Security of quantum protocols against coherent measurements

Andrew Chi-Chih Yao Department of Computer Science Princeton L’niversity Princeton, New Jersey (X3544 The goal of quantum cryptography is to design crypt ographic protocols whose security depends on quantum physics and little else. A serious obstacle to security proofs is the cheaters’ ability to make coherent measurements on the joint, properties of large composite states. WTith the exception of cornmtt protocols, no cryptographic primitit’es have been proved secure when coherent measurements are alIowed. In this paper we develop some mathematical techniques for analyzing probabilistic events in Hilbert spaces, and prove the security of a canonical quantum oblivious transfer protocol against coherent measurements.