sec000 / rctf_write-ups

Write-ups for the challanges presented in Rooters CTF

RCTF_write-ups

Here lies the write-ups for the challanges presented in Rooters CTF, hosted by Team 1ncogn1to, the CTF team of USICT.

RCTF was a worldwide Free-for-all competition dedicated to InfoSec and CyberSec Community. It was a Jeopardy type capture the flag competition, held online where participants were presented with questions related to Cryptography, Web Hacking, Forensics, Reverse, Steganography and other various fields of cyber and information security.

Overview

URL: http://www.rootersctf.in/ (still online)
Organizer: USICT
Duration: 15 Hrs
Team: 1ncogn1to

Title                           Category           Points         Flag
------------------------------- ------------------ -------------- ------------------------------------------------
Old Is Gold                     Crypto             10             RCTF{INFOXPRESSION}
Francis Secret                  Crypto             20             RCTF{BACONCIPHERISGREAT}
Automate or Die!                Crypto             30             RCTF{b@se64_1s_c00l}
Indecipherable                  Crypto             50             rctf{we_live_in_a_kingdom_of_bullshit}
I love numbers                	Crypto             150            RCTF{1_sh0uld_hav3_gone_with_Sha1_for_3ncrypti0n}

Crypto 10: Old Is Gold

Challenge

Decode this: 444-66-333-666-99-7-777-33-7777-7777-444-666-66
Put the flag in RCTF{}

Solution

Here, Old refers to the old fashioned basic cell phones and the given crypted text contains only repeated decimal numbers. Thus, it seems like the flag is encrypted with an old fashioned keypad just like it was used to type back then.

444 - I
66 - N
333 - F
666 - O
99 - X
7 - P
777 - R
33 - E
7777 - S
7777 - S
444 - I
666 - O
66 - N

Flag

RCTF{INFOXPRESSION}
Note: Flag is case-insensitive.

Crypto 30: Automate or Die!

Challenge

“Try, try and fail, but never fail to try!” Cipher Text

Solution

The given quote suggests repetition and Cipher Text contains a base64 encoeded value. So maybe it's the repeated base64 encyption.

A simple python script can decode it recursively until the flag is obtained.

#!/usr/bin/env python3

import base64

with open("cipher.txt", 'rb') as f:
   flag = f.read()

while True:
   flag = base64.b64decode(flag)
   if flag.decode("utf-8")[0:4] == 'RCTF':
       print(flag)
       exit()

Flag

RCTF{b@se64_1s_c00l}

Crypto 50: Indecipherable

Challange

Sometimes what we are looking for is right in front of us. Cipher Text

Solution

The given Cipher Text is an encrypted zip file which can be cracked by dictionary attack using fcrackzip tool.