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The Few Chosen(TFC) CTF Writeup

Forensics

AAAAA

Flag: TFCCTF{Gr4phic_d35ign_is_my_p455ion}

File given with this challenge: AAAAA

I tried to look what file it was by running the file command. But it showed only data. So I checked it in hexedit and saw a bunch of As in the beginning of the file and after those As there was some interesting stuffs. So I ran foremost AAAAA and got the flag as a png file:

Flag Image

Crypto

Sea Language 1

Flag: TFCCTF{WH4T-AR3-Y0U-S1NK1NG-AB0UT?!!!?}

Cipher given with the challenge:

.-- .... ....- - -....- .- .-. ...-- -....- -.-- ----- ..- -....- ... .---- -. -.- .---- -. --. -....- .- -... ----- ..- - ..--.. -.-.-- -.-.-- -.-.-- ..--.

I knew it was morse code just by looking at it. So I decoded it and got the flag.

Sea Language 2

Flag: TFCCTF{w417_4_m1nu73..._7h15_1s_n07_m0rs3!!!!!r1gh7?}

Cipher given with the challenge:

._._._.. ._...__. ._....__ ._....__ ._._._.. ._...__. .____.__ .___.___ ..__._..
..__..._ ..__.___ ._._____ ..__._.. ._._____ .__.__._ ..__..._ .__.___. .___._._
..__.___ ..__..__ .._.___. .._.___. .._.___. ._._____ ..__.___ .__._... ..__..._
..__._._ ._._____ ..__..._ .___..__ ._._____ .__.___. ..__.... ..__.___ ._._____
.__.__._ ..__.... .___.._. .___..__ ..__..__ .._...._ .._...._ .._...._ .._...._
.._...._ .___.._. ..__..._ .__..___ .__._... ..__.___ ..______ ._____._

When I first looked at the cipher, I thought it was morse code, but I was wrong. After some thoughts, I found out that all of them are splitted by 8 characters, so I translated it into binary by replacing . with 0 and _ with 1 and then put it on an online decoder and got the flag. The below code will do the same:

def binary_to_ascii(binaryString):
    return "".join([chr(int(binaryString[i:i+8],2)) for i in range(0,len(binaryString),8)])

encoded = """
._._._.. ._...__. ._....__ ._....__ ._._._.. ._...__. .____.__ .___.___ ..__._..
..__..._ ..__.___ ._._____ ..__._.. ._._____ .__.__._ ..__..._ .__.___. .___._._
..__.___ ..__..__ .._.___. .._.___. .._.___. ._._____ ..__.___ .__._... ..__..._
..__._._ ._._____ ..__..._ .___..__ ._._____ .__.___. ..__.... ..__.___ ._._____
.__.__._ ..__.... .___.._. .___..__ ..__..__ .._...._ .._...._ .._...._ .._...._
.._...._ .___.._. ..__..._ .__..___ .__._... ..__.___ ..______ ._____._
"""
encoded = encoded.replace(".", "0").replace("_", "1")  # Translating it into binary
encoded = encoded.replace(" ", "").replace("\n", "")   # Removing all the spaces and newline characters
print(binary_to_ascii(encoded))

Holiday

Flag: TFCCTF{don't_come_today_there_are_dogs}

Description
I've always wanted to visit my friend! He's not fluent in English,
but he does know a few words. This made communicating a problem.
We did, however, talk about each other a lot! He knows I'm allergic to dogs,
and I know that his favourite colour is green! Before leaving for the airport,
he left me a message. He's not much into technology so his crypted message really
confused me!Can you tell me what he said?

Maui: mai hele mai i kēia lā aia nā ʻīlio

So I tried putting mai hele mai i kēia lā aia nā ʻīlio into google translate and got this: don't come today there are dogs. So I tried changing this into the flag format by replacing spaces with underscores and got the flag!

Misc

Discord Shenanigans

Flag: TFCCTF{th1s_5t3g0_fl4g_w45_n0t_h1dden_w3ll}

Description
We considered giving you a free flag. However, we decided against it. In general, we would never do that! Or would we? That's the beginning of a good CTF! Discord is the new Twitter.

To be able to solve this challenge, you'll need to join our discord. Link in the Rules page.

So many people used bot commands in the CTF's server, but that was not how you could get the flag. I had found a suspicious old message from the author of this challenge in the general channel. A suspicious message from the author of the challenge

I googled so many decrypters for this but none I could find. Finally, a friend of mine gave me this link https://holloway.nz/steg/ which was a decoder for this message. So i took this message and put it in the decoder and got the flag!

Weird Friend

Flag: TFCCTF{why_ar3_QR_C0d3s_s0-complicated!?o00o0f}

Cipher given with this challenge:

1111111001110110010000111111110000010000110100110101000001101110100111001110010010111011011101010110100000000101110110111010101010001101001011101100000100110001011000010000011111111010101010101010111111100000000010010000000100000000110001110110110101000000110000010010000100011000101011010111000110110110011110010111100101001010011001100000010110111001111101101011101101110011111010100001011111001011111000011101101100011110101101000000010000100000000101111010110001000010100101100110000110000101111010101010111101101110001101101011111001110100001100110011001010100101001111001000100100101110110001011111111000000000010110001001110001001111111110101010010110101011100100000101010100000011000110111011101001010011000111111000010111010010110111110110101001101110100110000111000001111101000001010010010000110101110111111110101111100101000000100

At first I thought this was binary, but I was wrong. After a lot of playing around with this challenge, A friend of mine said maybe it will be a QR Code. So I googled for binary to qr code generator and got this site: https://bahamas10.github.io/binary-to-qrcode/. So I put the binary in the binary field and got a QR Code. Then I decoded it using https://zxing.org/w/decode.jspx and got the flag!

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