After studying this chapter, you should be able to: Discuss basic concepts related to concurrency, such as race conditions, OS concerns, and mutual exclusion requirements; understand hardware approaches to supporting mutual exclusion; define and explain semaphores; define and explain monitors. | Module 20: Security The Security Problem Authentication Program Threats System Threats Threat Monitoring Encryption Operating System Concepts The Security Problem Security must consider external environment of the system, and protect it from: unauthorized access. malicious modification or destruction accidental introduction of inconsistency. Easier to protect against accidental than malicious misuse. Operating System Concepts Authentication User identity most often established through passwords, can be considered a special case of either keys or capabilities. Passwords must be kept secret. Frequent change of passwords. Use of “non-guessable” passwords. Log all invalid access attempts. Operating System Concepts Program Threats Trojan Horse Code segment that misuses its environment. Exploits mechanisms for allowing programs written by users to be executed by other users. Trap Door Specific user identifier or password that circumvents normal security procedures. Could be included in a . | Module 20: Security The Security Problem Authentication Program Threats System Threats Threat Monitoring Encryption Operating System Concepts The Security Problem Security must consider external environment of the system, and protect it from: unauthorized access. malicious modification or destruction accidental introduction of inconsistency. Easier to protect against accidental than malicious misuse. Operating System Concepts Authentication User identity most often established through passwords, can be considered a special case of either keys or capabilities. Passwords must be kept secret. Frequent change of passwords. Use of “non-guessable” passwords. Log all invalid access attempts. Operating System Concepts Program Threats Trojan Horse Code segment that misuses its environment. Exploits mechanisms for allowing programs written by users to be executed by other users. Trap Door Specific user identifier or password that circumvents normal security procedures. Could be included in a compiler. Operating System Concepts System Threats Worms – use spawn mechanism; standalone program Internet worm Exploited UNIX networking features (remote access) and bugs in finger and sendmail programs. Grappling hook program uploaded main worm program. Viruses – fragment of code embedded in a legitimate program. Mainly effect microcomputer systems. Downloading viral programs from public bulletin boards or exchanging floppy disks containing an infection. Safe computing. Operating System Concepts The Morris Internet Worm Operating System Concepts Threat Monitoring Check for suspicious patterns of activity – ., several incorrect password attempts may signal password guessing. Audit log – records the time, user, and type of all accesses to an object; useful for recovery from a violation and developing better security measures. Scan the system periodically for security holes; done when the computer is relatively unused. Operating System Concepts Threat Monitoring (Cont.) Check for: .
