Cracking a Playfair Cipher

When I was a kid I used to take code books out from the library. I'd spend days writing secret messages to myself and trying to get friends to play along but no one else is insane enough to spend too much time encrypting and decrypting inane messages. As part of my ongoing treasure hunt I now have an encrypted message to decrypt using one of those old ciphers I used to mess around with. It's a Playfair Cipher, where essentially you build a 5x5 matrix from a keyword followed by the rest of the alphabet in order. You take your plaintext that you want to encrypt, split it into pairs of letters, and then encrypt the letters using the matrix. (Note a 5x5 matrix has only 25 spaces so you need to drop a letter. Generally this is done by eliminating Q or combining I and J together.) In this way you have 600 different 'characters' (or digraphs) instead of just 26 with most normal ciphers. This really ramps up the complexity when it comes to decrypting it without the key. (A normal substitution cipher is easy enough it gets included in standard puzzle magazines as Cryptograms or Cryptoquotes.)

At any rate, I'm working on one of the chapters in The World's Greatest Treasure Hunt. Each chapter has 20 questions to answer and I've worked out 18 of them. The two that remain are "What is the password given in this chapter?" (the real crux of the treasure hunt is figuring out what in the world these passwords might be I think) and a Playfair Cipher where they've encrypted a trivia question about Pirates of the Caribbean. They didn't give me the key, unfortunately, though they did include the note "the password is the key". I'm operating under the assumption that the answer to the first question is therefore the key to the code in the second question. They have a website up where you can enter in answers and check if they're right (that's how I know I have the other 18) and there is a fixed number of blanks for each answer. So, I believe the password has 6 characters.

Now, the ciphertext of the trivia question is pretty short so a lot of common codebreaking tricks won't work. I can't check for commonly occuring digraphs, for example, since there are 600 possible digraphs and only 25 in the ciphertext. My first thought was I should just write a program to brute force it, but there are 244 million possible 6 letter keys with 25 letters in my alphabet. Assuming 2 seconds per test I'd be looking at more than 15 years of processing time. My guess for how long each test might take could be off, but I doubt it's off enough to make up that gap. I could narrow things down more by only using common words in the hope the key is a real word, but that's not going to save enough time.

So I got to thinking... This is a trivia question, right? Most questions start with one of 5 words: who, what, when, where, or why. All 5 of those words start with the same two letters. So, what if I restricted my matrixes to ones where the first digraph (Ye) decrypts to Wh. I messed around a bit on the bus this morning and established 19 possible ways to have a 6 letter key which results in Wh turning into Ye. (That there is only 1 letter between W and Y and 2 between E and H narrow things down a lot and also make it pretty plausible that this is the right decryption of Ye.) I'm going to quantify things a little more when I get a chance but I'm pretty sure this will drastically reduce my search space for the key.

On top of that, 4 of the letters in the ciphertext are capitalized. The first letter, of course, but then 3 more later on. Most likely these are refering to a name or place from the movie and I may be able to find more restrictions on my key if I work from the capital letters. A digraph actually repeats itself shortly after two of the capitals as well, so the capitalized words share letters. I have a hunch I need to flesh out more on the bus, but I think I may be able to lock down a couple more conversions. The second digraph of the whole ciphertext (which I suspect is o_, at, en, er, or y_ if the first one is really Wh) is reversed and found in one of the capitalized words which now that I'm looking at it more really gives me an idea. Time will tell!

Gift Certificates

I'm not a big gifty person in general and gift certificates in particular are a little weird. On the one hand I get to get whatever I want, but on the other hand it feels even more impersonal. At any rate, I got a gift card to a book store and decided to buy some things not so much that I wanted but that I thought I might have gotten as gifts. Things people might think I want! Normally this wouldn't be very relevant here but some of it is at least tangentially gaming related and I wanted my mother to see what I got. Might as well put it here!

First up I actually wanted to get the next book in a series of mystery books I've been reading. I have the first 12 and figured someone might know that (they're on my bookshelf) and pick out #13. Well, it turned out they had books 1-12 along with 14, 15, and 16 of the series but no #13. Oh well. I wandered around the mystery section a bit and saw a book with dice on it. It was from a series but it looks like the books are all unrelated so who knows!

Then I headed over to the gaming section. I lent out my Backgammon for Blood book or lost it and can't find it and wanted to look for a replacement. Turns out they didn't have any backgammon books that I could find. But they did have a little book of celtic enigmas. 117 pages of puzzles and brain twisters attributed to celts? That sounds like something I might like!

I wandered a bit more and saw a big display with a board game marked 75% off. Probably terrible, but I gave it a look. Turned out it was a game based on a book series. The game didn't look very good but the premise sounded interesting. So I picked up the first book in the series and figure I can always go back and get the other two and the board game too if it ends up great. (The Hunger Games is the book. It's published by Scholastic so it may be a kids book, but we'll see.)

I was turning to leave when the ultimate book caught my eye. The second I saw it I knew my mother would have bought it if she'd seen it. "The World's Greatest Treasure Hunt. Quest for the Golden Eagle. A $1 Million Treasure is hidden SOMEWHERE in the world. All you have to do is FIND IT." I had Treasure Quest as a video game when I was in high school which purported to be a treasure hunt with a million dollar prize. According to Wikipedia there was some controversy over awarding that prize but I never came close. I was a failure at hunting for treasure in a video game. But maybe in book form I can pull it off? As an added bonus the book's writer is donating a lot of the proceeds from the books to breast cancer research, so it's win win. As I understand the book is a year old so it's either super hard or already solved and I'll have to do some searching on the topic to see but it should be interesting to say the least. I can remember reading a treasure hunt book my parent's had which had to do with cat puppets and tracing lines through their eyes or something. It was fun reading that despite the fact it had been solved years earlier.

At any rate, if it turns out the hunt is still on then I may try to harass other people into joining in on the hunt. If I can't find the Golden Eagle myself then maybe someone can help!