ABSTRACT

This chapter is concerned with security of cryptographic protocols and the role played by parallelism in breaking them. It focuses on to more complex scenarios, showing how a parallel approach is indispensable to threatening the security of two of the most important quantum cryptographic primitives: bit commitment and oblivious transfer. In both cases, the impossibility of designing an unconditionally secure protocol is mainly due to the ability of the participants to act simultaneously on groups of qubits in order to generate and manipulate entangled states. The treatment of entanglement will be done at the abstract level of qubits. The chapter explores the role played by parallelism for the security properties of two of the most important protocols in quantum cryptography: quantum bit commitment and quantum oblivious transfer. And once again, parallelism appears in the context of entangled states and distinguishing between quantum states.