Abstract. An improved optical security system based on correlation between two phase-only computer generated masks is proposed. The two phase masks are placed together at the input plane of a joint transform correlator. A priori known output image is obtained in the system output only if one mask is the right key for the other mask. In addition to a simple verification, our security system is capable of identifying the type of an input mask according to the corresponding output image that it generates. The two phase masks are designed using an iterative optimization algorithm with constraints in the input and output domains. Computer simulations are presented with the resultant images formed by the two phase-only elements. © 2001 Society of Photo-Optical Instrumentation Engineers.

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Abstract-The challenging characteristics of sensor nodes, including the constrained resources, the ad-hoc nature of their deployment and the vulnerability of wireless media, pose a need for unique security solutions. The advantages of Public Key Cryptography (PKC) for sensor network security are widely acknowledged and include resilience, scalability and decentralized management. Recent work has indicated that PKC is feasible in the wireless sensor network (WSN) environment, paving the way for many new security services and opportunities. However, the computational effort involved in performing PKC operations remains substantial. From an energy consumption perspective, it is imperative that the processing and communication resources be utilized only when required. To that end, PKC implementations are more vulnerable to Denial of Service (DoS) attacks, when compared to traditional security methods that require less resources. In particular, if a malicious party attacks a sensor node by repetitive requests to establish a key, the resources of the attacked node can be exhausted quite rapidly. In this paper, we propose a novel RSA-based framework for combating DoS attacks in WSN by ensuring that the malicious party will exhaust its resources prior to exhausting those of its counterparts. Under the proposed approach, the mathematical operations performed by the malicious party require two or three orders of magnitude more resources than those required by the attacked party. We also present three methodologies for establishing an ephemeral key, in which the proposed DoS mitigation mechanism is an embedded component. Implementation results on the Intel Mote 2 platform substantiate the clear advantages of the proposed method.

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Companding is a well-known signal processing technique exploited by a broad range of applications. It primarily offers reduction of the signal dynamic range while retaining its important attributes. Digital companders have been utilized by a variety of applications, such as voice and video coding, in which the non-linear compression/expansion is typically implemented in software. This paper proposes an efficient parallel architecture for implementing digital compander functionality at very highspeeds. A piecewise linear partitioning of the compression function is applied, driven by prescribed maximal error constraints. The scalability of the scheme in terms of speed and area is discussed. Moreover, it is shown that the architecture can be easily pipelined, yielding further speed enhancement. It is shown that using Xilinx Virtex-II Pro (XC2VP20) FPGA devices, a 20-bit to 8-bit compander is implemented using less than 1000 gates, while operating at over 200 MHz.

This paper presents a performance analysis of output queued packet switch architectures employing virtual input queueing (VIQ), whereby arrival rates are nonuniformly distributed between the sources and the service intervals are bursty. In particular, we study the case of a two-state Markov-modulated service discipline, reflecting on several pragmatic scenarios such as noisy packet radio networks. We show that by exploiting an extended Markov-modulated service process and the Geo/GI/1 queueing model, closed-form expressions for the mean queueing latencies can be obtained. The methodology established in this paper can be extended to derive additional performance metrics and expected behavior of more complex packet switching architectures. INTRODUCTIONOutput queued (OQ) switches have been extensively studied in the literature over the last two decades. To a large extent, they constitute the theoretical benchmark on the performance that can be achieved in any spacedivision switching fabric, in particular with regard to work conservation and minimization of the average queueing delay [1]. Consequently, analysis of input queued switching architectures is commonly carried out in comparison to that of an OQ switch [1][2] [3]. Pragmatic output queueing schemes, such as shared memory architectures [4], have been deployed in switches and routers as well as studied at length. In such realizations, a large shared memory space is utilized by all input and output ports to read and write packets traversing the switching fabric.In order to minimize the computational complexity of the output-link scheduling that is required at each output port, virtual input queueing (VIQ) is commonly employed. In VIQ, a unique logical queue is maintained at every output for packets arriving from each of the inputs, as shown in figure 1. This allows for FIFO scheduling, and other monotonic scheduling policies, to be deployed with great . . . ease. It should also be noted that each input can generate a different rate of arrivals to the studied output port, denoted here by λ 1 , λ 2 , … λ N .The majority of the studies conducted on OQ switches, however, consider a deterministic server, that in each time slot serves one of the non-empty logical queues with probability 1. The latter assumption is somewhat incoherent with realistic networking scenarios, such as radio packet networks and optical burst networks, in which, due to channel conditions, the server is not necessarily available at any time to serve a packet from the output buffers.In some wireless networks, a shared channel may be busy such that a switch is required to wait a given amount of time before reattempting to transmit packets. Hence, it is widely acknowledged that bursty conditions characterize many pragmatic wireless channels [5]. Consequently, the service interval durations are interpreted as bursty in nature, whereby such burstiness can be modeled as a Markovian process.This paper presents an analysis of OQ switches introduced with non-uniformly distributed Bernoulli arri...