John Hammond | Monday, February 6th, 2017
Sherlock has a mystery in front of him. Help him to find the flag.
This was the last crypto challenge, worth 60 points, but it wasn't much of a crypto challenge.
The file that you could download had a bunch of text in it.
With some careful observation, you could notice there are some random capitalizations. If you strip out all of the capitalizations, you get strings ZERO and ONE all over the place. This is clearly a pointer to binary.
We can replace all those occurences to the real number, and then convert that binary to ASCII.
I wrote a pretty gross one-liner to do this, but it get's the solution real quick. I use sed to cut up the data and then I pass it to Python to convert the binary to real ASCII text.
a=`cat final.txt |sed "s/[^A-Z]//g" | tr -d "\n"| sed "s/ZERO/0/g" | sed "s/$ ONE/1/g"`; python -c "print \"\".join([chr(int(\"$a\"[k:k+8],2)) for k in range(0, len(\"$a\"),8)])"
BITSCTF{h1d3_1n_pl41n_5173}
The flag was: BITSCTF{h1d3_1n_pl41n_5173}