System Architecture Design

pSHIELDSystem Architecture DesignPUcompensation or roll forward. Fault tolerance is not restricted to accidental faults. Malicious faultsare also the target of the error detection mechanisms• Fault removal: This is preformed during both development and operational phases. During thedevelopment life cycle, fault removal is consisting of three steps; verification, diagnosis,correction. During the normal operational phase, fault removal is performed via corrective andpre-emptive maintenance. Pre-emptive maintenance aims on removing faults before they causeerrors during operationFault forecasting: Is the outcome of the evaluation of the system behaviour with respect to faultoccurrence. The main metric used in this process is failure intensity. The alteration of correct-incorrectservice delivery is quantified to define reliability, availability and maintainability as measures ofdependability.4.2 Embedded Systems4.2.1 IntroductionIn addition to the typical requirements for responsiveness, reliability, availability, robustness andextensibility, many conventional embedded systems and applications have significant securityrequirements. However, security is a resource-demanding function that needs special attention inembedded computing. Furthermore, the wide deployment of small devices which are used in criticalapplications has triggered the development of new, strong attacks that exploit more systemiccharacteristics, in contrast to traditional attacks that focused on algorithmic characteristics, due to theinability of attackers to experiment with the physical devices used in secure applications. Thus, design ofsecure embedded systems requires special attention.4.2.2 Design of Secure Embedded SystemsSecure embedded systems must provide basic security properties, such as data integrity, as well asmechanisms and support for more complex security functions, such as authentication and confidentiality.Furthermore, they have to support the security requirements of applications, which are implemented, inturn, using the security mechanisms offered by the system.4.2.2.1 System Design IssuesDesign of secure embedded systems needs to address several issues and parameters ranging from theemployed hardware technology to software development methodologies. Although several techniquesused in general-purpose systems can be effectively used in embedded system development as well, thereare specific design issues that need to be addressed separately, because they are unique or weaker inembedded systems, due to the high volume of available low cost systems that can be used fordevelopment of attacks by malicious users. The major of these design issues are tamper-resistanceproperties, memory protection, Intellectual Property (IP) protection, management of processing power,communication security and embedded software design.Modern secure embedded systems must be able to operate in various environmental conditions, withoutloss of performance and deviation from their primary goals. In many cases they must survive variousphysical attacks and have tamper resistance mechanisms. Tamper resistance is the property that enablessystems to prevent the distortion of physical parts. Additionally to tamper resistance mechanisms, thereexist tamper evidence mechanisms, which allow users or technical stuff to identify tampering attacks andtake countermeasures.IP protection of manufacturers is an important issue addressed in secure embedded systems.Complicated systems tend to be partitioned in smaller independent modules leading to module reusabilityand cost reduction. These modules include IP of the manufacturers, which needs to be protected fromPUD2.3.2Issue 5 Page 53 of 122