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Generalized discrete timed automata: decidable approximations for safety verification
- Theoretical Computer Science
"... Abstract. We consider generalized discrete timed automata with general linearrelations over clocks and parameterized constants as clock constraints and with parameterized durations. We look at three approximation techniques (i.e., the r-reset-bounded approximation, the B-bounded approximation, and t ..."
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Cited by 4 (4 self)
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Abstract. We consider generalized discrete timed automata with general linearrelations over clocks and parameterized constants as clock constraints and with parameterized durations. We look at three approximation techniques (i.e., the r-reset-bounded approximation, the B-bounded approximation, and the hB; ri-crossing-bounded approximation), and derive automata-theoretic characterizations of the binary reachability under these approximations. The characteriza-tions allow us to show that the safety analysis problem is decidable for generalized discrete timed automata with unit durations and for deterministic generalizeddiscrete timed automata with parameterized durations. An example specification written in ASTRAL is used to run a number of experiments using one of theapproximation techniques. 1 Introduction As a standard model for analyzing real-time systems, timed automata [3] have receivedenormous attention during the past decade. A timed automaton can be considered as a finite automaton augmented with a finite number of clocks. The clocks can be reset orprogress at the same rate, and can be tested against clock constraints in the form of clock regions (i.e., comparisons of a clock or the difference of two clocks against an integerconstant, e.g.,
Proof Assistance for Real-Time Systems Using an Interactive Theorem Prover
- 5th International AMAST Workshop on RealTime and Probabilistic Systems, LNCS
"... . This paper discusses the adaptation of the PVS theorem prover for performing analysis of real-time systems written in the ASTRAL formal specification language. A number of issues were encountered during the encoding of ASTRAL that are relevant to the encoding of many real-time specification la ..."
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Cited by 3 (0 self)
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. This paper discusses the adaptation of the PVS theorem prover for performing analysis of real-time systems written in the ASTRAL formal specification language. A number of issues were encountered during the encoding of ASTRAL that are relevant to the encoding of many real-time specification languages. These issues are presented as well as how they were handled in the ASTRAL encoding. A translator has been written that translates any ASTRAL specification into its corresponding PVS encoding. After performing the proofs of several systems using the encoding, PVS strategies have been developed to automate the proofs of certain types of properties. In addition, the encoding has been used as the basis for a transition sequence generator tool. 1 Introduction A real-time system is a system that must perform its actions within specified time bounds. With the advent of cheap processing power and increasingly sophisticated consumer demands, real-time systems have become commonplace ...
Formal Specification and Analysis of an e-Voting System. In:
- The 5th International Conference on Availability Reliability and Security, IEEE
, 2010
"... Abstract-Electronic voting systems are a perfect example of security-critical computing. One of the critical and complex parts of such systems is the voting process, which is responsible for correctly and securely storing intentions and actions of the voters. Unfortunately, recent studies revealed ..."
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Abstract-Electronic voting systems are a perfect example of security-critical computing. One of the critical and complex parts of such systems is the voting process, which is responsible for correctly and securely storing intentions and actions of the voters. Unfortunately, recent studies revealed that various evoting systems show serious specification, design, and implementation flaws. The application of formal specification and verification can greatly help to better understand the system requirements of e-voting systems by thoroughly specifying and analyzing the underlying assumptions and the security specific properties. This paper presents the specification and verification of the electronic voting process for the Election Systems & Software (ES&S) system. We used the ASTRAL language to specify the voting process of ES&S machines and the critical security requirements for the system. Proof obligations that verify that the specified system meets the critical requirements were automatically generated by the ASTRAL Software Development Environment (SDE). The PVS interactive theorem prover was then used to apply the appropriate proof strategies and discharge the proof obligations.
Decidable Approximations on Generalized and Parameterized Discrete Timed Automata
- COCOON'01, LNCS 2108
"... . We consider generalized discrete timed automata with general linear relations over clocks and parameterized constants as clock constraints and with parameterized durations. We look at three approximation techniques (i.e., the r-reset-bounded approximation, the B-bounded approximation, and the hB ..."
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Cited by 2 (2 self)
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. We consider generalized discrete timed automata with general linear relations over clocks and parameterized constants as clock constraints and with parameterized durations. We look at three approximation techniques (i.e., the r-reset-bounded approximation, the B-bounded approximation, and the hB; ri-crossing-bounded approximation), and derive automata-theoretic characterizations of the binary reachability under these approximations. The characterizations allow us to show that the safety analysis problem is decidable for generalized discrete timed automata with unit durations and for deterministic generalized discrete timed automata with parameterized durations. An example specification written in ASTRAL is used to run a number of experiments using one of the approximation techniques. 1
Formal analysis of attacks for e-voting system
- In CRiSIS ’09: Fourth international
, 2009
"... Abstract-Recently, the use of formal methods to specify and verify properties of electronic voting (e-voting) systems, with particular interest in security, verifiability, and anonymity, is getting much attention. Formal specification and verification of such systems can greatly help to better unde ..."
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Abstract-Recently, the use of formal methods to specify and verify properties of electronic voting (e-voting) systems, with particular interest in security, verifiability, and anonymity, is getting much attention. Formal specification and verification of such systems can greatly help to better understand the system requirements by thoroughly specifying and analyzing the underlying assumptions and security specific properties. Unfortunately, even though these systems have been formally verified to satisfy the desired system security requirements, they are still vulnerable to attack. In this paper we extend a formal specification of the ES&S voting system by specifying attacks that have been shown to successfully compromise the system. We believe that performing such analysis is important for two reasons: first, it allows us to discover some missing critical requirements for the specification and/or assumptions that were not met. Second, it allows us to derive mitigation or counter-measure strategies when the system behaves differently than it should. We used the ASTRAL language for the specification, and the verification is performed using the PVS tool.
Parallel Refinement Mechanisms
"... Refinement is a fundamental design technique that has often challenged the "formal methods" community. In most cases, mathematical elegance and proof manageability have been chosen over flexibility and freedom, which are often needed in practice to deal with unexpected or critical situatio ..."
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Refinement is a fundamental design technique that has often challenged the "formal methods" community. In most cases, mathematical elegance and proof manageability have been chosen over flexibility and freedom, which are often needed in practice to deal with unexpected or critical situations. The issue of refinement becomes even more critical when dealing with real-time systems where time analysis is a crucial factor. In this case, the literature exhibits only a few, fairly limited proposals. In this paper, we propose general refinement mechanisms for real-time systems that allow several types of implementation strategies to be specified in a fairly natural way. Not surprisingly, generality has a price in terms of complexity. In our approach, however, this price is paid only when necessary. Furthermore, the proof system is amenable both for traditional hand-proofs, based on human ingenuity and only partially formalized, and for fully formalized, tool-supported proofs. The following is...
Parallel Refinement Mechanisms for Real-Time Systems
- PROC. 3RD INT. CONF. ON FUNDAMENTAL APPROACHES TO SOFTWARE ENGINEERING
, 2000
"... Refinement is a fundamental design technique that has often challenged the "formal methods" community. In most cases, mathematical elegance and proof manageability have exhibited a deep trade-off with the flexibility and freedom that are often needed in practice to deal with unexpected ..."
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Refinement is a fundamental design technique that has often challenged the "formal methods" community. In most cases, mathematical elegance and proof manageability have exhibited a deep trade-off with the flexibility and freedom that are often needed in practice to deal with unexpected or critical situations. The issue of refinement becomes even more critical when dealing with real-time systems where time analysis is a crucial factor. In this case, the literature exhibits only a few, fairly limited proposals. In this paper, we propose highly general refinement mechanisms for real-time systems that allow several types of implementation strategies to be specified in a fairly natural way. Not surprisingly, generality has a price in terms of complexity. In our approach, however, this price is paid only when necessary. Furthermore, the proof system is amenable both for traditional hand-proofs, based on human ingenuity and only partially formalized, and for fully formalized, t...
Classification Schemes to Aid in the Analysis of Real-Time Systems
, 2000
"... This paper presents three sets of classification schemes for processes, properties, and transitions that can be used to assist in the analysis of real-time systems. These classification schemes are discussed in the context of ASTRAL, which is a formal specification language for real-time systems. Ei ..."
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This paper presents three sets of classification schemes for processes, properties, and transitions that can be used to assist in the analysis of real-time systems. These classification schemes are discussed in the context of ASTRAL, which is a formal specification language for real-time systems. Eight testbed systems were specified in ASTRAL, and their proofs were performed to determine proof patterns that occur most often. The specifications were then examined in an attempt to derive specific characteristics that could be used to statically identify each pattern within a specification. Once the classifications were obtained, they were then used to provide systematic guidance for analyzing real-time systems by directing the prover to the proof techniques most applicable to each proof pattern. This paper presents the set of classification schemes that were developed and discusses how they can be used to assist the proof process.
