The Computer Scientist Who Boosts Privacy With Entropy – Quanta Magazine

October 18, 2022
Harry Halpin, photographed in Prague, has personal reasons for wanting the internet to be fundamentally more secure.
Klaudia Poloncova for Quanta Magazine
Contributing Writer
October 18, 2022
Harry Halpin works on internet privacy for many reasons, but perhaps the most pressing stems from an incident that occurred over a decade ago. Halpin, who was pursuing a doctorate in computer science at the University of Edinburgh at the time, was also a climate activist. In December 2009, while in Copenhagen for the United Nations Climate Change Conference, he was arrested by law enforcement authorities and, he says, beaten severely. It turned out the British police had been monitoring his protest activities, and they told their Danish counterparts that Halpin was one of the ringleaders they should apprehend. (He says his actions were always peaceful.) Privacy and secrecy have been on his mind ever since.
After earning his doctorate, Halpin spent nearly a decade in the Computer Science and Artificial Intelligence Lab at the Massachusetts Institute of Technology. There, he worked for Tim Berners-Lee, widely heralded as the inventor of the World Wide Web. As useful as the web has been, Halpin is quick to point out its shortcomings.
“The web was not built with security and privacy in mind, although people subsequently tried to address those concerns as sort of an afterthought,” Halpin said. He has done his best to fix these issues, working to introduce layers of protection where none existed before. For example, in his job for the World Wide Web Consortium, Halpin helped create uniform cryptography standards, making sure these standards were incorporated into every web browser in a form that web developers could readily use.
But Halpin soon recognized that simply stopping leaks of information at the highest level of the internet — the level of browsers, apps and other advanced functionality — was not enough. He also wanted to protect the lower, foundational level: the network through which the information is transmitted. In 2018, he started Nym Technologies to take on this problem. The idea was to create a new kind of “overlay network” that would make use of the existing internet but alter crucial components — by rerouting traffic, among other means — to make some of the communications truly anonymous.
Halpin spoke with Quanta from Nym’s headquarters in Neuchâtel, Switzerland. In several conversations over Zoom, he discussed being under surveillance, how to create a more private network, and the value of privacy itself. The interview has been condensed and edited for clarity.
My father was a salesman for Sun Microsystems, so I was around computers as a kid. But I started to rely on them as a middle school student in the early ’90s, just after my family moved from Charleston, South Carolina, to a more remote, wooded area in North Carolina. I kept in touch with my friends over the early internet and also got involved in multiplayer games. Then I took courses in programming in 1998 as a freshman at the University of North Carolina and worked as a systems administrator in the computer science department. I stopped playing online games altogether once I started attending protests and discovered that the real world was even more interesting.
It wasn’t until several years later — after entering graduate school in Edinburgh in 2002 and studying artificial intelligence — that I became aware of the possibilities of surveillance. I was struck by the fact that very little data had to be leaked before machine learning tools could infer large amounts of information about you, although I didn’t begin research in this area until later. And by then, things were starting to get personal.
In the fall of 2007, I was introduced to Mark Kennedy, who became active in the environmental groups I was involved with. My goal was to draw attention to climate issues, which I still regard as an existential threat. In 2010, the year I got my Ph.D., I discovered that Kennedy was an undercover agent working for the British police. What’s more, he seemed determined to destroy my life. I was constantly followed and interrogated every time I crossed a border. Kennedy was in touch with the FBI, and the FBI told MIT not to hire me, but fortunately that advice was ignored. I started working for the World Wide Web Consortium in January 2011, and by then it was abundantly clear that web security and privacy could stand some improvement.
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Earlier this month, Halpin traveled to Prague for the Hackers Congress Paralelní Polis, a conference dedicated to “new technologies, decentralization, and cryptoanarchy.”
Klaudia Poloncova for Quanta Magazine
Kennedy, incidentally, was soon discredited. A New York Times article in 2013 called his actions an “embarrassment to Scotland Yard.” That was also the year of the Snowden revelations, which showed that the [National Security Agency] was eavesdropping on a sizable proportion of telephone and internet communications. That reinforced the notion that internet privacy was not just my personal problem — it was everyone’s problem.
The notion of secret communications can be approached on two levels. We can use cryptography — a methodology based on number theory — to guarantee that no one, except the intended recipient, can understand what you’re saying. But the trickier problem is this: How do I communicate with you so that no one else knows I’m communicating with you, even if our messages are encrypted? You can get a sense of what people are saying from the pattern of communication: Who are you talking with, when are your conversations, how long do they last?
A couple of years ago, I spoke about this issue at a conference with Whitfield Diffie, a well-known computer scientist who invented “public key” cryptography. I asked him why he and others had focused almost solely on the cryptography part of the problem. “Because the other problem is too hard,” he said. That helped validate my decision to devote my efforts to the “other problem,” since there clearly was a need.
There are two key elements: One is the “mixnet,” a technology invented by David Chaum in 1979 that my team has improved. It relies on the premise that you can’t be anonymous by yourself; you can only be anonymous in a crowd. You start with a message and break it into smaller units, communications packets, that you can think of as playing cards. Next, you encrypt each card and randomly send it to a “mixnode” — a computer where it will be mixed with cards from other senders. This happens three separate times and at three separate mixnodes. Then each card is delivered to the intended recipient, where all the cards from the original message are decrypted and put back into the proper order. No person who oversees mixing at a single mixnode can know both the card’s origin and its destination. In other words, no one can know who you are talking to.
For one thing, we make use of the notion of entropy, a measure of randomness that was invented for this application by Claudia Diaz, a computer privacy professor at KU Leuven and Nym’s chief scientist. Each packet you receive on the Nym network has a probability attached to it that tells you, for instance, the odds that it came from any given individual. You can also calculate the average time it will take for a message to reach its destination, but you can’t know how long it will take for any single packet to get there.
Our system uses a statistical process that allows you both to measure entropy and to maximize it — the greater the entropy, the greater the anonymity. There are no other systems out there today that can let users know how private their communications are.
Mixnets, as I said, have been around a long time. The reason they’ve never taken off has a lot to do with economics. Where do the people who are going to do the mixing come from, and how do you pay them?
We think we have an answer. And the kernel of that idea came from a conversation I had in 2017 with Adam Back, a cryptographer who developed bitcoin’s central “proof of work” algorithm. I asked him what he would do if he were to redesign bitcoin. He said it would be great if all the computer processing done to verify cryptocurrency transactions — by solving so-called Merkle puzzles that have no practical value outside of bitcoin — could instead be used to ensure privacy.
The computationally expensive part of privacy is the mixing, so it occurred to me that we could use a bitcoin-inspired system to incentivize people to do the mixing. We built our company around that idea.
Halpin onstage at the Hackers Congress Paralelní Polis.
Klaudia Poloncova for Quanta Magazine
First there are the people who use their own computers (running software that we design) to do the mixing. Then there are the people who monitor the system and, in a sense, bet on the mixers, literally putting money down to say that they think this particular mixnode will be successful. Success in this case means doing a good job of mixing, which relates both to not dropping packets and throughput — how many packets are going in and how many mixed packets are going out. People who vote on the best mixnodes get some of the money, but most of it goes to the people who actually run the mixnodes. Payment comes in the form of cryptocurrency, which has the advantage of decentralization. No single person or company is writing checks or wiring money. Instead, it’s all done automatically, making use of algorithms that we invented.
Moreover, the system is designed to maintain decentralization and prevent the rich from getting richer. When one mixnode becomes too popular, the people who vote for it will make less money. It’s in their interest to find new mixnodes that are not “saturated” but still offer high-quality performance. That’s how we promote decentralization.
A new paper that came out in June shows that this approach can lead to an economically sustainable mixnet. Drawing on ideas from game theory, my colleagues Claudia Diaz and Aggelos Kiayias and I showed that we can maintain Nash equilibrium (in a single,“one-shot” game), which basically means there is no incentive to cheat or game the system. We then showed, via simulations, that the system is sustainable (in an “iterative” game), even if the players are not perfectly rational and the mixing is repeated over and over again. Everyone gains by playing by the rules, whether you are doing the mixing or voting for a particular mixer who you think will do a good job.
Halpin stands in front of a statue of Franz Kafka in Prague.
Klaudia Poloncova for Quanta Magazine
Although we are inspired by some of the ideas behind bitcoin, our fortunes in the long term are not tied to the value of bitcoin. We are not building a currency system or trying to replace the dollar. We just want to provide privacy to ordinary people.
It’s true that privacy does not come for free. It will cost some electricity. But our energy use is a lot less than that associated with bitcoin. In fact, we use the minimum necessary to provide privacy — we don’t want any extra computation because that just slows the system down.
An early test version of the network was launched in December 2019 at the Chaos Computer Congress in Germany. There were only about a dozen mixnodes at the time, but we’ve carried out larger-scale testing since then. There are currently about 500 mixnodes, but we think this approach could easily handle 10% of the world’s internet traffic, which would take about 20,000 mixnodes.
Our ultimate goal would be for everyone to use the Nym network, not just the people who have good reason to hide, like human rights activists. But we’ll start with those who really need it and hope that our bet is right — that people truly value their privacy. It’s then up to us to scale up our system so that it can accommodate everyday internet use.
My philosophy is that the good of privacy outweighs the bad. Selling drugs can be bad, of course, and there are a lot of other things that we as a society don’t support. But to me, privacy is a fundamental right, a cornerstone of our freedom. I think we should do everything we can to protect it.
Contributing Writer
October 18, 2022
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