Diffie, who is currently a cryptographer and security expert at Cryptomathic, said Turnbull's statement was one of the memorable lines from the whole debate over the encryption law which was passed by the Federal Parliament on 6 December last year.
He told the Cryptographers' Panel at the ongoing RSA Conference in San Francisco, "It's [the encryption law debate] given us this great line from the Prime Minister that the laws of mathematics may be all well and good but the laws of Australia apply in Australia.
"And I think he hasn't seen the possibilities, if he'd extended his views to cover the laws of physics and the laws of chemistry and then if he'd outlawed high-energy reactions and uranium and plutonium they could protect themselves from nuclear weapons... and I think with the right chemical laws they could protect themselves from global warming."
The Cryptographers' Panel at RSAC 2019. The encryption law is discussed starting at about 12:25.
The panel was moderated by Zulfikar Ramzan, the chief technology officer of RSA, and included Ron Rivest, professor at the Massachusetts Institute of Technology; Shafi Goldwasser, director of the Simons Institute for the Theory of Computing; Diffie, independent researcher Paul Kocher and Tal Rabin, Distinguished Researcher and manager of the Cryptographic Research Group at IBM Research.
Adi Shamir, co-founder of the RSA Conference, could not attend as he was denied a visa by the US Government.
Added Diffie: "But seriously, I think the problem is roughly this: that it's actually easy to disrupt the use of cryptography by legitimate large-scale commercial organisations to [give] them a lot of trouble. It's not clear whether those techniques are going to be the same amount of trouble to, for example, terrorists.
"And so I think this is a step that is not going to be productive. But my own view, probably lots of people see as radical: I would like to see issues of personal privacy and autonomy, many of them, taken out of the control of legislatures. Now that isn't easy to do when and I'm afraid I think that progress is likely to be in the other direction."
He said he was very worried about the situation as it existed. "At this moment, you still have a certain amount of privacy in your own thoughts. The mind-reading is kind of limited, it's not zero. They can now do things and find out whether you're familiar with something or not. Well, I think that electronic-brain interfaces may well come to the point where they can read your mind, and all that will protect you is a subpoena.
"If we look back 200 years, anyone could have a private conversation. You walked far off and away from other people and if they can't hear, then you had greater security than anyone in the world has today. I think if you look at other things that are still your own that way, they are eroding very quickly."
Kocher said the situation created by the encryption law was "100% backwards".
"Australia's new laws can put developers in prison if they refuse to put backdoors in their products or if they tell anybody that they've done it," he pointed out. "To me, this is 100% backwards. If anybody should be going to prison, it's developers who sneak backdoors into products and then don't tell their managers and their customers that they've done it.
"The other thing that's important to remember here is that secret backdoors are kind of like pathogens and governments have done a terrible job of managing them.
"For anybody who had to deal with the NotPetya situation — and that cost companies somewhere around US$10 billion — it was basically the weaponisation of exploits that were leaked from the US National Security Agency.
"I don't think Australia can do a better job than the NSA. So this is not going to end well, for, really any of us, to have this kind of policy being enacted whether it's in Australia or anywhere else in the world.
Rivest quipped that it was "a great example of the quote, the road to hell is paved with good intentions".
Kocher had the final word. "Forcing restaurants to poison bad customers might have net positives in certain situations, but it's not really a precedent we want to set," he said.