Cynthia Dwork (born 1958) is an American computer scientist and a Distinguished Scientist at Microsoft Research. She is known for her research placing privacy-preserving data analysis on a mathematically rigorous foundation, including the co-invention of differential privacy, a strong privacy guarantee frequently permitting highly accurate data analysis (with McSherry, Nissim, and Smith, 2006). Dwork has also made contributions in cryptography and distributed computing, and is a recipient of the Edsger W. Dijkstra Prize for her early work on the foundations of fault-tolerant systems. Her contributions in cryptography include Non-Malleable Cryptography (with Dolev and Naor, 1991), the first lattice-based cryptosystem (with Ajtai, 1997), which was also the first public-key cryptosystem for which breaking a random instance is as hard as solving the hardest instance of the underlying mathematical problem ("worst-case/average-case equivalence"), and the idea of, and a technique for, combating e-mail spam by requiring a proof of computational effort, also known as Proof-of-work, (with Naor, 1992). This is the technology underlying hashcash and bitcoin.