Intrusion detection systems (IDS) are quickly becoming a standard component of a network security infrastructure. Most IDS developed to date emphasize detection; response is mainly concentrated on blocking a part of the network after an intrusion has been detected. This mechanism can help in temporarily stopping the intrusion, but such a limited response means that attacking is free for the attacker. The idea behind our approach is to frustrate the intruder by attacking back. This requires developing a sense of trust in the network for the attacked host and establishing proof of the attack so the attack-back action can be justified. To develop this trust model, we propose a protocol that allows the attacked host to prove to the attacker’s edge router that it has been attacked. The model is quite flexible, and based on the level of trust developed for the host, an appropriate countermeasure is taken. Besides attack-back, other possible responses could be blocking a part of the network and use of network puzzles to limit the attacker’s access to network resources. We believe that the attack-back approach would certainly demoralize novice attackers, and even expert attackers will think twice before attacking again. In addition, the protocol prevents a host from pretending that it has been attacked. We are building a system that can handle a majority of known attacks (signature-based). We are also exploring the idea of adding a third trusted party into the system in order to provide countermeasure action for novel attacks (anomaly-based).
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