Invisible WORDs

CHALLENGE DESCRIPTION

SOLUTION

After trying some zsteg, exiftool, binwalk, steghide, strings,... and have nothing useful.

Let see its content in hex by hexeditor or cyberchef

We can see PK, it reminds me of ZIP file. Let search it, and we can see magic number of it is 50 4B 03 04. Let write a script to loop through 4 bytes and copy 2 bytes of it.

def extract_2_bytes_every_4(input_file_path, output_file_path):
    with open(input_file_path, 'rb') as infile, open(output_file_path, 'wb') as outfile:
        while True:
            chunk = infile.read(4)
            if len(chunk) < 4:
                break  # End of file or incomplete 4-byte block
            outfile.write(chunk[:2])  # Write only the first 2 bytes of every 4

extract_2_bytes_every_4('output.bmp', 'x')

After running the code, we have the output, binwalk -e [file] we can see the file hidden in it. Open the file and search for the flag.