Hello all,

I’m a newbie on this forum and I just want to share with you some thoughts I had about the Z13 cipher.

I don’t think I’ve seen elsewhere the approach which I’ll try to explain here, and which seems to provide a very simple (too simple ?) solution to the Z13 cipher (if this is not the case, my apologies in advance for having rediscovered something that has already been done before).

I assume that the Z13 code was designed to be deciphered (and not as an unbreakable code or gibberish) : we can easily imagine the Zodiac being torn between his desire to show his intellectual superiority by imagining complex ciphers, but also his will that these codes can be deciphered so that their content can be known to the public.

However, using a substitution cipher for the Z13 (as for the Z408 or Z340) would not easily lead to a decodable message, since the text here is too short to find the correct key. The various tests carried out, assuming that the code was written using the substitution method, do not seem to give very satisfactory results : so we can imagine that the coding method for the Z13 cipher is a little bit different from those used in other longer codes.

The hypothesis made here is that an extremely simple, even simplistic, coding method was used. Let’s just put the Z13 cipher upside down.

Assuming that the alphabetic signs stand for what they are (except for the letter M which becomes W because of the rotation), it’s very tempting to read something like "want to know …". Given the context ("My name is ___"), it is clear that the question "want to know my name?" would make sense.

I know that’s seeing in this code something like "want to know my name ?" is totally arbitrary and that the decryption of the others zodiac’s ciphers taught us that it’s not really a good idea to pick up directly readable words in the code (for example, the "wrong" signature ZOΔAIK at the end of the Z340 cipher). But let’s try and see where it takes us !

If we try to develop this intuition, we obtain something like that. Note in particular that :
– the letters of each word are generally mixed up and they are all the more mixed as we advance in the code ;
– when two words share a common letter, this letter appears only once and make the junction between these two words (the mixing is choised to allow this junction) : T for want/to, o for to/know et m for my/name (no junction letter for know/my).

As indicated above, the alphabetic signs are unaltered by the coding process, with the exception of the letter M, which becomes W due to the rotation of the code. And every non-alphabetic sign is decoded as follows:
– The "anchor sign" represents the letter T;
– The "O/8 sign" is a "joker sign", which can represent several letters : the first one (therefore the third one in the initial direction of the cipher) represents an O, the second one an N and the third one a Y. It’s a huge difference with the Z408 and Z340 ciphers, where each sign encodes only for a single letter ;
– The "crosshair sign" represents the letter M.

I stress the fact that, in this way, each non-alphabetic character must absolutely correspond to just one letter: there is no arbitrary choice to make it correspond to this or that letter. The "anchor sign" must be a T to give "WANT", the first "O/8 sign" must be a "O" to form "TO", the second one must be à "N" to form "KNOW", the "anchor sign" must be a "M" to make the junction beetween "MY" and "NAME", and the last "O/8 sign" must therefore be à "Y".

If we go back to the initial code, we obtain something like this :

There are several ways to continue, knowing that the more manipulations you add, the less realistic the solution is.

1/ We can just stop right here : the answer to the question "My name is ___" is simply a new question "want to know my name?", which is in the spirit of what we can expect from the Zodiac. Simply a new taunt about his identity (I don’t think it’s credible to wait for him to reveal his real name in this code …).

2/ Look only at the non alphabetical signs : one can imagine that the coded signs have a particular value. The non-alphabetical sequence can be read as "M / Y / N / O / T". If you absolutely want to see a name there, you can read from right to left "TONY M" or an anagram of "MONTY". But I don’t think these solutions are very credible and I write them only to try to review all possibilities.

3/ Search for particular words in the entire code : there can be a lot of different solutions but here are my favorites.

If we take only the odd letters, we get "A / N / Y / N / O / N / M" : it does not take too much imagination to see the word "ANONYM", in the form of an anagram (unfortunately with an extra N, which weakens this approach). Of course, we can also find this type of solution by arbitrarily selecting the letters in the code (and not just the odd letters) : the reading direction of the words is preserved here, but the letters are selected arbitrarily, which also weakens the solution. It is then easy to find "ANONYM" (6 letters used out of 13, which is not much) or "AN ANONYM" (8 letters used out of 13, which is already better)

Despite everything, this type of solution leading to the answer "ANONYM" or "AN ANONYM" to the question "my name is ___" is my favorite ! It is quite logical and corresponds well to the idea of a new taunt about the zodiac’s identity. We could also see a response like "ANYONE" and probably many other words, but I think that the "ANONYM" solution is the most satisfactory in my opinion.

Anyway, I am not claiming of course that this solution is the right one, but it doesn’t appear to me so unrealistic compared to what I’ve seen elsewhere. But it also has a number of disadvantages that should not be hidden :

Pros
– Its simplicity, which seems coherent with the fact of having a code that is both short, but also decodable ;
– The solution, which seems imo in the spirit of what we can expect from the Zodiac …

Cons
– Its simplicty again… maybe this method is too simplistic/childish ?
– Seeing in the code something like "want to know my name?" is totally arbitrary and just comes from an impression to see directly readable words in the original code ;
– The letters used to form "ANONYM" or "AN ANONYM" are selected randomly, and some unused letters are left : "EKMTAM" (maybe you can add a "ME" for "me, an anonym" ?). But if the code is really based on the method exposed above, there must necessarily be left letters (except the answer is a perfect anagram of the initial question, which is not obvious to achieve).

In any case, there are some elements to continue thinking about the meaning of the Z13 cipher !