This is the first set of number-theoretic cryptography challenges, and also our coverage of message authentication.
This set is significantly harder than the last set. The concepts are new, the attacks bear no resemblance to those of the previous sets, and... math.
On the other hand, our favorite cryptanalytic attack ever is in this set (you'll see it soon). We're happy with this set. Don't wimp out here. You're almost done!