Source-linked AI summary
Quantum Key Distribution with Classical Bob
Michel Boyer, Dan Kenigsberg, Tal Mor
TL;DR
The paper asks whether secure key distribution is possible when Alice is quantum but Bob has only classical capabilities. It presents such a protocol and proves complete robustness: any attack gaining information about the INFO string necessarily induces detectable errors.
Problem
Secure key distribution is unavailable to two classical parties without unproven computational assumptions, motivating the study of protocols with only one quantum party.
Method
The protocol lets Bob either measure and resend each qubit in the classical basis or reflect it, while Alice performs the quantum operations and uses TEST, CTRL, error correction, and privacy amplification.
Results
The protocol is completely robust: if an attack causes no errors on TEST and CTRL bits, Eve’s final state is independent of Alice’s sent states and contains no information about the INFO string.
Takeaways & Limitations
Secret key distribution can be achieved with Bob restricted to classical operations, clarifying how much quantumness is required for this task.
Abstract
from arXiv · showhide
Secure key distribution among two remote parties is impossible when both are classical, unless some unproven (and arguably unrealistic) computation-complexity assumptions are made, such as the difficulty of factorizing large numbers. On the other hand, a secure key distribution is possible when both parties are quantum. What is possible when only one party (Alice) is quantum, yet the other (Bob) has only classical capabilities? We present a protocol with this constraint, and prove its robustness against attacks: we prove that any attempt of an adversary to obtain information (and even a tiny amount of information) necessarily induces some errors that the legitimate users could notice.