After a quarter century of impetuous development, complexity-theoretic cryptography has succeeded in finding rigorous definitions of security and provably secure schemes. In complexity-theoretic cryptography, however, computation has been "abstracted away": an adversary may attack a cryptographic algorithm essentially only by exchanging messages with it. Consequently, this theory fails to take into account the physical nature of actual computation, and cannot protect against physical attacks cleverly exploiting the information leakage inherent to the physical execution of any cryptographic algorithm. Such "physical observation attacks" bypass the impressive barrier of mathematical security erected so far, and successfully break mathematically impregnable systems. The great practicality and the inherent availability of physical attacks threaten the very relevance of complexity-theoretic security. Why erect majestic walls if comfortable underpasses will always remain wide open? Responding to the present crisis requires extending the current mathematical models of cryptography to the physical setting. We do so by eliminating the mathematically convenient but physically unrealistic separation between the adversary and cryptographic computations. Specifically, • We put forward physically observable cryptography: a powerful, comprehensive, and precise model for defining and delivering cryptographic security when an adversary has full (and indeed adaptive) access to any information leaked from the physical execution of cryptographic algorithms; • We show that some of the basic theorems and intuitions of traditional cryptography no longer hold in a physically observable setting; and • We construct schemes (such as pseudorandom generators and digital signatures) that are provably secure against all physical-observation attacks.
See REF for a nice model of computation which explicitly captures physical attacks, and for schemes that are provably secure against all physically observable attacks.
Physically Observable Cryptography
TCC 2004, LNCS
Computer Science