Dec 9: Illegal Prime Number

Challenge

I’ve heard something about illegal prime numbers… Maybe this number contains the flag:

43158911230545192278004252344390244064068059909839469541549566950124312835516574175851795
74642755601169096280017484467053951914982126613234225200384245049037787654523558017678649
27807671610820027192757579149792909218423881361984672931551823792488162360311109497907128
60174071535290430666553883163784576942915907036813417525614927231374744822633736732102486
33961843479034160811982934510083276506238457901538373531195688165166964398815874378480986
164601388393975141268984935852959700100872597068350527482364309

Solution

Illegal primes or numbers are the idea that by making certain programs/files illegal, their numerical representation is also illegal. Therefore this number likely represents some files containing our flag.

Lets convert it to binary data:

import binascii

p=4315891123054519227800425234439024406406805990983946954154956695012431283551657417585179574642755601169096280017484467053951914982126613234225200384245049037787654523558017678649278076716108200271927575791497929092184238813619846729315518237924881623603111094979071286017407153529043066655388316378457694291590703681341752561492723137474482263373673210248633961843479034160811982934510083276506238457901538373531195688165166964398815874378480986164601388393975141268984935852959700100872597068350527482364309
p2 = binascii.unhexlify(hex(p)[2:-1])
p3 = bytearray(p2)

with open("dec9out",'w') as outfile:
    outfile.write(p2)

This gives us a zip file:

$ file dec9out
dec9out: Zip archive data, at least v2.0 to extract

The zipfile is password protected, but is found easily using a dictionary attack:

$ fcrackzip -v --use-unzip -D -p /path/to/wordlists/passwords dec9out
found file 'Flag.txt', (size cp/uc     43/    29, flags 9, chk 0a91)
checking pw buigts

PASSWORD FOUND!!!!: pw == qwerty

So the password is qwerty. The Flag.txt file inside the zip file contained the flag.