XOR 2 - 40 points
Writeup by poortho
Problem Statement: Miles just sent me a really cool article to read! Unfortunately, he encrypted it before he sent it to me. Can you crack the code for me so I can read the article? Article.txt
Did you know that in typical English writing, a character is the same as the one k characters in front of it about 8% of the time, regardless of k?
As the problem title suggests, the txt given to us is xor-encoded. However, it doesnt seem to be a single character key like last time.
The hint seems to indicate frequency analysis. However, we're all lazy and don't want to do it ourselves, and it turns out there's a handy tool called xortool that can solve this for us!
Running xortool using
$ xortool -x -c ' ' article.txt gives us the following output:
The most probable key lengths: 4: 11.0% 6: 14.3% 8: 9.2% 12: 20.5% 16: 6.5% 18: 8.1% 20: 5.6% 24: 11.9% 36: 7.7% 48: 5.4% Key-length can be 4*n 1 possible key(s) of length 12: frqncyislove Found 1 plaintexts with 95.0%+ printable characters See files filename-key.csv, filename-char_used-perc_printable.csv
Based on the key found, the plaintext probably has the flag! Opening up the file and ctrl+F 'flag' and we find
The flag is primes_are_cool.