Optimal bounds for quantum bit commitment

Understand

Bit commitment is a fundamental cryptographic primitive with numerous applications.

• Quantum information allows for bit commitment schemes in the information theoretic setting where no dishonest party can perfectly cheat.
• The previously best-known quantum protocol by Ambainis achieved a cheating probability of at most 3/4[Amb01].
• On the other hand, Kitaev showed that no quantum protocol can have cheating probability less than 1/sqrt{2} [Kit03] (his lower bound on coin flipping can be easily extended to bit commitment).