Indirect Eavesdropping in Quantum Networks
Stefan Raß, Sandra König · 2011
Quantum networks are communication networks in which adjacent nodes enjoy perfectly secure channels thanks to quantum key distribution (QKD). Drawing end- to-end security from QKD-supported point-to-point security can be done by virtue of multipath transmission. This concept buys security at the cost of strongly connected networks and perfect routing. Particularly the latter is hard to ensure, since congestions or (passive) may cause QKD key- buffers to run empty, thus enforcing local re-routing of packets. Hence, the adversary may use not to extract information, but to redirect the information flow towards a relay-node that he controls. Such attacks can readily invalidate the stringent requirements of multipath transmission protocols and thus defeat any formal arguments for perfect secrecy. Moreover, this form of indirect eavesdropping seems to be unconsidered in the literature so far. We investigate whether or not unconditional security in a quantum network with non- reliable routing is possible. Using Markov-chains, we derive various sufficient criteria for retaining perfect secrecy under imperfect packet relay. In particular, we explicitly do not assume trusted relay or quantum repeaters available. Keywords-Quantum Cryptography, Markov-Chain, Secure