In recent years, we have experienced a wave of DDoS attacks threatening the welfare of the internet. These are launched by malicious users whose only incentive is to degrade the performance of other, innocent, users. The traditional systems turn out to be quite vulnerable to these attacks. The objective of this work is to take a first step to close this fundamental gap, aiming at laying a foundation that can be used in future computer/network designs taking into account the malicious users. Our approach is based on proposing a metric that evaluates the vulnerability of a system. We then use our vulnerability metric to evaluate a data structure which is commonly used in network mechanisms-the Hash table data structure. We show that Closed Hash is much more vulnerable to DDoS attacks than Open Hash, even though the two systems are considered to be equivalent by traditional performance evaluation. We also apply the metric to queuing mechanisms common to computer and communications systems. Furthermore, we apply it to the practical case of a hash table whose requests are controlled by a queue, showing that even after the attack has ended, the regular users still suffer from performance degradation or even a total denial of service.

Channel aware schedulers of modern wireless networks - such as the popular Proportional Fairness Scheduler (PFS) - improve throughput performance by exploiting channel fluctuations while maintaining fairness among the users. In order to simplify the analysis, PFS was introduced and vastly investigated in a model where frame losses do not occur, which is of course not the case in practical wireless networks. Recent studies focused on the efficiency of various implementations of PFS in a realistic model where frame losses can occur. In this work we show that the common straight forward adaptation of PFS to frame losses exposes the system to a malicious attack (which can alternatively be caused by malfunctioning user equipment) that can drastically degrade the performance of innocent users. We analyze the factors behind the vulnerability of the system and propose a modification of PFS designed for the frame loss model which is resilient to such malicious attack while maintaining the fairness properties of original PFS.

Channel-aware scheduling strategies - such as the CDF Scheduler (CS) algorithm for the CDMA/HDR systems - provide an effective mechanism for utilizing the channel data rate for improving throughput performance in wireless data networks by exploiting channel fluctuations. A highly desired property of such a scheduling strategy is that its algorithm will be stable, in the sense that no user has incentive "cheating" the algorithm in order to increase his/her channel share (on the account of others). We present a scheme by which coordination allows a group of users to gain permanent increase in both their time slot share and in their throughput, on the expense of others, by misreporting their rates. We show that for large populations consisting of regular and coordinated users in equal numbers, the ratio of allocated time slots between a coordinated user and a regular one converges to e - 1 ap 1.7. Our scheme targets the very fundamental principle of CS (as opposed to just attacking implementation aspects), which bases its scheduling decisions on the cumulative distribution function (CDF) of the channel rates reported by users. Our scheme works both for the continuous channel spectrum and the discrete channel spectrum versions of the problem.

The design of computer and communication systems has been based, for decades, on the fundamental assumption that the objective of all users is to improve their own performance. In recent years we have experienced a wave of DDoS attacks threatening the welfare of the Internet. These are launched by malicious users whose pure incentive is to degrade the performance of other, innocent, users. The traditional systems turn out to be quite vulnerable to these attacks. The objective of this work is to take a first step to close this fundamental gap, aiming at laying a foundation that can be used in future computer/network designs taking into account the malicious users. Our approach is based on proposing a metric that evaluates the vulnerability of a system. We then evaluate the commonly used data structure in network mechanisms, the hash data structure, using our vulnerability metric. We show that a Closed Hash is much more vulnerable than an Open Hash to DDoS attacks, even though the two systems are considered to be equivalent via traditional performance evaluation. We also apply the metric to queueing mechanisms common to computer and communications systems. Lastly we apply it to the practical case of a hash table whose requests are controlled by a queue, showing that even after the attack has ended, the regular users still suffer from performance degradation or even a total denial of service.