Quantum Computation and Information Seminar 

02/03/2007, 15:00 — 16:00 — Room P4.35, Mathematics Building
Valerio Scarani, U Geneva

Device-independent security proofs for quantum cryptography

Using quantum non-locality, one can prove the security of quantum cryptography in a "device-independent scenario", that is, without any assumption on the nature of the quantum signal or on the measuring devices. This remarkable generality is a consequence of Bell's theorem applied to cryptography: if the Alice-Bob correlations violate a Bell inequality, then the eavesdropper Eve cannot have full information on Alice's and Bob's symbols, because otherwise Eve's symbol would be a hidden variable that reproduces the correlations. While this idea has been around since Ekert's 1991 paper, quantitative progress has been possible only very recently. In the first works, for mathematical simplicity, Eve was provided with more power than quantum physics, and other strong assumptions were made (zero error rate by Barrett, Hardy, Kent, PRL 2005; individual attacks by Acin et al, PRL 2006, Scarani et al PRA 2006). I shall discuss these pioneering approaches and present the latest achievement: a bound for security in the device-independent scenario against collective attacks of a quantum Eve (Acin et al, work in preparation).