The Sender-Excited Secret Key Agreement Model: Capacity, Reliability and Secrecy Exponents

We consider the secret key generation problem when sources are randomly excited by the sender and there is a noiseless public discussion channel. Our setting is thus similar to recent works on channels with action-dependent states where the channel state may be influenced by some of the parties involved. We derive single-letter expressions for the secret key capacity through a type of source emulation analysis. We also derive lower bounds on the achievable reliability and secrecy exponents, i.e., the exponential rates of decay of the probability of decoding error and of the information leakage. These exponents allow us to determine a set of strongly-achievable secret key rates. For degraded eavesdroppers the maximum strongly-achievable rate equals the secret key capacity; our exponents can also be specialized to previously known results. In deriving our strong achievability results we introduce a coding scheme that combines wiretap coding (to excite the channel) and key extraction (to distill keys from residual randomness). The secret key capacity is naturally seen to be a combination of both source- and channel-type randomness. Through examples we illustrate a fundamental interplay between the portion of the secret key rate due to each type of randomness. We also illustrate inherent tradeoffs between the achievable reliability and secrecy exponents. Our new scheme also naturally accommodates rate limits on the public discussion. We show that under rate constraints we are able to achieve larger rates than those that can be attained through a pure source emulation strategy.Comment: 18 pages, 8 figures; Submitted to the IEEE Transactions on Information Theory; Revised in Oct 201

Doctor of Philosophy

dissertationCross layer system design represents a paradigm shift that breaks the traditional layer-boundaries in a network stack to enhance a wireless network in a number of di erent ways. Existing work has used the cross layer approach to optimize a wireless network in terms of packet scheduling, error correction, multimedia quality, power consumption, selection of modulation/coding and user experience, etc. We explore the use of new cross layer opportunities to achieve secrecy and e ciency of data transmission in wireless networks. In the rst part of this dissertation, we build secret key establishment methods for private communication between wireless devices using the spatio-temporal variations of symmetric-wireless channel measurements. We evaluate our methods on a variety of wireless devices, including laptops, telosB sensor nodes, and Android smartphones, with diverse wireless capabilities. We perform extensive measurements in real-world environments and show that our methods generate high entropy secret bits at a signi cantly faster rate in comparison to existing approaches. While the rst part of this dissertation focuses on achieving secrecy in wireless networks, the second part of this dissertation examines the use of special pulse shaping lters of the lterbank multicarrier (FBMC) physical layer in reliably transmitting data packets at a very high rate. We rst analyze the mutual interference power across subcarriers used by di erent transmitters. Next, to understand the impact of FBMC beyond the physical layer, we devise a distributed and adaptive medium access control protocol that coordinates data packet tra c among the di erent nodes in the network in a best e ort manner. Using extensive simulations, we show that FBMC consistently achieves an order-of-magnitude performance improvement over orthogonal frequency division multiplexing (OFDM) in several aspects, including packet transmission delays, channel access delays, and e ective data transmission rate available to each node in static indoor settings as well as in vehicular networks

The Effect of Eavesdropper's Statistics in Experimental Wireless Secret-Key Generation

This paper investigates the role of the eavesdropper's statistics in the implementation of a practical secret-key generation system. We carefully conduct the information-theoretic analysis of a secret-key generation system from wireless channel gains measured with software-defined radios. In particular, we show that it is inaccurate to assume that the eavesdropper gets no information because of decorrelation with distance. We also provide a bound for the achievable secret-key rate in the finite key-length regime that takes into account the presence of correlated eavesdropper's observations. We evaluate this bound with our experimental gain measurements to show that operating with a finite number of samples incurs a loss in secret-key rate on the order of 20%.Comment: Submitted to the IEEE Transactions on Information Forensics and Securit

A Novel Physical Layer Key Generation and Authenticated Encryption Protocol Exploiting Shared Randomness

The use of wireless networks for communication has grown significantly in recent times, and continues to develop further. The broadcast nature of wireless communications makes them susceptible to a wide variety of security attacks. Unlike traditional solutions, which usually handle security at the application layer, the primary concern of this dissertation is to analyse and develop solutions for secure communication using channel coding techniques at the physical-layer. The topic of physical layer authenticated encryption using high rate key generation through shared randomness is investigated in this work. First, a physical layer secret key generation scheme is discussed exploiting channel reciprocity in wireless systems. In order to address the susceptibility of this family of schemes to active attacks, a novel physical layer authentication encryption protocol is presented along with its extension to multi-node networks in the presence of active adversaries. Unlike previous work in the area of generating secret keys through shared randomness, it is demonstrated that the proposed scheme is semantically secure with respect to chosen plaintext and chosen cipher text attacks. Secondly, in order to increase the rate in bits per seconds at which agreed cryptographic keys are been generated, a multi-level quantization algorithm with public feedback is discussed. It is demonstrated that the proposed scheme is superior to direct information distillation approaches and can substantially increase the key generation rates even at low and medium SNRs. Furthermore, the employment of this low-overhead feedback at the information distillation process can largely simplify the information reconciliation process. The proposed secret key generation schemes are tested for randomness such as required for cryptographic keys. The validation test is perfomed with the aid of National Institute of Standards and Technology (NIST) statistical test suite. The P-values obtained in each of the test carried out indicates that the key sequence generated by our algorithm is random

Information-theoretic security under computational, bandwidth, and randomization constraints

The objective of the proposed research is to develop and analyze coding schemes for information-theoretic security, which could bridge a gap between theory an practice. We focus on two fundamental models for information-theoretic security: secret-key generation for a source model and secure communication over the wire-tap channel. Many results for these models only provide existence of codes, and few attempts have been made to design practical schemes. The schemes we would like to propose should account for practical constraints. Specifically, we formulate the following constraints to avoid oversimplifying the problems. We should assume: (1) computationally bounded legitimate users and not solely rely on proofs showing existence of code with exponential complexity in the block-length; (2) a rate-limited public communication channel for the secret-key generation model, to account for bandwidth constraints; (3) a non-uniform and rate-limited source of randomness at the encoder for the wire-tap channel model, since a perfectly uniform and rate-unlimited source of randomness might be an expensive resource. Our work focuses on developing schemes for secret-key generation and the wire-tap channel that satisfy subsets of the aforementioned constraints.Ph.D

Secure key design approaches using entropy harvesting in wireless sensor network: A survey

Physical layer based security design in wireless sensor networks have gained much importance since the past decade. The various constraints associated with such networks coupled with other factors such as their deployment mainly in remote areas, nature of communication etc. are responsible for development of research works where the focus is secured key generation, extraction, and sharing. Keeping the importance of such works in mind, this survey is undertaken that provides a vivid description of the different mechanisms adopted for securely generating the key as well its randomness extraction and also sharing. This survey work not only concentrates on the more common methods, like received signal strength based but also goes on to describe other uncommon strategies such as accelerometer based. We first discuss the three fundamental steps viz. randomness extraction, key generation and sharing and their importance in physical layer based security design. We then review existing secure key generation, extraction, and sharing mechanisms and also discuss their pros and cons. In addition, we present a comprehensive comparative study of the recent advancements in secure key generation, sharing, and randomness extraction approaches on the basis of adversary, secret bit generation rate, energy efficiency etc. Finally, the survey wraps up with some promising future research directions in this area

Sizing the auxiliary system capacities for a pilot plant project

Opinnäytetyö on osa Stora Enso Oy:n projektia, jonka tarkoituksena on rakentaa Sunilan tehdasalueelle pilotmittakaavan tehdas ligniinin jatkojalostusta varten. Jatkojalostuksen tarkoituksena on parantaa ligniinin ominaisuuksia, niin että se voisi korvata fossiilipohjaisia materiaaleja tulevaisuudessa. Opinnäytetyö keskittyi käyttöhyödykejärjestelmien suunnittelun ympärille. Tarkoituksena oli selvittää jäähdytysvesijärjestelmän, typpijärjestelmän ja savukaasujenkäsittelyjärjestelmän vaatimukset ja niiden perusteella mitoittaa järjestelmät. Työ toteutettiin keräämällä aineistoa päälaitteina toimivista lämpökäsittelyuuneista. Nämä laitteet määrittelevät tärkeimmät vaatimukset apujärjestelmille. Kerättyä ainestoa analysoitiin ja erilaitteiden vaatimuksia vertailtiin, jotta voitiin määritellä järjestelmälle yhtenäiset vaatimukset. Vaatimusten määrittelyn jälkeen sopivan ratkaisun valinnassa hyödynnettiin kirjallisuutta, tutkimustietoa ja apujärjestelmätoimittajien tietotaitoa. Typpijärjestelmäksi valittiin PSA-teknologialla toimiva generaattori, koska se oli kustannustehokkain järjestelmä, joka pystyi täyttämään vaatimukset. Kompressoriksi järjestelmälle valittiin öljytönruuvikompressori. Järjestelmä varustettiin tarvittavilla säiliöllä ja puhdistuslaitteilla. Savukaasujen käsittelyjärjestelmän osalta päädyttiin ratkaisuun, joka sisälsi kaksi erillistä polttokammiota. Päälaitevalmistajat suunnittelevat ja toimittavat molemmat polttokammiot. Jäähdytysvesijärjestelmäksi suunniteltiin suljetuksi kierroksi. Suljettukierto vaatii lämmönvaihtimen, jäähdytysteholtaan n.200kW, jotta nesteen lämpötila pysyy tasaisena. Järjestelmien mitoituksen tarkkuuteen vaikuttivat lähtötietojen vähäisyys ja salassapitoasiat sekä referenssien puute. Nämä ovat tyypillisiä ongelmia pilotprojekteille. Suurin osa saaduista tuloksista on luotettavia ja niitä voidaan hyödyntää myöhemmin prosessisuunnittelussa.The thesis is a part of a Stora Enso’s project. The objective of the project is to build a pilot-scale plant where lignin can be processed. The aim of processing lignin is to improve its properties so that it can replace fossil-based materials in the future. The thesis focused on the design of auxiliary systems. The main objectives of the thesis were to determine the re-quirements for the nitrogen supply system, the exhaust gas treatment system, and the cool-ing water system and to select suitable equipment based on these requirements. The study was done by gathering material from heat treatment furnaces which are the main equipment of the process. The technical data of the furnaces provided the main require-ments for the auxiliary systems. The material was analyzed and the requirements from each furnace were compared with each another so that uniform requirements could be made for the systems. Once the requirements were set, literature, studies, and the knowledge of the auxiliary system suppliers were utilized to select the equipment for the systems. A generator with PSA-technology was chosen for the nitrogen supply system because it was found to be the most cost-efficient solution that met the requirements. An oil-free screw-compressor was selected as a compressor for the system. The system is equipped with the necessary vessels and cleaning equipment. For the exhaust gas treatment system, the solu-tion included two separate combustion chambers. The main equipment manufacturers de-sign and supply both combustion chambers. The cooling water system was designed to have a closed loop. The closed loop requires a heat exchanger with 200kW cooling power to keep the water temperature inside the loop stable. The scarcity and secrecy of the data, as well as the lack of references, affected the sizing accuracy of the systems. These are normal prob-lems for a pilot-project. However, most of the results are reliable and these results can be utilized in the process design