P. Malacaria, M. Khouzani, C. Pasareanu, Quoc-Sang Phan, K. S. Luckow
In this paper we describe symbolic side-channel analysis techniques for detecting and quantifying information leakage, given in terms of Shannon and min-entropy. Measuring the precise leakage is challenging due to the randomness and noise often present in program executions and side-channel observations. We account for this noise by introducing additional (symbolic) program inputs which are interpreted probabilistically, using symbolic execution with parametrized model counting. We also explore a sampling approach for increased scalability. In contrast to typical Monte Carlo techniques, our approach works by sampling symbolic paths, representing multiple concrete paths, and uses pruning to accelerate computation and guarantee convergence to the optimal results. A key novelty of our approach is to provide bounds on the leakage that are provably under- and over-approximating the exact leakage. We implemented the techniques in the Symbolic PathFinder tool and demonstrate them on Java programs.
{"title":"Symbolic Side-Channel Analysis for Probabilistic Programs","authors":"P. Malacaria, M. Khouzani, C. Pasareanu, Quoc-Sang Phan, K. S. Luckow","doi":"10.1109/CSF.2018.00030","DOIUrl":"https://doi.org/10.1109/CSF.2018.00030","url":null,"abstract":"In this paper we describe symbolic side-channel analysis techniques for detecting and quantifying information leakage, given in terms of Shannon and min-entropy. Measuring the precise leakage is challenging due to the randomness and noise often present in program executions and side-channel observations. We account for this noise by introducing additional (symbolic) program inputs which are interpreted probabilistically, using symbolic execution with parametrized model counting. We also explore a sampling approach for increased scalability. In contrast to typical Monte Carlo techniques, our approach works by sampling symbolic paths, representing multiple concrete paths, and uses pruning to accelerate computation and guarantee convergence to the optimal results. A key novelty of our approach is to provide bounds on the leakage that are provably under- and over-approximating the exact leakage. We implemented the techniques in the Symbolic PathFinder tool and demonstrate them on Java programs.","PeriodicalId":417032,"journal":{"name":"2018 IEEE 31st Computer Security Foundations Symposium (CSF)","volume":"45 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130588259","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Attack trees are a well-recognized formalism for security modeling and analysis, but in this work we tackle a problem that has not yet been addressed by the security or formal methods community – namely guided design of attack trees. The objective of the framework presented in this paper is to support a security expert in the process of designing a pertinent attack tree for a given system. In contrast to most of existing approaches for attack trees, our framework contains an explicit model of the real system to be analyzed, formalized as a transition system that may contain quantitative information. The leaves of our attack trees are labeled with reachability goals in the transition system and the attack tree semantics is expressed in terms of traces of the system. The main novelty of the proposed framework is that we start with an attack tree which is not fully refined and by exhibiting paths in the system that are optimal with respect to the quantitative information, we are able to suggest to the security expert which parts of the tree contribute to optimal attacks and should therefore be developed further. Such useful parts of the tree are determined by solving a satisfiability problem in propositional logic.
{"title":"Guided Design of Attack Trees: A System-Based Approach","authors":"Maxime Audinot, S. Pinchinat, Barbara Kordy","doi":"10.1109/CSF.2018.00012","DOIUrl":"https://doi.org/10.1109/CSF.2018.00012","url":null,"abstract":"Attack trees are a well-recognized formalism for security modeling and analysis, but in this work we tackle a problem that has not yet been addressed by the security or formal methods community – namely guided design of attack trees. The objective of the framework presented in this paper is to support a security expert in the process of designing a pertinent attack tree for a given system. In contrast to most of existing approaches for attack trees, our framework contains an explicit model of the real system to be analyzed, formalized as a transition system that may contain quantitative information. The leaves of our attack trees are labeled with reachability goals in the transition system and the attack tree semantics is expressed in terms of traces of the system. The main novelty of the proposed framework is that we start with an attack tree which is not fully refined and by exhibiting paths in the system that are optimal with respect to the quantitative information, we are able to suggest to the security expert which parts of the tree contribute to optimal attacks and should therefore be developed further. Such useful parts of the tree are determined by solving a satisfiability problem in propositional logic.","PeriodicalId":417032,"journal":{"name":"2018 IEEE 31st Computer Security Foundations Symposium (CSF)","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131052014","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We present the first computationally sound symbolic analysis of Yao's garbled circuit construction for secure two party computation. Our results include an extension of the symbolic language for cryptographic expressions from previous work on computationally sound symbolic analysis, and a soundness theorem for this extended language. We then demonstrate how the extended language can be used to formally specify not only the garbled circuit construction, but also the formal (symbolic) simulator required by the definition of security. The correctness of the simulation is proved in a purely syntactical way, within the symbolic model of cryptography, and then translated into a concrete computational indistinguishability statement via our general computational soundness theorem. We also implement our symbolic security framework and the garbling scheme in Haskell, and our experiment shows that the symbolic analysis performs well and can be done within several seconds even for large circuits that are useful for real world applications.
{"title":"Symbolic Security of Garbled Circuits","authors":"Baiyu Li, Daniele Micciancio","doi":"10.1109/CSF.2018.00018","DOIUrl":"https://doi.org/10.1109/CSF.2018.00018","url":null,"abstract":"We present the first computationally sound symbolic analysis of Yao's garbled circuit construction for secure two party computation. Our results include an extension of the symbolic language for cryptographic expressions from previous work on computationally sound symbolic analysis, and a soundness theorem for this extended language. We then demonstrate how the extended language can be used to formally specify not only the garbled circuit construction, but also the formal (symbolic) simulator required by the definition of security. The correctness of the simulation is proved in a purely syntactical way, within the symbolic model of cryptography, and then translated into a concrete computational indistinguishability statement via our general computational soundness theorem. We also implement our symbolic security framework and the garbling scheme in Haskell, and our experiment shows that the symbolic analysis performs well and can be done within several seconds even for large circuits that are useful for real world applications.","PeriodicalId":417032,"journal":{"name":"2018 IEEE 31st Computer Security Foundations Symposium (CSF)","volume":"26 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116690164","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Security of cryptographic schemes is traditionally measured as the inability of resource-constrained adversaries to violate a desired security goal. The security argument usually relies on a sound design of the underlying components. Arguably, one of the most devastating failures of this approach can be observed when considering adversaries such as intelligence agencies that can influence the design, implementation, and standardization of cryptographic primitives. While the most prominent example of cryptographic backdoors is NIST's Dual_EC_DRBG, believing that such attempts have ended there is naive. Security of many cryptographic tasks, such as digital signatures, pseudorandom generation, and password protection, crucially relies on the security of hash functions. In this work, we consider the question of how backdoors can endanger security of hash functions and, especially, if and how we can thwart such backdoors. We particularly focus on immunizing arbitrarily backdoored versions of HMAC (RFC 2104) and the hash-based key derivation function HKDF (RFC 5869), which are widely deployed in critical protocols such as TLS. We give evidence that the weak pseudorandomness property of the compression function in the hash function is in fact robust against backdooring. This positive result allows us to build a backdoor-resistant pseudorandom function, i.e., a variant of HMAC, and we show that HKDF can be immunized against backdoors at little cost. Unfortunately, we also argue that safe-guarding unkeyed hash functions against backdoors is presumably hard.
{"title":"Backdoored Hash Functions: Immunizing HMAC and HKDF","authors":"M. Fischlin, Christian Janson, Sogol Mazaheri","doi":"10.1109/CSF.2018.00015","DOIUrl":"https://doi.org/10.1109/CSF.2018.00015","url":null,"abstract":"Security of cryptographic schemes is traditionally measured as the inability of resource-constrained adversaries to violate a desired security goal. The security argument usually relies on a sound design of the underlying components. Arguably, one of the most devastating failures of this approach can be observed when considering adversaries such as intelligence agencies that can influence the design, implementation, and standardization of cryptographic primitives. While the most prominent example of cryptographic backdoors is NIST's Dual_EC_DRBG, believing that such attempts have ended there is naive. Security of many cryptographic tasks, such as digital signatures, pseudorandom generation, and password protection, crucially relies on the security of hash functions. In this work, we consider the question of how backdoors can endanger security of hash functions and, especially, if and how we can thwart such backdoors. We particularly focus on immunizing arbitrarily backdoored versions of HMAC (RFC 2104) and the hash-based key derivation function HKDF (RFC 5869), which are widely deployed in critical protocols such as TLS. We give evidence that the weak pseudorandomness property of the compression function in the hash function is in fact robust against backdooring. This positive result allows us to build a backdoor-resistant pseudorandom function, i.e., a variant of HMAC, and we show that HKDF can be immunized against backdoors at little cost. Unfortunately, we also argue that safe-guarding unkeyed hash functions against backdoors is presumably hard.","PeriodicalId":417032,"journal":{"name":"2018 IEEE 31st Computer Security Foundations Symposium (CSF)","volume":"171 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121794360","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Many high-level security requirements are about the allowed flow of information in programs, but are difficult to make precise because they involve selective downgrading. Quite a few mutually incompatible and ad-hoc approaches have been proposed for specifying and enforcing downgrading policies. Prior surveys of these approaches have not provided a unifying technical framework. Notions from epistemic logic have emerged as a good approach to policy semantics but are considerably removed from well developed static and dynamic enforcement techniques. We develop a unified framework for expressing, giving meaning and enforcing information downgrading policies that builds on commonly known and widely deployed concepts and techniques, especially static and dynamic assertion checking. These concepts should make information flow accessible and enable developers without special training to specify precise policies. The unified framework allows to directly compare different policy specification styles and enforce them by leveraging existing techniques.
{"title":"Assuming You Know: Epistemic Semantics of Relational Annotations for Expressive Flow Policies","authors":"A. Chudnov, D. Naumann","doi":"10.1109/CSF.2018.00021","DOIUrl":"https://doi.org/10.1109/CSF.2018.00021","url":null,"abstract":"Many high-level security requirements are about the allowed flow of information in programs, but are difficult to make precise because they involve selective downgrading. Quite a few mutually incompatible and ad-hoc approaches have been proposed for specifying and enforcing downgrading policies. Prior surveys of these approaches have not provided a unifying technical framework. Notions from epistemic logic have emerged as a good approach to policy semantics but are considerably removed from well developed static and dynamic enforcement techniques. We develop a unified framework for expressing, giving meaning and enforcing information downgrading policies that builds on commonly known and widely deployed concepts and techniques, especially static and dynamic assertion checking. These concepts should make information flow accessible and enable developers without special training to specify precise policies. The unified framework allows to directly compare different policy specification styles and enforce them by leveraging existing techniques.","PeriodicalId":417032,"journal":{"name":"2018 IEEE 31st Computer Security Foundations Symposium (CSF)","volume":"17 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115306898","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We put forward the notion of self-guarding cryptographic protocols as a countermeasure to algorithm substitution attacks. Such self-guarding protocols can prevent undesirable leakage by subverted algorithms if one has the guarantee that the system has been properly working in an initialization phase. Unlike detection-based solutions they thus proactively thwart attacks, and unlike reverse firewalls they do not assume an online external party. We present constructions of basic primitives for (public-key and private-key) encryption and for signatures. We also argue that the model captures attacks with malicious hardware tokens and show how to self-guard a PUF-based key exchange protocol.
{"title":"Self-Guarding Cryptographic Protocols against Algorithm Substitution Attacks","authors":"M. Fischlin, Sogol Mazaheri","doi":"10.1109/CSF.2018.00013","DOIUrl":"https://doi.org/10.1109/CSF.2018.00013","url":null,"abstract":"We put forward the notion of self-guarding cryptographic protocols as a countermeasure to algorithm substitution attacks. Such self-guarding protocols can prevent undesirable leakage by subverted algorithms if one has the guarantee that the system has been properly working in an initialization phase. Unlike detection-based solutions they thus proactively thwart attacks, and unlike reverse firewalls they do not assume an online external party. We present constructions of basic primitives for (public-key and private-key) encryption and for signatures. We also argue that the model captures attacks with malicious hardware tokens and show how to self-guard a PUF-based key exchange protocol.","PeriodicalId":417032,"journal":{"name":"2018 IEEE 31st Computer Security Foundations Symposium (CSF)","volume":"52 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128836358","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
M. Alvim, K. Chatzikokolakis, C. Palamidessi, A. Pazii
Local differential privacy (LPD) is a distributed variant of differential privacy (DP) in which the obfuscation of the sensitive information is done at the level of the individual records, and in general it is used to sanitize data that are collected for statistical purposes. LPD has the advantage it does not need to assume a trusted third party. On the other hand LDP in general requires more noise than DP to achieve the same level of protection, with negative consequences on the utility. In practice, utility becomes acceptable only on very large collections of data, and this is the reason why LDP is especially successful among big companies such as Apple and Google, which can count on a huge number of users. In this talk, we propose a variant of LDP suitable for metric spaces, such as location data or energy consumption data, and we show that it provides a much higher utility for the same level of privacy. Furthermore, we discuss algorithms to extract the best possible statistical information from the data obfuscated with this metric variant of LDP.
{"title":"Invited Paper: Local Differential Privacy on Metric Spaces: Optimizing the Trade-Off with Utility","authors":"M. Alvim, K. Chatzikokolakis, C. Palamidessi, A. Pazii","doi":"10.1109/CSF.2018.00026","DOIUrl":"https://doi.org/10.1109/CSF.2018.00026","url":null,"abstract":"Local differential privacy (LPD) is a distributed variant of differential privacy (DP) in which the obfuscation of the sensitive information is done at the level of the individual records, and in general it is used to sanitize data that are collected for statistical purposes. LPD has the advantage it does not need to assume a trusted third party. On the other hand LDP in general requires more noise than DP to achieve the same level of protection, with negative consequences on the utility. In practice, utility becomes acceptable only on very large collections of data, and this is the reason why LDP is especially successful among big companies such as Apple and Google, which can count on a huge number of users. In this talk, we propose a variant of LDP suitable for metric spaces, such as location data or energy consumption data, and we show that it provides a much higher utility for the same level of privacy. Furthermore, we discuss algorithms to extract the best possible statistical information from the data obfuscated with this metric variant of LDP.","PeriodicalId":417032,"journal":{"name":"2018 IEEE 31st Computer Security Foundations Symposium (CSF)","volume":"57 6 Suppl 1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123385633","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In random sample voting, only a randomly chosen subset of all eligible voters are selected to vote. This poses new security challenges for the voting protocol used. In particular, one must ensure that the chosen voters were randomly selected while preserving their anonymity. Moreover, the small number of selected voters leaves little room for error and only a few manipulations of the votes may significantly change the outcome. We propose Alethea, the first random sample voting protocol that satisfies end-to-end verifiability and receipt-freeness. Our protocol makes explicit the distinction between human voters and their devices. This allows for more fine-grained statements about the required capabilities and trust assumptions of each agent than is possible in previous work. We define new security properties related to the randomness and anonymity of the sample group and the probability of undetected manipulations. We prove correctness of the protocol and its properties both using traditional paper and pen proofs and with tool support.
{"title":"Alethea: A Provably Secure Random Sample Voting Protocol","authors":"D. Basin, S. Radomirovic, Lara Schmid","doi":"10.1109/CSF.2018.00028","DOIUrl":"https://doi.org/10.1109/CSF.2018.00028","url":null,"abstract":"In random sample voting, only a randomly chosen subset of all eligible voters are selected to vote. This poses new security challenges for the voting protocol used. In particular, one must ensure that the chosen voters were randomly selected while preserving their anonymity. Moreover, the small number of selected voters leaves little room for error and only a few manipulations of the votes may significantly change the outcome. We propose Alethea, the first random sample voting protocol that satisfies end-to-end verifiability and receipt-freeness. Our protocol makes explicit the distinction between human voters and their devices. This allows for more fine-grained statements about the required capabilities and trust assumptions of each agent than is possible in previous work. We define new security properties related to the randomness and anonymity of the sample group and the probability of undetected manipulations. We prove correctness of the protocol and its properties both using traditional paper and pen proofs and with tool support.","PeriodicalId":417032,"journal":{"name":"2018 IEEE 31st Computer Security Foundations Symposium (CSF)","volume":"7 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115240735","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
During the secure boot process for a trusted execution environment, the processor must provide a chain of certificates to the remote client demonstrating that their secure container was established as specified. This certificate chain is rooted at the hardware manufacturer who is responsible for constructing chips according to the correct specification and provisioning them with key material. We consider a semi-honest manufacturer who is assumed to construct chips correctly, but may attempt to obtain knowledge of client private keys during the process. Using the RISC-V Rocket chip architecture as a base, we design, document, and implement an attested execution processor that does not require secure non-volatile memory, nor a private key explicitly assigned by the manufacturer. Instead, the processor derives its cryptographic identity from manufacturing variation measured by a Physical Unclonable Function (PUF). Software executed by a bootloader built into the processor transforms the PUF output into an elliptic curve key pair. The (re)generated private key is used to sign trusted portions of the boot image, and is immediately destroyed. The platform can therefore provide attestations about its state to remote clients. Reliability and security of PUF keys are ensured through the use of a trapdoor computational fuzzy extractor. We present detailed evaluation results for secure boot and attestation by a client of a Rocket chip implementation on a Xilinx Zynq 7000 FPGA.
{"title":"Invited Paper: Secure Boot and Remote Attestation in the Sanctum Processor","authors":"Ilia A. Lebedev, Kyle Hogan, S. Devadas","doi":"10.1109/CSF.2018.00011","DOIUrl":"https://doi.org/10.1109/CSF.2018.00011","url":null,"abstract":"During the secure boot process for a trusted execution environment, the processor must provide a chain of certificates to the remote client demonstrating that their secure container was established as specified. This certificate chain is rooted at the hardware manufacturer who is responsible for constructing chips according to the correct specification and provisioning them with key material. We consider a semi-honest manufacturer who is assumed to construct chips correctly, but may attempt to obtain knowledge of client private keys during the process. Using the RISC-V Rocket chip architecture as a base, we design, document, and implement an attested execution processor that does not require secure non-volatile memory, nor a private key explicitly assigned by the manufacturer. Instead, the processor derives its cryptographic identity from manufacturing variation measured by a Physical Unclonable Function (PUF). Software executed by a bootloader built into the processor transforms the PUF output into an elliptic curve key pair. The (re)generated private key is used to sign trusted portions of the boot image, and is immediately destroyed. The platform can therefore provide attestations about its state to remote clients. Reliability and security of PUF keys are ensured through the use of a trapdoor computational fuzzy extractor. We present detailed evaluation results for secure boot and attestation by a client of a Rocket chip implementation on a Xilinx Zynq 7000 FPGA.","PeriodicalId":417032,"journal":{"name":"2018 IEEE 31st Computer Security Foundations Symposium (CSF)","volume":"78 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115742345","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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