How coronavirus lockdown boredom led Melbourne mathematician Samuel Blake to cracking a Zodiac Killer cipher
Some people spent their time in COVID-19 isolation knitting or learning a musical instrument.
Melbourne applied mathematician Samuel Blake spent his extra time at home following a hobby that would lead to the cracking of a mystery which has puzzled cryptologists for more than 50 years.
For the past week, Dr Blake has been waiting for the US Federal Bureau of Investigation to make public the solution he and two fellow cryptologists made to the Zodiac killer's "340 cipher", a distinctive code sent to the San Francisco Chronicle newspaper in 1969.
Early this morning he was able to proudly announce his role in the solution, fielding media enquiries from around the world in between taking time to celebrate the achievement.
"We've sat on it all week while the FBI informed the concerned parties involved in the case that a breaking story was coming," he said.
"It came out this morning and the last few hours have been quite a rollercoaster."Passing interest leads to active involvement
The case of the Zodiac serial killer has puzzled detectives and captured the imagination of amateur sleuths around the world for decades.
The killer is credited with five unsolved murders in Northern California in the late 1960s and early 1970s, including two young couples as well as a male taxi driver.
A further two victims survived his attacks.
Desperate for attention, Zodiac mailed letters to local police and newspapers, sometimes in code, as well as bloodied items of clothing as proof of his actions.
In his letters, he claimed to have killed 37 people.
A 408-symbol cryptogram he wrote to Californian newspapers in August 1969 was cracked within days of its publishing while the infamous 340 cipher was sent in November of the same year and remained unsolved until this month.
Dr Blake, who usually works in steganography and spread-spectrum watermarking as well as cryptography, has had a passing interest in the ciphers since watching the film Zodiac, starring Robert Downey Jr, soon after its 2007 release.
He's no expert in the details of the case, but videos Zodiac cryptologist David Oranchak released discussing a statistical analysis of the 340-cipher caught his interest over time.
When he found himself with an abundance of time during COVID lockdowns in Melbourne, he began contacting Mr Oranchak about potential algorithmic solutions to the cipher.
Dr Blake's new approach to the cipher caught Mr Oranchak's attention and throughout the year, the pair began working through different reading directions together over Slack.
"There was one particular thing that David showed in his talk, where he talked about a period 19 — so if you read every 19th character through the cipher, statistically it would be more likely to contain a message," Dr Blake said.
"What I noticed was a symmetry in the way the cipher was arranged. And that symmetry was actually to do with my normal research.
"I recognised that a period 19 is very similar to a one, two diagonal reading through the cipher."International cooperation from their homes
Throughout the year, Dr Blake and Mr Oranchak worked on the cipher together while being on different sides of the world, Dr Blake remotely accessing the University of Melbourne' supercomputer Spartan from home to eliminate possible reading directions.
"To help with COVID boredom I started working on it in earnest, where we looked at all these different possible ways that you could read through the cipher before you tried to actually solve it," he said.
After months working on algorithms testing different ways to read the cipher, Dr Blake and Mr Oranchak had a breakthrough on Thursday, December 3.
"We tried about 650,000 different ways to read through it and they all turned up nothing," he said.
"We were about to then generalise what we had done, but I said to David of a certain set of them that statistically look good, 'Could we try them again?'"
The pair reran about 10,000 to 50,000 reading directions which had good statistical properties.
"Out of those reruns just one cipher had some phrases in it that looked like they were fragments of a solution," he said.
"The fragments were 'I hope you are having', 'Try to catch me' and 'Gas chamber'.
"I had no idea because I'm not an expert on the Zodiac killer, I'm a mathematician, so I had to google whether the gas chamber was a method of execution back [in the 1960s] in California.
"Once I saw that it was, I said, 'We have got to be getting close to the right direction here'."A deciphered section of the code
I HOPE YOU ARE HAVING LOTS OF FUN IN TRYING TO CATCH ME
THAT WASNT ME ON THE TV SHOW
WHICH BRINGS UP A POINT ABOUT ME
I AM NOT AFRAID OF THE GAS CHAMBER
BECAUSE IT WILL SEND ME TO PARADICE ALL THE SOONER
BECAUSE I NOW HAVE ENOUGH SLAVES TO WORK FOR ME
WHERE EVERYONE ELSE HAS NOTHING WHEN THEY REACH PARADICE
SO THEY ARE AFRAID OF DEATH
I AM NOT AFRAID BECAUSE I KNOW THAT MY NEW LIFE IS
LIFE WILL BE AN EASY ONE IN PARADICE DEATH
While Dr Blake was hopeful about his finding, Mr Oranchak was weary, having worked on the cipher for 15 years.
"He was probably more pessimistic that we weren't just being led down another rabbit hole," he said.
Dr Blake went to bed that night as Mr Oranchak continued to work through the cipher in the United States.
The next morning, Dr Blake received a message from David telling him to check his email.
"I found out he'd cracked the first nine lines of the cipher. It was amazing," he said.
"Once we found the correct way to read the cipher, those first nine lines were the easiest part of it."Killer's errors prevented cracking of code
The next nine lines proved to be a struggle, as the cryptologists later realised the Zodiac had made an error in his code.
"In general, you put a symbol on the cipher then you move one line down and two columns across and put the next symbol, and you repeat that throughout the entire cypher," Dr Blake said.
"But once [the Zodiac] made a mistake and had only gone one line down and one column across, instead of two, it completely broke the symmetry, and we had to discover that."
Mr Oranchak called in the software programmer who created the cryptology program that was used to decipher the first nine lines, Belgian Jarl van Eycke, to help with the final nine lines.
"He just smashed it out of the park once we'd given him the part of the solution we'd already got," Dr Blake said.
"He was able to reverse engineer the mistake so quickly.
"That mistake would have definitely helped this cipher from being decrypted for so long."
By Saturday night, the trio had the complete solution and sent their work to the FBI for verification.
Using their team of cryptologists at the Cryptanalysis and Racketeering Records Unit, the FBI approved their solution within a day.
"Even prior to getting confirmation from the FBI, we were so confident in this solution because it didn't require artistical creativity in order for us to get this solution out," Dr Blake said.
"Over that weekend was when David and Jarl's expertise solving these ciphers took over.
"My contribution primarily was recognising those symmetries in the cipher and then applying a big data approach of 'let's just try to enumerate all these possible directions', we'll be wrong millions of times — potentially — but we might get just lucky and be right once."
LoadingMystery around Zodiac's identity remains
Of the four ciphers the Zodiac killer sent out to San Francisco newspapers, now only two remain unsolved, including one which is expected to reveal the killer's name.
But both ciphers are much shorter than the 340 cipher, making it much more difficult to crack the code.
"In the third cipher, that is 13 characters long, he writes, 'My name is' and then it lists these 13 characters," Dr Blake said.
"From a cryptographic point of view, there's not enough information in there to solve that on its own with any certainty.
"You could run a computer program that could generate millions of candidate solutions to that without any trouble."
But Dr Blake hopes the trio's breakthrough will have broader implications for solving those two ciphers.
"What we are hoping, as a follow on to this, is that we can use a hybrid of the solution from the first cipher and our solution we have come up with to solve his next two ciphers," he said.
"That's what me and David are looking at at the moment, once we've had a chance to digest what is going at the moment."
Mr Oranchak has released a YouTube video explaining how they cracked the code but was disappointed it didn't lead to the identity of the killer, who has avoided capture for 50 years.
"The message doesn't really say a lot. It's more of the same attention-seeking junk from Zodiac," he says in the video.
"We were disappointed that he didn't put any personally identifying information in the message, but we didn't expect him to.
"Maybe his name really is in the 13-character cipher he sent nearly six months after the 340.
"Unfortunately there is not much hope of confirming any solutions for such a short cipher, without getting really lucky and discovering new evidence, or finding Zodiac is still alive and asking him."