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Hitanshu Gedam
Hitanshu Gedam

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picoCTF transposition-trial writeup

In this challenge we are given a message.txt file. Using wget we download it on the webshell and read it

pico webshell

We see a pattern: Every third character is supposed to be transported 2 places back.
I wrote a simple python script on Programiz:

def decode_message(txt):
    n = 3
    txt_3 = [txt[i:i+n] for i in range(0, len(txt), n)]
    decode_lst = [chunk[2] + chunk[0] + chunk[1] for chunk in txt_3 if len(chunk) == 3]

    return ''.join(decode_lst)

encoded = "heTfl g as iicpCTo{7F4NRP051N5_16_35P3X51N3_V9AAB1F8}7"

print(decode_message(encoded))
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And we get the flag!

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