An Unlinkable Key Update Scheme Based on Bloom Filters for Random Key Pre-distribution

Eschenauer et al. presented an efficient random key predistribution scheme for WSNs that assigns symmetric keys to sensor nodes by randomly sampling from a large key pool. Most research in this line assume nodes exchange key identifiers to determine common keys between them. However, an adversary can learn topology information of the underlying random key graph by intercepting exchanged key identifiers. In addition, when key exposure occurs, compromised nodes should be revoked and uncompromised nodes’ key rings should be updated securely. In this paper, we design an unlinkable key update mechanism that can revoke compromised nodes while an adversary is infeasible to link key identifiers with a node. A key update node is responsible for distributing a random seed among uncompromised nodes in order to update their key rings securely. The revoked keys are represented by a bloom filter to avoid exchange of key identifiers when checking whether a node is compromised. As a bloom filter has zero false negative rate, we utilize negative answers returned by a bloom filter to identify uncompromised keys and nodes with high probability. Then a local broadcast mechanism is used to speed up update of uncompromised nodes’ key ring securely.