Resource Inflation Threats to Denial of Service Countermeasures

Currency-based mechanisms have been proposed as a way to use resource fairness among contenders for a service to thwart Denial of Service (DoS) attacks. Under resource fairness, a server allocates its service to the clients in proportion to their payment of a resource, making the resource serve as a kind of currency. We consider the vulnerability of currency-based DoS defense mechanisms to various resource inflation attacks in which an attacker can substantially inflate its possession of the resource at low cost and in a way that may be either difficult or undesirable for a valid client to do. We provide a simple theoretical analysis of resource inflation attacks and investigate its application to a number of payment schemes to rank their likely vulnerability. We find that the threat of Graphics Processing Units (GPUs) for inflation attacks is especially severe: we are able to demonstrate inflation of up to 630x with common inexpensive GPUs. We also review threats from other capabilities, including multi-core processors, cloud computing, and bandwidth inflation schemes.