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Modern cryptography is more than sending secret messages, and quantum cryptography is more than quantum key distribution. One example is oblivious transfer, which is interesting partly because it can be used to implement secure multiparty computation. We discuss a protocol for quantum XOR oblivious transfer, and how non-interactive quantum oblivious transfer protocols can be “reversed”, so that oblivious transfer is still implemented from a sender to a receiver, but so that it is the receiver who sends a quantum state to the sender, who measures it, instead of the other way round. This is useful when one party can only prepare and send quantum states, and the other party can only measure them, which is often the case in practical quantum communication systems. Both the “original” XOR oblivious transfer protocol and its reversed version have been implemented optically. We also discuss how quantum random access codes can be connected with quantum oblivious transfer.

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Oblivious transfer is an important primitive in modern cryptography. Applications include secure multiparty computation, oblivious sampling, e-voting, and signatures. Information-theoretically secure perfect 1-out-of 2 oblivious transfer is impossible to achieve. Imperfect variants, where both participants' ability to cheat is still limited, are possible using quantum means while remaining classically impossible. Precisely what security parameters are attainable remains unknown. We introduce a theoretical framework for studying semirandom quantum oblivious transfer, which is shown to be equivalent to regular oblivious transfer in terms of cheating probabilities. We then use it to derive bounds on cheating. We also present a protocol with lower cheating probabilities than previous schemes, together with its optical realization. We show that a lower bound of 2/3 on the minimum achievable cheating probability can be directly derived for semirandom protocols using a different method and definition of cheating than used previously. The lower bound increases from 2/3 to approximately 0.749 if the states output by the protocol are pure and symmetric. The oblivious transfer scheme we present uses unambiguous state elimination measurements and can be implemented with the same technological requirements as standard quantum cryptography. The cheating probabilities are 3/4 and approximately 0.729 for sender and receiver respectively, which is lower than in existing protocols. Using a photonic test-bed, we have implemented the protocol with honest parties, as well as optimal cheating strategies., 22 pages, 1 figure, v2 moderate changes, published version