操作系统课件第15章.ppt

Chapter 15: Security Chapter 15: Security The Security Problem Program Threats System and Network Threats Cryptography as a Security Tool User Authentication Implementing Security Defenses Firewalling to Protect Systems and Networks Computer-Security Classifications An Example: Windows XP Objectives To discuss security threats and attacks To explain the fundamentals of encryption, authentication, and hashing To examine the uses of cryptography in computing To describe the various countermeasures to security attacks The Security Problem Security must consider external environment of the system, and protect the system resources Intruders (crackers) attempt to breach security Threat is potential security violation Attack is attempt to breach security Attack can be accidental or malicious Easier to protect against accidental than malicious misuse Security Violations Categories Breach of confidentiality Breach of integrity Breach of availability Theft of service Denial of service Methods Masquerading (breach authentication) Replay attack Message modification Man-in-the-middle attack Session hijacking Standard Security Attacks Security Measure Levels Security must occur at four levels to be effective: Physical Human Avoid social engineering, phishing, dumpster diving Operating System Network Security is as week as the weakest chain Program Threats Trojan Horse Code segment that misuses its environment Exploits mechanisms for allowing programs written by users to be executed by other users Spyware, pop-up browser windows, covert channels Trap Door Specific user identifier or password that circumvents normal security procedures Could be included in a compiler Logic Bomb Program that initiates a security incident under certain circumstances Stack and Buffer Overflow Exploits a bug in a program (overflow either the stack or memory buffers) C Program with Buffer-overflow Condition #include stdio.h #define BUFFER SIZE 256 int main(int argc, char *argv[]) { char buffer[BUFF