This challenge was pretty interesting when I tried it, as I’ve never encountered a “blank” .txt file before.
As per normal, we first download the provided file by using wget <link> to understand what we’re dealing with.
Downloaded file
The downloaded file is called whitepages.txt. As both the name of the challenge and the downloaded file suggest, there was “nothing” inside this file when I ran cat on it. I received the same output when I usedstrings.
I actually tried exiftool and other methods when I first attempted this challenge as well, but they did not provide me with any clue on how I should proceed.
Viewing the hex
I then tried to use hexedit to view the file in hexadecimal. Other hex editors are also fine. Since hexedit shows a file both in ASCII and in hexadecimal, the presence of the dots (‘.’) on the right show that the file was not empty, but contains non-printable ASCII characters. This is because dots usually appear in place of non-printable ASCII characters or characters that cannot be displayed properly.
I realised that throughout the entire file, there were 2 recurring values. These are e28083 and 20.
Binary?
Since there were exactly 2 recurring values, I thought that they could be hinting about binary numbers, 0 and 1.
Obtaining the flag
With this idea, I used xxd to store the hex dump of whitepages.txt in a file called output.txt. I will be using a Python script to convert the 2 recurring values in the hex dump into 0s and 1s.
Conversion
Python script
hex = ""with open("output.txt", "r") as file: for line in file: row = line.strip()[10:49].split() # Example row: ['e280', '83e2', '8083', 'e280', '83e2', '8083', '20e2', '8083'] hex += "".join(row)bin = hex.replace("e28083", "0").replace("20", "1")print(f"Binary:\n{bin}")for i in range(0, len(bin), 8): byte = bin[i:i+8] print(chr(int(byte,2)), end='')
I tried to replace e28083 with 1 and 20 with 0 at first, but the output I received was gibberish. After swapping the substituted values, I could finally get the flag.
I then tried to use 