Quantum bit commitment protocols

• Grant number: 21/12855-7
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Effective date (Start): January 01, 2022
• Effective date (End): December 31, 2022
• Field of knowledge: Physical Sciences and Mathematics - Physics
• Principal Investigator: Bárbara Lopes Amaral
• Grantee: Letícia Maria Paz de Lima
• Host Institution: Instituto de Física (IF). Universidade de São Paulo (USP). São Paulo , SP, Brazil
• Associated research grant: 20/06454-7 - Non-locality and contextuality as resources for quantum information, quantum computation and the certification of quantum devices, AP.JP

Abstract

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. A bit commitment protocol can be compared with a safe: to commit to a bit b, Alice writes b on a piece of paper, locks the paper in the safe, and sends the safe to Bob while keeping the key. When she wants to reveal her commitment, she sends the key to Bob who opens the safe and reads the value of b. 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 where it was shown, or so was it believed for over 20 years, that all proposed quantum bit commitment protocols are insecure. The aim of this project is to offer a general idea of classical and quantum bit commitment protocols and their applications, their limitations, and the no-go theorems of Mayers and Lo, and Chau. (AU)