This paper describes an active attack against the Transport Control Protocol (TCP) which allows a cracker to redirect the TCP stream through his machine thereby permitting him to bypass the protection offered by such a system as a one-time password[SKEY] or by ticketing authentication [Kerberos]. The TCP COnnection is vulnerable to anyone with a TCP packet sniffer and generator locates on the path followed by the connection. Some schemes to detect this attack are presented as well as some methods of prevention and some interesting details of the TCP protocol behaviors.

The Asychronous Transfer Mode (ATM) is the transport mode of choice for B-ISDN. In order for high speed networks to become a reality, a number of performance issues has to be resolved.

Distributed, heterogeneous, and autonomous hardware and software systems are the product of legnthy and diverse computational and information processing requirements. The introduction of harmonious cooperation among such systems carries the potential for great increases in productivity and improvment in applications processing. However, such harmonious cooperation must be supportedby an integrated system that would allow the developement of global applications.

As the size of system software increases, the algorithms and data structures of the computation no longer constitute the major design problems. When systema are constructed from many components, the organization of the overall system - the software architecture - presents a new set of dsign problems. This level of design has been address a number of ways including informal diagrams and descriptive terms, module interconnection languages, templates and frmeworks for systems that serve the needs of specific domains, and formal models of component integration mechanisms.

This paper describes the fundamentals and some of the details of task commincation in DEMCS, the operating system for the CRAY-1 computer being developed at the Los Alamos Scientific Laboratory. The communication mech- anism is a message system with several novel features. Meesages are sent from one task to another over links. Links are the primary protected objects in the system; they provide messages paths and optional data sharing between tasks. They can be used to represent other objects with capability-like ac- cess controls. Links point to the tasks that created them. A task that creates a link determines its contents and possibly restricts its use. A link may be passed on from on task to another along with a message sent over some other link suject to the restrictions imposed by the creatorof the link be- ing passed. The link based message and sata sharing system is an attractive alternative to semaphore or monitor type shared variable based operating system on machines with only very simple memory protection mechanisms or on machines connected together in a network.

This paper discussesthe design of the file system for DEMCS, an operating system being developed for the CRAY-1 somputer at Los Alamos Scientific Laboratory. The goals to be met, in particular the performance and usability considerations are outlined. A descriptionis given of the user interface and the general structure of the file systemand the file system routines. A simple model of program behavior is used to demonstrate the effet of buffer- ing data by the file system routines. A disk space allocation strategy is descibed which will take advantage of this buffering. The last section out- lines how the performance mechanisms are itegrated into the file system routines.