Python Wrangling

  • Given 3 files : ende.py , flag.txt.en , pw.txt

Analyze ende.py :

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import sys
import base64
from cryptography.fernet import Fernet

usage_msg = "Usage: "+ sys.argv[0] +" (-e/-d) [file]"
help_msg = usage_msg + "\n" +\
"Examples:\n" +\
" To decrypt a file named 'pole.txt', do: " +\
"'$ python "+ sys.argv[0] +" -d pole.txt'\n"

if len(sys.argv) < 2 or len(sys.argv) > 4:
print(usage_msg)
sys.exit(1)

if sys.argv[1] == "-e":
if len(sys.argv) < 4:
sim_sala_bim = input("Please enter the password:")
else:
sim_sala_bim = sys.argv[3]

ssb_b64 = base64.b64encode(sim_sala_bim.encode())
c = Fernet(ssb_b64)

with open(sys.argv[2], "rb") as f:
data = f.read()
data_c = c.encrypt(data)
sys.stdout.write(data_c.decode())


elif sys.argv[1] == "-d":
if len(sys.argv) < 4:
sim_sala_bim = input("Please enter the password:")
else:
sim_sala_bim = sys.argv[3]

ssb_b64 = base64.b64encode(sim_sala_bim.encode())
c = Fernet(ssb_b64)

with open(sys.argv[2], "r") as f:
data = f.read()
data_c = c.decrypt(data.encode())
sys.stdout.buffer.write(data_c)

elif sys.argv[1] == "-h" or sys.argv[1] == "--help":
print(help_msg)
sys.exit(1)

else:
print("Unrecognized first argument: "+ sys.argv[1])
print("Please use '-e', '-d', or '-h'.")
  • help_msg tells us we can use -d to do decryption.

  • The program needs a password to decrypt the encrypted message.

My thoughts to get the flag :

  • Use decrypt option -d .

  • Use pw.txt as the password.

Command to get the flag

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python3 ende.py -d ./flag.txt.en < pw.txt