Luisa Lima

Random Walks on Sensor Networks

We consider the mobile data gathering problem in large-scale wireless sensor networks with static sensor nodes and a mobile patrol node. Based on the assumptions that (a) the sensor positions are unknown and (b) the network may not be entirely connected, we formulate the problem as one of random walks in random geometric graphs and derive analytical bounds for the node coverage, i.e. the number of queried sensor nodes within a given time frame. Based on this metric, we propose an algorithm that improves the data gathering performance by generating constrained random walks, in which the probability mass function at each step reflects the available side information (e.g. the memory of past visited sites).

An information-theoretic cryptanalysis of network coding - is protecting the code enough?

We consider the issue of confidentiality in multicast network coding, by assuming that the encoding matrices, based upon variants of random linear network coding, are given only to the source and sinks. Based on this assumption, we provide a characterization of the mutual information between the encoded data and the two elements that can lead to information disclosure: the matrices of random coefficients and, naturally, the original data itself. Our results, some of which hold even with finite block lengths, show that, predicated on optimal source-coding, information-theoretic security is achievable for any field size without loss in terms of decoding probability. It follows that protecting the encoding matrix is generally sufficient to ensure confidentiality of network coded data.

Trusted Storage over Untrusted Networks

We consider distributed storage over two untrusted networks, whereby coding is used as a means to achieve a prescribed level of confidentiality. The key idea is to exploit the algebraic structure of the Vandermonde matrix to mix the input blocks, before they are stored in different locations. The proposed scheme ensures that eavesdroppers with access to only one of the networks are unable to decode any symbol even if they are capable of guessing some of the missing blocks. Information-theoretic techniques allow us to quantify the achievable level of confidentiality. Moreover, the proposed approach is shown to offer low complexity and optimal rate.

Coding for Trusted Storage in Untrusted Networks

We focus on the problem of secure distributed storage over multiple untrusted clouds or networks. Our main contribution is a low complexity scheme that relies on erasure coding techniques for achieving prescribed levels of confidentiality and reliability. Using matrices that have no singular square submatrices, we subject the original data to a linear transformation. The resulting coded symbols are then stored in different networks. This scheme allows users with access to a threshold number of networks to reconstruct perfectly the original data, while ensuring that eavesdroppers with access to any number of networks smaller than this threshold are unable to decode any of the original symbols. This holds even if the attackers are able to guess some of the missing symbols. We further quantify the achievable level of security, and analyze the complexity of the proposed scheme.

On the Performance of Network Coding in Multi-Resolution Wireless Video Streaming

Scalable video can be used to provide video streaming reliably to an heterogeneous set of receivers with different subscription levels. However, the performance of such schemes can be highly affected by scheduling constraints and unreliable feedback. Network coding, on the other hand, has been shown to reduce scheduling and prioritization problems and to perform well in wireless scenarios with perfect feedback. Motivated by this observation, we implement and analyze a system architecture for network coding-based multiresolution video streaming in a wireless environment. In contrast to existing work, we take into account realistic feedback, where the control packets are sent over the same unreliable channel as data packets, and compare it to the case of perfect feedback, where the server has perfect knowledge of the state of the buffer at every receiver. We provide an evaluation of the system via simulation and show that even in highly volatile environments, a network coding-based scheme with limited and unreliable feedback can achieve a good performance.

Topology matters in network coding

Seeking to understand the potential of network coding in future internet endeavors, we consider the vital role of network topology with respect to the potential benefits of Random Linear Network Coding (RLNC). First, we propose a set of metrics that capture the essential trade-offs between throughput, confidentiality and decoding delay. Using large network simulation, we are able to evaluate the behavior of RLNC for various topological classes based on random graphs. Our results show significant differences between local dissemination of information (typical of wireless networks) and long range connectivity (typical of peer-to-peer environments). We believe that our results can help pave the way for the creation of better overlay topologies for RLNC protocols in future internet applications.

Security and privacy issues for the network of the future

The vision towards the Network of the Future cannot be separated from the fact that todays networks, and networking services are subject to sophisticated and very effective attacks. When these attacks first appeared, spoofing and distributed denial-of-service attacks were treated as apocalypse for networking. Now, they are considered moderate damage, whereas more sophisticated and inconspicuous attacks, such as botnets activities, might have greater and far reaching impact. As the Internet is expanding to mobile phones and ‘smart dust’ and as its social coverage is liberalized towards the realization of ubiquitous computing (with communication), the concerns on security and privacy have become deeper and the problems more challenging than ever. Re-designing the Internet as the Network of the Future is self-motivating for researchers, and security and privacy cannot be provided again as separate, external, add-on, solutions. In this paper, we discuss the security and privacy challenges of the Network of the Future and try to delimit the solutions space on the basis of emerging techniques. We also review methods that help the quantification of security and privacy in an effort to provide a more systematic and quantitative treatment of the area in the future. Copyright

NECO: NEtwork COding simulator

We present NECO, a high-performance simulation framework dedicated to the evaluation of network coding based protocols. Its main features include (1) definition of graphs representing the topology (which can be generated randomly or pre-defined by means of a standard representation), (2) modular specification of network coding protocols, (3) visualization of the network operation and (4) extraction of key statistics. The simulator is entirely written in Python and can be easily extended to account for extra functionalities.

Byzantine attacks against network coding in peer to peer distributed storage

We consider the impact of Byzantine attackers on peer-to-peer topologies for distributed storage using network coding. First, the problem is formulated as one of data flow in random evolving graphs, in which a data source and a data collector are connected to data keepers who may behave in a Byzantine fashion. We then derive analytical results for the probability of carrying out a successful distributed denial of service attack (that is, collecting contaminated information from the network), as well as the expected number of contaminated nodes at each timestep. Our results show that, even for a small number of Byzantine attackers in the network, the probability of collecting contaminated information is overwhelming, and that the dissemination of information by peers as opposed to a selected subset of nodes in the network increases the probability of contaminated information collection.

Towards secure multiresolution network coding

Emerging practical schemes indicate that algebraic mixing of different packets by means of random linear network coding can increase the throughput and robustness of streaming services over wireless networks. However, concerns with the security of streaming multimedia, in particular when only a subset of the users in the network is entitled to the highest quality, have uncovered the need for a network coding scheme capable of ensuring different levels of confidentiality under stringent complexity requirements. We consider schemes which exploit the algebraic structure of network coding to achieve the dual goal of hierarchical fidelity levels and efficient security. The key idea is to limit the encryption operations to the encoding vector, in combination with multi-resolution multimedia coding.