writeups

Juniors CTF - 300 - Six Strange Tales - Web

noraj (Alexandre ZANNI)
, , ,
🇬🇧

Information#

Version#

By Version Comment
noraj 1.0 Creation

CTF#

Description#

categories: web

  • Gruncle Stan, what's the secret of the six fingered hand?
  • Can you see these codes? When the six fingered hand touches them, one of the Gravity Falls secrets opens!
  • Gruncle, but how should we read the secret? From left to right or right to left? Or maybe upside down?
  • It depends on whether you are a Christian, a Muslim or a Taoist...

Lupanov M.Iu.

Solution#

Let's see source code of the web page:

[...]
<canvas id="img" width="717" height="380">
flag={fH7eAHJT3tXWD1e7afAvVfhcb}      
</canvas>
<script type="text/javascript"> <!--
window.addEventListener('load', function () {
var b = document.getElementById('img');
var a = b.getContext('2d');
var d = new Image();
d.src = "http://i.imgur.com/GIYH3fA.png";
d.addEventListener('load', function () {
a.drawImage(this, 0, 0);
k = 174;
l = 345;
m = 12;
n = 89;
o = 671;
p = 18;
q = 222;
r = q-1;
c="rgba(0,0,0,0)";
if (navigator.userAgent == "Gravity Falls")
c=c.replace(/(0)(\))/,"$1.5$2");
a.fillStyle = c;         
a.fillRect(q%m-6, k-3, n+r-q-2, 5-(p-q));
a.fillRect(2*(q+1), p+1, n+r-q+2, l+16);
a.fillRect(l+r-30, o%p-5, 2*l-600, q+5-p);
a.fillRect(q%n+42, o%p-5, o-600+p+1, 2*(p+1));
a.fillRect(176, o%p-5, 2*l-600, q/2*3+47);
a.fillRect(2*k+p-100, q%m-6, o-600+p+1, n+r-m/2);
a.fillRect(o%p-5, q%m-6, 2*l-604, k-p-4);
a.fillRect(2*k+p-100, q/2*3-10, 3*m+p*3, (p+1)*3);
a.fillRect(2*k+p-m+2, q%m-6,2*l-600, q+n+m-190);
a.fillRect(2*k+p-10, k-p-m/3, o-600+p+1, r+m*2/3+p);
a.fillRect(n-3, q-k+9, 2*(l-300), q+n+m);
a.fillRect(l+q-31, q+m/2,2*l-600, k-p-m/3);
a.fillRect(o-2*p-p/2, q%m-6, 2*l-600, q/2*3+47);
},false);},false);
// --></script>

flag={fH7eAHJT3tXWD1e7afAvVfhcb} is not the good flag, it needs transformations.

We can see that we need a different user agent: Gravity Falls.

We changed our user agent to Gravity Falls and reloaded the page, the image has changed:

Let's mix them: AhWae2Oh, Is4feeh3, ud2juD9a, aej8eeTh, Maiy2au0, dawu0Aeb.

  • left to right: AhWae2OhIs4feeh3ud2juD9aaej8eeThMaiy2au0dawu0Aeb
  • right to left: dawu0AebMaiy2au0aej8eeThud2juD9aIs4feeh3AhWae2Oh
  • upside down: Maiy2au0Is4feeh3aej8eeThAhWae2Ohdawu0Aebud2juD9a

http://gravityfalls.wikia.com/wiki/Scary-oke is no help.

AhWae2OhIs4feeh3ud2juD9aaej8eeThMaiy2au0dawu0Aeb was the flag.

Feedback: This is more a joy than a web and this isn't really about security. I'm tired to see challenge like that. No flag format, flag are meaningless so it may be hard to know when you get the flag or not, they need to use a flag format or give in the description what the flag have to look like.

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