28.05.2012. :: Seminar - Nikola Paunkovic
U ponedeljak 28.05. u 11h na Institutu za fiziku, u sali 300, odrzace se seminar pod naslovom
Quantum contract signing
dr Nikola Paunkovic
Instituto Superior Tecnico
Universidade Tecnica de Lisboa
We present a fair and optimistic quantum-contract-signing protocol between two clients that requires no communication with the third trusted party during the exchange phase. We discuss its fairness and show that it is possible to design such a protocol for which the probability of a dishonest client to cheat becomes negligible and scales as N−1/2, where N is the number of messages exchanged between the clients. Our protocol is not based on the exchange of signed messages: Its fairness is based on the laws of quantum mechanics. Thus, it is abuse free, and the clients do not have to generate new keys for each message during the exchange phase. We discuss a real-life scenario when measurement errors and qubit-state corruption due to noisy channels and imperfect quantum memories occur and argue that for a real, good-enough measurement apparatus, transmission channels, and quantum memories, our protocol would still be fair. Apart from stable quantum memories, the other segments of our protocol could be implemented by today`s technology, as they require in essence the same type of apparatus as the one needed for the Bennett-Brassard 1984 (BB84) cryptographic protocol. Finally, we briefly discuss two alternative versions of the protocol, one that uses only two states [based on the Bennett 1992 (B92) protocol] and the other that uses entangled pairs, and show that it is possible to generalize our protocol to an arbitrary number of clients.