Hello everyone!
It’s Maruf here from Knight Squad.
Recently we’ve played a CTF. And this is a writeup for a cryptography challenge named “CJK”.
Though I’ve solved that problem, I would love to solve it again with you.
So,let’s solve it together.
In the challenge, we can see that we need to find out a pin number to unlock a locker. And as a clue we got a google drive link.
Following the link, we can find a photo.
The Photo includes Three special symbols with “Plus” signs in between them.
But what are these symbols?
We have no Idea!
So let’s dig a bit more.
We don’t have any major clue in the challenge except that the Flag is a Pin Number and it will be a positive number.
The another thing that is catching my eyes is the Challenge name “Cjk”.
What does Cjk stand for?
Okay. Let’s google for it.
Now we can see that CJK is an abbreviation for Chinese Japanese & Korean. And we also get a rich wikipedia page about CJK Characters.
And in the wikipedia, we can see, CJK is unicode encoded as well.
So, let’s google for CJK unicodes and we get www.unicode-table.com at the top of the search result. So, let’s look inside it.
In the page we find lot of cjk characters.
But none of them looks like the characters we have in our clue picture.
So, what they actually are?
Maybe they are some kind of special characters.
Okay, let’s google for it.
And google returns us this.
Let’s follow the first link.
Viola! Can you see something similar with our picture?
Look at the 5th Symbol U+3004. It is the same symbol we have in the second position in our picture.
Let’s scroll the page a bit down if we can find the other two symbols.
And here we can find U+3012 and U+3013 a bit similar with our picture.
But we have a circle around the U+3012 symbol in our picture.
Let’s scroll a bit down if we can find something more similar.
Aha! here we have U+3036. Which is similar to the first symbol of our picture.
So, now we have three unicodes that are similar to our pictures.
They are:
- U+3036
- U+3004
- U+3013
In the picture, we can see that we have Plus sign between the symbols.
What does it mean?
Are they telling us to sum up the symbols!
But it is not possible. And even if we manage to add the symbols somehow, that won’t be our flag. Because the flag is just a pin number.
What can we do now?
I have an idea.
Let’s sum up the Unicodes of the characters and see if it gives us any flag or not.
So,
3036+3004+3013 = 9053
Let’s wrap up 9053 with SHELL{} and check the flag.
And Yeah! That was our flag.
The challenge was interesting. Hope you enjoyed it too.
Don’t forget to share your feedbacks in the comment section below and stay tuned with us for more interesting challenge walkthroughs in the future.