## Quantum Bit Commitment - Colóquio DFMA

Resumo: Bit commitment is a cryptographic protocol between two mistrusting parties, Alice and Bob, in which Alice wants to commit to a bit while keeping it hidden from Bob. Bit commitment is an important primitive in cryptography since it can serve as a building block to achieve various cryptographic tasks, such as secure coin flipping, zero knowledge proofs, secure computation, user authentication, signature schemes, and verifiable secret sharing. It was accepted that exemplary valid quantum protocols for bit commitment were available, but the optimism in the development of secure quantum bit commitment protocols was put into very serious doubt in works by Mayers and by Lo and Chau were it was shown, or so was it believed for over 20 years, that all proposed quantum bit commitment protocols are insecure. In this seminar I will talk about the development of the project Unconditionally Secure Quantum Bit Commitment, developed in partnership with Prof. Paulo Nussenzveig (USP) and Prof. Charles Tresser (IMPA), and funded by the Call 04/2020 of Instituto Serrapilheira, in which our goal is to understand the assumptions in Mayers and Lo and Chau results and search for a quantum protocol that evades these assumptions and thus accomplishes unconditionally secure quantum bit commitment. If successful, this will be a major contribution to the field, not only for the practical applications of a bit commitment scheme but also for our understanding of the limits of quantum cryptography and quantum information, changing our perspective of what can or can not be done with quantum systems.