Cryptography Reference
In-Depth Information
propagation and modulation issues), and is vulnerable to disruptions such as
fiber cuts because it relies on single points of failure.
To a surprising extent, however, these limitations can be mitigated or
even completely removed by building QKD
networks
instead of the tradi-
tional stand-alone QKD links. Accordingly, a team of participants from BBN
Technologies, Boston University, and Harvard University has recently built
and begun to operate the world's first quantum key distribution network
under Defense Advanced Research Projects Agency (DARPA) sponsorship.
∗
The DARPA Quantum Network became fully operational on October 23,
2003, in BBN's laboratories, and in June 2004 it was fielded through dark fiber
underneath the streets of Cambridge, Massachusetts, to link our campuses
with nonstop quantum cryptography, 24 hours per day. It is the world's first
quantum cryptography network and indeed probably the first metro-area
QKD deployment in continuous operation. As of December 2004, it consists
of six QKD nodes. Four are used in BBN-built, interoperable weak-coherent
QKD systems running at a 5-MHz pulse rate through telecommunications
fiber and inter-connected via a photonic switch. Two are electronics built by
the National Institute of Standards and Technology (NIST) for a high-speed
free-space QKD system. All run BBN's full suite of production-quality QKD
protocols. In the near future, we plan to add four more quantum cryptographic
nodes based on a variety of physical phenomena and start testing the resulting
network against sophisticated attacks.
This chapter introduces the DARPA Quantum Network as it currently
exists and briefly outlines our plans for the near future. We first describe the
motivation for our work and define the basic principles of a quantum crypto-
graphic
network
(which may be composed of a number of QKD systems with
relays and/or photonic switches). We then discuss the specifics of our current
weak-coherent QKD network, including its QKD links, photonic switches for
“untrusted” networks, and key relay protocols for “trusted” networks. We
conclude with future plans and our acknowledgments.
4.2 Current Status of the DARPA
Quantum Network
Figure 4.1 displays a fiber diagram of the DARPA Quantum Network's build-
out through Cambridge, Massachusetts, as of December 2004. The network
consists of two weak-coherent BB84 transmitters (Alice, Anna), two compati-
ble receivers (Bob, Boris), and a 2
2 switch that can couple any transmitter to
any receiver under program control. Alice, Bob, and the switch are in BBN's
laboratory; Anna is at Harvard; and Boris is at Boston University (BU). The
fiber strands linking Alice, Bob, and the switch are several meters long. The
×
∗
The opinions expressed in this article are those of the author alone and do not nec-
essarily reflect the views of the United States Department of Defense, DARPA, or the
United States Air Force.
