DOCSLIB.ORG

Research Statement

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Research Statement Research Statement Andrew Miller November 2015 Over the past several years, Bitcoin and other cryptocurrencies have been an empirical suc- cess [1]. These are decentralized systems that allow users to transmit money, compose financial instruments, and enforce contracts between mutually distrusting peers. They currently represent a market cap of almost $5B of users' wealth, have precipitated almost $1B of venture capital in- vestment in related technology firms, and have evoked responses from policy makers and regulators the world over. Perhaps most surprisingly, they mostly operate independently of, and even in direct competition with, the traditional institutions that ordinarily provide such services. This competition holds great promise to yield a financial infrastructure that is more robust, efficient and equitable than ours today. Cryptocurrencies are a microcosm exhibiting many of the challenges faced in securing complex information systems more broadly. Without a rigorous and realistic security model, it is difficult to predict whether these systems will survive future attacks, and to evaluate whether potential protocol changes and performance tradeoffs are safe. Furthermore, the appeal of cryptocurrencies as an application platform has led to a large community of enthusiastic developers; but cryptographic expertise remains a bottleneck, so few systems are deployed with thorough validation. My goal is to build a research program that provides provable security for emer- gent decentralized systems, especially by combining techniques from programming languages and cryptography. In my dissertation, I developed (the first) formal models for Bitcoin's security. Using this as a scaffolding, I invented novel constructions that preserve security while providing additional benefits, such as reducing waste and improving incentives. Adapting formal models to real-world systems provides a principled way to explore vast design spaces. In my dissertation I also created programming languages that safely encapsulate cryptographic protocols, so that even non-expert application developers can use them in cryptocurrency ap- plications. Here, the methods of programming language design and cryptography fundamentally complement each other; cryptography provides powerful and general primitives, while programming language abstractions provide the means to safely compose with them. Provable Security for Cryptocurrencies. Cryptocurrencies do not fit neatly into existing theoretical frameworks for distributed computing and cryptography, but rather seem to rely on weaker (or at least incomparable) assumptions than those previously studied. In my dissertation I developed the \Scratch-Off Puzzles" (SOP) model, a formal network model more suited for Bitcoin, including the presence of anonymous communication channels with no pre-established PKI, as well as assumptions about the allocation of computational resources (i.e., \hashpower") among the participants. The SOP model is useful for exploring and validating new cryptocurrency designs. To demon- strate this I invented several new constructions which can be proven secure in this model, yet also 1 achieve additional desirable effects. First, with Permacoin, I show that the otherwise-\wasted" work of Bitcoin mining can be recycled to provide a global backup storage system for public datasets [8]. Second, most miners join large coalitions called mining pools; for the past several years, influence over the network has been largely consolidated by just a handful of such coalitions, which threat- ens the assumptions underlying Bitcoin's security. My research shows these coalitions are only possible as a consequence of Bitcoin's puzzle construction. I therefore developed a new approach, called \nonoutsourceable puzzles," that use succinct zero-knowledge proofs [5] to enable coalition members to defect [9], thus discouraging coalitions from forming. Programming Languages for Secure Protocols by Non-Experts Cryptocurrencies provide a useful and general abstraction: a \world-wide database" instance that's publicly accessible and globally consistent. The convenience of these systems as a platform has attracted a broad community of developers, enthusiastic to implement a wide variety of applications beyond just money transmission, ranging from prediction markets [2] to crowdsourced file storage services [8]. However, successful applications built atop this platform still demand the careful composition of cryptographic primitives. These compositions are typically prone to implementation error, often to catastrophic effect, especially when implemented by non-experts [3]. My research aims to shift the burden of secure cryptography composition from the program- mer to the compiler, which generates \secure-by-construction" protocols from simple specifications written by non-specialist programmers. A Programming Language for Authenticated Data Structures. In my dissertation, I developed a programming language, λ• (pronounced Lambda-Auth) for hash-based Authenticated Data Structures (ADS) [6]. ADS's are a well known and widely applicable cryptographic technique that allow clients to offload their storage costs to an untrusted server. ADS protocols are used widely in many systems (including Git, Bittorrent, and Bitcoin). However, there remain many suitable applications that do not yet utilize these protocols (or fail to utilize them to their full benefit). This is partly because of the specialized effort needed to implement the authenticated version of each new data structure. In λ•, the programmer simply writes an ordinary data structure program in a functional language. This program serves as a specification, which our λ• compiler elaborates into a correct-by-construction ADS protocol for the clients and servers. As a case study, I used λ• to model the Bitcoin \blockchain" as an authenticated data structure. I then used λ• to prototype an alternative proposal for a blockchain-like data structure that offers a performance optimization: it yields a transaction validation client that requires only constant-size storage. Privacy-preserving Smart Contracts. In another project, Hawk [4], I developed a program- ming language for privacy-preserving smart contracts. While several existing cryptocurrencies, such as Ethereum, provide a general purpose programming environment, my collaborators and I showed that used na¨ıvely, they leak significant amounts of information to to adversaries [3], and are thus unsuitable for many applications (e.g., involving business finances, health data, and other sensitive information). In Hawk, the programmer specifies an application (e.g., a private sealed-bid auction) as an arbitrary computable function, written in a subset of C. Our compiler generates a cryptographic protocol, combining zero-knowledge proofs and public key encryption. The protocol underlying Hawk is a novel composition of commitments and zero-knowledge proofs. It guarantees on-chain privacy, in the sense that input values are revealed to a semi-trusted \manager," who learns the input values at the end of the protocol, but cannot interfere with the 2 correct computation of the contract. The role of manager can also be instantiated with trusted hardware or multi-party computation. Future Work. Security of cryptocurrencies under composition. So far, formal models of cryptocurrencies analyze only a single network in isolation. However, in reality, there are already hundreds of competing cryptocurrency networks. And, in fact, they already interact in surprising ways (for example, a well-known Bitcoin miner used its hashpower to launch a devastating attack against a weaker cryptocurrency). Can cryptocurrency designs be proved secure under composition, even when considering arbitrary interactions between them? Universal Composability as a practical framework for modular protocols. The cryp- tography community has converged on a framework called \Universal Composability" (UC), which guarantees security even when arbitrary protocols are executed concurrently. In the UC framework, network models, primitive building blocks, and application specifications are all as \Ideal Function- alities:" i.e., as processes written in an ordinary programming language, and executed as though by an incorruptible server. Ideal functionalities therefore serve as simple models for more complicated cryptographic protocols. So far, this approach has been underappreciated outside of cryptography theory; and even in cryptography, proofs in this framework are unwieldy to write and verify. This is in part because the framework exists only as prose, without a concrete realization. After my experience formalizing Hawk in UC [4], I now believe this framework can serve as the basis for a practical library of modular protocols. My plan is to provide a concrete process calculus seman- tics for Universal Composability, and develop a modular, mechanically checkable system of proofs. This will be especially useful to reign in the complexity of cryptocurrency applications, which are diverse, built through concurrent composition of primitives, and whose interactions require care to analyze. Outreach and visibility. Cryptocurrencies have piqued a common interest in industry, open source projects, and academia alike. They therefore provide an effective avenue for the practical deployment of cryptography. Simply put, the cryptocurrency development industry is hungry for cryptography. Part of my research method is to embed myself in the development community surrounding the emergent systems I study.
Load more

Recommended publications
  • A Second Note on the Feasibility of Generalized Universal Composability
    A final version of this paper appeared in Math. Struct. in Comp. Science, 2016. This is the preliminary full version. A Second Note on the Feasibility of Generalized Universal Composability ALONSOGONZ ALEZ´ y and A L E J A N D R O H E V I Az Departamento de Ciencias de la Computaci´on,Universidad de Chile. [email protected], [email protected]. Received 2 October 2014; revised 11 May 2016 Yao et al. (YYZ09a; YYZ07) claimed a potential limitation on the class of protocols that could be securely implemented in the Generalized Universal Composability (GUC) framework proposed by Canetti et al. (CDPW07). Specifically, Yao et al. presented a concrete attack on a GUC Zero Knowledge (GUCZK) protocol, a natural adaptation Blum's ZK proof for Directed Hamiltonicity using the general GUC feasibility of (CDPW07). Interestingly, the attack was not analyzed in the GUC model in (YYZ09a) but in the FUC model, a new UC-like framework proposed in the same work. Nonetheless, Yao et al. (YYZ09a) argued that, in light of this attack, GUC would lose its concurrent general composability and proof of knowledge properties. Concretely, they argue that GUC composability would now be with respect to some adversaries with limited access to external arbitrary protocols. In this work, we show that the claimed attack from Yao et al. is indeed harmless and does not contradict the security of the mentioned GUCZK protocol, thus restoring the general feasibility for GUC. 1. Introduction The Universal Composability framework (UC), introduced by Canetti (Can01), allows designing protocols whose security is maintained even when composed with any other arbitrary protocol (i.e.
    [Show full text]
  • Universally Composable Security: a New Paradigm for Cryptographic Protocols∗
    Universally Composable Security: A New Paradigm for Cryptographic Protocols∗ Ran Canettiy February 11, 2020 Abstract We present a general framework for describing cryptographic protocols and analyzing their security. The framework allows specifying the security requirements of practically any crypto- graphic task in a unified and systematic way. Furthermore, in this framework the security of protocols is preserved under a general composition operation, called universal composition. The proposed framework with its security-preserving composition operation allows for mod- ular design and analysis of complex cryptographic protocols from simpler building blocks. More- over, within this framework, protocols are guaranteed to maintain their security in any context, even in the presence of an unbounded number of arbitrary protocol sessions that run concur- rently in an adversarially controlled manner. This is a useful guarantee, which allows arguing about the security of cryptographic protocols in complex and unpredictable environments such as modern communication networks. Keywords: cryptographic protocols, security analysis, protocol composition, universal composi- tion. ∗An extended abstract of this work appears in the proceedings of the 42nd Foundations of Computer Science conference, 2001. This is an updated version. While the overall spirit and the structure of the definitions and results in this paper has remained the same, many important details have changed. We point out and motivate the main differences as we go along. Earlier versions of this work appeared in December 2018, July 2013, Decem- ber and January 2005, and October 2001, under the same title, and in December 2000 under the title \A unified framework for analyzing security of protocols". These earlier versions can be found at the ECCC archive, TR 01-16 (http://eccc.uni-trier.de/eccc-reports/2001/TR01-016); however they are not needed for understanding this work and have only historic significance.
    [Show full text]
  • Careful with Composition: Limitations of Indifferentiability and Universal Composability
    A preliminary version of this paper appeared in: T. Ristenpart, H. Shacham, and T. Shrimpton. Careful with Composition: Limitations of the Indifferentia- bility Framework. Advances in Cryptology – EUROCRYPT ’11, LNCS vol. 6632, pp. 487–506, Kenneth Paterson ed., Springer, 2011. Careful with Composition: Limitations of Indifferentiability and Universal Composability Thomas Ristenpart∗ Hovav Shachamy Thomas Shrimptonz June 22, 2011 Abstract We exhibit a hash-based storage auditing scheme which is provably secure in the random-oracle model (ROM), but easily broken when one instead uses typical indifferentiable hash constructions. This contradicts the widely accepted belief that the indifferentiability composition theorem applies to any cryptosystem. We characterize the uncovered limitation of the indifferentiability framework by show- ing that the formalizations used thus far implicitly exclude security notions captured by experiments that have multiple, disjoint adversarial stages. Examples include deterministic public-key encryption (PKE), password-based cryptography, hash function nonmalleability, key-dependent message security, and more. We formalize a stronger notion, reset indifferentiability, that enables an indifferentiability- style composition theorem covering such multi-stage security notions, but then show that practical hash constructions cannot be reset indifferentiable. We discuss how these limitations also affect the universal composability framework. We finish by showing the chosen-distribution attack security (which requires a multi-stage game) of some important public-key encryption schemes built using a hash construction paradigm introduced by Dodis, Ristenpart, and Shrimpton. 1 Introduction The indifferentiability framework of Maurer, Renner, and Holenstein (MRH) [51] supports modular proofs of security for cryptosystems. It can be viewed, informally, as a special case of the Universal Composition (UC) framework [27, 53], which inspired it.
    [Show full text]
  • Universally Composable RFID Identification and Authentication
    Universally Composable RFID Identification and Authentication Protocols MIKE BURMESTER Florida State University, Tallahassee TRI VAN LE and BRENO DE MEDEIROS Google, Inc. 1600 Amphitheatre, Parkway Mountain View and GENE TSUDIK University of California, Irvine As the number of RFID applications grows and RFID tags begin to enter many aspects of everyday life, concerns about their security and privacy become greatly amplified. At the same time, the acutely restricted and cost-sensitive nature of RFID tags rules out simple re-use of existing traditional security/privacy solutions and calls for a new generation of extremely lightweight identification and authentication protocols. This paper describes a universally composable security framework tuned especially for RFID applications. By making RFID-specific setup, communication, and concurrency assumptions, we arrive at a model that guarantees strong security, privacy and availability properties, while per- mitting the design of practical RFID protocols. The framework supports modular deployment, which is most appropriate for ubiquitous applications. As an instantiation of the proposed frame- work, this paper describes a set of simple, efficient, secure and anonymous (untraceable) RFID identification and authentication protocols. These protocols involve minimal interaction between a tag and a reader and place only a small computational load on the tag. They also impose little computational burden on the back-end server. We show that our protocols are provably secure within the proposed universally composable framework. Categories and Subject Descriptors: K.6.5 [Management of Computing and Information Systems]: Security and Protection—Authentication; K.6.5 [Management of Computing and Information Systems]: Miscellaneous—Security; C.3 [Special-Purpose and Application- Based Systems]: Real-time and embedded systems General Terms: Design, Security, Theory Additional Key Words and Phrases: RFID Security, Authentication and Key-Exchange Protocols, Universal Composability 1.
    [Show full text]
  • Hawk: the Blockchain Model of Cryptography and Privacy-Preserving Smart Contracts
    Hawk: The Blockchain Model of Cryptography and Privacy-Preserving Smart Contracts Ahmed Kosba∗, Andrew Miller∗, Elaine Shiy, Zikai Weny, Charalampos Papamanthou∗ ∗University of Maryland and yCornell University fakosba, [email protected], frs2358, [email protected], [email protected] Abstract—Emerging smart contract systems over decentralized privacy. Such a blockchain provides a powerful abstraction for cryptocurrencies allow mutually distrustful parties to transact the design of distributed protocols. safely without trusted third parties. In the event of contrac- The blockchain’s expressive power is further enhanced by tual breaches or aborts, the decentralized blockchain ensures that honest parties obtain commensurate compensation. Existing the fact that blockchains naturally embody a discrete notion systems, however, lack transactional privacy. All transactions, of time, i.e., a clock that increments whenever a new block including flow of money between pseudonyms and amount is mined. The existence of such a trusted clock is crucial transacted, are exposed on the blockchain. for attaining financial fairness in protocols. In particular, We present Hawk, a decentralized smart contract system that malicious contractual parties may prematurely abort from a does not store financial transactions in the clear on the block- chain, thus retaining transactional privacy from the public’s view. protocol to avoid financial payment. However, with a trusted A Hawk programmer can write a private smart contract in an clock, timeouts can be employed to make such aborts evident, intuitive manner without having to implement cryptography, and such that the blockchain can financially penalize aborting our compiler automatically generates an efficient cryptographic parties by redistributing their collateral deposits to honest, protocol where contractual parties interact with the blockchain, non-aborting parties.
    [Show full text]
  • Theoretical Computer Science a Note on Universal Composable
    Theoretical Computer Science 410 (2009) 1099–1108 Contents lists available at ScienceDirect Theoretical Computer Science journal homepage: www.elsevier.com/locate/tcs A note on universal composable zero-knowledge in the common reference string modelI Andrew C.C. Yao a, Frances F. Yao b, Yunlei Zhao c,∗ a Institute for Theoretical Computer Science, Tsinghua University, Beijing, China b Department of Computer Science, City University of Hong Kong, China c Software School, Fudan University, Shanghai, China article info a b s t r a c t Keywords: Pass observed that universal composable zero-knowledge (UCZK) protocols in the common Cryptographic protocols reference string (CRS) model lose deniability that is a natural security property and Universal composability implication of the ZK functionality in accordance with the UC framework. An open problem Zero-knowledge Proof of knowledge (or, natural query) raised in the literature is: are there any other essential security Common reference string properties, other than the well-known deniability property, that could be lost by UCZK in the CRS model, in comparison with the ZK functionality in accordance with the UC framework? In this work, we answer this open question (or, natural query), by showing that when running concurrently with other protocols UCZK in the CRS model can lose proof of knowledge (POK) property that is very essential and core security implication of the ZK functionality. This is demonstrated by concrete attack against naturally existing UCZK protocols in the CRS model. Then, motivated by our attack, we make further clarifications of the underlying reasons beneath the concrete attack, and investigate the precise security guarantee of UC with CRS.
    [Show full text]
  • Universally Composable Protocols with Relaxed Set-Up Assumptions ¡ Boaz Barak Ran Canetti Jesper Buus Nielsen Rafael Pass Inst
    Universally Composable Protocols with Relaxed Set-up Assumptions ¡ Boaz Barak Ran Canetti Jesper Buus Nielsen Rafael Pass Inst. for Advanced Study IBM Research ETH Zurich¨ MIT [email protected] [email protected] [email protected] [email protected] Abstract of instances of the protocol, as well as arbitrary other pro- tocols. Indeed, it has been demonstrated time and again A desirable goal for cryptographic protocols is to guar- that adversarially-coordinated interactions between differ- antee security when the protocol is composed with other ent protocol instances can compromise the security of pro- protocol instances. Universally Composable (UC) protocols tocols that were demonstrated to be secure when run in provide this guarantee in a strong sense: A protocol re- isolation (see, e.g., [GK90, DDN00, KSW97, DNS98]). A nat- mains secure even when composed concurrently with an un- ural way for guaranteeing security of protocols in such bounded number of instances of arbitrary protocols. How- complex execution environments is to require that pro- ever, UC protocols for carrying out general tasks are known tocols satisfy a notion of security that provides a gen- to exist only if a majority of the participants are honest, or eral secure composability guarantee. That is, it should in the common reference string (CRS) model where all par- be guaranteed that a secure protocol maintains its se- ties are assumed to have access to a common string that curity even when composed with (i.e., runs alongside) is drawn from some pre-defined distribution. Furthermore, arbitrary other protocols. Such a general notion of secu- carrying out many interesting tasks in a UC manner and rity is provided by the universally composable (UC) security without honest majority or set-up assumptions is impos- framework [C01], which provides a very general com- sible, even if ideally authenticated communication is pro- posability property: A secure protocol is guaranteed to vided.
    [Show full text]
  • New Notions of Security: Achieving Universal Composability Without Trusted Setup
    New Notions of Security: Achieving Universal Composability without Trusted Setup Manoj Prabhakaran∗ Amit Sahai† Princeton University Princeton University June 12, 2004 Preliminary Version Abstract We propose a modification to the framework of Universally Composable (UC) security [3]. Our new notion, involves comparing the protocol executions with an ideal execution involving ideal functionalities (just as in UC-security), but allowing the environment and adversary access to some super-polynomial computational power. We argue the meaningfulness of the new notion, which in particular subsumes many of the traditional notions of security. We generalize the Universal Composition theorem of [3] to the new setting. Then under new com- putational assumptions, we realize secure multi-party computation (for static adversaries) without a common reference string or any other set-up assumptions, in the new framework. This is known to be impossible under the UC framework. 1 Introduction Over the last two decades, there has been tremendous success in placing cryptography on a sound theoretical foundation, and building an amazingly successful theory out of it. The key elements in this Modern Cryp- tographic Theory are the definitions capturing the intuitive, yet elusive notions of security in the various cryptographic settings. The definitions of early 80’s proved to be extremely successful in this regard. But with time, as the theory started addressing more and more complex concerns, further notions of security had to be introduced. One of the most important concerns theory ventured into is of complex environments where the different parties are communicating with each other concurrently in many different protocols. The original definitions turned out to be inadequate to handle this.
    [Show full text]
  • Universally Composable Key-Management Steve Kremer, Robert Kunnemann, Graham Steel
    Universally Composable Key-Management Steve Kremer, Robert Kunnemann, Graham Steel To cite this version: Steve Kremer, Robert Kunnemann, Graham Steel. Universally Composable Key-Management. 2012. hal-00686535 HAL Id: hal-00686535 https://hal.inria.fr/hal-00686535 Preprint submitted on 10 Apr 2012 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Universally Composable Key-Management Steve Kremer1, Robert Kunnemann¨ 2, and Graham Steel2 1 LORIA & INRIA Nancy { Grand-Est 2 LSV & INRIA Saclay { ^Ile-de-France Abstract. We present the first key-management functionality in the Universal Composability (UC) framework. It allows the enforcement of a wide range of security policies and can be extended by diverse key usage operations with no need to repeat the security proof. We illustrate its use by proving an implementation of a Security API secure with respect to arbitrary key-usage operations and explore a proof technique that allows the storage of cryptographic keys externally, a novel development in the UC framework. Keywords: Key management, Security APIs, Universal Composability Table of Contents Universally Composable Key-Management ::::::::::::::::::::::::::: 1 Steve Kremer, Robert Kunnemann,¨ and Graham Steel 1 Introduction...................................................2 2 A key-management functionality .
    [Show full text]
  • Adaptive Universal Composability Framework for Server-Aided Threshold Signature
    Research Journal of Applied Sciences, Engineering and Technology 5(1): 270-274, 2013 ISSN: 2040-7459; e-ISSN: 2040-7467 © Maxwell Scientific Organization, 2013 Submitted: June 02, 2012 Accepted: June 23, 2012 Published: January 01, 2013 Adaptive Universal Composability Framework for Server-Aided Threshold Signature Xuan Hong and Luqun Li Department of Computer Science and Technology, Shanghai Normal University, Shanghai 200234, China Abstract: The threshold signature scheme is a protocol that allows any subset of t parties out of n to generate a signature. Since the t members can cooperate together to compute the secret key, we introduce the server-aided threshold signature, which provides controllability for activating the signing function in a certain enhanced way. In this study, we present a server-aided threshold RSA signature protocol against the adaptive attacks. We give the universally composable secure model for the server-aided threshold signature primitive and prove that the proposed protocol is claimed to be well-formed, correct and unforgeability. As a separate contribution we also prove that it is also secure in the adaptive universal composability framework. After the discussion about the security and the performance, we claim that the protocol is practical and efficient. Keywords: Adaptive security, server-aided, threshold signature, universal composability framework INTRODUCTION that the password is divided into several pieces which are shared among a group of members. Only at least t A threshold signature scheme is a protocol that members together have the privilege to access the allows any subset of t parties out of n to generate a classified file. However, when some t members are signature.
    [Show full text]
  • A Framework for Practical Universally Composable Zero-Knowledge Protocols?
    A Framework for Practical Universally Composable Zero-Knowledge Protocols? Jan Camenisch1, Stephan Krenn2, and Victor Shoup3 1 IBM Research { Zurich, R¨uschlikon, Switzerland [email protected] 2 Bern University of Applied Sciences, Biel-Bienne, Switzerland, and University of Fribourg, Switzerland [email protected] 3 Department of Computer Science, New York University, USA [email protected] Abstract. Zero-knowledge proofs of knowledge (ZK-PoK) for discrete logarithms and related problems are indispensable for practical crypto- graphic protocols. Recently, Camenisch, Kiayias, and Yung provided a specification language (the CKY-language) for such protocols which al- lows for a modular design and protocol analysis: for every zero-knowledge proof specified in this language, protocol designers are ensured that there exists an efficient protocol which indeed proves the specified statement. However, the protocols resulting from their compilation techniques only satisfy the classical notion of ZK-PoK, which is not retained are when they used as building blocks for higher-level applications or composed with other protocols. This problem can be tackled by moving to the Universal Composability (UC) framework, which guarantees retention of security when composing protocols in arbitrary ways. While there exist generic transformations from Σ-protocols to UC-secure protocols, these transformation are often too inefficient for practice. In this paper we introduce a specification language akin to the CKY- language and a compiler such that the resulting protocols are UC-secure and efficient. To this end, we propose an extension of the UC-framework addressing the issue that UC-secure zero-knowledge proofs are by defini- tion proofs of knowledge, and state a special composition theorem which allows one to use the weaker { but more efficient and often sufficient { notion of proofs of membership in the UC-framework.
    [Show full text]
  • Key Confirmation and Adaptive Corruptions in the Protocol Security
    Key confirmation and adaptive corruptions in the protocol security logic Prateek Gupta and Vitaly Shmatikov The University of Texas at Austin Abstract. Cryptographic security for key exchange and secure session estab- lishment protocols is often defined in the so called “adaptive corruptions” model. Even if the adversary corrupts one of the participants in the middle of the proto- col execution and obtains the victim’s secrets such as the private signing key, the victim must be able to detect this and abort the protocol. This is usually achieved by adding a key confirmation message to the protocol. Conventional symbolic methods for protocol analysis assume unforgeability of digital signatures, and thus cannot be used to reason about security in the adaptive corruptions model. We present a symbolic protocol logic for reasoning about authentication and key confirmation in key exchange protocols. The logic is cryptographically sound: a symbolic proof of authentication and secrecy implies that the protocol is secure in the adaptive corruptions model. We illustrate our method by formally proving security of an authenticated Diffie-Hellman protocol with key confirmation. 1 Introduction The two dominant models for analysis of security protocols are the conventional cryptographic model, which aims to prove that the protocol is secure against any efficient adversarial algorithm, and the so called “Dolev-Yao” model, in which proofs are carried out in a symbolic logic or a process calculus. For many (but by no means all) cryptographic primitives, the Dolev-Yao abstraction is computationally sound, that is, symbolic proofs of security for protocols in which the primitive is replaced by its Dolev-Yao abstraction imply cryptographic security.
    [Show full text]