As a field, cryptography has advanced far beyond securing communication, now pushing boundaries in securing computation. Rather than just sending messages securely between two people, cryptography has expanded into many other areas of computation, such as in the way we now store data: on cloud servers, where computation is often done by cloud services. This shift raises new questions in both privacy, which is the bread and butter of cryptography, and also authenticity. How do we know that the cloud server is doing what it is supposed to be doing, and when we send computation to the cloud, how do we know that the actual computation that we requested is being performed? Cryptographic theory can be applied to numerous questions related to computing, and cryptographic tools can address new challenges as they arise.

Professor Yael Kalai is a theoretical computer scientist who focuses on the field of cryptography, both its theoretical nature and its real-world applications. She is an Adjunct Professor in the MIT Computer Science and Artificial Intelligence Laboratory (CSAIL) and is a member of the Theory of Computation research group in CSAIL. She is also a Senior Principal Researcher at Microsoft Research New England.

Prof. Kalai graduated from the Hebrew University of Jerusalem in 1997 and earned a master’s degree at the Weizmann Institute of Science in 2001. Working with Professor Shafi Goldwasser as her doctoral advisor, she completed her PhD at MIT in 2006. She did postdoctoral study at Microsoft Research and the Weizmann Institute before becoming a faculty member at the Georgia Institute of Technology, and now works at both Microsoft Research and MIT CSAIL.

“The work I do in collaboration between MIT and MSR goes beyond specific projects, it is about the connection of people and minds:  Sitting together with brilliant people from both MIT and MSR and brainstorming,” she says of the relationship.

Prof. Kalai is known for co-inventing ring signatures with Professor Ron Rivest of MIT and Adi Shamir of the Weizmann Institute. In cryptography, ring signatures let users specify a set of possible signers without revealing which member actually produced the signature, made possible with a secret key. Her master’s thesis introducing ring signatures won an outstanding master’s thesis award, and her MIT PhD dissertation was awarded the George M. Sprowls Award for Outstanding PhD Thesis in Computer Science.

Her goal is to address cryptographic questions by modeling the truth to reality, asking the right questions and solving them on a fundamental level in the hopes that people will make the most efficient and optimal solutions. She builds upon foundational concepts, such as classical proofs, and much more recent work in zero-knowledge interactive proofs to both hide information and allow for more efficient verification.

Many cryptocurrencies, for example, use zero-knowledge proofs to ensure private transactions and the storage of transaction data, making them far less traceable, as well as adding proof that the transactions are valid each step of the way, including for efficient blockchain verification. These types of zero-knowledge interactive proof applications are exciting for both researchers in academia and fintech researchers interested in using such ideas in banking infrastructure.

Prof. Kalai is also interested in fault tolerant communication and computation. She focuses on constructing interactive protocols that are resilient to errors: namely, even if some of the back-and-forth communication is corrupted, the intended communication can still be recovered. Similarly, she is focusing on constructing circuits (or other computational models) that are resilient to error, so that even if some of the gates in the computation are done incorrectly, the correct output can still be obtained. 

Another area of research that she is pursuing is that of program obfuscation, which has had major breakthroughs recently in the crypto community. Program obfuscation is all about taking a program and making it completely unintelligible, so people cannot reverse engineer or learn new information, but are still able to run the program. Once this concept is made practical, it will be extremely useful for many application areas. Until very recently, there weren’t any heuristics for obfuscation, but in the last several years there have been promising mathematical breakthroughs that could lead to promising new technology in the near future.

As new challenges arise, from cloud storage privacy and integrity to the cryptographic challenges involved with contact tracing for COVID-19, Prof. Kalai is ready to tackle the fundamental math problems in cryptography that lead her to solving much larger technological and social engineering questions and improve the systems that affect our everyday lives. Her hope is that the future will be digitally secure without compromising usability.