Security-critical Systems Research Articles

Run-Time Security Traceability for Evolving Systems

Security-critical systems are challenging to design and implement correctly and securely. A lot of vulnerabilities have been found in current software systems both at the specification and the implementation levels. This paper presents a comprehensive approach for model-based security assurance. Initially, it allows one to formally verify the design models against high-level security requirements such as secrecy and authentication on the specification level, and helps to ensure that their implementation adheres to these properties, if they express a system's run-time behaviour. As such, it provides a traceability link from the design model to its implementation by which the actual system can then be verified against the model while it executes. This part of our approach relies on a technique also known as run-time verification. The extra effort for it is small as most of the computation is automated; however, additional resources at run-time may be required. If during run-time verification a security weakness is uncovered, it can be removed using aspect-oriented security hardening transformations. Therefore, this approach also supports the evolution of software since the traceability mapping is updated when refactoring operations are regressively performed using our tool-supported refactoring technique. The proposed method has been applied to the Java-based implementation Jessie of the Internet security protocol SSL, in which a security weakness was detected and fixed using our approach. We also explain how the traceability link can be transformed to the official implementation of the Java secure sockets extension that was recently made open source by Sun.

On the Role of Formal Methods in Software Certification: An Experience Report

This paper describes how formal methods were used to produce evidence in a certification, based on the Common Criteria, of a security-critical software system. The evidence included a top level specification (TLS) of the security-relevant software behavior, a formal statement of the required security properties, proofs that the specification satisfied the properties, and a demonstration that the source code, which had been annotated with preconditions and postconditions, was a refinement of the TLS. The paper also describes those aspects of our approach which were most effective and research that could significantly increase the effectiveness of formal methods in software certification.

A domain-specific language for cryptographic protocols based on streams

Developing security-critical systems is difficult and there are many well-known examples of security weaknesses exploited in practice. Thus a sound methodology supporting secure systems development is urgently needed. In particular, an important missing link in the construction of secure systems is finding a practical way to create reliably secure crypto protocol implementations. We present an approach that aims to address this need by making use of a domain-specific language for crypto protocol implementations. One can use this language to construct a compact and precise yet executable representation of a cryptographic protocol. This high-level program can be verified against the security goals using automated theorem provers for first order logic. One can then use it to provide assurance for legacy implementations of crypto protocols by generating test-cases.

Model-based Security Testing Using UMLsec: A Case Study

Designing and implementing security-critical systems correctly is very difficult. In practice, most vulnerabilities arise from bugs in implementations. We present work towards systematic specification-based testing of security-critical systems based on UMLsec models. We show how to systematically generate test sequences for security properties based on the model that can be used to test the implementation for vulnerabilities. We explain our method at the example of a part of the Common Electronic Purse Specifications (CEPS), a candidate for an international electronic purse standard.

High-Level Side-Channel Attack Modeling and Simulation for Security-Critical Systems on Chips

The design flow of a digital cryptographic device must take into account the evaluation of its security against attacks based on side channels observation. The adoption of high level countermeasures, as well as the verification of the feasibility of new attacks, presently require the execution of time-consuming physical measurements on the prototype product or the simulation at a low abstraction level. Starting from these assumptions, we developed an exploration approach centered on high level simulation, in order to evaluate the actual implementation of a cryptographic algorithm, being it software or hardware based. The simulation is performed within a unified tool based on SystemC, that can model a software implementation running on a microprocessor-based architecture or a dedicated hardware implementation as well as mixed software-hardware implementations with cycle-accurate resolution. Here we describe the tool and provide a large set of design explorations and characterizations based on actual implementations of the AES cryptographic algorithm, demonstrating how the execution of a large set of experiments allowed by the fast simulation engine can lead to important improvements in the knowledge and the identification of the weaknesses in cryptographic algorithm implementations.

Identification of safety and security critical systems and activities

There are many initiatives taken to identify safety and security critical systems and activities, at different levels and in different contexts, ranging from infrastructures at the societal level to equipment on the production plant level. Different approaches are implemented to define the critical systems and activities. Some of these relate to vulnerabilities, others incorporate the probability dimension and are risk based. We also see approaches taking into account values of the decision-maker and relevant stakeholders. In this paper, we discuss the rationale for these approaches. Is vulnerability an adequate measure to be used as a basis for determining criticality? Is it meaningful to specify safety and security critical systems and activities without addressing risk? How should we take into account the limitations of the risk assessments? Should we extend the concept of criticality to also cover utility aspects? We bring new insights into the discussion by being precise on the key risk concepts—including uncertainty, probability and expected value—and considering alternative risk perspectives. A novel approach is suggested based on expected values and uncertainties in underlying phenomena and processes. Our main concern is activities with potential severe consequences and large uncertainties.

Cryptographically-masked flows

Cryptographic operations are essential for many security-critical systems. Reasoning about information flow in such systems is challenging because typical (noninterference-based) information-flow definitions allow no flow from secret to public data. Unfortunately, this implies that programs with encryption are ruled out because encrypted output depends on secret inputs: the plaintext and the key. However, it is desirable to allow flows arising from encryption with secret keys provided that the underlying cryptographic algorithm is strong enough. In this article we conservatively extend the noninterference definition to allow safe encryption, decryption, and key generation. To illustrate the usefulness of this approach, we propose (and implement) a type system that guarantees noninterference for a small imperative language with primitive cryptographic operations. The type system prevents dangerous program behavior (e.g., giving away a secret key or confusing keys and nonkeys), which we exemplify with secure implementations of cryptographic protocols. Because the model is based on a standard noninterference property, it allows us to develop some natural extensions. In particular, we consider public-key cryptography and integrity, which accommodate reasoning about primitives that are vulnerable to chosen-ciphertext attacks.

White and grey-box verification and validation approaches for safety- and security-critical software systems

In this article, the problem of assessing software trustworthiness is considered from a holistic perspective addressing both safety- and security-critical application domains. In particular, the importance of achieving high structural coverage during component and integration testing phases is stressed. In view of the immense effort required by manual testing activities, the present article suggests novel automatic test case generation techniques, capable of maximizing test coverage and minimizing test amount. The tools developed on the basis of these approaches were successfully applied to achieve high control flow, data flow and interface coverage by means of a low number of test cases.

Addressing dependability by applying an approach for model-based risk assessment

This paper describes how an approach for model-based risk assessment (MBRA) can be applied for addressing different dependability factors in a critical application. Dependability factors, such as availability, reliability, safety and security, are important when assessing the dependability degree of total systems involving digital instrumentation and control (I&C) sub-systems. In order to identify risk sources their roles with regard to intentional system aspects such as system functions, component behaviours and intercommunications must be clarified. Traditional risk assessment is based on fault or risk models of the system. In contrast to this, MBRA utilizes success-oriented models describing all intended system aspects, including functional, operational and organizational aspects of the target. The EU-funded CORAS project developed a tool-supported methodology for the application of MBRA in security-critical systems. The methodology has been tried out within the telemedicine and e-commerce areas, and provided through a series of seven trials a sound basis for risk assessments. In this paper the results from the CORAS project are presented, and it is discussed how the approach for applying MBRA meets the needs of a risk-informed Man–Technology–Organization (MTO) model, and how methodology can be applied as a part of a trust case development.

A common criteria based security requirements engineering process for the development of secure information systems

In order to develop security critical Information Systems, specifying security quality requirements is vitally important, although it is a very difficult task. Fortunately, there are several security standards, like the Common Criteria (ISO/IEC 15408), which help us handle security requirements. This article will present a Common Criteria centred and reuse-based process that deals with security requirements at the early stages of software development in a systematic and intuitive way, by providing a security resources repository as well as integrating the Common Criteria into the software lifecycle, so that it unifies the concepts of requirements engineering and security engineering.

Robust Disaster Recovery System Model

Highly security-critical system should possess features of continuous service. We present a new Robust Disaster Recovery System Model (RDRSM). Through strengthening the ability of safe communications, RDRSM guarantees the secure and reliable command on disaster recovery. Its self-supervision capability can monitor the integrality and security of disaster recovery system it-self. By 2D and 3D real-time visible platform provided by GIS, GPS and RS, the model makes the using, management and maintenance of disaster recovery system easier. RDRSM possesses predominant features of security, robustness and controllability. And it can be applied to highly security-critical environments such as E-government and bank. Conducted by RDRSM, an important E-government disaster recovery system has been constructed successfully. The feasibility of this model is verified by practice. We especially emphasize the significance of some components of the model, such as risk assessment, disaster recovery planning, system supervision and robust communication support.

Foundations for Designing Secure Architectures

Developing security-critical systems is difficult and there are many well-known examples of security weaknesses exploited in practice. In particular, so far little research has been performed on the soundly based design of secure architectures, which would be urgently needed to develop secure systems reliably and efficiently. In this abstract, we sketch some research on a sound methodology supporting secure architecture design. We give an overview over an extension of UML, called UMLsec, that allows expressing security-relevant information within the diagrams in an architectural design specification. We define foundations for secure architectural design patterns. We present tool-support which has been developed for the UMLsec secure architecture approach.

Modeling System Integrity Of A Security CriticalSystem Using Colored Petri Nets

Recently, the need for techniques for quantification of security attributes of IKT systems has been raised. This relates both to security requirements in QoS architectures, as well as input to trade-off analysis regarding the design and choice of security mechanisms to comply with an established security policy. Early research in this area has focused on state transition models, such as Markov or semi-Markov models. In the dependability domain these techniques are used to measure values such as mean time between failures (MTBF), and to quantify frequency and consequences of risks. The dynamics of security attacks makes it intractable to use, due to the problems with state explosions. To be able to express the complete state space of a security critical system, one needs to consider not only hardware, operating system. And application/services faults, but also the survivability of the system in terms of intentional and accidental security breaches. This paper builds a stochastic prediction system to estimate the system integrity of a security critical system. The paper makes use of Colored Petri Nets (CPN), a higher-level formalism for stochastic modeling, analysis, and simulation. The prediction system is implemented as a generic and hierarchic CPN model.

Enhancing structured review with model-based verification

We propose a development framework that extends the scope of structured review by supplementing the structured review with model-based verification. The proposed approach uses the Unified Modeling Language (UML) as a modeling notation. We discuss a set of correctness arguments that can be used in conjunction with formal verification and validation (V&V) in order to improve the quality and dependability of systems in a cost-effective way. Formal methods can be esoteric; consequently, their large scale application is hindered. We propose a framework based on the integration of lightweight formal methods and structured reviews. Moreover, we show that structured reviews enable us to handle aspects of V&V that cannot be fully automated. To demonstrate the feasibility of our approach, we have conducted a study on a security-critical system - a patient document service (PDS) system.

Static verification and extreme programming

At first glance, the worlds of high-integrity software engineering and Extreme Programming (XP) seem to have little in common. Somewhat surprisingly, we have found the reverse to be the case-indeed it seems that many practices advocated by the XP community are familiar to us from many years' of experience in building safety- and security-critical systems. This paper discusses our experiences in applying some XP practices in critical projects. Secondly, we discuss how static verification can augment XP, particularly in the Pairwise Programming and Refactoring practices.

Fault trees for security system design and analysis

The academic literature concerning fault tree analysis relates almost entirely to the design and development of safety-critical systems. This paper illustrates how similar techniques can be applied to the design and analysis of security-critical systems. The application of this technique is illustrated in an example inspired by a current public-key cryptosystem.

Secure systems development based on the common criteria

Security is a very important issue in information processing, especially in open network environments like the Internet. The Common Criteria (CC) is the standard requirements catalogue for the evaluation of security critical systems. Using the CC, a large number of security requirements on the system itself and on the system development can be defined. However, the CC does not give methodological support.In this paper, we show how integrate security aspects into the software engineering process. The activities and documents from the Common Criteria are tightly intertwined with the system development, which improves the quality of the developed system and reduces the additional cost and effort due to high security requirements. For modelling and verification of critical parts of the system, we use formal description techniques and model checking (supported by the graphical CASE tool A UTO F OCUS ), which increases both the understanding of the system specification and the system's reliability. We demonstrate our ideas by means of a case-study, the PalME project--an electronic purse application for Palm handhelds.

3.4.2 Improving Systems Integrity by Using Thread Analysis for Design Validation

AbstractThe techniques described in this paper have been developed and applied on a series of major systems engineering projects, most recently including the BOWMAN programme. BOWMAN will encompass the design, development, manufacture, conversion (rollout) and support of the new communications systems for the British Army. The BOWMAN contract will be valued in excess of £1.5 Billion and be delivered and installed over a period of 6 years.Thread Analysis is a technique that enables systems design to be systematically inspected with respect to a number of desirable properties. Threads analysis finds application in domains including safety critical systems; security critical systems; concurrent, real‐time systems and systems with complex and diverse behaviour.Thread Analysis is concerned with ‘unravelling’ and documenting sequences of dependent events within complex systems. The consideration of the way in which one event leads to one or more other events in the system and the consequent changes in that systems state can provide deep insight into its functioning and integrity.This paper shows how the essentially simple technique of inspecting dependent sequences of system events can be applied in a surprising variety of ways to yield useful and powerful results.

Interfacing users with very severe mobility restrictions with a semi-automatically guided wheelchair

TetraNauta is an on-going R&D project aimed to develop a controller for standard electric-powered wheelchairs that permits users with very severe mobility restrictions (such as people with tetraplegy) to easily navigate in closed environments (home, hospital, school, etc.). This project intends to design a non-expensive guidance system to help this kind of users to drive the wheelchair with the minimum effort, but maintaining the user as active as possible. For this reason the design of the user interface is a key factor. Some characteristic of this interface can be taken as a workbench for the design of more complex and security critical mobile systems.

Applying formal specification in industry

Industrial software developers confront a bewildering array of software engineering techniques, each with its own promised benefits. The authors introduced formal methods into the specification and modeling activities of a security-critical system's development. They gauged the methods' effectiveness by comparing the results of the group that used them with those of the group that did not. They present their results in this paper.