Emmanuel Zambrini Cruzeiro

Quantum communication ensures security by using quantum mechanics, typically through Quantum Key Distribution (QKD) which is limited to a few hundred kilometers for useful secret key rates. This study examines Quantum Keyless Private Communication (QKPC), inspired by the classical wiretap model, which allows secure one-way communication without shared keys. Two implementations are explored: the original On-Off Keying (OOK) and a new polarization-based version. Both methods are implemented experimentally and the results confirm their effectiveness and potential as practical alternatives to traditional QKD for secure, long-distance communication.

Few primitives are as intertwined with the foundations of cryptography as Oblivious Transfer (OT). Not surprisingly, with the advent of quantum resources in information processing, OT played a central role in establishing new possibilities (and defining impossibilities) pertaining to the use of these novel assets. A major research path is minimizing the required assumptions to achieve OT, and studying their consequences. Regarding its computation, it is impossible to construct unconditionally-secure OT without extra assumptions; and, regarding communication complexity, achieving one-shot (and even non-interactive) OT has proved to be an elusive task, widely known to be impossible classically. In this work, we devise a extit{one-shot OT}, showig how this construction is indeed possible using quantum resources, if we assume the existence of one-way functions and sequential functions in the Noisy-Quantum-Storage Model.

Device-independence (DI) is the golden standard for quantum key distribution (QKD) security: it allows unconditional security based on the laws of physics even for untrusted or maliciously designed devices. Nevertheless, DI-QKD, for now, remains extremely challenging. The first proof-of-principle experiments having been performed only very recently, almost 40 years after the invention of BB84. It then becomes naturally interesting to study scenarios which may reach a compromise between experimental challenge and security: for example, by assuming than the users have a partial description of the devices. This intermediate scenario is called semi-device-independent (SDI) QKD and aims for a reasonable trade-off between the highest level of security, device-independence, and experimental feasibility.