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Mihir Bellare Curriculum Vitae Contents
Mihir Bellare Curriculum vitae August 2018 Department of Computer Science & Engineering, Mail Code 0404 University of California at San Diego 9500 Gilman Drive, La Jolla, CA 92093-0404, USA. Phone: (858) 534-4544 ; E-mail: [email protected] Web Page: http://cseweb.ucsd.edu/~mihir Contents 1 Research areas 2 2 Education 2 3 Distinctions and Awards 2 4 Impact 3 5 Grants 4 6 Professional Activities 5 7 Industrial relations 5 8 Work Experience 5 9 Teaching 6 10 Publications 6 11 Mentoring 19 12 Personal Information 21 2 1 Research areas ∗ Cryptography and security: Provable security; authentication; key distribution; signatures; encryp- tion; protocols. ∗ Complexity theory: Interactive and probabilistically checkable proofs; approximability ; complexity of zero-knowledge; randomness in protocols and algorithms; computational learning theory. 2 Education ∗ Massachusetts Institute of Technology. Ph.D in Computer Science, September 1991. Thesis title: Randomness in Interactive Proofs. Thesis supervisor: Prof. S. Micali. ∗ Massachusetts Institute of Technology. Masters in Computer Science, September 1988. Thesis title: A Signature Scheme Based on Trapdoor Permutations. Thesis supervisor: Prof. S. Micali. ∗ California Institute of Technology. B.S. with honors, June 1986. Subject: Mathematics. GPA 4.0. Class rank 4 out of 227. Summer Undergraduate Research Fellow 1984 and 1985. ∗ Ecole Active Bilingue, Paris, France. Baccalauréat Série C, June 1981. 3 Distinctions and Awards ∗ PET (Privacy Enhancing Technologies) Award 2015 for publication [154]. ∗ Fellow of the ACM (Association for Computing Machinery), 2014. ∗ ACM Paris Kanellakis Theory and Practice Award 2009. ∗ RSA Conference Award in Mathematics, 2003. ∗ David and Lucille Packard Foundation Fellowship in Science and Engineering, 1996. (Twenty awarded annually in all of Science and Engineering.) ∗ Test of Time Award, ACM CCS 2011, given for [81] as best paper from ten years prior. -
Stronger Security Notions for Trapdoor Functions and Applications
STRONGER SECURITY NOTIONS FOR TRAPDOOR FUNCTIONS AND APPLICATIONS A Thesis Presented to The Academic Faculty by Adam O'Neill In Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the College of Computing Georgia Institute of Technology December 2010 STRONGER SECURITY NOTIONS FOR TRAPDOOR FUNCTIONS AND APPLICATIONS Approved by: Professor Alexandra Boldyreva, Professor Chris Peikert Advisor College of Computing College of Computing Georgia Institute of Technology Georgia Institute of Technology Professor Mihir Bellare Professor Dana Randall Computer Science and Engineering College of Computing University of California, San Diego Georgia Institute of Technology Professor Richard Lipton Professor Patrick Traynor College of Computing College of Computing Georgia Institute of Technology Georgia Institute of Technology Date Approved: 9 August 2010 To my parents, John (Chuck) and Phyllis O'Neill, and my sister Katie, for their unconditional support. iii ACKNOWLEDGEMENTS My Ph.D. studies have been a significant undertaking, which would not have been possible without the help and guidance of many people (please forgive any omissions). First of all, I'd like to thank my parents, for encouraging me to pursue higher education and giving me the opportunity to do so. My intellectual development was greatly fostered during my time as an undergrad- uate at UCSD, and for that I have many friends and teaching assistants to thank. I would especially like to thank Daniel Bryant for helping me during my freshman year, and Derek Newland for inviting me to do an independent study with him. I would also like to thank Mihir Bellare for taking the time to help undergraduates find out about graduate school and encouraging them to take graduate-level courses. -
Universit`A Di Pisa Post Quantum Cryptography
Universit`adi Pisa Facolt`a di Scienze Matematiche, Fisiche e Naturali Corso di Laurea Magistrale in Fisica Anno Accademico 2013/2014 Elaborato Finale Post Quantum Cryptography Candidato: Relatori: Antonio Vaira Prof. Oliver Morsch Ing. Cristiano Borrelli Alla mia mamma Abstract I started my experience with cryptography within the Airbus environment working on this master thesis. I have been asked to provide a framework, or in other words, a big picture about present-day alternatives to the most used public key crypto-system, the RSA, that are supposed to be quantum resistant. The final application of my work eventually resulted in recommendations on how to handle the quantum threat in the near future. This was quite a complex task to accomplish because it involves a huge variety of topics but by physical background was really helpful in facing it. Not because of specific and previous knowledge but for the mathematical toolsacquired during the studies and especially for that attitude that belongs to out category that make us, physicist problem solver in a large variety of fields. Indeed I also tried to go a bit further with my studies. I took one of the most promising algorithm on my opinion, but not well known yet so unfeasible for a recommendation and therefore an implementation in the close future, and I tried to figure out how to enhance it from both a security and an operational point of view (how to increase the correctness ratio of the decryption and the speed of the cryptographic operations). It followed a period of time in which I improved my skills with few computing languages and in the end I decided to implement a toy model at a high level using an interface that already implements all the mathematical and algebraical structures used to build the model. -
Part V Public-Key Cryptosystems, I. Key Exchange, Knapsack
Part V Public-key cryptosystems, I. Key exchange, knapsack, RSA CHAPTER 5: PUBLIC-KEY CRYPTOGRAPHY I. RSA The main problem of secret key (or symmetric) cryptography is that in order to send securely A secret message we need to send at first securely a secret key and therefore secret key cryptography is clearly not a sufficiently good tool for massive communication capable to protect secrecy, privacy and anonymity. prof. Jozef Gruska IV054 5. Public-key cryptosystems, I. Key exchange, knapsack, RSA 2/67 SECURE ENCRYPTION - a PRACTICAL POINT OF VIEW From practical point of view encryptions by a cryptosystem can be considered as secure if they cannot be broken by many (thousands) superomputeers with exaflop performance working for some years. prof. Jozef Gruska IV054 5. Public-key cryptosystems, I. Key exchange, knapsack, RSA 3/67 CONTENT In this chapter we describe the birth of public key cryptography, that can better manage key distribution problem, and three of its cryptosystems, especially RSA. The basic idea of a public key cryptography: In a public key cryptosystem not only the encryption and decryption algorithms are public, but for each user U also the key eU for encrypting messages (by anyone) for U is public. Moreover, each user U keeps secret another (decryption) key, dU , that can be used for decryption of messages that were addressed to him and encrypted with the help of the public encryption key eU . Encryption and decryption keys could (and should) be different - we can therefore speak also about asymmetric cryptography. Secret key cryptography, that has the same key for encryption and for decryption is also called symmetric cryptography. -
Private Searching on Streaming Data∗
J. Cryptology (2007) 20: 397–430 DOI: 10.1007/s00145-007-0565-3 © 2007 International Association for Cryptologic Research Private Searching on Streaming Data∗ Rafail Ostrovsky Department of Computer Science and Department of Mathematics, University of California, Los Angeles, CA 90095, U.S.A. [email protected] William E. Skeith III Department of Mathematics, University of California, Los Angeles, CA 90095, U.S.A. [email protected] Communicated by Dan Boneh Received 1 September 2005 and revised 16 July 2006 Online publication 13 July 2007 Abstract. In this paper we consider the problem of private searching on streaming data, where we can efficiently implement searching for documents that satisfy a secret criteria (such as the presence or absence of a hidden combination of hidden keywords) under various cryptographic assumptions. Our results can be viewed in a variety of ways: as a generalization of the notion of private information retrieval (to more general queries and to a streaming environment); as positive results on privacy-preserving datamining; and as a delegation of hidden program computation to other machines. Key words. Code obfuscation, Public-key program obfuscation, Program obfus- cation, Crypto-computing, Software security, Database security, Public-key encryp- tion with special properties, Private information retrieval, Privacy-preserving keyword search, Secure algorithms for streaming data, Privacy-preserving datamining, Secure delegation of computation, Searching with privacy, Mobile code. 1. Introduction 1.1. Data Filtering for the Intelligence Community As our motivating example, we examine one of the tasks of the intelligence community, which is to collect “potentially useful” information from huge streaming sources of ∗ An abridged version appeared at CRYPTO 2005. -
The Cramer-Shoup Strong-RSA Signature Scheme Revisited
The Cramer-Shoup Strong-RSA Signature Scheme Revisited Marc Fischlin Johann Wolfgang Goethe-University Frankfurt am Main, Germany marc @ mi.informatik.uni-frankfurt.de http://www.mi.informatik.uni-frankfurt.de/ Abstract. We discuss a modification of the Cramer-Shoup strong-RSA signature scheme. Our proposal also presumes the strong RSA assump- tion (and a collision-intractable hash function for long messages), but |without loss in performance| the size of a signature is almost halved compared to the original scheme. We also show how to turn the signature scheme into a \lightweight" anonymous (but linkable) group identifica- tion protocol without random oracles. 1 Introduction Cramer and Shoup [CS00] have presented a signature scheme which is secure against adaptive chosen-message attacks under the strong RSA (aka. flexible RSA) assumption, and which does not rely on the random oracle model. For a 1024-bit RSA modulus and a 160-bit (hash value of a) message a signature has about 2200 bits. Cramer and Shoup also discuss a variation of their scheme which, in addition to the strong RSA assumption, requires the discrete-log as- sumption and which produces signatures of roughly half the length (about 1350 bits). Here, we show that we can achieve the same signature size under the strong RSA assumption only, even with a slightly improved performance than in the original strong-RSA-only case or the discrete-log & strong-RSA case. Our signature scheme also has the feature that for short messages, e.g., of 120 bits, a collision-intractable (or universal one-way) hash function becomes obsolete. -
Solving NTRU Challenges Using the New Progressive BKZ Library
Solving NTRU Challenges Using the New Progressive BKZ Library Erik Mårtensson Department of Electrical and Information Technology Lund University Advisors: Professor Thomas Johansson and Qian Guo 2016-08-24 Printed in Sweden E-huset, Lund, 2016 Abstract NTRU is a public-key cryptosystem, where the underlying mathematical problem is currently safe against large-scale quantum computer attacks. The system is not as well investigated, as for example RSA and the company behind NTRU has created the NTRU Challenges, to remedy this. These challenges consist of 27 different public keys of increasing size, where the task in each challenge is to calculate (something similar to) the private key. The goal of this thesis was to examine different attacks against the NTRU Challenges and solve as many challenges as possible. By lattice reduction attacks, using a recently published new progressive BKZ algorithm, the first five challenges were solved, while the current biggest solved challenge by any researcher is challenge number seven. Keywords: NTRU Challenge, Progressive BKZ , BDD, Enumeration, SVP i ii Acknowledgements I would like to thank my main supervisor Professor Thomas Johansson for all his help and feedback during the project, for introducing me to the lattice-based cryptography area and last but not least for pointing out the necessity of solving a small problem correctly before tackling a big problem. I would like to thank my assistant supervisor Qian Guo for all his help and feed- back during the project and for introducing me to the progressive BKZ algorithm that turned out to become the focus of this thesis. I would like to thank all the researchers that patiently answered my many ques- tions during this project, with special thanks to Yoshinori Aono, Léo Ducas and Zhenfei Zhang for answering questions regarding the progressive BKZ algorithm and library, the BKZ plus BDD enumeration strategy for attacking NTRU and the NTRU Challenges respectively. -
How to Strengthen Ntruencrypt to Chosen-Ciphertext Security in the Standard Model
NTRUCCA: How to Strengthen NTRUEncrypt to Chosen-Ciphertext Security in the Standard Model Ron Steinfeld1?, San Ling2, Josef Pieprzyk3, Christophe Tartary4, and Huaxiong Wang2 1 Clayton School of Information Technology Monash University, Clayton VIC 3800, Australia [email protected] 2 Div. of Mathematical Sciences, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore, 637371 lingsan,[email protected] 3 Centre for Advanced Computing - Algorithms and Cryptography, Dept. of Computing, Macquarie University, Sydney, NSW 2109, Australia [email protected] 4 Institute for Theoretical Computer Science, Tsinghua University, People's Republic of China [email protected] Abstract. NTRUEncrypt is a fast and practical lattice-based public-key encryption scheme, which has been standardized by IEEE, but until re- cently, its security analysis relied only on heuristic arguments. Recently, Stehlé and Steinfeld showed that a slight variant (that we call pNE) could be proven to be secure under chosen-plaintext attack (IND-CPA), assum- ing the hardness of worst-case problems in ideal lattices. We present a variant of pNE called NTRUCCA, that is IND-CCA2 secure in the standard model assuming the hardness of worst-case problems in ideal lattices, and only incurs a constant factor overhead in ciphertext and key length over the pNE scheme. To our knowledge, our result gives the rst IND- CCA2 secure variant of NTRUEncrypt in the standard model, based on standard cryptographic assumptions. As an intermediate step, we present a construction for an All-But-One (ABO) lossy trapdoor function from pNE, which may be of independent interest. Our scheme uses the lossy trapdoor function framework of Peik- ert and Waters, which we generalize to the case of (k −1)-of-k-correlated input distributions. -
One-Time Trapdoor One-Way Functions
One-Time Trapdoor One-Way Functions Julien Cathalo?1 and Christophe Petit??2 1 Smals Avenue Fonsny 20, 1060 Bruxelles, Belgium 2 UCL Crypto Group Universit´ecatholique de Louvain, Place du Levant 3, 1348 Louvain-la-Neuve, Belgium Abstract. Trapdoors are widely used in cryptography, in particular for digital signatures and public key encryption. In these classical applica- tions, it is highly desirable that trapdoors remain secret even after their use. In this paper, we consider positive applications of trapdoors that do not remain secret when they are used. We introduce and formally de- fine one-time trapdoor one-way functions (OTTOWF), a primitive simi- lar in spirit to classical trapdoor one-way functions, with the additional property that its trapdoor always becomes public after use. We provide three constructions of OTTOWF. Two of them are based on factoring assumptions and the third one on generic one-way functions. We then consider potential applications of our primitive, and in particular the fair exchange problem. We provide two fair exchange protocols using OTTOWF, where the trapdoor is used to provide some advantage to one of the parties, whereas any (abusive) use of this trapdoor will make the advantage available to the other party as well. We compare our proto- cols with well-established solutions for fair exchange and describe some scenarios where they have advantageous characteristics. These results demonstrate the interest of one-time trapdoor one-way functions, and suggest looking for further applications of them. Keywords Cryptographic primitive, trapdoor one-way function, fair exchange 1 Introduction In cryptography, a trapdoor is a secret piece of information that provides its holder with some special power or advantage. -
Practical Lattice-Based Digital Signature Schemes J
Practical Lattice-based Digital Signature Schemes J. Howe1, T. Pöppelmann2, M. O’Neill1, E. O’Sullivan1, T. Güneysu2 1 Centre for Secure Information Technologies (CSIT), Queen’s University Belfast, UK 2Horst Görtz Institute for IT-Security, Ruhr-University Bochum, Germany Abstract: Among the various post-quantum techniques that exist (such as multivariate, code or hash-based), the most promising is lattice-based cryptography, which has become a very viable alternative to number-theoretic cryptography. Its main advantage is that it allows for extended functionality and is, at the same time, more efficient for the basic primitives of public-key encryption and digital signatures. The focus of this presentation will be to survey recent developments in lattice-based digital signature schemes and in particular practical schemes that have been shown to improve upon the performance of equivalent RSA designs. Propositions for future research areas that are essential for the continued development of lattice-based cryptography will also be discussed. 1 Introduction With the onset of quantum computers ever looming, the computational power it could provide would cause instant insecurity to many of today’s universally used cryptographic schemes by virtue of Shor’s [1] algorithm. Specifically, schemes based on the discrete-logarithm problem or number-theoretic hard problems, which subsume almost all public-key encryption schemes used on the Internet, including elliptic-curve cryptography (ECC), RSA and DSA would be vulnerable. Accordingly, this has motivated the post-quantum era of cryptography, which refers to the construction of cryptographic algorithms to withstand quantum reductions. Amongst many important areas in post-quantum research (such as multivariate, code or hash-based) lattice-based cryptography is disputably the most auspicious. -
A Weak-Randomizer Attack on RSA-OAEP with E = 3
A Weak-Randomizer Attack on RSA-OAEP with e = 3 Daniel R. L. Brown∗ July 6, 2005 Abstract Coppersmith's heuristic algorithm for finding small roots of bivariate modular equations can be applied against low-exponent RSA-OAEP if its randomizer is weak. An adversary that knows the randomizer can recover the entire plaintext message, provided it is short enough for Coppersmith's algorithm to work. In practice, messages are symmetric cipher keys and these are potentially short enough for certain sets of key sizes. Weak randomizers could arise in constrained smart cards or in kleptographic implementations. Because RSA's major use is transporting symmetric keys, this attack is a potential concern. In this respect, OAEP's design is more fragile than necessary, because a secure randomizer is critical to prevent a total loss of secrecy, not just a loss of semantic security or chosen-ciphertext security. Countermeasures and more robust designs that have little extra performance cost are proposed and discussed. 1 Introduction Evidence exists that RSA encryption when the public exponent e = 3 is weaker than the general problem of inverting the raw RSA function with e = 3 at random values. Examples are Copper- smith's [Cop96] and Hastad's broadcast attack. (Boneh [Bon99] surveys some of these results.) Security proofs aim to rule out unforeseen attacks by reducing security to a hard problem. The RSA-OAEP encryption scheme [BR94] has a proof that reduces its security to the problem of in- verting the RSA function. The proof applies even if e = 3, so therefore RSA-OAEP avoids the attacks mentioned above. -
How to Share a Lattice Trapdoor: Threshold Protocols for Signatures and (H)IBE
How to Share a Lattice Trapdoor: Threshold Protocols for Signatures and (H)IBE Rikke Bendlin∗ Sara Krehbiely Chris Peikertz Abstract We develop secure threshold protocols for two important operations in lattice cryptography, namely, generating a hard lattice Λ together with a “strong” trapdoor, and sampling from a discrete Gaussian distribution over a desired coset of Λ using the trapdoor. These are the central operations of many crypto- graphic schemes: for example, they are exactly the key-generation and signing operations (respectively) for the GPV signature scheme, and they are the public parameter generation and private key extraction operations (respectively) for the GPV IBE. We also provide a protocol for trapdoor delegation, which is used in lattice-based hierarchical IBE schemes. Our work therefore directly transfers all these systems to the threshold setting. Our protocols provide information-theoretic (i.e., statistical) security against adaptive corruptions in the UC framework, and they are private and robust against an optimal number of semi-honest or malicious parties. Our Gaussian sampling protocol is both noninteractive and efficient, assuming either a trusted setup phase (e.g., performed as part of key generation) or a sufficient amount of interactive but offline precomputation, which can be performed before the inputs to the sampling phase are known. ∗Department of Computer Science, Aarhus University. Email: [email protected]. Supported by the Danish National Research Foundation and The National Science Foundation of China (under the grant 61061130540) for the Sino-Danish Center for the Theory of Interactive Computation, within which part of this work was performed; and also from the CFEM research center (supported by the Danish Strategic Research Council).