SpyCast 4.2.24
Ep 627 | 4.2.24

“I Helped Solve the Final Zodiac Killer Cipher” – with David Oranchak

Show Notes


David Oranchak (X, LinkedIn) joins Andrew (XLinkedIn) to discuss his work helping to solve the 340 Zodiac cipher. Dave is a software developer and avid puzzle solver. 

What You’ll Learn


  • The difference between codes and ciphers
  • The cryptological methods used by the Zodiac killer 
  • The history of cryptography and its importance to intelligence
  • How Dave and his team cracked the 340 Cipher


  • Persistence and dedication
  • Average citizens as avid participants 

And much, much more …

Episode Notes

David Oranchak was born in 1974, the same year that the Zodiac Killer wrote his final message to the world. 46 years later, David would be a part of a small team of code-breaking enthusiasts who cracked the Zodiac 340 cipher. For decades, the message eluded even the best cryptanalysts from across the intelligence field. 

David joined Andrew in the studio this week to discuss how he, along with mathematician Sam Blake and programmer Jarl Van Eycke, finally put an answer to the puzzle after 51 years. They talk through the methods Dave’s team used to decrypt the 340, how the cipher went unsolved for so long, and how it felt to read the words of a serial killer. Tune in to learn more about one of the most amazing feats of cryptanalysis in our modern age. 


To learn even more and follow along with the journey to solve the Z340, check out Dave’s YouTube channel. Make sure to watch his video on cracking the historical ciphers from Mary, Queen of Scots – A piece of intelligence history we cover here at the International Spy Museum! 

Quotes of the Week

“It felt like we had gotten a brand new letter from the Zodiac Killer. You know, the case had been dormant for so long … We started to see the message coming through, it was like he was back to life so to speak, he was talking to us again after so many years of not saying anything. So that was kind of eerie to kind of hear the voice of a serial killer.” – David Oranchak.




*Beginner Resources*



  • Zodiac: The Shocking True Story of the Hunt for the Nation's Most Elusive Serial Killer, R. Graysmith (Berkley, 2007) 
  • The Code Book: The Science of Secrecy from Ancient Egypt to Quantum Cryptography, S. Singh (Anchor, 2000)
  • The Codebreakers: The Comprehensive History of Secret Communication from Ancient Times to the Internet, D. Kahn (Scribner, 1996) 



Primary Sources 

*Wildcard Resource*

If you’re an amateur codebreaker and you feel inspired by this episode, try your hand at cryptanalysis with this FBI-created dot code. Erin tried, but could not begin to crack it – She’ll stick to podcasting.