this is from an IT Security exercise which my friend and me cannot solve.
- 2 AES-CTR stream-cipher encrypted files
- Same known initalizing vector
- Same (unkown) key
- Same 128bit Counter initialized with 0
- Files are .png so there is known plain text in both files (the file header)
Our approach was to use the known equivalence of
$E(A) \oplus E(B) = A \oplus B$
From there the only option we see is to brute force $A$ and $B$ for the known $\oplus$ product.
Is there a smarter way to get $A$, $B$? Thanks for any hints!