Quarantine inspired me to create a new video series on Youtube.

It’s called “Let’s Crack Zodiac”.

True crime meets classical cryptography.

Episode 1: Graysmith

Almost 35 years ago, Robert Graysmith published his blockbuster book, “Zodiac”, and claimed to solve a famous unsolved Zodiac Killer cipher.  But did he really solve it?  Let’s break it down.

Here’s a great conversation I had with Michael Butterfield for the first episode of his podcast, “Zodiac: A to Z”:

HistoCrypt 2019, an annual conference on historical cryptology, convenes this week. The proceedings have been published and include many fascinating papers:


Those here who like to tinker with solvers and the Zodiac ciphers need to read these:

Nils Kopal, “Cryptanalysis of Homophonic Substitution Ciphers Using Simulated Annealing with Fixed Temperature” (This paper in particular is the first to formally acknowledge and accurately describe the long-available solvers such as ZKDecrypto and AZDecrypt)

Tom S Juzek, “Using the Entropy of N-Grams to Evaluate the Authenticity of Substitution Ciphers and Z340 in Particular” Notable conclusion:

We applied those two SVM models to the the Zodiac Killer’s two major ciphers, z408 and z340. z408, which has been solved, is correctly predicted to be a real substitution cipher. z340, which remains unsolved, is predicted to not be a substitution cipher. We think that it is likely that z340 is either another type of cipher, e.g. a transpose cipher or a Vigenere cipher, or that it might not be a bona fide substitution cipher after all.

Also, while this one is about PlayFair ciphers, the algorithmic techniques described in the paper would well apply to homophonic solvers:

George Lasry, “Solving a 40-Letter Playfair Challenge with CrypTool 2”

The proceedings are definitely worth a read if you have any technical interest in cryptology in general and the Zodiac ciphers in particular!

Here is the latest trailer for the upcoming Zodiac-focused episode of “Very Scary People”, hosted by Donnie Wahlberg:

HLN interviewed many folks for this show, including me for the cipher-related material. Apparently the episode is split between two episodes, so it looks like there will be a lot of detail.

Here are two other promos:

I’m getting a real Zodiac vibe from these French ads for the “Megamac” burger from McDonalds.


Here are three promos from the Zodiac Killer special episode of Mysteries at the Museum, a popular show on the Travel Channel:


In the late 60s and early 70s, the San Francisco Bay area was terrorized by a killer who called himself the Zodiac. Through letters mailed to the press, the Zodiac claimed to have murdered up to 37 people. He toyed with police sending them cryptic codes that allegedly contained his identity. But he was never caught, much less identified. So, what happened to the Zodiac?

Don Wildman sets out to discover the true-identity of the Zodiac — one of America’s most notorious serial killers. He visits the actual crimes scenes and learns about the victims. Don works with an expert cryptographer to unravel the famous Z340 cipher – a mysterious code, written by the Zodiac, that to this day has not been solved. He speaks with an amateur detective who’s spent the last ten years looking for the killer. And finally, he learns a new theory on who may be responsible for these brutal crimes.

I will be playing the role of the “expert cryptographer.” Assuming they didn’t leave my scenes on the cutting room floor. 🙂

The episode airs Wednesday, October 3rd, 2018 at 9PM EDT on the Travel Channel.

Earlier this month I gave a talk about Zodiac’s unsolved 340-character cipher at the annual convention of the American Cryptogram Association in Hendersonville, NC. It is full of things I’ve learned over the years about the cipher. My goal was to try to summarize all the interesting “clues” in the cipher, and hopefully get more people interested in trying to solve it. Here is a video I made of the talk, including updated visuals:

It gets rather technical at times but that’s because the audience is full of fellow codebreaking enthusiasts.

The other talks at the convention were fascinating and covered a wide variety of topics, such as ancient Latin manuscripts, playing card ciphers, competitive codebreaking for kids, an NSA case study involving dictionary codes, cryptocurrencies, a code on William Friedman’s tombstone, puzzles as on-stage entertainment, and interrupted key ciphers. To top it off, the keynote talk was by Will Shortz, the famous New York Times crossword editor, in which he gave many interesting examples of devious crossword puzzles that contained hidden messages beyond the normal solutions.

There were so many intelligent and friendly codebreaking enthusiasts at the convention, and I hope some of them will turn their efforts to working towards a solution to Zodiac’s 340 cipher!

Newspapers.com recently added more old issues of the S.F. Examiner newspaper to its archives. I found this old article about Z340. I’ve never seen it before!

Someone on Quora asked, “How do people know that the Zodiac Killer’s cyphers aren’t just gibberish that have no real meaning?” I responded with the following article which I also posted on Quora:

There are four total ciphers: Z408, Z340, Z13 and Z32. Of the four, only Z408 has been solved. Z13 and Z32 are too short, so verifying solutions would rely on extraordinary evidence such as discovering the keys from Zodiac himself, or by finally catching and questioning him if he’s still alive.

As for Z340, there are a few bits of evidence that could be put in the “it’s gibberish” column:

  1. A non-gibberish cipher would probably have been solved by now.
  2. Zodiac liked to mess with people (especially to make law enforcement look bad), so making gibberish ciphers is right up his alley.

But there’s really no good test to conclude once and for all that the ciphers are gibberish, apart from an admission from Zodiac himself. You could easily create a gibberish plaintext yourself and make a cipher from it, and it could be the next famous unsolved cipher.

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On the other hand, there have been some interesting papers on the topic of the Beale ciphers that present some evidence that they are hoaxed:

  2. Cryptanalysis of Beale Cipher Number Two

But apparently they are not enough of a “smoking gun” to fully convince everyone of the hoax hypothesis for the Beale ciphers.

It is possible that there is some characteristic of Z340 that could be discovered, and would only be present if the message was gibberish. I’m really curious to know if such characteristics could be discovered from homemade gibberish ciphers made to resemble Z340.

Nevertheless, there are still many things that can be put in the “it’s not gibberish” columns:

  1. Z340 uses an encoding scheme that hasn’t been fully tested yet. Maybe he used a traditional type of pen and paper cipher that hasn’t yet been exhaustively explored. For example, there are so many ways to rearrange the plaintext before assigning symbols. Or maybe he invented his own scheme that no one has guessed yet. When Z408 was cracked, the papers talked about how the solvers took advantage of patterns found in the cipher text. Zodiac could have focused on somehow removing those patterns from Z340. Or maybe he found some obscure idea in a book or one of those pulp fiction detective stories from back in those days (they were popular and often included ciphers)
  2. Zodiac was sloppy in making Z408 (details here), and thus may have made too many mistakes in Z340, which makes it more difficult (or impossible) to solve. (I suppose this could have effectively turned it into gibberish)
  3. There are clues in Z340 that have significance to cryptanalysts. Many of them are detailed here: Encyclopedia of observations For example, would a gibberish cipher really have the periodic ngram bias described there?
  4. On the 6th row the cipher text, he crossed out some symbol and wrote a backwards K above it:

    If the message is gibberish, why did he bother to correct the mistake? Was it just to give the false appearance of a real message? Or was he truly concerned about the integrity of the cipher text?

So, I think gibberish is a real possibility, but I still believe there might be a real message in there, especially since we still haven’t exhausted all the codebreaking possibilities.

On the other hand, if another 50 years goes by without a solution… 🙂

(Note: here’s a similar article I wrote a long time ago about this same topic: Cipher Legitimacy)