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.
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}
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.
Challenge
โTry, try and fail, but never fail to try!โ 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}
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.