Yesterday, the 2012 ACM Turing Award was awarded to Shafi Goldwasser and Silvio Micali of MIT:
For transformative work that laid the complexity-theoretic foundations for the science of cryptography, and in the process pioneered new methods for efficient verification of mathematical proofs in complexity theory.
Longtime collaborators, they pioneered the field of provable security (see the Goldwasser–Micali cryptosystem), which laid the mathematical foundations that made modern cryptography possible. By formalising the concept that cryptographic security had to be computational rather than absolute, they created mathematical structures that turned cryptography from an art into a science.
Read the full award citations for Goldwasser and Micali.
(also see: the 2011 recipient, as well as the full chronological listing of awards)