A defense against clock skew replication attacks in wireless sensor networks

As studies to date have demonstrated that the clock skew of every physical device differs and so is suitable for device identification in network communications, the fact that any adversary can easily produce a fake clock skew by altering the timestamp of the sent packets remains a concern. This study contributes to this issue by realizing a replication attack of an indistinguishable fake clock skew and by developing its countermeasure in a wireless sensor network environment. In the first part of the study, a method of timestamp back calculation is developed for imitating the clock skew of a neighbor node. Given the relative clock skews of a victim node and an imitated node, our method calculates the time difference between the attacker node and the imitated one, which makes the biased timestamps of the attacker node's packets, when measured by the victim node, derive to the exactly the same clock skew as the imitated node. Our experiment results show that the success rate of physical replication attacks ranges from 82.5% to 95%. In the second part of this study, a novel approach is proposed to defend against such clock skew replication attacks. This approach is based on our observation that a precise skew estimation can be performed only when the packets are sent at fixed time intervals. When the time period of the synchronization is changed frequently, our experiments show that the success rate of an attack is considerably reduced to less than 2.4%, or even 0% in most cases. (C) 2013 Elsevier Ltd. All rights reserved.