- The message is not encrypted with ecb (the simplest cipher mode, not needing an iv - see wiki), but instead something like cbc, cfb or ofb, all of which need an initialization vector. For cbc, its length is 16-bytes (32 hexadecimal digits), for the others I'm not sure, but I'd guess it's the same. I have tested cbc with the two first suggestions by danm, any ideas about what other iv's I can test?
- There are typos in the already decrypted parts of the code. Can someone double check their correctness?
- There are a lot of successful decryptions that turn out to be nonsense, so I use the simple heuristic of discarding messages containing character codes higher than 127. It may be possible that Randall put some "invalid" characters in the message just to mess with this approach.
As this is the pagetopper, I will include the unsolved puzzle for easy reference:
(edited for error pointed out by TrueJournals; thanks!)