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Soundness of formal encryption in the presence of active adversaries
 In Proc. 1st Theory of Cryptography Conference (TCC), volume 2951 of LNCS
, 2004
"... Abstract. We present a general method to prove security properties of cryptographic protocols against active adversaries, when the messages exchanged by the honest parties are arbitrary expressions built using encryption and concatenation operations. The method allows to express security properties ..."
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Cited by 97 (11 self)
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Abstract. We present a general method to prove security properties of cryptographic protocols against active adversaries, when the messages exchanged by the honest parties are arbitrary expressions built using encryption and concatenation operations. The method allows to express security properties and carry out proofs using a simple logic based language, where messages are represented by syntactic expressions, and does not require dealing with probability distributions or asymptotic notation explicitly. Still, we show that the method is sound, meaning that logic statements can be naturally interpreted in the computational setting in such a way that if a statement holds true for any abstract (symbolic) execution of the protocol in the presence of a DolevYao adversary, then its computational interpretation is also correct in the standard computational model where the adversary is an arbitrary probabilistic polynomial time program. This is the first paper providing a simple framework for translating security proofs from the logic setting to the standard computational setting for the case of powerful active adversaries that have total control of the communication network. 1
Symmetric Encryption in a Simulatable DolevYao Style Cryptographic Library
 In Proc. 17th IEEE Computer Security Foundations Workshop (CSFW
, 2004
"... Recently we solved the longstanding open problem of justifying a DolevYao type model of cryptography as used in virtually all automated protocol provers under active attacks. The justification was done by defining an ideal system handling DolevYaostyle terms and a cryptographic realization wi ..."
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Cited by 72 (20 self)
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Recently we solved the longstanding open problem of justifying a DolevYao type model of cryptography as used in virtually all automated protocol provers under active attacks. The justification was done by defining an ideal system handling DolevYaostyle terms and a cryptographic realization with the same user interface, and by showing that the realization is as secure as the ideal system in the sense of reactive simulatability. This definition encompasses arbitrary active attacks and enjoys general composition and propertypreservation properties. Security holds in the standard model of cryptography and under standard assumptions of adaptively secure primitives.
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 57 (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.
Relating Symbolic and Cryptographic Secrecy
 IN PROC. IEEE SYMPOSIUM ON SECURITY AND PRIVACY
, 2004
"... We investigate the relation between symbolic and cryptographic secrecy properties for cryptographic protocols. Symbolic secrecy of payload messages or exchanged keys is arguably the most important notion of secrecy shown with automated proof tools. It means that an adversary restricted to symboli ..."
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Cited by 48 (9 self)
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We investigate the relation between symbolic and cryptographic secrecy properties for cryptographic protocols. Symbolic secrecy of payload messages or exchanged keys is arguably the most important notion of secrecy shown with automated proof tools. It means that an adversary restricted to symbolic operations on terms can never get the entire considered object into its knowledge set. Cryptographic secrecy essentially
Universally composable symbolic analysis of mutual authentication and keyexchange protocols
 In Shai Halevi and Tal Rabin, editors, TCC, volume 3876 of LNCS
, 2006
"... Abstract. Symbolic analysis of cryptographic protocols is dramatically simpler than fullfledged cryptographic analysis. In particular, it is simple enough to be automated. However, symbolic analysis does not, by itself, provide any cryptographic soundness guarantees. Following recent work on crypto ..."
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Cited by 48 (3 self)
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Abstract. Symbolic analysis of cryptographic protocols is dramatically simpler than fullfledged cryptographic analysis. In particular, it is simple enough to be automated. However, symbolic analysis does not, by itself, provide any cryptographic soundness guarantees. Following recent work on cryptographically sound symbolic analysis, we demonstrate how DolevYao style symbolic analysis can be used to assert the security of cryptographic protocols within the universally composable (UC) security framework. Consequently, our methods enable security analysis that is completely symbolic, and at the same time cryptographically sound with strong composability properties. More specifically, we concentrate on mutual authentication and keyexchange protocols. We restrict attention to protocols that use publickey encryption as their only cryptographic primitive and have a specific restricted format. We define a mapping from such protocols to DolevYao style symbolic protocols, and show that the symbolic protocol satisfies a certain symbolic criterion if and only if the corresponding cryptographic protocol is UCsecure. For mutual authentication, our symbolic criterion is similar to the traditional DolevYao criterion. For key exchange, we demonstrate that the traditional DolevYao style symbolic criterion is insufficient, and formulate an adequate symbolic criterion. Finally, to demonstrate the viability of our treatment, we use an existing tool to automatically verify whether some prominent keyexchange protocols are UCsecure. 1
Towards plaintextaware publickey encryption without random oracles
 Advances in Cryptology – Asiacrypt 2004, volume 3329 of Lecture Notes in Computer Science
, 2004
"... Abstract. We consider the problem of defining and achieving plaintextaware encryption without random oracles in the classical publickey model. We provide definitions for a hierarchy of notions of increasing strength: PA0, PA1 and PA2, chosen so that PA1+INDCPA → INDCCA1 and PA2+INDCPA → INDCCA2 ..."
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Cited by 47 (0 self)
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Abstract. We consider the problem of defining and achieving plaintextaware encryption without random oracles in the classical publickey model. We provide definitions for a hierarchy of notions of increasing strength: PA0, PA1 and PA2, chosen so that PA1+INDCPA → INDCCA1 and PA2+INDCPA → INDCCA2. Towards achieving the new notions of plaintext awareness, we show that a scheme due to Damg˚ard [12], denoted DEG, and the “lite ” version of the CramerShoup scheme [11], denoted CSlite, are both PA0 under the DHK0 assumption of [12], and PA1 under an extension of this assumption called DHK1. As a result, DEG is the most efficient proven INDCCA1 scheme known. 1
Soundness of formal encryption in the presence of keycycles
 In Proc. 10th European Symposium on Research in Computer Security (ESORICS’05), volume 3679 of LNCS
, 2005
"... Abstract. Both the formal and the computational models of cryptography contain the notion of message equivalence or indistinguishability. An encryption scheme provides soundness for indistinguishability if, when mapping formal messages into the computational model, equivalent formal messages are map ..."
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Cited by 45 (5 self)
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Abstract. Both the formal and the computational models of cryptography contain the notion of message equivalence or indistinguishability. An encryption scheme provides soundness for indistinguishability if, when mapping formal messages into the computational model, equivalent formal messages are mapped to indistinguishable computational distributions. Previous soundness results are limited in that they do not apply when keycycles are present. We demonstrate that an encryption scheme provides soundness in the presence of keycycles if it satisfies the recentlyintroduced notion of keydependent message (KDM) security. We also show that soundness in the presence of keycycles (and KDM security) neither implies nor is implied by security against chosen ciphertext attack (CCA2). Therefore, soundness for keycycles is possible using a new notion of computational security, not possible using previous such notions, and the relationship between the formal and computational models extends beyond chosenciphertext security. 1
A cryptographically sound security proof of the NeedhamSchroederLowe publickey protocol
 JOURNAL ON SELECTED AREAS IN COMMUN.
, 2004
"... We present a cryptographically sound security proof of the wellknown NeedhamSchroederLowe publickey protocol for entity authentication. This protocol was previously only proved over unfounded abstractions from cryptography. We show that it is secure against arbitrary active attacks if it is imp ..."
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Cited by 39 (15 self)
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We present a cryptographically sound security proof of the wellknown NeedhamSchroederLowe publickey protocol for entity authentication. This protocol was previously only proved over unfounded abstractions from cryptography. We show that it is secure against arbitrary active attacks if it is implemented using standard provably secure cryptographic primitives. Nevertheless, our proof does not have to deal with the probabilistic aspects of cryptography and is hence in the scope of current automated proof tools. We achieve this by exploiting a recently proposed DolevYaostyle cryptographic library with a provably secure cryptographic implementation. Besides establishing the cryptographic security of the NeedhamSchroederLowe protocol, our result exemplifies the potential of this cryptographic library and paves the way for the cryptographically sound verification of security protocols by automated proof tools.
Cryptographically Sound Theorem Proving
 In Proc. 19th IEEE CSFW
, 2006
"... We describe a faithful embedding of the DolevYao model of Backes, Pfitzmann, and Waidner (CCS 2003) in the theorem prover Isabelle/HOL. This model is cryptographically sound in the strong sense of reactive simulatability/UC, which essentially entails the preservation of arbitrary security proper ..."
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Cited by 33 (10 self)
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We describe a faithful embedding of the DolevYao model of Backes, Pfitzmann, and Waidner (CCS 2003) in the theorem prover Isabelle/HOL. This model is cryptographically sound in the strong sense of reactive simulatability/UC, which essentially entails the preservation of arbitrary security properties under active attacks and in arbitrary protocol environments. The main challenge in designing a practical formalization of this model is to cope with the complexity of providing such strong soundness guarantees. We reduce this complexity by abstracting the model into a sound, lightweight formalization that enables both concise property specifications and efficient application of our proof strategies and their supporting proof tools. This yields the first toolsupported framework for symbolically verifying security protocols that enjoys the strong cryptographic soundness guarantees provided by reactive simulatability/UC. As a proof of concept, we have proved the security of the NeedhamSchroederLowe protocol using our framework.
A cryptographically sound DolevYao style security proof of the OtwayRees protocol
 In Proc. 9th European Symposium on Research in Computer Security (ESORICS
, 2004
"... We present the first cryptographically sound DolevYaostyle security proof of a comprehensive electronic payment system. The payment system is a slightly simplified variant of the 3KP payment system and comprises a variety of different security requirements ranging from basic ones like the impossibi ..."
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Cited by 25 (10 self)
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We present the first cryptographically sound DolevYaostyle security proof of a comprehensive electronic payment system. The payment system is a slightly simplified variant of the 3KP payment system and comprises a variety of different security requirements ranging from basic ones like the impossibility of unauthorized payments to more sophisticated properties like disputability. We show that the payment system is secure against arbitrary active attacks, including arbitrary concurrent protocol runs and arbitrary manipulation of bitstrings within polynomial time if the protocol is implemented using provably secure cryptographic primitives. Although we achieve security under cryptographic definitions, our proof does not have to deal with probabilistic aspects of cryptography and is hence within the scope of current proof tools. The reason is that we exploit a recently proposed DolevYaostyle cryptographic library with a provably secure cryptographic implementation. Together with composition and preservation theorems of the underlying model, this allows us to perform the actual proof effort in a deterministic setting corresponding to a slightly extended DolevYao model. 1.