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Abstrac tThis paper presents my firs t experience in teaching third year compute r science majors a course entitled , "Principles of Programming Languages" a t the Chinese University of Hong Kong . Th e course has been aimed at teaching th e students to analyze and to evaluate a high-level programming language ; it als o enables the students to gain knowledge i n a wide spectrum of current programmin g languages . In this paper, th e preparation, the teaching materials, th e organization, and the actual running o f the course are described . Introductio n

Network Denial-of-Service (DoS) attacks, which exhaust server resources and network bandwidth, can cause the target servers to be unable to provide proper services to the legitimate users and in some cases render the target systems inoperable and/or the target networks inaccessible. DoS attacks have now become a serious and common security threat to the Internet community. Public Key Infrastructure (PKI) has long been incorporated in various authentication protocols to facilitate verifying the identities of the communicating parties. The use of PKI has, however, an inherent problem as it involves expensive computational operations such as modular exponentiation. An improper deployment of the publickey operations in a protocol could create an opportunity for DoS attackers to exhaust the server's resources. This paper presents a public-key based authentication and key establishment protocol coupled with a sophisticated client puzzle, which together provide a versatile solution for possible DoS attacks and various other common attacks during an authentication process. Besides authentication, the protocol also supports a joint establishment of a session key by both the client and the server, which protects the session communications after the mutual authentication. The proposed protocol has been validated using a formal logic theory and has been shown, through security analysis, to be able to resist, besides DoS attacks, various other common attacks.

Considerableinterest continues to be shown in the use of logic programming in many areas of expert systems.

Computer-assisted itZStruction (CAl) has long been used to facilitate teaching and learning in academic institutions. The slow growth in the we of CAl can be attributed to a number of factors. Paramount among these are the lac* of in!elligence in most traditional CAL and the lack of very high-level programming tools which aiiow experienced teachers to develop quality courseware quickly and comparatively inexpensively. This paper describes a prototype expert system construction environment for developing CAl programs having an expert system architecture. With such an environment, the development of a CAl program would entail merely the construction of a knowledge base for a subject domain. Examples are used to highlight certain features of th£ underlying CAL Such an expen system approach to CAl development is cost-effective, and :.he underlyir.g CAl i'.as innovative applications in the educational arena and can forgo some of the drawbacks oftraditirJJ1al CAL (