Ramen Lockdown
This is a writeup of the Forensics challenge Ramen lockdown by apoorvCTF
Points: 304
Premise
A criminal mastermind named larry stole Chef Tataka ultimate ramen recipe and yeeted it into a password-protected zip file. Inside? A sacred file with the secret to flavor nirvana. Crack the zip, save the slurp. No pressure. 🍜💀
Challenge files:
Observations
Looking at the challenge file and as mentioned in the description, we’re working with a password protected zip file. We can look Inside the zip file and find a PNG image. There is a method to crack the keys of the password protected zip file as explained here, but essentially, if we have enough known bytes, we can crack the keys of the file. Since the first 12 bytes of a PNG file are known to us, that being 89 50 4E 47 0D 0A 1A 0A 00 00 00 0D 49 48 44 52, we can attempt to run a tool such as bkcrack against the file. We do this with the following command, and get the following output:
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./bkcrack -C recipe.zip -c secret_recipe.png -x 0 89504E470D0A1A0A0000000D49484452
bkcrack 1.7.1 - 2024-12-21
[01:49:06] Z reduction using 9 bytes of known plaintext
100.0 % (9 / 9)
[01:49:06] Attack on 721680 Z values at index 6
Keys: 7cfefd6a 4aedd214 970c7187
41.3 % (297843 / 721680)
Found a solution. Stopping.
You may resume the attack with the option: --continue-attack 297843
[01:50:43] Keys
7cfefd6a 4aedd214 970c7187
We now have our keys, 7cfefd6a 4aedd214 970c7187, with this we can run bkcrack again to generate a passwordless zip file:
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./bkcrack -C recipe.zip -k 7cfefd6a 4aedd214 970c7187 -D passwordless_recipe.zip
bkcrack 1.7.1 - 2024-12-21
[01:53:24] Writing decrypted archive passwordless_recipe.zip
100.0 % (1 / 1)
Solution
Unzipping the unprotected password file, we get the following image: 
Which gives us the flag:
apoorvctf{w0rst_r4m3n_3v3r_ong}