Abstract
The purpose of this paper is to advance the current state of physical layer security through the design and analysis of a discrete jamming scheme that exploits the reciprocal characteristic of the wireless channel with the aim to create equivocation to a passive multiple-antenna eavesdropper. Closed form solutions of the secrecy capacity for different configurations of the jamming component were obtained and successfully compare with the simulation results. Furthermore, the secrecy level provided by the developed scheme is analyzed taking into account the number of bits extracted from the channel. The asymptotic study of the proposed secrecy technique allowed to conclude that in the high-power regime, full secrecy is obtained even considering that the eavesdropper is equipped with an unlimited number of antennas.

Abstract
Its distributed nature and ubiquitous service make the cloud subject to several vulnerabilities. One of the main tools used for reporting suspicious activity in the network's traffic is the Intrusion Detection System. However, two significant problems arise: the huge volume of control messages between the virtual machines and the servers; and the associated transfer costs. In this work, we propose a Triple-Similarity Mechanism (T-SyM) for grouping similar alarms that may correspond to the same attack (or attempt) in order to reduce the number of messages and, consequently, the total amount of information. In addition, we propose an algorithm for calculating the severity level of the alarms. T-SyM works on the basis of 3 steps: individual similarity (Euclidian distance), clustering relevant features (k-means algorithm) and generating the output (the Tanimoto coefficient). An evaluation of the most common attacks is performed using real traces from an IDS. Our mechanism was able to decrease the number of alarms by up to 90% and reduce the total amount of data by more than 80%.

Abstract
We propose an adaptive secrecy scheme using polar codes with random frozen bits for a general wiretap channel, in which to protect the data from a potential eavesdropper, part or all of the frozen bits are randomly generated per message. To assess the secrecy level of the proposed scheme, three types of decoding strategies are evaluated: a matching decoder which knows the positions of all inserted bits inside the blocklength and tries to estimate them using the same decoding techniques, a blind decoder which treats all the frozen bits as the same value, and a random decoder which considers those dynamic bits as random at the receiver. Results are presented in terms of the system security gap, assuming an adaptive decoding strategy. It is shown that the system achieves combined secrecy and reliability. The proposed scheme does not assume knowledge of the eavesdropper's channel when defining the indices of information and frozen bits.

Abstract
Uncoordinated Frequency Hopping (UFH) has been proposed as a mechanism to address denial-of-service attacks, and consists of legitimate devices hopping uniformly at random between frequencies to cope with an attacker that aims to disrupt communication. We consider the use of UFH against an eavesdropper adversary that aims to overhear as much information as possible. We characterize the secrecy level of wireless networks under UFH, showing the harmful security effect of broadband eavesdropper adversaries capable of overhearing in multiple frequencies. To counter such eavesdroppers, we consider the use of broadband friendly jammers that are available to cause interference on eavesdroppers. Our results show that adding a limited number of broadband friendly jammers effectively improves the security level of such systems.

Abstract
Uncoordinated Frequency Hopping (UFH) has been proposed as a mechanism to address denial-of-service attacks, and consists of legitimate devices hopping uniformly at random between frequencies to cope with an attacker that aims to disrupt communication. We consider the use of UFH against an eavesdropper adversary that aims to overhear as much information as possible. We characterize the secrecy level of wireless networks under UFH, showing the harmful security effect of broadband eavesdropper adversaries capable of overhearing in multiple frequencies. To counter such eavesdroppers, we consider the use of broadband friendly jammers that are available to cause interference on eavesdroppers. Our results show that adding a limited number of broadband friendly jammers effectively improves the security level of such systems. © 2015 IEEE.

Abstract
Due to the differences in terms of antenna height, scatterer density, and relative speed, V2I links exhibit different propagation characteristics compared to V2V links. We develop a geometry-based path loss and shadow fading model for V2I links. We separately model the following types of V2I links: line-of-sight, non-line-of-sight due to vehicles, non-line-of-sight due to foliage, and non-line-of-sight due to buildings. We validate the proposed model using V2I field measurements. We implement the model in the GEMV2 simulator, and make the source code publicly available.