Ninoslav Marina

Improved rate-equivocation regions for secure cooperative communication

A simple four node network in which cooperation improves the information-theoretic secrecy is studied. The channel consists of two senders, a receiver, and an eavesdropper. One or both senders transmit confidential messages to the receiver, while the eavesdropper tries to decode the transmitted message. The main result is the derivation of a newly achievable rate-equivocation region that is shown to be larger than a rate-equivocation region derived by Lai and El Gamal for the relay-eavesdropper channel. When the rate of the helping interferer is zero, the new rate-equivocation region reduces to the capacity-equivocation region over the wire-tap channel; hence, the new achievability scheme can be seen as a generalization of a coding scheme proposed by Csiszár and Körner.

Technoeconomic evaluation of cooperative relaying transmission techniques in OFDM cellular networks

We evaluate the costs in the deployment of a 4G relay-assisted network in the 2.6GHz band following a technoeconomic methodology that departs fromcell dimensioning based on spectral efficiency and outage capacity requirements. Different decode-and-forward relaying protocols are considered in the analysis, assuming a certain traffic load evolution over a period of ten years, different geotypes, and a progressive deployment of base stations and relay stations. Results show significant benefits for operators as well as reduction in the total radiated power.

Security in Twin-code framework

Achieving reliability, availability, efficient node repair and security of the data stored in a Distributed Storage System (DSS) is of great importance for improving the functioning of these systems. In this work, we apply a data distribution concept, Twin-code framework, and compare it with a DSS that uses minimum bandwidth regenerating (MBR) and minimum storage regenerating (MSR) codes. We demonstrate that the Twin-code framework gives better performance in the distribution process. Moreover, we construct a new secure Twin MDS code and investigate its security performance comparing to the security of the MBR and MSR codes. The new constructed code is resistant against a threat model where a passive eavesdropper can access to the stored data and the downloaded data during the repair process of a failed node. We demonstrate that the Twin MDS code framework achieves better results than the MBR and MSR codes regarding the security in the system.

Improving DSS efficiency with shortened MSR codes

The distributed storage system (DSS) is a network constructed by large number of nodes interconnected among themselves. The main issues in this area are the reconstruction process or obtaining the entire original message out of the DSS and the repair process or recovering the lost stored data of a failed node. The product matrix regenerating codes as class of codes in such networks offer an optimal tradeoff between the repair bandwidth and the data amount stored per node. In our paper, we are proposing a new code, a shortened MSR code, that gives new bound of the wanted tradeoff. The shortened MSR code is constructed by introducing modification on the mother code, product matrix MSR code. By comparing both constructions we prove that our code gives better performances regarding the repair bandwidth and the number of connected nodes needed for the repair and the reconstruction processes, while maintaining the storage per node unchanged. The comparison is extended between the new shortened MSR code and a new product matrix MSR code designed according to the parameter values obtained from our new code. The necessity of this is having a fair and convincing comparison results, which shows again that our code has some improvements in the overall distributed system.

Increasing the information-theoretic secrecy by cooperative relaying and jamming

The use of cooperation to increase the information-theoretic secrecy in a decentralized ad-hoc wireless network is investigated. In particular, four cases of cooperative relaying are analyzed and compared. These cases include the no-cooperation case, the case with single-hop cooperation with multiple relays, the case with single-hop cooperation with the strongest relay, and finally the case of multi-hop cooperation with the strongest relay. From the results, it is seen that cooperation increases the probability of a positive secrecy rate between two nodes in a network with friendly (cooperative) nodes and eavesdropping nodes. The improved information-theoretic secrecy increases the probability that two nodes can share a secret message with perfect secrecy using a multi-hop route of trusted nodes. Cooperative jamming is also studied, and it is observed that very often it is more beneficial to use friendly nodes for cooperative jamming than cooperative relaying. Finally, a combination of cooperative relaying and jamming is considered.

Secure shortened MSR codes

This paper proposes code for secure distributed storage systems (sDSS), called secure shortened product-matrix minimum storage regenerating code (PM-ssMSR). The code uses shortening technique applied on the mother code, product-matrix minimum storage regenerating (PM-MSR), for maintenance of the DSS efficiency and two different methods for achieving the system security. The first method enables by performing random keys technique on the PM-ssMSR code to guarantee perfectly secure system. Hence, the second technique using an outer code achieves weakly secure system. For both cases, their information-theoretic secrecy is proven and is shown that the weakly secure code achieve higher secrecy bandwidth than the perfectly secure code.

Efficient distribution and improved security for reliable cloud storage system

The distributed storage systems (DSS) are constructed by large number of nodes which are interconnected over a network. Each node in the network is vulnerable and a potential risk of attack. The attackers can eavesdrop the nodes and possibly modify their data. Despite the considerable efforts, both in industry and in academia, high reliability and security remain major challenges in running large scale distributed systems. Therefore, we design a secure Twin code framework for a distributed storage network that simplifies both data reconstruction and efficient node repair. We examine it in an eavesdropper model, where the passive attackers can access to the stored data or/and downloaded data during the node repair and prove that the new Twin code gives better results than the MBR and MSR codes, regarding the security in the system.

Improved bounds on secrecy capacity in twin-code cloud storage framework

Security and reliability in cloud storage networks are important features for achieving system efficiency. An explicit construction of regenerating codes that perform reliability, availability and security of the stored data, and at the same time perform efficient node repair is already provided. Understanding and achieving the optimal tradeoff among the above listed features is of great importance for improving the functioning in all cloud storage systems. Therefore in this work, we propose a new code construction that includes an outer and an inner code in the process. The outer code, Gabidulin code, as a pre-coding step achieves improved security level in the storage system and the inner one, Twin-code framework, performs efficient distribution, reconstruction and repair process. The proposed code is resilient to an eavesdropper model and gives better results regarding the achievements when are used the minimum bandwidth regenerating (MBR) and minimum storage regenerating (MSR) codes, respectively.

Improved perfect secrecy of distributed storage systems using interference alignment

Regenerating codes based on the approach of interference alignment for wireless interference channel achieve the cut-set bound for distributed storage systems (DSS). These codes are especially important for efficient repair of a failed node in a minimum storage regenerating (MSR) codes. Moreover, they achieve perfect security against the eavesdropper attacks, i.e., the observer can not reveal the whole message. Here the aim is information protection of individual files and small groups from the entire message, when the attacker has access to a limited number of storage nodes. This paper considers improving the perfect security in such DSS. The enhanced secrecy is presented by performing explicit code construction by using an outer and an inner code. The proposed construction code model includes coset code as an outer code or pre-coding step that ensures the security of the system and an MSR interference alignment code as an inner one that performs an efficient reconstruction and repair process. Using this construction we show that the eavesdropper can not reveal the message, and, that he can not access any subset of individual information from the original message, without any significant loss in the storage capacity.

Adversarial attacks in the twin-code framework

Ensuring the security and reliability of the stored data in a Distributed Storage System (DSS) is a pivotal issue in a distributed storage network. The storage system must be secured against passive and active types of attacks for efficient protection of the stored data. The aim is achieving satisfactory level of security of the storage system and at the same time maintaining the desired level of reliability, which arises when there are node failures. In our work we apply this concept in a Twin-code framework, in presence of an intruder who can observe and modify the stored data on the networks nodes. We are making a new code construction, which is simultaneously secure against passive and active attacks and at the same time satisfies particular bound for reliability. Moreover, for this construction we are proving the level of security under the above mentioned constraints.