Arts & Sciences Magazine

By Michael S. Goldberg

It takes a sharp ear and more than a little curiosity about a computer’s inner workings to register that the sounds emanating from a hard drive follow a different rhythm depending on who’s accessing it. That’s exactly what Eran Tromer noticed while, in his childhood bedroom, he ran a pre-internet bulletin board system for gaming enthusiasts. He observed that each user navigating the community’s menus and games induced a signature pattern of clicks and whirs from his PC.

Years later as a PhD student at the Weizmann Institute of Science in Israel, Tromer realized such signals sounded in all kinds of computers, from the most advanced data centers used by businesses and governments to the smartphone in your pocket. Those signals were announcing technical vulnerabilities to people who—with the right equipment and the wrong motives—could decode computing activities with enough specificity to uncover secret information.

“This observation evolved into papers where we show that you can just point a microphone at someone’s computer and steal their secrets, just from the high-pitched noises that the electronics are making,” says Tromer, a professor of computer science who joined the Arts & Sciences faculty in 2023.

Identifying these types of risks is an important theme in Tromer’s work—but it’s only one strand in a braid of related pursuits. Through his lab work, business startups, and open-source software projects, Tromer has built a career in which he pinpoints the security holes in information systems that we all use and invents ways to mitigate them. 

Building Trust in Information Systems and Cryptocurrency

In information security parlance, the audio spying that Tromer began documenting in 2004 is called a side-channel attack. As Tromer’s team and his research colleagues uncover vulnerabilities, they share their findings publicly, including with technology companies. Often, computer hardware and software makers ignore the warnings, he says. The side-channel problem was serious enough that Amazon Web Services began to offer its cloud computing customers the chance to have their own dedicated resources, so their machines would not be in proximity to other companies’ systems and thus at risk of attack. “Amazon got it right,” Tromer says, “and Google Cloud adopted this as well.”

But the ongoing study of vulnerabilities and seeing how difficult they can be to fix created a new desire. “As we were appreciating all the ways things can go wrong, we also became curious about how we can fix them—and realized the practical urgency of building robust systems that avoid such vulnerabilities​​,” he says. 

This prompted him to examine the potential for using modern cryptography— approaches that use math and computer science to enable secure communications—to address computer system security risks. The work led to one of his highest-profile techniques: zero-knowledge proofs.

Zero-knowledge proofs, first conceived in the 1980s, enable two parties to conduct a transaction—for example, the sharing of confidential information—that includes extra layers of verification. Both parties use mathematical formulae to demonstrate that their shared information is trustworthy without having to reveal facts they don’t want to share. Even untrusting adversaries can know their counterparty is sharing what they promised by using this method, Tromer says. 

“It’s an extremely powerful idea,” he says. But it was only a theory until recently because scientists didn’t believe that computers were fast enough to do the many calculations required to create proofs for real-world applications. “We started looking at, can we make zero-knowledge proofs practical? Can we make them efficient enough to solve business and security needs? And this led to various prototypes, and gradually, improvements in performance and demonstrations of capabilities,” he says.

Practical Applications for Research 

Research turned theory into a software protocol called Zerocash, designed to enable payment in digital currencies like Bitcoin using zero-knowledge proofs. Tromer was among the creators of Zerocash and a coauthor of a 2014 paper describing how it works. In May 2024, the Institute of Electrical and Electronics Engineers honored the paper with its “test of time award” for research with a lasting impact in the field of security and privacy. 

In 2015, Tromer took the Zerocash paper a step further as a founding scientist of Electric Coin Company, which launched Zcash, a cryptocurrency that uses zero-knowledge proofs to protect the privacy of its users. Tromer says that hundreds of companies involved in digital currencies have adopted Zcash and its underlying cryptography. Zcash also made its work open source, freely available to software coders to develop further. 

Zcash is important because in addition to the question of trust, it answers a drawback of the blockchain technology underpinning digital currencies like Bitcoin, Tromer says. Blockchain, a digital ledger system, is valuable for its verification of every transaction. But most blockchains lack privacy; observers can examine data about a transaction’s parties, amounts, and timing. Zcash preserves the verification capability of blockchains while cloaking participants’ identifying data. 

“You don’t want your business competitors to see your transactions, or your national adversaries to spy on your citizens,” Tromer says, adding that zero-knowledge proofs provide the way to verify that transactions are done correctly without seeing their contents. For example, if a company wanted to place an order for new equipment using Bitcoin, but didn’t want competitors to see their strategic move, Zcash would provide the means to, first, verify the purchase was accurate, and second, cloak the contents of the sale from everyone except the equipment buyer and seller. 

You might ask: if the invention of an application like Zcash makes the parties to a Bitcoin transaction invisible, doesn’t that open the door to bad actors to use it for malevolent ends? 

“We’ve grappled a lot with this challenge and how to combine privacy with what society needs to prevent crime and terrorism,” says Tromer, who has discussed this issue with regulators and law enforcement agencies. “What we realized is that the robust guarantees of zero-knowledge proofs are actually not just the problem, they’re also the solution.”

Here again, research led to another application and a new company: Sealance, which Tromer cofounded in 2020. Using zero-knowledge proofs, Sealance offers a “trust platform” for cryptocurrency users that adds more verification gates for a transaction. Using this platform, cryptocurrency users can verify that a transaction is not just financially correct, but also legitimate—for example, that none of the parties involved are subject to sanctions, are tracked back to illicit activity, or trigger other red flags as spelled out by government authorities.

In this situation, Tromer says Sealance is attempting to replicate the security measures of traditional finance. Think of using a physical ID card to identify yourself to a bank. “The bank uses this record to check against sanction lists and other red flags. And sure, if you forge someone’s ID, then you might be able to move some money—until you are detected by some anomalies or red flags. We are trying to basically replicate all this in a privacy-preserving, fully digitalized, blockchain-based world,” he says.

National security represents another application for Tromer’s work. The Securing Information for Encrypted Verification and Evaluation program, funded by the US Defense Department’s DARPA, is working to increase the efficiency of zero-knowledge proofs that may contain “billions of gates or more.” The program aims to make complex uses of zero-knowledge proofs possible, to ensure the correct operation of computer systems even under adversarial attacks.

Advanced Theory, Real World Applications 

In an interview, Tromer uses the word “curious” more than once to describe what drives his work. Back in his old bedroom, he was curious about the sounds his PC made. He was curious about the vulnerabilities of systems designed to be trustworthy (but weren’t). He wondered about the potential for zero-knowledge proofs to address these risks, and whether modern computational power could make them practical.

Curiosity is the glue that binds his theoretical work to the real world. And the questions don’t end. One proposed solution (like Zcash) can prompt more questions (how to deter bad actors) which in turn leads to new answers (Sealance). This dynamic is a core lesson he tries to impart to his students. 

“Intellectually, what I’m trying to instill is the curiosity and skepticism, the drive to understand what’s really going on. Find the ways that we’ve been lied to or that we’ve deluded ourselves. Dig into the gears, understand what makes them tick, and figure out how they may, instead, tock,” he says. “And I strive to ground this in real world impact, by doing all this analysis for systems that are widely used, and for problems we hear about from our government and business partners. And then we bring to bear the intellectual and technological firepower of modern cryptography, to ward off the things that go buzz at night.”