Q&A: cracking OTP encryption?

On October 13, 2008 , in the course of an email chain with a reader B.L. (name redacted for privacy)  we received the following question. This post is placed behind a cut for minor spoilers through about Evenfall chapter 17. Note: the conversation we had back and forth following the initial question/answer might be interesting for people to read so I included the reader’s question and my answer, and then after that included our back and forth. It’s labeled B.L. for the reader and Ais for me (if that last part wouldn’t have been, you know, self-evident or anything ^_~). Since this conversation happened years ago I didn’t get express permission from the reader to repost this. I am hoping that it is acceptable to share this since there are no identifying details, but if you are the reader and wish for me to remove the conversation please let me know and I will do so immediately. Thank you! Q: How did Jeffrey break the OTP encryption on the second half of Thierry’s disk? A: Good question. Actually, if Thierry hadn’t subtly helped them out, it would have basically been impossible. Jeffrey didn’t mention it but what ended up happening was that as he dug further on the disc, he’d located some small, hidden,encrypted files that at first he’d thought to be throw away, nonsense files. They were each encrypted with a different, long key in a Vigenère square and they’d seemed to just be inconsequential, incomprehensible information to distract from the two larger, more heavily encrypted files. But when he deciphered all those he eventually figured out that mixed in with the mess was the private...