文档介绍：Chapter 15 SECURITY
A password may e known to other users in a variety of ways. Is there a simple method for detecting that such an event has occurred? Explain your answer.
Answer:
Whenever a user logs in, the system prints the last time that user was logged on the system.
The list of all passwords is kept within the operating system. Thus, if a user manages to read this list, password protection is no longer provided. Suggest a scheme that will avoid this problem. (Hint: Use different internal and external representations.)
Answer:
Encrypt the passwords internally so that they can only be accessed in coded form. The only person with access or knowledge of decoding should be the system operator.
An experimental addition to UNIX allows a user to connect a watchdog program to a file, such that the watchdog is invoked whenever a program requests access to the file. The watchdog then either grants or denies access to the file. Discuss the pros and cons of using watchdogs for security.
Answer:
No answer.
The UNIX program, COPS, scans a given system for possible security holes and alerts the user to possible problems. What are the potential hazards of using such a system for security? How can these problems be limited or eliminated?
Answer:
The COPS program itself could be modified by an intruder to disable some of its features or even to take a