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Relativistic and Quantum Cryptography

4. Bit Commitment

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In this mini-lecture, we explore the concept of bit commitment. As we move through this mini-lecture, we consider: (i) the problem that bit commitment addresses: Alice wants to send Bob an encrypted prediction, but they do not trust each other, thus Alice wants to ensure Bob doesn’t decrypt her message until she gives him the key and Bob wants to ensure that Alice is committed to her prediction; (ii) an example of an imperfect bit commitment scheme: locking the prediction in a safe with a combination; (iii) a secure bit commitment scheme in which Alice and Bob are networks of people and the principles of Special Relativity and Quantum Theory introduced previously are used; and (iv) the practicality of long-term bit commitment along with some relevant research.


In this course, Professor Adrian Kent (University of Cambridge) explores relativistic and quantum cryptography. In the first mini-lecture, we introduce the key principles in the Special Theory of Relativity and in Quantum Theory that are needed to understand the cryptographic schemes used in subsequent videos. In the second mini-lecture, we discuss the polarisation of light and how it can be affected by measurement. In the third mini-lecture, we introduce the No-Cloning Theorem and the Relativistic No-Summoning Theorem. In the fourth mini-lecture, we explore the concept of bit commitment. In the fifth mini-lecture, we discuss how to use one-time pads to encrypt messages and prevent eavesdropping. In the sixth mini-lecture, we introduce the BB84 (Bennett-Brassard, 1984) quantum key distribution protocol, which utilises polarisation states to encrypt messages.


Adrian Kent is Professor of Quantum Physics in the Department of Applied Mathematics and Theoretical Physics (DAMTP) at the University of Cambridge. He is also a member of the Cambridge Centre for Quantum Information and Foundations and a Distinguished Visiting Research Chair at the Perimeter Institute for Theoretical Physics. His principal research interests are in quantum foundations, quantum information theory, and quantum cryptography. He is a pioneer in the field of relativistic quantum cryptography, having provided the first relativistic cryptography protocols for bit commitment and ideal coin tossing that achieve unconditional security in 1999. He has published papers extensively on this topic as well as other topics such as quantum key distribution. Professor Kent is a co-editor of the book Many Worlds?: Everett, Quantum Theory, and Reality (2010).

Cite this Lecture

APA style

Kent, A. (2022, January 13). Relativistic and Quantum Cryptography - Bit Commitment [Video]. MASSOLIT.

MLA style

Kent, Adrian. "Relativistic and Quantum Cryptography – Bit Commitment." MASSOLIT, uploaded by MASSOLIT, 13 Jan 2022,

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