Device-Independent Relativistic Quantum Bit Commitment

We examine the possibility of device-independent relativistic quantum bit commitment. We note the potential threat of {\it location attacks}, in which the behaviour of untrusted devices used in relativistic quantum cryptography depends on their space-time location. We describe relativistic quantum bit commitment schemes that are immune to these attacks, and show that these schemes offer device-independent security against hypothetical post-quantum adversaries subject only to the no-signalling principle. We compare a relativistic classical bit commitment scheme with similar features, and note some possible advantages of the quantum schemes

Quantum Cryptography Based Solely on Bell's Theorem

Information-theoretic key agreement is impossible to achieve from scratch and must be based on some - ultimately physical - premise. In 2005, Barrett, Hardy, and Kent showed that unconditional security can be obtained in principle based on the impossibility of faster-than-light signaling; however, their protocol is inefficient and cannot tolerate any noise. While their key-distribution scheme uses quantum entanglement, its security only relies on the impossibility of superluminal signaling, rather than the correctness and completeness of quantum theory. In particular, the resulting security is device independent. Here we introduce a new protocol which is efficient in terms of both classical and quantum communication, and that can tolerate noise in the quantum channel. We prove that it offers device-independent security under the sole assumption that certain non-signaling conditions are satisfied. Our main insight is that the XOR of a number of bits that are partially secret according to the non-signaling conditions turns out to be highly secret. Note that similar statements have been well-known in classical contexts. Earlier results had indicated that amplification of such non-signaling-based privacy is impossible to achieve if the non-signaling condition only holds between events on Alice's and Bob's sides. Here, we show that the situation changes completely if such a separation is given within each of the laboratories.Comment: 32 pages, v2: changed introduction, added reference

Income Distribution, Institutions and Conflicts: An Exploratory Analysis for Latin America and the Caribbean

income distribution, polarisation, cohesion, inequality, poverty, institutions, instability, conflict, corruption, Latin America, Caribbean

Universally-composable privacy amplification from causality constraints

We consider schemes for secret key distribution which use as a resource correlations that violate Bell inequalities. We provide the first security proof for such schemes, according to the strongest notion of security, the so called universally-composable security. Our security proof does not rely on the validity of quantum mechanics, it solely relies on the impossibility of arbitrarily-fast signaling between separate physical systems. This allows for secret communication in situations where the participants distrust their quantum devices.Comment: 4 page