Curriculum Vitae
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Analysing Secret Sharing Schemes for Audio Sharing
International Journal of Computer Applications (0975 – 8887) Volume 137 – No.11, March 2016 Analysing Secret Sharing Schemes for Audio Sharing Seema Vyavahare Sonali Patil, PhD Department of Computer Engineering Department of Computer Engineering Pimpri Chinchwad College of Engineering Pimpri Chinchwad College of Engineering Pune-44 Pune-44 ABSTRACT which if cover data is attacked then the private data which is In various applications such as military applications, hidden may also lost. commercial music systems, etc. audio needs to be transmitted over the network. During transmission, there is risk of attack through wiretapping. Hence there is need of secure transmission of the audio. There are various cryptographic methods to protect such data using encryption key. However, such schemes become single point failure if encryption key get lost or stolen by intruder. That's why many secret sharing schemes came into picture. There are circumstances where an action is required to be executed by a group of people. Secret sharing is the technique in which secret is distributed among n participants. Each participant has unique secret share. Secret can be recovered only after sufficient number of shares (k out of n) combined together. In this way one can secure secret in reliable way. Fig.1 Information Security System In this paper we have proposed Audio Secret Sharing based on Li Bai's Secret Sharing scheme in Matrix Projection. Then Secret sharing scheme (SSS) [4] is the method of sharing the proposed scheme is critically analysed with the strengths secret information in scribbled shares among number of and weaknesses introduced into the scheme by comparing it partners who needs to work together. -
CHURP: Dynamic-Committee Proactive Secret Sharing
CHURP: Dynamic-Committee Proactive Secret Sharing Sai Krishna Deepak Maram∗† Cornell Tech Fan Zhang∗† Lun Wang∗ Andrew Low∗ Cornell Tech UC Berkeley UC Berkeley Yupeng Zhang∗ Ari Juels∗ Dawn Song∗ Texas A&M Cornell Tech UC Berkeley ABSTRACT most important resources—money, identities [6], etc. Their loss has We introduce CHURP (CHUrn-Robust Proactive secret sharing). serious and often irreversible consequences. CHURP enables secure secret-sharing in dynamic settings, where the An estimated four million Bitcoin (today worth $14+ Billion) have committee of nodes storing a secret changes over time. Designed for vanished forever due to lost keys [69]. Many users thus store their blockchains, CHURP has lower communication complexity than pre- cryptocurrency with exchanges such as Coinbase, which holds at vious schemes: O¹nº on-chain and O¹n2º off-chain in the optimistic least 10% of all circulating Bitcoin [9]. Such centralized key storage case of no node failures. is also undesirable: It erodes the very decentralization that defines CHURP includes several technical innovations: An efficient new blockchain systems. proactivization scheme of independent interest, a technique (using An attractive alternative is secret sharing. In ¹t;nº-secret sharing, asymmetric bivariate polynomials) for efficiently changing secret- a committee of n nodes holds shares of a secret s—usually encoded sharing thresholds, and a hedge against setup failures in an efficient as P¹0º of a polynomial P¹xº [73]. An adversary must compromise polynomial commitment scheme. We also introduce a general new at least t +1 players to steal s, and at least n−t shares must be lost technique for inexpensive off-chain communication across the peer- to render s unrecoverable. -
Improved Threshold Signatures, Proactive Secret Sharing, and Input Certification from LSS Isomorphisms
Improved Threshold Signatures, Proactive Secret Sharing, and Input Certification from LSS Isomorphisms Diego F. Aranha1, Anders Dalskov2, Daniel Escudero1, and Claudio Orlandi1 1 Aarhus University, Denmark 2 Partisia, Denmark Abstract. In this paper we present a series of applications steming from a formal treatment of linear secret-sharing isomorphisms, which are linear transformations between different secret-sharing schemes defined over vector spaces over a field F and allow for efficient multiparty conversion from one secret-sharing scheme to the other. This concept generalizes the folklore idea that moving from a secret-sharing scheme over Fp to a secret sharing \in the exponent" can be done non-interactively by multiplying the share unto a generator of e.g., an elliptic curve group. We generalize this idea and show that it can also be used to compute arbitrary bilinear maps and in particular pairings over elliptic curves. We include the following practical applications originating from our framework: First we show how to securely realize the Pointcheval-Sanders signature scheme (CT-RSA 2016) in MPC. Second we present a construc- tion for dynamic proactive secret-sharing which outperforms the current state of the art from CCS 2019. Third we present a construction for MPC input certification using digital signatures that we show experimentally to outperform the previous best solution in this area. 1 Introduction A(t; n)-secure secret-sharing scheme allows a secret to be distributed into n shares in such a way that any set of at most t shares are independent of the secret, but any set of at least t + 1 shares together can completely reconstruct the secret. -
Asynchronous Verifiable Secret Sharing and Proactive Cryptosystems
Asynchronous Verifiable Secret Sharing and Proactive Ý Cryptosystems£ Christian Cachin Klaus Kursawe Anna LysyanskayaÞ Reto Strobl IBM Research Zurich Research Laboratory CH-8803 R¨uschlikon, Switzerland {cca,kku,rts}@zurich.ibm.com ABSTRACT However, when a threshold cryptosystem operates over a longer Verifiable secret sharing is an important primitive in distributed time period, it may not be realistic to assume that an adversary cor- cryptography. With the growing interest in the deployment of rupts only Ø servers during the entire lifetime of the system. Proac- threshold cryptosystems in practice, the traditional assumption of tive cryptosystems address this problem by operating in phases; a synchronous network has to be reconsidered and generalized to they can tolerate the corruption of up to Ø different servers dur- an asynchronous model. This paper proposes the first practical ing every phase [18]. They rely on the assumption that servers may verifiable secret sharing protocol for asynchronous networks. The erase data and on a special reboot procedure to remove the adver- protocol creates a discrete logarithm-based sharing and uses only sary from a corrupted server. The idea is to proactively reboot all a quadratic number of messages in the number of participating servers at the beginning of every phase, and to subsequently refresh servers. It yields the first asynchronous Byzantine agreement pro- the secret key shares such that in any phase, knowledge of shares tocol in the standard model whose efficiency makes it suitable for from previous phases does not give the adversary an advantage. use in practice. Proactive cryptosystems are another important ap- Thus, proactive cryptosystems tolerate a mobile adversary [20], plication of verifiable secret sharing. -
El Gamal Mix-Nets and Implementation of a Verifier
KTH Royal Institute of Technology School of Computer Science and Communication El Gamal Mix-Nets and Implementation of a Verifier SA104X Degree Project in Engineering Physics Erik Larsson ([email protected]) Carl Svensson ([email protected]) Supervisor: Douglas Wikstr¨om Abstract A mix-net is a cryptographic protocol based on public key cryptography which enables untraceable communication through a collection of nodes. One important application is electronic voting where it enables the construction of systems which satisfies many voting security requirements, including veri- fiability of correct execution. Verificatum is an implementation of a mix-net by Douglas Wikstr¨om. This report concerns the implementation of a verifier and evaluation of the implementation manual for the Verificatum mix-net. The purpose of the document is to enable third parties to convince themselves that the mix- net has behaved correctly without revealing any secret information. This implementation is a simple version of the verifier using the document and some test vectors generated by the mix-net. The document contains all information but there are still some possibilities for further clarification in order to make it comprehensible to a larger audience. Contents 1 Introduction 2 1.1 Verificatum . 2 1.2 Goals and Scope . 3 2 Background 3 2.1 El Gamal Cryptography . 3 2.1.1 Definition . 4 2.1.2 Security . 4 2.1.3 Properties . 5 2.2 Cryptographic Primitives . 6 2.2.1 Hash functions . 6 2.2.2 Pseudo Random Generators . 6 2.2.3 Random Oracles . 7 2.3 Mix Networks . 7 2.3.1 Overview . 7 2.3.2 El Gamal Mix-Nets . -
Multiparty Routing: Secure Routing for Mixnets
Multiparty Routing: Secure Routing for Mixnets Fatemeh Shirazi Elena Andreeva Markulf Kohlweiss Claudia Diaz imec - COSIC KU Leuven imec - COSIC KU Leuven Microsoft Research imec - COSIC KU Leuven Leuven, Belgium Leuven, Belgium Cambridge, UK Leuven, Belgium Abstract—Anonymous communication networks are impor- re-mailer, Freenet [5], [6] used for anonymous file-sharing, and tant building blocks for online privacy protection. One approach DC-Nets [7] that can be deployed for broadcast applications to achieve anonymity is to relay messages through multiple such as group messaging. routers, where each router shuffles messages independently. To achieve anonymity, at least one router needs to be honest. The goal of ACNs is to anonymize communications by In the presence of an adversary that is controlling a subset relaying them over multiple routers. There are three main types of the routers unbiased routing is important for guaranteeing of anonymous routing in terms of how routers are chosen to anonymity. However, the routing strategy also influenced other form the path. factors such as the scalability and the performance of the system. One solution is to use a fixed route for relaying all messages First, in deterministic routing, the paths are predetermined with many routers. If the route is not fixed the routing decision by the system configuration. Chaum’s original ACN pro- can either be made by the communication initiator or the posal [1] considered a sequence of mixes organized in a intermediate routers. However, the existing routing types each cascade. Systems that adopted the cascade network topology have limitations. For example, one faces scalability issues when in their designs include JAP [8], and voting systems, such as increasing the throughput of systems with fixed routes. -
Walking Onions: Scaling Anonymity Networks While Protecting Users Chelsea H
Walking Onions: Scaling Anonymity Networks while Protecting Users Chelsea H. Komlo, University of Waterloo; Nick Mathewson, The Tor Project; Ian Goldberg, University of Waterloo https://www.usenix.org/conference/usenixsecurity20/presentation/komlo This paper is included in the Proceedings of the 29th USENIX Security Symposium. August 12–14, 2020 978-1-939133-17-5 Open access to the Proceedings of the 29th USENIX Security Symposium is sponsored by USENIX. Walking Onions: Scaling Anonymity Networks while Protecting Users Chelsea H. Komlo Nick Mathewson Ian Goldberg University of Waterloo The Tor Project University of Waterloo Abstract Anonymity networks in practice [13] have prevented these Scaling anonymity networks offers unique security chal- attacks by requiring all participants to share a globally consis- lenges, as attackers can exploit differing views of the net- tent view of the entire state of the network, and giving clients work’s topology to perform epistemic and route capture at- complete control over selecting relays for their paths. While tacks. Anonymity networks in practice, such as Tor, have this approach prevents the described attacks, requiring a glob- opted for security over scalability by requiring participants ally consistent view results in quadratic bandwidth growth as to share a globally consistent view of all relays to prevent the number of clients increases [26], because the number of these kinds of attacks. Such an approach requires each user relays must also increase to provide more capacity, and all to maintain up-to-date information about every relay, causing parties must download information about all relays. While the total amount of data each user must download every epoch today’s Tor network requires only approximately half a per- to scale linearly with the number of relays. -
Network Security
Cristina Nita-Rotaru CS6740: Network security Anonymity. Sources 1. Crowds: http://avirubin.com/crowds.pdf 2. Chaum mix: http://www.ovmj.org/GNUnet/papers/p84-chaum.pdf 3. To r : https://svn.torproject.org/svn/projects/design-paper/tor-design.pdf 4. Predecessors attack: http://prisms.cs.umass.edu/brian/pubs/wright-tissec.pdf 5. Also based on slides prepared by Chi-Cun Chan. 2 Anonymity systems. 1: Motivation Anonymity Anonymity (``without name’’) means that a person is not identifiable within a set of subjects } Unlinkability of action and identity } For example, sender and his email are no more related after adversary’s observations than they were before } Who talks to whom } Unobservability } Adversary cannot tell whether someone is using a particular system and/or protocol 4 Anonymity systems. There is no anonymity on the Internet } Your IP address can be linked directly to you } ISPs store communications records } Usually for several years (Data Retention Laws) } Law enforcement can subpoena these records } Your browser is being tracked } Cookies, Flash cookies, E-Tags, HTML5 Storage } Browser fingerprinting } Your activities can be used to identify you } Unique websites and apps that you use } Types of links that you click 5 Anonymity systems. Wiretapping is ubiquitous } Wireless traffic can be trivially intercepted } Airsnort, Firesheep, etc. } Wifi and Cellular traffic! } Encryption helps, if it’s strong } WEP and WPA are both vulnerable! } Tier 1 ASs and IXPs are compromised } NSA, GCHQ, “5 Eyes” } ~1% of all Internet traffic } Focus on encrypted traffic 6 Anonymity systems. Who uses anonymity systems? } “If you’re not doing anything wrong, you shouldn’t have anything to hide.” } Implies that anonymous communication is for criminals } The truth: who uses Tor? } Journalists } Law enforcement ¤ Business executives } Human rights activists ¤ Military/intelligence personnel } Normal people ¤ Abuse victims } In fact, the predecesor of Tor was developed by the U.S. -
A System for Privacy-Preserving Mobile Health and Fitness Data Sharing: Design, Implemen- Tation and Evaluation Master Thesis SEEMOO-MSC-0076
A SYSTEM FOR PRIVACY-PRESERVING MOBILE HEALTH AND FITNESSDATASHARING:DESIGN,IMPLEMENTATIONAND E VA L U AT I O N max jakob maaß Master Thesis April 15, 2016 Secure Mobile Networking Lab Department of Computer Science A System for Privacy-Preserving Mobile Health and Fitness Data Sharing: Design, Implemen- tation and Evaluation Master Thesis SEEMOO-MSC-0076 Submitted by Max Jakob Maaß Date of submission: April 15, 2016 Advisor: Prof. Dr.-Ing. Matthias Hollick Supervisor: Prof. Dr.-Ing. Matthias Hollick Technische Universität Darmstadt Department of Computer Science Secure Mobile Networking Lab ABSTRACT The growing spread of smartphones and other mobile devices has given rise to a number of health and fitness applications. Users can track their calorie intake, get reminders to take their medication, and track their fitness workouts. Many of these services have social com- ponents, allowing users to find like-minded peers, compete with their friends, or participate in open challenges. However, the prevalent ser- vice model forces users to disclose all of their data to the service provider. This may include sensitive information, like their current position or medical conditions. In this thesis, we will design, imple- ment and evaluate a privacy-preserving fitness data sharing system. The system provides privacy not only towards other users, but also against the service provider, does not require any Trusted Third Par- ties (TTPs), and is backed by strong cryptography. Additionally, it hides the communication metadata (i.e. who is sharing data with whom). We evaluate the security of the system with empirical and formal methods, including formal proofs for parts of the system. -
DSMIX: a Dynamic Self-Organizing Mix Anonymous System Renpeng Zou∗, Xixiang Lv∗, ∗School of Cyber Engineering, Xidian University, Xian 710071, China
1 DSMIX: A Dynamic Self-organizing Mix Anonymous System Renpeng Zou∗, Xixiang Lv∗, ∗School of Cyber Engineering, Xidian University, Xian 710071, China Abstract—Increasing awareness of privacy-preserving has led There are, however, concerns about the lack of efficiency to a strong focus on anonymous systems protecting anonymity. and security in anonymous systems [6], [7], as explained By studying early schemes, we summarize some intractable below: problems of anonymous systems. Centralization setting is a universal problem since most anonymous system rely on central proxies or presetting nodes to forward and mix messages, which • Centralization. Most of anonymous systems, i.e. compromises users’ privacy in some way. Besides, availability Anonymizer [8], LPWA [9] and cMix [10], rely on central becomes another important factor limiting the development of proxies or preset nodes to hide the address information, anonymous system due to the large requirement of additional ad- then still use these proxies to blind and forward messages. ditional resources (i.e. bandwidth and storage) and high latency. Moreover, existing anonymous systems may suffer from different The centralized anonymous systems bring privacy leakage attacks including abominable Man-in-the-Middle (MitM) attacks, risks to users since the service providers can control Distributed Denial-of-service (DDoS) attacks and so on. In this all proxies and mix node to infer the users’ identities. context, we first come up with a BlockChain-based Mix-Net What’s worse, the public proxies or preset nodes are (BCMN) protocol and theoretically demonstrate its security and easily exposed to attackers. For instance, an attacker can anonymity. Then we construct a concrete dynamic self-organizing BlockChain-based MIX anonymous system (BCMIX). -
2014 Bis 2015
Tätigkeitsbericht 2014/2015 Horst Görtz Institut für IT-Sicherheit Vorwort Sehr geehrte Damen und Herren, liebe Freunde des Horst Görtz Instituts, das HGI steht für Exzellenz in For- senschaftler im Berichtszeitraum aus- schung, Lehre und Nachwuchsförderung. gezeichnet wurden, den Erfolg und die In dieser Ausgabe möchten wir Ihnen – internationale Sichtbarkeit des Instituts zusätzlich zu den Einblicken in unsere veranschaulichen. Forschungsvorhaben, die Sie in der Son- derausgabe 2016 von RUBIN nachlesen Nicht zuletzt blicken wir auf unsere vier können – einige Statistiken zu unserer jüngsten Firmenausgründungen, die Forschung und Ausbildung in der IT-Si- das im Studium erworbene theoretische cherheit aus den Jahren 2014 und 2015 Wissen erfolgreich in eigene Geschäftsi- angeben. deen umgewandelt haben und florieren- de junge Start-ups erschaffen haben. In diesen beiden überaus eindrucksvollen Jahren haben insgesamt 210 Absolven- tinnen und Absolventen erfolgreich ein Studium der IT-Sicherheit an der Wir wünschen Ihnen und Euch viel Spaß Ruhr-Universität Bochum beendet, davon beim Lesen. 123 Bachelor- und 87 Masterabschlüsse. Hinzu kommen 15 Promotionen aus den verschiedensten Bereichen der IT-Sich- erheit. Ihr Wir blicken auf insgesamt 210 wis- senschaftliche Veröffentlichungen auf renommierten internationalen Kon- Prof. Christof Paar ferenzen und in Zeitschriften zurück, die ebenso wie die 11 Preise, mit denen Geschäftsführender Direktor des unsere Wissenschaftlerinnen und Wis- Horst Görtz Instituts Vorwort 3 Abschlussarbeiten Bachelor -
Anonymous Network Concepts & Implementation
FORENSIC INSIGHT; DIGITAL FORENSICS COMMUNITY IN KOREA Anonymous Network Concepts & Implementation [email protected] Overview 1. Overview & Background 2. Anonymous Network tor freenet Gnunet I2P 3. Circumvention Techniques against Censorships Obfsproxy flashproxy forensicinsight.org Page 2 Overview . Attack Trends Summary Modern attack mostly involves malware, which Attempts to conceal attack itself Makes it hard to trace themselves down from network perspective Makes it difficult to find artifacts by wiping out themselves from system perspective Employs many techniques to be hard for analysis including: Anti-VM, Anti-disassembly, Anti-debugging and cryptography Infects a target but do nothing harm until they achieve their goals Imagine how future malware will evolve, which Employs the combination of existing – even legitimate – tools/techniques in a malicious fashion Emerges new variables targeting cloud computing Focuses highly on target-oriented attack which does not affect others Uses steganography technique in a wild more often Forms private tor network with exploited zombie machines forensicinsight.org Page 3 Overview . Malware/Crimeware Let’s briefly take a look at what to have, how to spread and what to do. Key Loggers Attachment Information Compromise Screenscrapers Peer-to-Peer Networks Spam Transmission Email, IM Redirectors Piggybacking Denial-of-Service, DDoS Session Hijackers Internet Worms, Virus Click Fraud Web Trojans Web Browser Exploits Data Ransoming Transaction Generators Server Compromise Identity Stealing Data Theft Affiliate Marketing Credit Card Abuse Man-in-the-Middle Phishing Defamation Rootkits Pharming Embezzlement Political Argument Misuse Distribution Features forensicinsight.org Page 4 Background . Necessity / Motivation (1/2) “Anonymity serves different interests for different user groups.” by Roger Dingledine, the creator of the Tor forensicinsight.org Page 5 Background .