Cryptography Reference
In-Depth Information
4.8 BBN Key Relay Protocols for Trusted
Networks
When two QKD endpoints do not have a direct or photonically switched QKD
link between them, but there is a path between them over QKD links through
trusted relays, novel BBN-designed networking protocols allow them to agree
upon shared QKD bits. They do so by choosing a path through the network,
creating a new random number R, and essentially sending R one-time-pad
encrypted across each link. We call this process “key relay” and the resultant
network a “trusted network” since the chief characteristic of this scheme is that
the secrecy of the key depends not just on the endpoints being trustworthy;
the intermediate nodes must also be trusted.
The BBN key relay protocols have been continuously operational in the
DARPA Quantum Network since October 2003. In fact, they run continuously
in our network through Cambridge and allow Alice to build up a reservoir
of shared key material with Anna, even though both entities are transmitters,
via a trusted relay at Bob or Boris. Similarly Bob and Boris continuously build
up shared key material via trusted relays at Alice or Anna.
The four main aspects of the key relay process are illustrated in Figure 4.11.
Figure 4.11(A) makes it clear that a key relay network is parallel to an overar-
ching network conveying communication messages and control traffic such
as the QKD protocols. Here the Internet is the communications network, each
link underneath it is a separate QKD link, and circular nodes are key relay
stations. In Figure 4.11(B), one particular source QKD endpoint (S) wishes
to agree upon key material with a far-away destination QKD endpoint (D).
Since both endpoints, S and D, are connected to a ubiquitous communications
A.
B.
Internet
Internet
Internet
Internet
Internet
connection
2 - Message transport
2 - Message transport
Private
Enclave
Private
Enclave
Private
Enclave
Private
Enclave
S
S
D
D
S
S
D
D
1 - Key agreement
1 - Key agreement
QKD Link
C.
D.
Internet
Internet
Internet
Internet
Routing
around failure
QKD Key Pairs:
K(S,R1)
K(R1,R2)
K(R2,D)
R1
R1
R2
R2
R1
R1
X
X
R2
R2
S
S
D
D
R3
R3
S
S
D
D
R3
R3
R5
R5
R4
R4
R5
R5
R4
R4
Figure 4.11
Major aspects of the key relay protocols.
