《操作系统》课程教学资源（PPT课件）第十九章 Security（安全）

Module19: Security(安全) The Security Problem(安全问题 ° Authentication(授权) ° Program Threats(来自程序的威胁) System Threats(来自系统的威胁) Threat Monitoring(威胁的监控) Encryption(加密) Applied Operating System Concepts Silberschatz, Galvin, and Gagne @1999

19.1 Silberschatz, Galvin, and Gagne ©1999 Applied Operating System Concepts Module 19: Security（安全） • The Security Problem（安全问题） • Authentication（授权） • Program Threats（来自程序的威胁） • System Threats（来自系统的威胁） • Threat Monitoring（威胁的监控） • Encryption（加密）

The Security Problem(安全问题) ° Security must consider external environment of the system, and protect it fror om:(安全必须考虑系统的外环境,以下方面防护:) unauthorized access.(未授权访问) malicious modification or destruction(恶意的修改和破坏) accidental introduction of inconsistency.(意外的引入和不 致) Easier to protect against accidental than malicious misuse.(s] 止意外的误用比防止恶意的误用更加容易) Applied Operating System Concepts 192 Silberschatz, Galvin, and Gagne @1999

19.2 Silberschatz, Galvin, and Gagne ©1999 Applied Operating System Concepts The Security Problem（安全问题） • Security must consider external environment of the system, and protect it from:（安全必须考虑系统的外环境，以下方面防护：） – unauthorized access.（未授权访问） – malicious modification or destruction（恶意的修改和破坏） – accidental introduction of inconsistency.（意外的引入和不一 致） • Easier to protect against accidental than malicious misuse.（防 止意外的误用比防止恶意的误用更加容易）

Authentication(授权) User identity most often established through passwords, can be considered a special case of either keys or capabilities.(用户身 份通常使用密码确立,可以认为密码就是某种权限或者钥匙) ° Passwords must be kept secret.(密码必须保持秘密的状态 Frequent change of passwords.(经常更换密码) Use of“ne sabe" passwords.(使用难猜的密码) og lid access attempts.(记录所有非法访问企图) Applied Operating System Concepts Silberschatz, Galvin, and Gagne @1999

19.3 Silberschatz, Galvin, and Gagne ©1999 Applied Operating System Concepts Authentication（授权） • User identity most often established through passwords, can be considered a special case of either keys or capabilities.（用户身 份通常使用密码确立，可以认为密码就是某种权限或者钥匙） • Passwords must be kept secret.（密码必须保持秘密的状态） – Frequent change of passwords.（经常更换密码） – Use of “non-guessable” passwords.（使用难猜的密码） – Log all invalid access attempts.（记录所有非法访问企图）

Program Threats(程序的威胁 ° Trojan Horse(特洛伊木马) Code segment that misuses its environment.(代码段滥用 环境 Exploits mechanisms for allowing programs written by users to be executed by other users.(利用机制使得某个用户写的 程序可以被其他用户运行) mDo(后门 Specific user identifier or password that circumvents normal securit! y procedures.(特殊的用户标识符或者密码可以绕过 通常的安全检查) Could be included in a compiler.(有可能包含在编译器中) Applied Operating System Concepts 194 Silberschatz, Galvin, and Gagne @1999

19.4 Silberschatz, Galvin, and Gagne ©1999 Applied Operating System Concepts Program Threats（程序的威胁） • Trojan Horse（特洛伊木马） – Code segment that misuses its environment.（代码段滥用 环境） – Exploits mechanisms for allowing programs written by users to be executed by other users.（利用机制使得某个用户写的 程序可以被其他用户运行） • Trap Door（后门） – Specific user identifier or password that circumvents normal security procedures.（特殊的用户标识符或者密码可以绕过 通常的安全检查） – Could be included in a compiler.（有可能包含在编译器中）

System Threats(系统的威胁) Worms- use spawn mechanism; standalone program(蠕虫:使用 大量复制机制;独立的程序) nternet worn(因特网蠕虫) Exploited UNIX networking features(remote access)and bugs in finger and sendmail programs.(使用UNX网络特性以及 finger、 sendmail等程序的漏洞) Grappling hook program uploaded main worm program.(ttl 程序启动蠕虫程序的主体) ° Viruses- fragment of code embedded in a legitimate program.(病毒 嵌入到合法程序中的代码片断) Mainly effect microcomputer systems.(主要影响微机系统) Downloading viral programs from public bulletin boards or exchanging floppy disks containing an infection.(从网络下载带 毒程序或者使用受到感染的软盘) Safe computing.(安全计算) Applied Operating System Concepts 19.5 Silberschatz, Galvin, and Gagne @1999

19.5 Silberschatz, Galvin, and Gagne ©1999 Applied Operating System Concepts System Threats（系统的威胁） • Worms – use spawn mechanism; standalone program（蠕虫：使用 大量复制机制；独立的程序） • Internet worm（因特网蠕虫） – Exploited UNIX networking features (remote access) and bugs in finger and sendmail programs.（使用UNIX网络特性以及 finger、sendmail等程序的漏洞） – Grappling hook program uploaded main worm program.（挂钩 程序启动蠕虫程序的主体） • Viruses – fragment of code embedded in a legitimate program.（病毒 ：嵌入到合法程序中的代码片断） – Mainly effect microcomputer systems.（主要影响微机系统） – Downloading viral programs from public bulletin boards or exchanging floppy disks containing an infection.（从网络下载带 毒程序或者使用受到感染的软盘） – Safe computing.（安全计算）

The morris internet worm( Morris因特网蠕虫) rsh attack finger attack grappling sendmail attack hook request for worm worm sent worm worm target system infected system Applied Operating System Concepts 196 Silberschatz, Galvin, and Gagne @1999

19.6 Silberschatz, Galvin, and Gagne ©1999 Applied Operating System Concepts The Morris Internet Worm（Morris因特网蠕虫）

Threat Monitoring(威胁监控) Check for suspicious patterns of activity -i.e. several incorrect password attempts may signal password guessing.(检査可疑的 行动模式:例如,多次错误的密码尝试可能表示有人在猜密码) 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.(审计日志:记录所有对象访问的时间、用户 以及类型;对于受损后的恢复以及开发更好的安全措施有用) Scan the system periodically for security holes; done when the computer is relatively unused.(定期扫描系统安全漏洞;系统不 用的时候关闭) Applied Operating System Concepts Silberschatz, Galvin, and Gagne @1999

19.7 Silberschatz, Galvin, and Gagne ©1999 Applied Operating System Concepts Threat Monitoring（威胁监控） • Check for suspicious patterns of activity – i.e., several incorrect password attempts may signal password guessing.（检查可疑的 行动模式：例如，多次错误的密码尝试可能表示有人在猜密码） • 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.（审计日志：记录所有对象访问的时间、用户 、以及类型；对于受损后的恢复以及开发更好的安全措施有用） • Scan the system periodically for security holes; done when the computer is relatively unused.（定期扫描系统安全漏洞；系统不 用的时候关闭）

Threat Monitoring(Cont)(威胁监控) Check for:(检查) Short or easy-to-guess passwords(过短的或易猜的密码) Unauthorized set-uid programs(未授权的 set-uid程序) Unauthorized programs in system directories(系统目录中的 未授权程序) Unexpected long- running processes(程序的意外超常时间运一 行) mproper directory protections(不恰当的目录保护) - mproper protections on system data files(不恰当的系统数 据文件保护) Dangerous entries in the program search path (Trojan horse) (危险的程序搜索路径入口) Changes to system programs: monitor checksum values 统程序的改变:监控器检查程序代码的校验和) Applied Operating System Concepts 198 Silberschatz, Galvin, and Gagne @1999

19.8 Silberschatz, Galvin, and Gagne ©1999 Applied Operating System Concepts Threat Monitoring (Cont.)（威胁监控） • Check for:（检查） – Short or easy-to-guess passwords（过短的或易猜的密码） – Unauthorized set-uid programs（未授权的set-uid程序） – Unauthorized programs in system directories（系统目录中的 未授权程序） – Unexpected long-running processes（程序的意外超常时间运 行） – Improper directory protections（不恰当的目录保护） – Improper protections on system data files（不恰当的系统数 据文件保护） – Dangerous entries in the program search path (Trojan horse) （危险的程序搜索路径入口） – Changes to system programs: monitor checksum values（系 统程序的改变：监控器检查程序代码的校验和）

Network Security Through Domain Separation Via Firewall 网络安全通过使用防火墙分离的域实现 Internet access from company's computers Internet company computers DMZ access from Internet firew access between DMz and rs computers DMZ Applied Operating System Concepts 199 Silberschatz, Galvin, and Gagne @1999

19.9 Silberschatz, Galvin, and Gagne ©1999 Applied Operating System Concepts Network Security Through Domain Separation Via Firewall 网络安全通过使用防火墙分离的域实现

Encryption(加密 ° Encrypt clear text into cipher text.(加密使得明文变成密文 Properties of good encryption technique:(优秀加密技术的特征) Relatively simple for authorized users to incrypt and decrypt data,(对于授权用户,加密和解密都相对的简单) Encryption scheme depends not on the secrecy of the algorithm but on a parameter of the algorithm called the 的盘 tion key(加密模式依赖于算法的密钥参数,而不是算法 encr Extremely difficult for an intruder to determine the encryption t key.(入侵者确定密钥极为困难 Data Encryption Standard substitutes characters and rearranges users via a secure mechanism. Scheme only as secure as ho ed their order on the basis of an encryption key provided to author mechanism.(数据加密标准使用通过安全机制提供给授权用户的密 钥代替了打乱次序文字串。模式和机制一样安全) Applied Operating System Concepts 19.10 Silberschatz, Galvin, and Gagne @1999

19.10 Silberschatz, Galvin, and Gagne ©1999 Applied Operating System Concepts Encryption（加密） • Encrypt clear text into cipher text.（加密使得明文变成密文） • Properties of good encryption technique:（优秀加密技术的特征） – Relatively simple for authorized users to incrypt and decrypt data. （对于授权用户，加密和解密都相对的简单） – Encryption scheme depends not on the secrecy of the algorithm but on a parameter of the algorithm called the encryption key.（加密模式依赖于算法的密钥参数，而不是算法 的保密） – Extremely difficult for an intruder to determine the encryption key.（入侵者确定密钥极为困难） • Data Encryption Standard substitutes characters and rearranges their order on the basis of an encryption key provided to authorized users via a secure mechanism. Scheme only as secure as the mechanism. （数据加密标准使用通过安全机制提供给授权用户的密 钥代替了打乱次序文字串。模式和机制一样安全）