The information stored in the system (both data and code), as well as the physical resources of the computer system, need to be protected from unauthorized access, malicious destruction or alteration, and accidental introduction of inconsistency. In this chapter, we examine the ways in which information may be misused or intentionally made inconsistent. We then present mechanisms to guard against this occurrence. | Lecture Operating system concepts Fifth edition Module 20 - Avi Silberschatz Peter Galvin Module 20 Security The Security Problem Authentication Program Threats System Threats Threat Monitoring Encryption Silberschatz and Galvin 1999 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. Silberschatz and Galvin 1999 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. Silberschatz and Galvin 1999 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. Silberschatz and Galvin 1999 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. Silberschatz and Galvin 1999 The Morris Internet Worm Silberschatz and Galvin 1999 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
