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Unformatted text preview: CIS 4360 Introduction to Computer Security Home Assignment 5, Fall 2011 with answers Due: Tue 9:30pm, 10/11/2011 This concerns access control structures . Examples taken from: Dieter Gollmann, Computer Security, John Wiley. 1. You are given two bits to capture access operations on a directory. How would you use four operations available to you? Answer. An obvious solution is to assign to each operation one of the four values the two bits can take. So read would be 00, write (create or delete) 01, append 01 and execute 11. How would you control the creation and deletion of files? Answer. You could use different values of the pair of bits. For example, create can be written 00, and delete can be grouped with write. How would you implement the concept of hidden files with these access operations? (Hidden files are only visible to authorized subjects.) Answer. A solution for hidden files would be to set a (new) bit in a file descriptor and have the directory operations check that the caller of the file is authorized; in turn, this requires to define what is authorized...
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This document was uploaded on 12/04/2011.
- Fall '09
- Computer Security