Abstract

Abstract
We show that the full PCF language can be encoded in L-rec, a syntactically linear lambda-calculus extended with numbers, pairs, and an unbounded recursor that preserves the syntactic linearity of the calculus. We give call-by-name and call-by-value evaluation strategies and discuss implementation techniques for L-rec, exploiting its linearity.

Abstract
Signal interference and packet collisions are typically viewed as negative factors that hinder wireless communication networks. When security is the primary concern, signal interference may actually be very helpful. Starting with a stochastic network model, we are able to show that packet collisions caused by jamming nodes can indeed be used effectively to attain new levels of secrecy in multiterminal wireless environments. To this effect, we propose a practical jamming protocol that uses the well-known request-to-send/clear-to-send (RTS/CTS) handshake of the IEEE 802.11 standard as a signaling scheme. Various jammer selection strategies are investigated depending on the position of source, destination, and jamming nodes. The goal is to cause asmuch interference as possible to eavesdroppers that are located in unknown positions, while limiting the interference observed by the legitimate receiver. To evaluate the performance of each strategy, we introduce and compute a measure for the secure throughput. Our results show that jamming can increase the levels of secrecy significantly albeit at a substantial cost in terms of energy efficiency.

Abstract
Inspired by recent results on information-theoretic security, we consider the transmission of confidential messages over wireless networks, in which the legitimate communication partners are aided by friendly jammers. We characterize the security level of a confined region in a quasi-static fading environment by computing the probability of secrecy outage in connection with two new measures of physical-layer security: the jamming coverage and the jamming efficiency. Our analysis for various jamming strategies based on different levels of channel state information provides insight into the design of optimal jamming configurations and shows that a single jammer is not sufficient to maximize both figures of merit simultaneously. Moreover, a single jammer requires full channel state information to provide security gains in the vicinity of the legitimate receiver.

Abstract
We consider a wireless network scenario in which the communicating nodes are assisted by a number of jammers. The goal of the jammers is to obstruct potential eavesdroppers while restricting the harmful interference experienced by the legitimate receiver. Based on a stochastic network model, we are able to show that packet collisions caused by jamming nodes can be used effectively to increase the level of secrecy. Various jammer selection policies are investigated depending on the position of source, destination and jamming nodes. Our results shed some light on the trade-off between secure throughput and energy efficiency. © 2011 IEEE.

Abstract
Technological evolution is leading telecommunications to all-IP networks where multiple services are transported as IP packets. Among these are the group communications services with confidentiality requirements. Secure IP multicast may be used to secure the broadcast of video channels. However, in scenarios such as cable TV where the concept of video channel and bundle are present, groups are very large, and users switch very rapidly between channels (zapping), a sort of problems still need to be addressed. The solution proposed in this paper addresses these problems. For that purpose, a centralized form of secure group communications is proposed also used to transmit, not data, but group cryptographic material. Threes types of cryptographic keys are used. End systems use this material to decrypt the data sent by the content providers.