Check out “Criminology”, a fantastic podcast about the Zodiac Killer. I’m honored to be featured in Episode 11, in which we dissect the ciphers in more detail:

Thanks, Morf and Mike Ferguson for inviting me to be a part of it. The entire series is very good. Over the course of Season One, they have given a very well-researched and factual account of many of the details of the case. I learned a lot of things about the case that I didn’t know before!

A friend of mine teaches a Network Security course at a local community college and he invited me to give a talk about criminal codes and ciphers. Here is the video of the talk:

Topics include the Unabomber, BTK Killer, prison gangs, spies, the Zodiac Killer, and more.

Tom Voigt managed to gain access to the evidence room (presumably at SFPD) to have a closer look one of the three parts of the original Z408 cipher:

He says that inspecting the back of the paper reveals Zodiac used a second pen of a different color. Click the above link to see his short video of the experience. I look forward to hearing more about his visit.

Good news: My presentation proposal for this year’s crypto symposium was accepted!

Title: The Unsolved Zodiac 340 Cipher: Features or Phantoms?

Abstract: The Zodiac Killer’s first cipher was a simple substitution cipher that was quickly solved by amateur codebreakers. But after almost 50 years, his second cipher is still unsolved. Current research is focused on unusual statistical features found in the unsolved cipher. Are these features evidence of the underlying encryption scheme used by the killer? Did he use a type of classical cipher or invent a homemade scheme? Or are the features actually phantoms leading us down the wrong path? This talk will try to sort out the good and bad clues in the cipher text, and will invite the codebreaking audience to participate in this promising research.

The 2015 symposium was really fascinating and I was privileged to attend many interesting presentations. In my own presentation there, I presented a broad overview of the Zodiac ciphers and some of their unusual clues and features. In my upcoming talk I will try to provide more details about the interesting cryptographic clues in the unsolved 340-character cipher. My hope is that attendees will gain information that will help them make new discoveries about the 340 that may one day lead to its solution.

I believe the best way to keep attacking the Zodiac’s 340-character cipher is to create more test ciphers that share many of its features. If we can easily crack test ciphers under many different schemes, and the Zodiac 340 still won’t break under the same attacks, then the schemes can be systematically eliminated.

I collected about 200 test ciphers to compare with the 340, and posted a detailed summary of my approach here:

Long story short: Many people have created many test ciphers, and in most cases they share some but not all of the features of Zodiac’s 340. I’m hoping to help close that gap so we can at least start with a really good set of test ciphers.

Here is a video of my talk from the 2015 Cryptologic History Symposium held at the Johns Hopkins University Applied Physics Lab:

I had limited time for the talk, so I recorded a new bonus section at the end to go over some additional material about the ciphers. The talk is basically a snapshot of what we know about the unsolved Zodiac ciphers, and a way to rule out different ideas of how the 340 was constructed. I was in the “Crimes and Ciphers” panel, moderated by FBI historian John Fox. Also presenting in this panel was Dan Olson, the chief of the FBI’s Cryptanalysis and Racketeering Records Unit (CRRU). He gave an interesting talk about the history and achievements of the CRRU. During his talk he played this short NBC news clip featuring Dan and the work of CRRU:

German author Klaus Schmeh, who has written several books on encryption technology, also gave an interesting talk about unsolved ciphers from unsolved crimes. You can watch Klaus’ talk here:

The conference was a really enjoyable experience for anyone interested in the history of codemaking and codebreaking. I met many fascinating people, heard many interesting stories, and learned many new things. I posted some details of my experiences here:

A similar meeting is coming up in Charlotte in Spring 2015:

Conference goers, thanks for attending my talk. Here are the slides: (slideshare link)

I will work to post a video of the talk soon. So far the conference is filled with many interesting topics. Here’s the agenda if anyone’s curious:

UPDATE, Feb 7, 2016: The Zodiac Pattern Drawer site at went down, so I attempted to mirror the tool here:

Computer science professor Ryan Garlick at the University of North Texas has been enlisting his students to try out different ways to solve Zodiac’s 340-character cryptogram. Many people believe that the 340 needs to be re-arranged before it can be cracked. So, this year, Dr. Garlick’s students developed the “Zodiac Pattern Drawer”, a web-based tool that lets you re-arrange the 340 and download the result.

Screenshot of Zodiac Pattern Drawer

Basically, you start with the original cryptogram, and click around in it to draw a different path through its symbols. Your rearranged symbols appear on the right, and when you are done, you can download a text file that contains a numerical representation of the new cryptogram. You can then take that file and feed it to an automatic solver such as zkdecrypto or AZdecrypt.

To get started, read the user guide and watch the tutorial video.

Hopefully someone can find a rearrangement that leads to a solution!

The Cryptologic History Symposium sponsored by the NSA’s Center for Cryptologic History is coming up this fall, and they have accepted a paper proposal I recently submitted. The symposium will be on October 22nd and 23rd this year in Laurel, MD, and covers many fascinating topics involving the history of cryptology. I attended the 2013 symposium and it was extremely interesting – be sure to read my article about it to get a sense of what’s covered.

For this year’s symposium, I will be giving a presentation in the “Ciphers and Crime” panel called “The Zodiac Ciphers: What do we know and when do we stop trying to solve them?” The talk will be a quick overview of the case, details on the ciphers, many observations about their contents, and results of my experiments designed to rule out different ways Zodiac may have constructed the unsolved 340-character cryptogram. It’s going to be very challenging to pack so much info into the 25 minutes they have allotted to me. Here is the abstract for my paper:

Over 45 years ago, the serial killer known as Zodiac taunted the San Francisco Bay area with cryptic letters that were widely published in newspapers. One letter contained a cryptogram (Z408) which was quickly solved by a high school teacher. A second cryptogram (Z340) was sent a few months later. It appeared similar in construction to the first, but remains unsolved to this day. The killer later mailed two additional smaller cryptograms (Z13 and Z32) which also remain unsolved. Here we summarize many facts and observations known about Zodiac’s cryptograms. Many hypotheses on the construction of Z340 have been explored but no solution has been found. Systematic exclusion of hypotheses is difficult and tedious. We attempt to address this with multi-objective optimization programming to generate cryptograms simulated under various construction hypotheses. The simulated cryptograms are artificially evolved to maximize similarities to the real Z340. If, under a given hypothesis, we can solve the numerous simulated cryptograms, and Z340 was constructed using the same hypothesis, then the solution to Z340 should be easily found. If it is not, then this failure provides strong evidence against a specific hypothesis. Thus hypotheses can be systematically excluded.

There is more information about the conference at this link. The proceedings may seem dry and academic, but if you have any interest at all in the history of codemaking and codebreaking, I guarantee you will be intrigued by the range of topics covered at these symposiums.

Hope to see you there! And thanks to Klaus Schmeh for encouraging me to submit a presentation.

The World Chess Federation in Las Vegas, NV is involved in a dispute over trademark infringement. The web site for the World Chess Federation has a profile of its founder Stan Vaughan which includes this claim:

Grand Master Stan’s expertise as a cryptanalyst led him being noted for having solved two of the most important previously unsolved ciphers in the world: The Shugborough Hall Monument cipher for which he had received an award from the Reform Club, and the Zodiac Serial Killer 340 character cipher. Stan was also a National Trivial Pursuit Champion of 1986.

I cannot find any references that mention his solution. Does anyone know anything about it? I am attempting to contact Mr. Vaughan to see if he will give more information about his solution.