Collusion Detection and Resolution

The problem of protecting against attacks perpetrated by valid users in possession of “correct” keys, is one that all cryptographic key management schemes aim to prevent. In this chapter, we consider an attack type, termed a “collusion attack”, that can be provoked by users in possession of valid keys. A collusion attack occurs when two or more users at the same level in the hierarchy collaboratively compute (using a contrived mathematical function), from their respective keys, a key (higher up in the hierarchy) to which they are not entitled. Collusion detection and resolution is an important issue in guaranteeing the security of any key management scheme because it enables the scheme to enforce precautionary measures against collusion attacks which can be carried out by users in possession of valid keys. We propose a method of addressing this problem that is based on the concept of maximum dispersion.