Communication-Optimal Proactive Secret Sharing for Dynamic Groups
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Anna Lysyanskaya Curriculum Vitae
Anna Lysyanskaya Curriculum Vitae Computer Science Department, Box 1910 Brown University Providence, RI 02912 (401) 863-7605 email: [email protected] http://www.cs.brown.edu/~anna Research Interests Cryptography, privacy, computer security, theory of computation. Education Massachusetts Institute of Technology Cambridge, MA Ph.D. in Computer Science, September 2002 Advisor: Ronald L. Rivest, Viterbi Professor of EECS Thesis title: \Signature Schemes and Applications to Cryptographic Protocol Design" Massachusetts Institute of Technology Cambridge, MA S.M. in Computer Science, June 1999 Smith College Northampton, MA A.B. magna cum laude, Highest Honors, Phi Beta Kappa, May 1997 Appointments Brown University, Providence, RI Fall 2013 - Present Professor of Computer Science Brown University, Providence, RI Fall 2008 - Spring 2013 Associate Professor of Computer Science Brown University, Providence, RI Fall 2002 - Spring 2008 Assistant Professor of Computer Science UCLA, Los Angeles, CA Fall 2006 Visiting Scientist at the Institute for Pure and Applied Mathematics (IPAM) Weizmann Institute, Rehovot, Israel Spring 2006 Visiting Scientist Massachusetts Institute of Technology, Cambridge, MA 1997 { 2002 Graduate student IBM T. J. Watson Research Laboratory, Hawthorne, NY Summer 2001 Summer Researcher IBM Z¨urich Research Laboratory, R¨uschlikon, Switzerland Summers 1999, 2000 Summer Researcher 1 Teaching Brown University, Providence, RI Spring 2008, 2011, 2015, 2017, 2019; Fall 2012 Instructor for \CS 259: Advanced Topics in Cryptography," a seminar course for graduate students. Brown University, Providence, RI Spring 2012 Instructor for \CS 256: Advanced Complexity Theory," a graduate-level complexity theory course. Brown University, Providence, RI Fall 2003,2004,2005,2010,2011 Spring 2007, 2009,2013,2014,2016,2018 Instructor for \CS151: Introduction to Cryptography and Computer Security." Brown University, Providence, RI Fall 2016, 2018 Instructor for \CS 101: Theory of Computation," a core course for CS concentrators. -
Malicious Cryptography: Kleptographic Aspects
Malicious Cryptography: Kleptographic Aspects Adam Young1 and Moti Yung2 1 Cigital Labs [email protected] 2 Dept. of Computer Science, Columbia University [email protected] Abstract. In the last few years we have concentrated our research ef- forts on new threats to the computing infrastructure that are the result of combining malicious software (malware) technology with modern cryp- tography. At some point during our investigation we ended up asking ourselves the following question: what if the malware (i.e., Trojan horse) resides within a cryptographic system itself? This led us to realize that in certain scenarios of black box cryptography (namely, when the code is inaccessible to scrutiny as in the case of tamper proof cryptosystems or when no one cares enough to scrutinize the code) there are attacks that employ cryptography itself against cryptographic systems in such a way that the attack possesses unique properties (i.e., special advantages that attackers have such as granting the attacker exclusive access to crucial information where the exclusive access privelege holds even if the Trojan is reverse-engineered). We called the art of designing this set of attacks “kleptography.” In this paper we demonstrate the power of kleptography by illustrating a carefully designed attack against RSA key generation. Keywords: RSA, Rabin, public key cryptography, SETUP, kleptogra- phy, random oracle, security threats, attacks, malicious cryptography. 1 Introduction Robust backdoor attacks against cryptosystems have received the attention of the cryptographic research community, but to this day have not influenced in- dustry standards and as a result the industry is not as prepared for them as it could be. -
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. -
Chapter 2: an Implementation of Cryptoviral Extortion Using Microsoft's Crypto API∗
Chapter 2: An Implementation of Cryptoviral Extortion Using Microsoft's Crypto API∗ Adam L. Young and Moti M. Yung Abstract This chapter presents an experimental implementation of cryptovi- ral extortion, an attack that we devised and presented at the 1996 IEEE Symposium on Security & Privacy [16] and that was recently covered in Malicious Cryptography [17]. The design is based on Mi- crosoft's Cryptographic API and the salient aspects of the implemen- tation were presented at ISC '05 [14] and were later refined in the International Journal of Information Security [15]. Cryptoviral extor- tion is a 2-party protocol between an attacker and a victim that is carried out by a cryptovirus, cryptoworm, or cryptotrojan. In a cryp- toviral extortion attack the malware hybrid encrypts the plaintext of the victim using the public key of the attacker. The attacker extorts some form of payment from the victim in return for the plaintext that is held hostage. In addition to providing hands-on experience with this cryptographic protocol, this chapter gives readers a chance to: (1) learn the basics of hybrid encryption that is commonly used in every- thing from secure e-mail applications to secure socket connections, and (2) gain a basic understanding of how to use Microsoft's Cryptographic API that is present in modern MS Windows operating systems. The chapter only provides an experimental version of the payload, no self- replicating code is given. We conclude with proactive measures that can be taken by computer users and computer manufacturers alike to minimize the threat posed by this type of cryptovirology attack. -
Cyber Security Cryptography and Machine Learning
Lecture Notes in Computer Science 12716 Founding Editors Gerhard Goos Karlsruhe Institute of Technology, Karlsruhe, Germany Juris Hartmanis Cornell University, Ithaca, NY, USA Editorial Board Members Elisa Bertino Purdue University, West Lafayette, IN, USA Wen Gao Peking University, Beijing, China Bernhard Steffen TU Dortmund University, Dortmund, Germany Gerhard Woeginger RWTH Aachen, Aachen, Germany Moti Yung Columbia University, New York, NY, USA More information about this subseries at http://www.springer.com/series/7410 Shlomi Dolev · Oded Margalit · Benny Pinkas · Alexander Schwarzmann (Eds.) Cyber Security Cryptography and Machine Learning 5th International Symposium, CSCML 2021 Be’er Sheva, Israel, July 8–9, 2021 Proceedings Editors Shlomi Dolev Oded Margalit Ben-Gurion University of the Negev Ben-Gurion University of the Negev Be’er Sheva, Israel Be’er Sheva, Israel Benny Pinkas Alexander Schwarzmann Bar-Ilan University Augusta University Tel Aviv, Israel Augusta, GA, USA ISSN 0302-9743 ISSN 1611-3349 (electronic) Lecture Notes in Computer Science ISBN 978-3-030-78085-2 ISBN 978-3-030-78086-9 (eBook) https://doi.org/10.1007/978-3-030-78086-9 LNCS Sublibrary: SL4 – Security and Cryptology © Springer Nature Switzerland AG 2021 This work is subject to copyright. All rights are reserved by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. -
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. -
Cryptovirology: Extortion-Based Security Threats and Countermeasures
Crypt ovirology : Extortion-Based Security Threats and Countermeasures* Adam Young Moti Yung Dept. of Computer Science, IBM T.J. Wi3tson Research Center Columbia University. Yorktown Heights, NY 1.0598. Abstract atomic fission is to energy production), because it al- lows people to store information securely and to con- Traditionally, cryptography and its applications are duct private communications over large distances. It defensive in nature, and provide privacy, authen tica- is therefore natural to ask, “What are the potential tion, and security to users. In this paper we present the harmful uses of Cryptograplhy?” We believe that it is idea of Cryptovirology which employs a twist on cryp- better to investigate this aspect rather than to wait tography, showing that it can also be used offensively. for such att,acks to occur. In this paper we attempt By being offensive we mean that it can be used to a first step in this directioin by presenting a set of mount extortion based attacks that cause loss of access cryptographiy-exploiting computer security attacks and to information, loss of confidentiality, and inform,ation potential countermeasures. leakage, tasks which cryptography typically prevents. In this paper we analyze potential threats and attacks The set of attacks that we present involve the that rogue use of cryptography can cause when com- unique use of strong (public key and symmetric) cryp- tographic techniques in conjunction with computer bined with rogue software (viruses, Trojan horses), and virus and Trojan horse technology. They demon- demonstrate them experimentally by presenting an im- strate how cryptography (namely, difference in com- plementation of a cryptovirus that we have tested (we putational capability) can allow an adversarial virus took careful precautions in the process to insure that writer to gain explicit access control over the data the virus remained contained). -
Malicious Cryptography Exposing Cryptovirology
Malicious Cryptography Exposing Cryptovirology Adam Young Moti Yung Wiley Publishing, Inc. Malicious Cryptography Malicious Cryptography Exposing Cryptovirology Adam Young Moti Yung Wiley Publishing, Inc. Executive Publisher: Robert Ipsen Executive Editor: Carol A. Long Developmental Editor: Eileen Bien Calabro Editorial Manager: Kathryn A. Malm Production Manager: Fred Bernardi This book is printed on acid-free paper. Copyright c 2004 by Adam Young and Moti Yung. All rights reserved. Published by Wiley Publishing, Inc., Indianapolis, Indiana Published simultaneously in Canada No part of this publication may be reproduced, stored in a retrieval system, or trans- mitted in any form or by any means, electronic, mechanical, photocopying, recording, scanning, or otherwise, except as permitted under Section 107 or 108 of the 1976 United States Copyright Act, without either the prior written permission of the Publisher, or authorization through payment of the appropriate per-copy fee to the Copyright Clear- ance Center, Inc., 222 Rosewood Drive, Danvers, MA 01923, (978) 750-8400, fax (978) 750-4470. Requests to the Publisher for permission should be addressed to the Legal Department, Wiley Publishing, Inc., 10475 Crosspoint Blvd., Indianapolis, IN 46256, (317) 572-3447, fax (317) 572-4447, E-mail: [email protected]. Limit of Liability/Disclaimer of Warranty: While the publisher and author have used their best efforts in preparing this book, they make no representations or warranties with respect to the accuracy or completeness of the contents of this book and specif- ically disclaim any implied warranties of merchantability or fitness for a particular purpose. No warranty may be created or extended by sales representatives or written sales materials. -
Efficient Dynamic-Resharing “Verifiable Secret Sharing” Against Mobile Adversary
Efficient Dynamic-Resharing \Verifiable Secret Sharing" Against Mobile Adversary Noga Alon∗ Zvi Galily Moti Yungz March 25, 1995 Abstract We present a novel efficient variant of Verifiable Secret Sharing (VSS) where the dealing of shares is dynamically refreshed (without changing or corrupting the secret) against the threat of the recently considered mobile adversary that may control all the trustees, but only a bounded number thereof at any time period. VSS enables a dealer to distribute its secret to a set of trustees, so that they are assured that the sharing is valid and that they can open it later, and further no small group of trustees can open it prematurely. Recently, such sharing of cryptographic tools gained much attention, e.g., in the context of \escrowed cryptography" where a user enables a group of trustees to potentially open its information (when authorized by the court). Our dynamic-sharing VSS allows for mobile adversary attacking different sets of trustees at different time periods (modeling, e.g., network viruses that get spread as well as get killed). Technically, we concentrate on simple direct methods that are combinatorial and number- theoretic in nature, and employ only simple public-key functions (and no other cryptographic tools as did previous methods). We also present constant round protocols (e.g., a single round VSS) and do not use general (polynomial time, but inefficient) tools. We essentially reduce n out of t < n=2 VSS to n out-of n one (assuming ex-or homomorphic encryption), then we reduce dynamic resharing VSS to static VSS, finally we reduce proactive VSS (dynamic VSS with no dealer presence after sharing) to our dynamic resharing VSS. -
Multi-Authority Secret-Ballot Elections with Linear Work
In Advances in Cryptology|EUROCRYPT'96, Vol. 1070 of Lecture Notes in Computer Science, Springer-Verlag, 1996. pp. 72-83. Multi-Authority Secret-Ballot Elections with Linear Work Ronald Cramer? Matthew Franklin?? Berry Schoenmakers??? Moti Yungy Abstract. We present new cryptographic protocols for multi-authority secret ballot elections that guarantee privacy, robustness, and univer- sal verifiability. Application of some novel techniques, in particular the construction of witness hiding/indistinguishable protocols from Cramer, Damg˚ardand Schoenmakers, and the verifiable secret sharing scheme of Pedersen, reduce the work required by the voter or an authority to a linear number of cryptographic operations in the population size (com- pared to quadratic in previous schemes). Thus we get significantly closer to a practical election scheme. 1 Introduction An electronic voting scheme is viewed as a set of protocols that allow a collection of voters to cast their votes, while enabling a collection of authorities to collect the votes, compute the final tally, and communicate the final tally that is checked by talliers. In the cryptographic literature on voting schemes, three important requirements are identified: Universal Verifiability ensures that any party, including a passive observer, can convince herself that the election is fair, i.e., that the published final tally is computed fairly from the ballots that were correctly cast. Privacy ensures that an individual vote will be kept secret from any (reasonably sized) coalition of parties that does not include the voter herself. Robustness ensures that the system can recover from the faulty behavior of any (reasonably sized) coalition of parties. The main contribution of this paper is to present an efficient voting scheme that satisfies universal verifiability, privacy and robustness.