26 September 2006

9/26 cryptogram solution

Here is yesterday's cryptogram:
ICLAVYCO AVIA YT MPZAV HCPMYCO PCW SZIJAYJIUUL AWIJVWT PCWTWUN, ICQ AVW ZWTA PGAZEQWT YATWUN TPPCWZ PZ UIAWZ. -- TIHY
Even as I type this post (I started composing it yesterday right after I posted the cryptogram), I don't know the answer. So hopefully you'll see how I go about solving it. You might compare that to how you solved it.

My first guess is that this is a quote from a notable person, thus "TIHY" is the name of the person.

The second part that sticks out to me are the second and third word from the end: "TPPCWZ PZ". I think its important to take these two words together. Why? PZ is a two-letter word, presumably a common one (it, is, of, in, and to). Assuming of one those is correct, P is equal to i, o, or t. The previous word (TPPCWZ) contains too consecutive Ps. The most common double letters in order of frequency are SS, EE, TT, FF, LL, MM, and OO. Combining these two ideas, it seems likely that P represents o or t as a double i is very unlikely.

How would frequency analysis help? Perhaps some. A and W appear the most at 11 times, while C, I, P, and T appear 8 times. Z appears 7 times, while Y appears 6, and U and V appear 5 times. Every other letter is 3 or less. Six letters (B, D, F, K, R, and X) don't appear at all. Based on this, we might guess that either A or W represents e. Absent any additional information, it would be hard to take frequency analysis much further.

However, we do have more to go on: there is an additional two-letter word YT and two three-letter words, ICQ and AVW. Remember how we said A or W represents e? Here's a three-letter word AVW and we know the is the most common three-letter word. So let's assume W represents e. Furthermore, A represents t because it appears 11 times (tied for first, and T is second most common in frequency analysis) and V would represent h. Here is our cryptogram so far:
ICLthYCO thIt YT MPZth HCPMYCO PCe SZIJtYJIUUL teIJheT PCeTeUN, ICQ the ZeTt PGtZEQeT YtTeUN TPPCeZ PZ UIteZ. -- TIHY
No solution yet but we have more clues! The second word "thIt" is "that" as nothing else fits reasonably, thus I represents a. This gives us a three-letter work aCQ (and? ask?). Let's try and because C is about as common as we can expect n to be:
anLthYnO that YT MPZth HnPMYnO Pne SZaJtYJaUUL teaJheT PneTeUN, and the ZeTt PGtZEdeT YtTeUN TPPneZ PZ UateZ. -- TaHY
We're making progress! The first word "anLthYnO" is probably anything, so we can assume L represents y, Y represents i, and O represents G:
anything that iT MPZth HnPMing Pne SZaJtiJaUUy teaJheT PneTeUN, and the ZeTt PGtZEdeT itTeUN TPPneZ PZ UateZ. -- TaHi
How about "teaJheT"? Looks like teacher to me. However, we have a two-letter work iT remaining: ir doesn't seem right, so teacher is probably teaches. So J represents c and T represents s:
anything that is MPZth HnPMing Pne SZacticaUUy teaches PneseUN, and the Zest PGtZEdes itseUN sPPneZ PZ UateZ. -- saHi
SZacticaUUy is our next challenge. Could UU be anything other than ll? Probably not. The word appears to be practically. So S represents p, Z represents r, and U represents l:
anything that is MPrth HnPMing Pne practically teaches PneselN, and the rest PGtrEdes itselN sPPner Pr later. -- saHi
We're almost there! Remember how we said that PP was oo or tt? Now it becomes clear: sPPner is sooner; P reprents o. MPrth becomes Morth and thus M represents w (worth); HnPMing becomes Hnowing and thus H reprents k (knowing); PneselN becomes oneselN and thus N represents f (oneself):
anything that is worth knowing one practically teaches oneself, and the rest oGtrEdes itself sooner or later. -- saki
Our last two letters to solve are G and E. They only appear once so frequency analysis doesn't help. Our only solution is to figure out the word based on the context of the rest of the quote. In this case, the only word that makes sense to be is obtrudes, so G represents b and E represents u.

Checking the solution, we find (quite anticlimatically) that we were correct (as if anything else could possibly make sense; capitalization added):
Anything that is worth knowing one practically teaches oneself, and the rest obtrudes itself sooner or later. -- Saki
I confess I have no idea who Saki is, so that last word didn't help me at all during the process of solving this cryptogram. If you had no idea either, go here and find out for yourself!

We talked a little bit about frequency analysis, but we acknowledged the cipher text was probably too short to be of much help. So how does our final solution compare to our twelve most common letters EATOINSHRDLC?

EATOINSHRDLC
TENAOSRILHCK

Not bad, considering. Eleven of the twelve letters match; only K replaces D (and the extra K due to Saki's name is the cause for that; remember what I said about proper names and frequency analysis).
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