[hep-th] seminar u ponedeljak

[Branislav Cvetkovic]

Postovane kolege,

u ponedeljak 28.05. u 11 h na Institutu za fiziku, u sali 300,  dr 
Nikola Paunkovic sa Instituto Superior Technico u Lisabonu,
ce odrzati seminar pod naslovom  "Quantum contract signing". Abstrakt 
vam prosledjujem u prilogu.

                                                     Pozdrav Branislav

Abstract:
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.