CR1: Ultracoded

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Fady didn’t understand well the difference between encryption and encoding, so instead of encrypting some secret message to pass to his friend, he encoded it!

Hint: Fady’s encoding doens’t handly any special character

zero_one

The input file is a set of words ZERO and ONE. Further analysis shows that it is a Base64-encoded Morse code. Let’s put this knowledge in a script:

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from pwn import *
import morse_talk as mtalk

with open('zero_one', 'r') as f:
    data = f.read().translate(None, ' \n')

data = data.replace("ZERO","0").replace("ONE","1")
data = b64d(''.join(chr(int(data[i:i+8], 2)) for i in xrange(0, len(data), 8)))

data = mtalk.decode(data)

print data

When we run the script we get the flag:

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$ python solve.py 
ALEXCTFTH15O1SO5UP3RO5ECR3TOTXT

Because Morse code does not handle special characters we have to fiddle with the flag a bit more. Here is the final version: ALEXCTF{TH15_1S_5UP3R_5ECR3T_TXT}.