Cracking the Zodiac Killer's 340 Cipher

First of all, I'd like to be honest and tell you that I didn't have much time to do the analysis of the cipher, so consider this to be a really short overview of my ideas and suggestions. Nevertheless I think that some of my findings are quite interesting and maybe even surprising.

Why brute force attacks just won't work with the 340

To perform my brute force attack I wrote a small program (a shell script in fact) that sequentially tests keywords often used by the Zodiac in various positions and then runs a 1000 word dictionary to see if the chosen combinations allow a maximum of common words to be placed, followed by a ranking algorithm to highlight the most promising results.



I ran about 250 million tests on the cipher, without any results. That's exactly what I had to expect, as the cipher is very hard to crack by design when applying brute force methods: it uses 62 different symbols to represent a 25 character set - which means that there are 62 * 61 * 60 * 59 * 58 * 57 * 56 * 55 * 54 * 53 * 52 * 51 * 50 * 49 * 48 * 47 * 46 * 45 * 44 * 43 * 42 * 41 * 40 * 39 * 38 = 2.28643838 × 1042 possible solutions for the key, that's around 2.3*1042 possible keys! On the other hand we have only 340 characters of data.

Cracking this cipher using pure brute force methods would require a terrific amount of computing power, and it should even be impossible for large clusters. But it becomes even more complicated if we consider what we learned from the first Zodiac cipher: single symbols could represent series of characters (I'm quite sure the + is such a character for example), and the Zodiac (intentionally?) misspelled a lot of words so that a dictionary attack might not work at all.

In other words: I don't believe this cipher can be cracked using pure brute force techniques (at least not today). You'll either need a lot of luck or really good intuition when selecting predefined keywords as input if you want to crack it (or both of them).

Some strange coincidences...

I took a closer look at the cipher and found some interesting points - maybe these are just coincidences, but I think they're quite remarkable:

The first three symbols in the cipher are "HER", which looks rather strange. In the second line symbols 4, 7, 9 and 11 could be interpreted as "BODY" ("HER BODY"?) In the last line you'll find Zodiac's symbol right in the middle, followed by the symbols "ZO^AIK"



Could there be a hint?

As far as I know the official interpretation of the 340's complexity is that the Zodiac was quite upset that his first cipher was cracked so quickly, so therefore he made this one so hard to nobody would ever be able to crack it.

If that's true then it will in fact be really hard, if not impossible, to crack it. Therefore I think that the only chance we have is to consider the possibility that the Zodiac made a mistake, that he didn't want to make it that hard and that he *did* want it to be cracked. I think this could be the case, after all the Zodiac was always anxious to get a lot of press coverage. So *if* he absolutely wanted it to be cracked, wouldn't he have tried give us some hints to help us out?

I checked out all the letters the Zodiac sent to the newspapers and found some strange coincidences on the Halloween card he sent about 1 year after the 340 cipher, which says "FROM YOUR SECRET PAL: I feel it in my bones, You ache to know me name, And so I'll clue you in...". It was mailed on Oct 27, 1970, and this is what it looks like:



When comparing the cipher to the Halloween card I noted some really strange things - as already mentioned these could all be just odd coincidences, but I'd say that they're at least notable.

The Zodiac used the word "paradice" on several occasions and always misspelled it (probably intentionally, replacing the "s" character by a "c"). Now take the Halloween card text and map it onto the cipher by skipping characters, you'll instantly note the vertically positioned chacaters "D-I-C-E" in the cipher's center. There's a "P" on the center top of the cipher, and you'll even be able to map "SLAVES" onto it if you consider the minus "-" represents an "S" (maybe the reversed "L" could even represent an "L"?). The following snapshot illustrates what I'm talking about:



But there are more strange coincidences, take the word "BY" for example which is used four times in the Halloween card - you'll find it four times on the cipher too, even if not placed correctly and partially reversed (would it be possible to find the words "FIRE", "GUN", "KNIFE" and "ROPE" too?) This snapshot shows where the word "BY" can be found:



Okay, this is where my current analysis ends, as I just can't afford spending that much time on this. Maybe everything's just strange coincidence, but I find it quite amazing and amusing though.