What format is the answer expected to be in? It isn't accepting the concatenation of the plaintexts.

The solution is the two plaintexts concatenated in alphabetical order. There may be more than one solution, but the correct one should be obvious. If the plaintexts are jibberish it's not the correct solution. If you think you have the correct solution but it's not being accepted feel free to email us.

Accidently posted here instead of the solutions page

I believe I got the right answer but its not accepting. Corresponding to two ciphers, I got p1 & p2 and then I did p1 concat p2 ( since first char of p1 < first char of p2)

You can email us with the specifics if you think your answer is correct.

https://crypto.stackexchange.com/questions/2991/why-must-iv-key-pairs-not-be-reused-in-ctr-mode

I don't expect a response, since there is little activity in this thread.

The problem I have is the punctuation. There are a few choices that make sense. Which is correct?

I have tried submitting every possibility with printable characters that could make sense at the end of each message, and capital letters at the beginning of each. All are rejected. My email goes unanswered.