#Crypto

It turns out that in Python 3, attempting to write non-ASCII characters to a file without using ‘binary mode’ (a mode which deals with ’non-textual data’, hence the name of the challenge) has some less-than-ideal results. Indeed, if you tried providing your plain text to xor.py you might have noticed that there are somehow more bytes in the cypher-text after XORing that you started with in your plaintext. Ultimately, it appears that the write....

The challenge description starts ‘My buddies Whitfield and Martin were trying to share a secret key’, so googling something like ‘Whitfield Martin cypher’ seems like a good place to begin. Immediately we get results for the Diffie–Hellman key exchange, which fortunately can be described in terms of A, B, p, g, and s (the value of the secret key we need). Scripts to brute-force this secret key are easy to find on GitHub....

We’re given the encrypted flag wmysau{foeim_Tfusoli} along with some additional encrypted text to help us ‘Hkgxologflutleiaymt xgf Azutgkrftmtf ltmntf ERW wfr ELW wfmtk Rkweq’. Some familiarity with common cyphers, along with the hint ‘This is a substitution cypher’, give us a pretty good direction to pursue so we decided to use this online tool for brute-forcing the solution. However, trying brute-forcing the text rendered nothing more decipherable than the initial text....