Quantum oblivious transfer is secure against all individual measurements

Shows that the BBCS-protocol (Bennett, Brassard, Cre´peau and Skubiszewska, CRYPTO´91, 1992) implementing one of the most important cryptographic primitives-`oblivious transfer´-is secure against any individual measurement allowed by quantum mechanics. We analyze the common situation where successive measurements on the same photon could be used to cheat in the protocol. We model this situation by using a single inner-product-preserving (IPP) operator, followed by a complete composite-outcome Von Neumann measurement. A lower bound on the residual collision entropy is then obtained under the assumption that only individual measurements can be performed. This bound is used to apply privacy amplification techniques in order to conclude the security of the BBCS-protocol