  Let us consider a situation where two information brokers, whose currency is,
of course, information, need to reciprocally exchange information. The two
brokers, being somewhat distrustful, would like a third, mutually trusted,
entity to be involved in the exchange process so as to guarantee the successful
completion of the transaction, and also verify that it indeed took place. Can
this be done in such a way that both brokers receive their information
simultaneously and securely, and without the trusted intermediary ending up
knowing the exchanged information? This work presents and rigorously analyzes a
new quantum entanglement-based protocol that provides a solution to the above
problem. The proposed protocol is aptly named entanglement-based reciprocal
simultaneous information exchange protocol. Its security is ultimately based on
the assumption of the existence of a third trusted party. Although, the
reciprocal information flow is between our two information brokers, the third
entity plays a crucial role in mediating this process, being a guarantor and a
verifier. The phenomenon of quantum entanglement is the cornerstone of this
protocol, as it makes possible its implementation even when all entities are
spatially separated, and ensuring that, upon completion, the trusted third
party remains oblivious of the actual information that was exchanged.

Quantum Physics