Ragavendran Gopalakrishnan

An architectural view of game theoretic control

Game-theoretic control is a promising new approach for distributed resource allocation. In this paper, we describe how game-theoretic control can be viewed as having an intrinsic layered architecture, which provides a modularization that simplifies the control design. We illustrate this architectural view by presenting details about one particular instantiation using potential games as an interface. This example serves to highlight the strengths and limitations of the proposed architecture while also illustrating the relationship between game-theoretic control and other existing approaches to distributed resource allocation.

Potential Games Are Necessary to Ensure Pure Nash Equilibria in Cost Sharing Games

We consider the problem of designing distribution rules to share “welfare” (cost or revenue) among individually strategic agents. There are many known distribution rules that guarantee the existence of a (pure) Nash equilibrium in this setting, e.g., the Shapley value and its weighted variants; however, a characterization of the space of distribution rules that guarantees the existence of a Nash equilibrium is unknown. Our work provides an exact characterization of this space for a specific class of scalable and separable games that includes a variety of applications such as facility location, routing, network formation, and coverage games. Given arbitrary local welfare functions 𝕨, we prove that a distribution rule guarantees equilibrium existence for all games (i.e., all possible sets of resources, agent action sets, etc.) if and only if it is equivalent to a generalized weighted Shapley value on some “ground” welfare functions 𝕨′, which can be distinct from 𝕨. However, if budget-balance is required in ...

Dispatching to incentivize fast service in multi-server queues

As a field, queueing theory predominantly assumes that the arrival rate of jobs and the system parameters, e.g., service rates, are fixed exogenously, and then proceeds to design and analyze scheduling policies that provide efficient performance, e.g., small response time (sojourn time). However, in reality, the arrival rate and/or service rate may depend on the scheduling and, more generally, the performance of the system. For example, if arrivals are strategic then a decrease in the mean response time due to improved scheduling may result in an increase in the arrival rate.

Cryptanalysis of Mu et al.'s and Li et al.'s Schemes and a Provably Secure ID-Based Broadcast Signcryption (IBBSC) Scheme

In applications like wireless content distribution, a central authority needs to deliver encrypted data to a large number of recipients in such a way that only a privileged subset of users can decrypt it. In addition, to avert junk content or spam, subscribers must have source authentication with respect to their broadcasters. The limited memory and computational power of mobile devices, coupled with escalating costs of wireless bandwidth make efficiency a major concern. Broadcast signcryption , which enables the broadcaster to simultaneously encrypt and sign the content meant for a specific set of users in a single logical step, provides the most efficient solution to this dual problem of confidentiality and authentication. It is arguably most efficiently implemented in the ID-based setting because of its well known advantages. Only three IBBSC schemes exist in literature, one of which has already been shown to be flawed and its security leaks fixed. In this paper, we show that the remaining two -- Mu et al.s scheme and Li et al.s scheme are also flawed. Specifically, we show that while Mu et al.s scheme is insecure with respect to unforgeability, Li et al.s scheme can be totally broken (with respect to both unforgeability and confidentiality). Following this, we propose a new IBBSC scheme and formally prove its security under the strongest existing security models for broadcast signcryption (IND-CCA2 and EUF-CMA).

Cryptanalysis of Bohio et al.'s ID-Based Broadcast Signcryption (IBBSC) Scheme for Wireless Ad-Hoc Networks

Broadcast signcryption enables the broadcaster to simultaneously encrypt and sign the content meant for a specific set of users in a single logical step. It provides a very efficient solution to the dual problem of achieving confidentiality and authentication during content distribution. Among other alternatives, ID-based schemes are arguably the best suited for its implementation in wireless ad-hoc networks because of the unique advantage that they provide - any unique, publicly available parameter of a user can be his public key, which eliminates the need for a complex public key infrastructure. In 2004, Bohio et al. proposed an ID-based broadcast signcryption (IBBSC) scheme which achieves constant ciphertext size. They claim that their scheme provides both message authentication and confidentiality, but do not give formal proofs. In this paper, we demonstrate how a legitimate user of the scheme can forge a valid signcrypted ciphertext, as if generated by the broadcaster. Moreover, we show that their scheme is not IND-CCA secure. Following this, we propose a fix for Bohio et al.s scheme, and formally prove its security under the strongest existing security models for broadcast signcryption (IND-CCA2 and EUF-CMA). While fixing the scheme, we also improve its efficiency by reducing the ciphertext size to two elements compared to three.

Routing and Staffing When Servers Are Strategic

Traditionally, research focusing on the design of routing and staffing policies for service systems has modeled servers as having fixed (possibly heterogeneous) service rates. However, service systems are generally staffed by people. Furthermore, people respond to workload incentives; that is, how hard a person works can depend both on how much work there is and how the work is divided between the people responsible for it. In a service system, the routing and staffing policies control such workload incentives; and so the rate servers work will be impacted by the system’s routing and staffing policies. This observation has consequences when modeling service system performance, and our objective in this paper is to investigate those consequences. We do this in the context of the M/M/N queue, which is the canonical model for large service systems. First, we present a model for “strategic” servers that choose their service rate to maximize a trade-off between an “effort cost,” which captures the idea that se...