input type="button" value="OK" onClick="checkPW()"/>
    <script type="text/javascript">

        function checkPW()
        {
            var pw = document.getElementById("pw");
            var user = document.getElementById("user");
            document.location.href="?pw="+pw.value+"&name="+user.value;
        }

    </script>
<!-- ::::::::::::::::::==== GAME ENDS HERE ====:::::::::::::::::: -->

This is another challenge where it’s more about being able to read the code and think logically. The PHP function we are given essentially checks that the length of the $username is equal to the variable $password. From this, we know that the function will take a username, calculate its length and check if the entered password is equal to that length.

Flag

Username: admin
Password: 5

Level 14

Challenge notes

The following function defines the login process

function pwCheck($guid,$password)
{
	if(!$guid || !$password) return false;
    $users = implode(file('/data/login_info.json'));
	$json = json_decode($users,true);

	foreach($json['result'] as $data)
		if($data['guid']==$guid && $data['password'] == $password && $data['account_status']=='active')
			return true;
	return false;
}

<!-- :::::::::::::::::==== GAME STARTS HERE ====::::::::::::::::: -->
    <h1>Level 14</h1>
    <p>The following function defines the login process</p>

    <div></div>
    <pre><code class="language-php">function pwCheck($guid,$password)
{
if(!$guid || !$password) return false;
$users = implode(file('/data/login_info.json'));
$json = json_decode($users,true);

foreach($json['result'] as $data)
if($data['guid']==$guid &amp;&amp; $data['password'] == $password &amp;&amp; $data['account_status']=='active')
    return true;
return false;
}
</code></pre>
    GUID<br/>
    <input id="guid" type="text" />
    <br/>
    Password<br/>
    <input id="pw" type="password" />
    <br/><input type="button" value="OK" onClick="checkPW()"/>
    <script type="text/javascript">
        function checkPW()
        {
            var el = document.getElementById("guid");
            var pw = document.getElementById("pw");
            window.location.href="?pw="+pw.value+"&guid="+el.value;
        }
    </script>
<!-- ::::::::::::::::::==== GAME ENDS HERE ====:::::::::::::::::: -->

For this challenge we are given another snippet of PHP. We can see from the $users variable, that the information is gathered from a file found at /data/login_info.json. The implode() function is a bit of a red-herring here as it’s not exactly joining array elements beyond printing out the file.

From the rest of the code, we can see that it’s looking for the account_status to be active. When we look at the file, only one user is active and the user data holds the necessary pieces to the flag.

Flag

        {
            "id": 4,
            "guid": "bc3c1364-4b24-4f60-8fe4-7628e72391ed",
            "password": "Vencom",
            "age": 40,
            "account_status": "active",
            "name": "Paige Youmans",
            "gender": "female",
            "phone": "857-579-3847",
            "email": "[email protected]",
            "address": "14622, Flint, Harrison Street",
            "registered": "2007-07-15T09:55:40 -02:00"
        },

GUID: bc3c1364-4b24-4f60-8fe4-7628e72391ed
Password: Vencom

Level 15

Challenge notes

You have to decode the following encrypted password. We don’t know how to decrypt it but you can play around with the algorithm that was used to encode it. Maybe you’ll figure it out

npveei

<!-- :::::::::::::::::==== GAME STARTS HERE ====::::::::::::::::: -->
    <h1>Level 15</h1>
    <p>You have to decode the following encrypted password.<br/>We don't know how to decrypt it but you can play around with the algorithm that was used to encode it. Maybe you'll figure it out</p>

<pre><code class="">npveei
</code></pre>

<form method="GET">
    Testing input:
    <input name="text" type="text" /> <input type="submit" name="submit" value="Test algorithm"/>
    <br/><br/>
    Decoded password:<br/>
    <input name="pw" type="text" />
    <br/><input type="submit" name="submit" value="OK"/>
</form>

<!-- ::::::::::::::::::==== GAME ENDS HERE ====:::::::::::::::::: -->

On this challenge we are given a string, which is meant to be encoded - npveei. We are then provided with two input boxes, one to provide arbitary data to encrypt using the same method npveei was generated with and the other to submit our password.

Testing the encryption with abcdef we can start to observe a behavior. The encrypted version of the string is acegik. From this it looks like each character is shifted by its position:

Position 1 - a => a
Position 2 - b => c
Position 3 - c => e
Position 4 - d => g
Position 5 - e => i
Position 6 - f => k

We can use this knowledge to reverse engineer our encrypted string. While this can be done programmatically, I found it quicker to solve it by pulling up the English alphabet in a numbered chart and calculated it.

Flag

notbad

Level 16

Challenge notes

The password of this level is calculated by the following function

function pwCheck($password)
{
    if(base64_encode($password)=="ODNhMjNmYjU4MmUxMDU5ODhkMjI2YmVjMw==")
        return true;
    else return false;
}

<!-- :::::::::::::::::==== GAME STARTS HERE ====::::::::::::::::: -->
    <h1>Level 16</h1>
    <p>The password of this level is calculated by the following function</p>
    <pre><code class="language-php">function pwCheck($password)
{
if(base64_encode($password)=="ODNhMjNmYjU4MmUxMDU5ODhkMjI2YmVjMw==")
return true;
else return false;
}</code></pre>
    <input id="pw" type="password" />
    <br/><input type="button" value="OK" onClick="checkPW()"/>
    <script type="text/javascript">

        function checkPW()
        {
            var el = document.getElementById("pw");
            document.location.href="?pw="+el.value;
        }

    </script>

<!-- ::::::::::::::::::==== GAME ENDS HERE ====:::::::::::::::::: -->

This was an overall very straight forward challenge. The password we enter into the input box gets Base64 encoded (base64_encode($password))and is matched against a fixed value (ODNhMjNmYjU4MmUxMDU5ODhkMjI2YmVjMw==). To complete this challenge, we can decode this value.

Flag

83a23fb582e105988d226bec3

Level 17

Challenge notes

Now let’s play: regEx Find out what password will make the preg_match function return 1

function pwCheck($password)
{
    return preg_match('/^[_a-z0-9-]+(\.[_a-z0-9-]+)*@[a-z0-9-]+(\.[a-z0-9-]+)*(\.[a-z]{2,})$/i', $password, $found);
}

<!-- :::::::::::::::::==== GAME STARTS HERE ====::::::::::::::::: -->
    <h1>Level 17</h1>
    <p>Now let's play: regEx<br/>Find out what password will make the preg_match function return 1</p>
<pre><code class="language-php">function pwCheck($password)
{
return preg_match('/^[_a-z0-9-]+(\.[_a-z0-9-]+)*@[a-z0-9-]+(\.[a-z0-9-]+)*(\.[a-z]{2,})$/i', $password, $found);
}</code></pre>
<input id="pw" type="password" />
<br/><input type="button" value="OK" onClick="checkPW()"/>
<script type="text/javascript">
    function checkPW()
    {
        var pw = document.getElementById("pw");
        window.location.href="?pw="+pw.value;
    }
</script>
<!-- ::::::::::::::::::==== GAME ENDS HERE ====:::::::::::::::::: -->

The key here is to understand what the regex is doing. Having used regex in the past, it appears to primarily be a validation for an email address. I tested the following string to complete the level:

Flag

[email protected]

Level 18

Challenge notes

The following password is encoded in morse code. Each character is seperated by a blank. After 60 seconds this page will submit/refresh automatically. So.. be faster than that.

−−... .−−−− ...−− −.. ....− −.. −.−. −...

<!-- :::::::::::::::::==== GAME STARTS HERE ====::::::::::::::::: -->
    <h1>Level 18</h1>
    <p>The following password is encoded in morse code. Each character is seperated by a blank.<br/>After 60 seconds this page will submit/refresh automatically. So.. be faster than that.</p>
<pre><code class="language-php">..... −.. ..−−− −.. −−−.. ....− −.. −−−−. </code></pre>
<input id="pw" type="password" />
<br/><input type="button" value="OK" onClick="checkPW()"/>
<script type="text/javascript">
    function checkPW()
    {
        var pw = document.getElementById("pw");
        window.location.href="?pw="+pw.value;
    }
    setTimeout(function(){checkPW();}, 60000);
</script>
<!-- ::::::::::::::::::==== GAME ENDS HERE ====:::::::::::::::::: -->

On this challenge we are presented with a string, which appears to be morse code. I tried a variety of morsecode converters, however for whatever reason they did not work on this string. Much like Level 15, I opted to manually convert the values using this International Morse Code sheet.

I was able to manually convert the values within the provided 60 seconds. For the above example the flag was:

Flag

..... => 5
-.. => D
..--- => 2
-.. => D
---.. => 8
....- => 4
-.. => D
----. => 9

Flag: 5D2D84D9

Level 19

Challenge notes

<!-- :::::::::::::::::==== GAME STARTS HERE ====::::::::::::::::: -->
    <h1>Level 19</h1>
    <p>Remember them old phone pads?</p>
<div>
        <img src="/data/imgs/keypad.png" /><br/><br/>
    The following password has been encrypted by the telephone alphabet pattern. The solution for this level is the <strong>digit sum</strong> of the number code<br/><br/>
    <strong>Example:</strong><br/>
    A =&gt; <span class="blue">22</span><br/>
    B =&gt; <span class="blue">222</span><br/>
    C =&gt; <span class="blue">2222</span><br/>
    1 =&gt; <span class="blue">1</span><br/>
    2 =&gt; <span class="blue">2</span><br/>
    5 =&gt; <span class="blue">5</span><br/>
    I =&gt; <span class="blue">4444</span><br/>
    W =&gt; <span class="blue">99</span><br/>
    Z =&gt; <span class="blue">99999</span><br/><br/>

    <p>"HEY" =&gt; <span class="blue">444 333 9999</span> =&gt; <span class="blue">4+4+4+3+3+3+9+9+9+9</span> = <u>57</u></p>

    <p>You have <strong>15 seconds</strong> to submit the right solution. Each time you reload this page the password changes.</p>
</div>
<pre><code class="">f77738e4bbcb039b5b04c7c15f60cb98</code></pre>
<input id="pw" type="password" />
<br/><input type="button" value="OK" onClick="checkPW()"/>
<script type="text/javascript">
    function checkPW()
    {
        var pw = document.getElementById("pw");
        window.location.href="?pw="+pw.value;
    }
    setTimeout(function(){checkPW();}, 15000);
</script>
<!-- ::::::::::::::::::==== GAME ENDS HERE ====:::::::::::::::::: -->

This was a bit more challenging. We are given a keypad and instructions to convert the characters on the keypad to numbers. We are only given 15 seconds to solve this and the string given is 32 characters long, therefore we have to look at this programmatically. I used Python to build out a dictionary where I calculated the sum of each character. The script than takes the string we are given to calculate the sum of and creates a list of its characters.

We can then iteratre through the list of characters and match them against the dictionary keys to get the sum (value) of it. If the character is not in our dictionary, we can assume it’s a number and we can use the number to add to the sum.

import sys

char_sums = {'a': '4', 'b': '6', 'c': '8', 'd': '6', 'e': '9', 'f': '12', 'g': '8', 'h': '12', 'i': '16', 'j': '10', 'k': '15', 'l': '20', 'm': '12', 'n': '18', 'o': '24', 'p': '14', 'q': '21', 'r': '28', 's': '35', 't': '16', 'u': '24', 'v': '32', 'w': '18', 'x': '27', 'y': '36', 'z': '45'}

input = sys.argv[1]
char = list(input)
sum = 0
for c in char:
    if c in char_sums.keys():
        sum += int(char_sums.get(c))
    else:
        sum += int(c)
print(sum)

Running the above script and supplying the string provided by the challenge gets us the flag.

Flag

python level20.py 53bc79918220509808a10046f70c67e4
158

Level 20

Challege notes

The password of this level is an MD5 encrypted string which was calculated by combining two random words (without spaces) from »this wordlist« (144kb). Can you find out which two words were used?

94038af05987a8f39820992dbc2d7fea

At this stage the challenges are becoming more and more reliant on programming. This challenge has us download a word list that contains 68847 words. Two random words are taken and their MD5 hash is generated. To solve the challenge, we are asked to find the two random words that were encrypted.

I decided to use Python to figure this out. On an initial research, I found an article. We can use the hashlib to encrypt our combined words to get their MD5 hash. We can then run through the list combining the words from our wordlist, calculate their MD5 hash and compare if this matches the one we are provided.

I am personally not familiar with threading, therefore my script is relatively slow in that respect and this could be considerably sped up with multi-threading, however that wasn’t my aim. Another option is GoLang is meant to have decent multi-threading capabilities.

I essentially came up with two ideas and it was the second idea that worked but either is an option. One thing to consider, I use the 0xf.at Docker container and each time the container is restarted, a new hash is generated.

Solution one

The first solution is to create an application that will run through the word list, combining the two wods and compare the generated hash to the one 0xf.at provided. The script can then alert us to which two words successfully matched the hash.

import hashlib
import sys

def open_file():
    with open('wordlist.txt', 'r') as f:
        words = f.read().splitlines()
    return words

a = open_file()
b = open_file()

for x in a:
    for y in b:
        c = x + y
        calc_hash = hashlib.md5(c.encode())
        hash_val = calc_hash.hexdigest()
        password = "0d5d4abe4a0c61bd3117e895cf90da83"
        print(c)
        if hash_val == password:
            print("The decrypted value is: " + c)
            sys.exit()

Solution two

The second idea is to create a Rainbow Table, which is essentially a pre-compiled table of cryptographic hashes and their plaintext value that can be searched. The idea still works the same, create a table with the combined words and their MD5 hash and once done, search through it for the given hash.

I ran into some limitations with this one. I built the script out on my RaspberryPi and left it running overnight in a screen. By the morning my rainbow table was sitting at 45GB with 939,645,348 lines generated. The first record being aaaa: 74b87337454200d4d33f80c4663dc5e5 and the table only getting to bucktoothbanquets: 93e073c8fb9fd8439fe9bcc28d4b6b41.

This script essentially saves the result of the combined words and their hash to a file.

import hashlib
import sys

def open_file(filename):
    with open(filename, 'r') as f:
        words = f.read().splitlines()
    return words

def save_file(filename,result):
    with open (filename, "a+") as file:
        file.write(result)

a = open_file('wordlist.txt')
b = open_file('wordlist.txt')

for x in a:
    for y in b:
        c = x + y
        calc_hash = hashlib.md5(c.encode())
        hash_val = calc_hash.hexdigest()

        result = "\n" + c + ": " + hash_val
        save_file('rainbowtable.txt', result)

I ended up rebooting my Docker container running 0xf.at and searching through the existing table, I was able to find the result.

Flag

grep -m 1 08b2e0dfcae2a7597fc59b11428179a9 rainbowtable.txt
beckoninghandiworks: 08b2e0dfcae2a7597fc59b11428179a9

Level 21

Challenge notes

The text below are semicolon seperated and scrambled words from »THIS DICTIONARY« (134 KB). Can you unscramble them in 30 Seconds or less?

enisrtven;iecsnlsh;teiava;foeshodrwe;isedvas;ednoida;melslbul;snleos;iaetllr;ictuzedni

I approached Python again to automate out this task. We are again given a wordlist to download and instructions to solve the channel. In this case we are given a string of jumbled words separated by semicolons. When unscrambled, these words match words within the provided word list.

I went through a lot of variations of this script. I first tried to generate each possible combination of a word and compare it to existing words in the list, however this was taking forever.

I then tried to get the length of the longest and shortest words in the provided string and filter out words that did not meet the criteria when reading in the word list, however in the end this removed roughly 3000 words of again 68847 words.

I tried permutating functions, libraries and such but again was taking forever. The winning idea was to read in the provided string, split it at the semicolons and break down each word into characters. Using set() I could ensure we filtered it down to unique characters and I could then use sort() to ensure they were in order. This method was applied to both the word from the provided string and the one from the word list. If the letters matched, the length of the word would be considered to ensure it matched the length of the word from 0xf.at.

Unfortunately this can mean that multiple words are matched that contain the same number of the same characters so it’s currently a few tries before I get a successful string. I’ll update this article if I figure out a better way to solve this challenge.

import sys

input_string = sys.argv[1]
input_list = list(input_string.split(';'))

def open_file(filename):
    with open(filename) as f:
        words = f.read().splitlines()
    return words

def check_words(s,ch):
    return set(sorted(s)) == set(sorted(ch))

word_list = open_file('wordlist.txt')

result = []
for i in input_list:
    char_list = list(set(i))
    char_list = ''.join(char_list)
    for word in word_list:
        wordz = list(set(word))
        if check_words(char_list, wordz):
            if len(i) == len(word):
                result.append(word)
print(';'.join(result))

Flag

python unscramble.py "arccaresi;nliosgh;nllicyoca;esfbiauite;dsroweb;gljoeg;aategidvnl;rntmdaoen;nasnmtaieenis;nactselua"
cercarias;longish;conically;beautifies;browsed;joggle;galivanted;adornment;inanimateness;canulates

Level 22

Challenge notes

You have 10 Seconds to mirror the text below after the last character

04411d099838c1039acdf00d9353ceab

Example: Text: abcdefg1234567890 Solution: abcdefg1234567890987654321gfedcba

For this challenge we are provided with a random string that we are asked to reverse and supply the combined value of the two as the password. What I found based on the example is the last character of the string is skipped, ie in the above example instead of ...78900987... we have ...7890987....

This just required an additional step to remove the last character from the string before reversing it:

import sys

string = sys.argv[1]
remove_char = string [:-1]
reverse = remove_char [::-1]
print(string+reverse)

Flag

python level22.py e86e6429f0ea5c3b91bf3b683202bedf
e86e6429f0ea5c3b91bf3b683202bedfdeb202386b3fb19b3c5ae0f9246e68e