How to overcome the ´Trusted Node Model´ in Quantum Cryptography

Among the various proposals for quantum network design, the trusted node model is still the most flexible one for delivery of messages over arbitrary long distances. However, the outstanding security features of these networks are equally well defeated by the trusted relay. In brief this means, that messages sent over a certain node become completely insecure as soon as the node is compromised and the attacker hence knows the keys stored within this node. In this paper we propose a simple technique to reduce the damage in case of a compromised node. More precisely we will show, that none of the messages handled by the compromised node becomes insecure, as long as the compromised node is shut down in a certain time interval after detecting the attack. Additionally, our approach reduces the memory needed to store key material inside the nodes by 50%, whilst increasing security.