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178
Universally composable security: A new paradigm for cryptographic protocols
, 2013
"... We present a general framework for representing cryptographic protocols and analyzing their security. The framework allows specifying the security requirements of practically any cryptographic task in a unified and systematic way. Furthermore, in this framework the security of protocols is preserved ..."
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Cited by 842 (43 self)
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We present a general framework for representing cryptographic protocols and analyzing their security. The framework allows specifying the security requirements of practically any cryptographic task in a unified and systematic way. Furthermore, in this framework the security of protocols is preserved under a general protocol composition operation, called universal composition. The proposed framework with its securitypreserving composition operation allows for modular design and analysis of complex cryptographic protocols from relatively simple building blocks. Moreover, within this framework, protocols are guaranteed to maintain their security in any context, even in the presence of an unbounded number of arbitrary protocol instances that run concurrently in an adversarially controlled manner. This is a useful guarantee, that allows arguing about the security of cryptographic protocols in complex and unpredictable environments such as modern communication networks.
Analysis of keyexchange protocols and their use for building secure channels
, 2001
"... Abstract. We present a formalism for the analysis of keyexchange protocols that combines previous definitional approaches and results in a definition of security that enjoys some important analytical benefits: (i) any keyexchange protocol that satisfies the security definition can be composed with ..."
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Cited by 328 (21 self)
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Abstract. We present a formalism for the analysis of keyexchange protocols that combines previous definitional approaches and results in a definition of security that enjoys some important analytical benefits: (i) any keyexchange protocol that satisfies the security definition can be composed with symmetric encryption and authentication functions to provide provably secure communication channels (as defined here); and (ii) the definition allows for simple modular proofs of security: one can design and prove security of keyexchange protocols in an idealized model where the communication links are perfectly authenticated, and then translate them using general tools to obtain security in the realistic setting of adversarycontrolled links. We exemplify the usability of our results by applying them to obtain the proof of two classes of keyexchange protocols, DiffieHellman and keytransport, authenticated via symmetric or asymmetric techniques. 1
Direct Anonymous Attestation
, 2004
"... This paper describes the direct anonymous attestation scheme (DAA). This scheme was adopted by the Trusted Computing Group as the method for remote authentication of a hardware module, called trusted platform module (TPM), while preserving the privacy of the user of the platform that contains the ..."
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Cited by 205 (21 self)
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This paper describes the direct anonymous attestation scheme (DAA). This scheme was adopted by the Trusted Computing Group as the method for remote authentication of a hardware module, called trusted platform module (TPM), while preserving the privacy of the user of the platform that contains the module. Direct anonymous attestation can be seen as a group signature without the feature that a signature can be opened, i.e., the anonymity is not revocable. Moreover, DAA allows for pseudonyms, i.e., for each signature a user (in agreement with the recipient of the signature) can decide whether or not the signature should be linkable to another signature. DAA furthermore allows for detection of "known" keys: if the DAA secret keys are extracted from a TPM and published, a verifier can detect that a signature was produced using these secret keys. The scheme is provably secure in the random oracle model under the strong RSA and the decisional Di#eHellman assumption.
Universally Composable Commitments
, 2001
"... We propose a new security measure for commitment protocols, called Universally Composable ..."
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Cited by 177 (10 self)
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We propose a new security measure for commitment protocols, called Universally Composable
Indifferentiability, impossibility results on reductions, and applications to the random oracle methodology
 Theory of Cryptography  TCC 2004, Lecture Notes in Computer Science
, 2004
"... Abstract. The goals of this paper are threefold. First we introduce and motivate a generalization of the fundamental concept of the indistinguishability of two systems, called indifferentiability. This immediately leads to a generalization of the related notion of reducibility of one system to anot ..."
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Cited by 96 (2 self)
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Abstract. The goals of this paper are threefold. First we introduce and motivate a generalization of the fundamental concept of the indistinguishability of two systems, called indifferentiability. This immediately leads to a generalization of the related notion of reducibility of one system to another. Second, we prove that indifferentiability is the necessary and sufficient condition on two systems S and T such that the security of any cryptosystem using T as a component is not affected when T is substituted by S. In contrast to indistinguishability, indifferentiability is applicable in settings where a possible adversary is assumed to have access to additional information about the internal state of the involved systems, for instance the public parameter selecting a member from a family of hash functions. Third, we state an easily verifiable criterion for a system U not to be reducible (according to our generalized definition) to another system V and, as an application, prove that a random oracle is not reducible to a weaker primitive, called asynchronous beacon, and also that an asynchronous beacon is not reducible to a finitelength random string. Each of these irreducibility results alone implies the main theorem of Canetti, Goldreich and Halevi stating that there exist cryptosystems that are secure in the random oracle model but for which replacing the random oracle by any implementation leads to an insecure cryptosystem. Key words. Indistinguishability, reductions, indifferentiability, security proofs, random oracle methodology, hash functions.
MerkleDamg˚ard Revisited: How to Construct a Hash Function
 Advances in Cryptology, Crypto 2005
"... The most common way of constructing a hash function (e.g., SHA1) is to iterate a compression function on the input message. The compression function is usually designed from scratch or made out of a blockcipher. In this paper, we introduce a new security notion for hashfunctions, stronger than col ..."
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Cited by 94 (8 self)
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The most common way of constructing a hash function (e.g., SHA1) is to iterate a compression function on the input message. The compression function is usually designed from scratch or made out of a blockcipher. In this paper, we introduce a new security notion for hashfunctions, stronger than collisionresistance. Under this notion, the arbitrary length hash function H must behave as a random oracle when the fixedlength building block is viewed as a random oracle or an ideal blockcipher. The key property is that if a particular construction meets this definition, then any cryptosystem proven secure assuming H is a random oracle remains secure if one plugs in this construction (still assuming that the underlying fixedlength primitive is ideal). In this paper, we show that the current design principle behind hash functions such as SHA1 and MD5 — the (strengthened) MerkleDamg˚ard transformation — does not satisfy this security notion. We provide several constructions that provably satisfy this notion; those new constructions introduce minimal changes to the plain MerkleDamg˚ard construction and are easily implementable in practice.
A General Composition Theorem for Secure Reactive Systems
 In TCC 2004
, 2004
"... We consider compositional properties of reactive systems that are secure in a cryptographic sense. We follow the wellknown simulatability approach of modern cryptography, i.e., the specification is an ideal system and a real system should in some sense simulate this ideal one. We show that if a ..."
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Cited by 78 (8 self)
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We consider compositional properties of reactive systems that are secure in a cryptographic sense. We follow the wellknown simulatability approach of modern cryptography, i.e., the specification is an ideal system and a real system should in some sense simulate this ideal one. We show that if a system consists of a polynomial number of arbitrary ideal subsystems such that each of them has a secure implementation in the sense of blackbox simulatability, then one can securely replace all ideal subsystems with their respective secure counterparts without destroying the blackbox simulatability relation. We further prove our theorem for universal simulatability by showing that blackbox simulatability implies universal simulatability under reasonable assumptions. We show all our results with concrete security.
Universally composable signature, certification, and authentication
 In CSFW 2004
, 2004
"... Recently some efforts were made towards capturing the security requirements from digital signature schemes as an ideal functionality within a composable security framework. This modeling of digital signatures potentially has some significant analytical advantages (such as enabling componentwise ana ..."
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Cited by 60 (9 self)
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Recently some efforts were made towards capturing the security requirements from digital signature schemes as an ideal functionality within a composable security framework. This modeling of digital signatures potentially has some significant analytical advantages (such as enabling componentwise analysis of complex systems that use signature schemes, as well as symbolic and automatable analysis of such systems). However, it turns out that formulating ideal functionalities that capture the properties expected from signature schemes in a way that is both sound and enjoys the above advantages is not a trivial task. This work has several contributions. We first correct some flaws in the definition of the ideal signature functionality of Canetti, 2001, and subsequent formulations. Next we provide a minimal formalization of “ideal certification authorities ” and show how authenticated communication can be obtained using ideal signatures and an ideal certification authority. This is done while guaranteeing full modularity (i.e., each component is analyzed as standalone), and in an unconditional and errorless way. This opens the door to symbolic and automated analysis of protocols for these tasks, in a way that is both modular and cryptographically sound.
Symmetric Encryption in Automatic Analyses for Confidentiality against Active Adversaries
, 2004
"... In this article we present a technique for static analysis, correct with respect to complexitytheoretic definitions of security, of cryptographic protocols for checking whether these protocols satisfy confidentiality properties. The approach is similar to Abadi and Rogaway  we define patterns fo ..."
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Cited by 58 (3 self)
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In this article we present a technique for static analysis, correct with respect to complexitytheoretic definitions of security, of cryptographic protocols for checking whether these protocols satisfy confidentiality properties. The approach is similar to Abadi and Rogaway  we define patterns for cryptographic protocols (they did it for formal expressions), such that the protocol is secure iff the patterns are. We then statically analyse the patterns, they should be easier to analyse than the protocols themselves. We consider symmetric encryption as the cryptographic primitive in protocols. Handling this primitive has so far received comparatively less attention in approaches striving to unite the formal and computational models of cryptography.