This monograph on Security in Computing Systems: Challenges, Approaches and Solutions aims at introducing, surveying and assessing the fundamentals of secu rity with respect to computing. Here, “computing” refers to all activities which individuals or groups directly or indirectly perform by means of computing sys tems, i.e., by means of computers and networks of them built on telecommunica tion. We all are such individuals, whether enthusiastic or just bowed to the inevitable. So, as part of the ‘‘information society’’, we are challenged to maintain our values, to pursue our goals and to enforce our interests, by consciously design ing a ‘‘global information infrastructure’’ on a large scale as well as by appropri ately configuring our personal computers on a small scale. As a result, we hope to achieve secure computing: Roughly speaking, computer-assisted activities of indi viduals and computer-mediated cooperation between individuals should happen as required by each party involved, and nothing else which might be harmful to any party should occur.

The notion of security circumscribes many aspects, ranging from human quali ties to technical enforcement. First of all, in considering the explicit security requirements of users, administrators and other persons concerned, we hope that usually all persons will follow the stated rules, but we also have to face the possi bility that some persons might deviate from the wanted behavior, whether acci dently or maliciously. So, in order to achieve security, we have to protect our activities and cooperations against threatening ‘‘attackers’’. Surely, however, as in everyday life, we also have to rely on trust in some partners. Otherwise, we would end up with staying in complete isolation and doing nothing. Second, since we have delegated a number of actions still increasing to computers, the components of a computing system themselves appear as subjects: we have to decide which components are to be trusted and which ones are to be considered as potential attackers. Additionally, while attacks are performed by technical components, usu ally under outside control, security enforcement also has to be achieved by use of technical components, preferably under our own control or under the control of trustworthy persons. Finally, we are left with a central problem of computer sci ence: how to design, implement and verify trusted components which will enforce our security requirements technically when running in a potentially hostile envi ronment?