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Jumbled snake

Category: Crypto

Description

Can you unravel the jumbled snake?

Attachments: print_flag.py.enc jumble.py

Write-up

  • Our objective in this challenge is to obtain the original, decoded version of print_flag.py by decoding print_flag.py.enc.
  • The code snippet in jumble.py indicates that the encoded content of print_flag.py starts from the second line in print_flag.py.enc, as seen in the following code:
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    dst.write(doc + '\n')
dst.write(subs(src.read(), key))
  • Furthermore, jumble.py contains the shebang /usr/bin/env python3, which is likely used in print_flag.py.
  • To begin decoding the file, we can use a hexdump tool to examine the encoded file content and attempt to map it to the given shebang. By doing so, we can partially decode print_flag.py.
  • We can further improve our mapping by solving the characters in {'the_quick_brown_fox_jumps_over_the_lazy_dog': 123456789.0, 'items':[]}, which is part of decode_flag.__doc__.
  • We can then continue refining our mapping by solving the characters in check.__doc__.
  • Using these information, our mapping can be used to obtain the fully decoded print_flag.py.
  • Within print_flag.py, the value of the variable coded_flag can be base64 decoded to obtain the flag.
  • The script to fully decode print_flag.py.enc can be found here.

Flag: sdctf{U_unRav3led_tH3_sn3k!}