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Client Software

In an Internet commerce system, the use of Web browsers or other client software requires special analysis.

  • Can unanticipated user events cause unwanted effects?

    As in other systems in which an end user operates the terminal, Internet commerce systems that rely on Web browsers for their user interfaces can expect to receive as input arbitrary sequences of events with arbitrary timing. The user may click any link or button at any time, enter arbitrary information into forms, click the same button over and over again, or simply vanish at any point, only to return hours later. The system must be completely bulletproof against such activities. This problem is much more difficult in Internet commerce than in other systems, because the user terminal—the browser—is a general-purpose device and cannot be easily constrained. In networks of ATMs, for example, the terminal is operated by the end user, but the user's behavior is carefully constrained by the terminal software. While the system is considering a request, for example, all keys but Cancel can be locked. On the Internet, the browser works the same way for all applications, and the standard user interface model grants a great deal of power to the user.

  • Can unfriendly users generate errors in system behavior?

    Although it sometimes seems as though the desired user population can create the most stressful situations for the system, unfriendly users (or crackers) can also cause havoc. Because the system is available to the open network, an unfriendly user can transmit arbitrary bit strings to the system as though they were valid inputs. The system must carefully validate all inputs from any source that is not trusted, and should probably carefully check all inputs, trusted or not. Unfriendly users could even reprogram the user terminal or browser to give it completely different behavior.


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