Join me for a deep dive into the Zodiac Killer’s first mysterious cipher, as told through a combination of newspaper articles, police reports, FBI documents and books.  Learn about Zodiac’s crimes, his taunting letters, the mysterious cryptogram he sent to local newspapers, all the efforts to solve it, the breakthrough solution by the Hardens, the involvement of a prominent cryptographer, evidence and leads revealed in the police reports, cipher analysis by the FBI, unanswered questions, and much more!

Is Zodiac’s unsolved cipher a hoax, or does it have a real message? Let’s investigate some possible clues, in Episode 2 of “Let’s Crack Zodiac”:

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!