Cryptography Reference
In-Depth Information
chapter 4
The DARPA Quantum
Network
C. Elliott
BBN Technologies
Contents
4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
4.2 Current Status of the DARPA Quantum Network . . . . . . . . . . . . . . . . . . . . 84
4.3 Motivation for the DARPA Quantum Network . . . . . . . . . . . . . . . . . . . . . . . 86
4.4 What Is a QKD Network? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
4.4.1 Photonic Switching for “Untrusted Networks” . . . . . . . . . . . . . . . 89
4.4.2 Key Relay for “Trusted Networks” . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
4.4.3 The Major Benefits of QKD Networks . . . . . . . . . . . . . . . . . . . . . . . . . 89
4.5 BBN's “Mark 2'' Weak Coherent Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
4.6 BBN QKD Protocols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
4.7 Photonic Switching for Untrusted Networks . . . . . . . . . . . . . . . . . . . . . . . . . 97
4.8 BBN Key Relay Protocols for Trusted Networks . . . . . . . . . . . . . . . . . . . . . . 99
4.9 Future Plans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
4.10 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
4.1 Introduction
It now seems likely that quantum key distribution (QKD) techniques can
provide practical building blocks for highly secure networks and in fact may
offer valuable cryptographic services, such as unbounded secrecy lifetimes,
which can be difficult to achieve by other techniques. Unfortunately, how-
ever, QKD's impressive claims for information assurance have been to date at
least partly offset by a variety of limitations. For example, traditional QKD is
distance limited, can only be used across a single physical channel (e.g., free-
space or telecommunications fiber, but not both in series due to frequency
