Lecture 21 Chapter 14: Protection Chapter 15: Security

1. Lecture 21Chapter 14: Protection Chapter 15: Security

2. Chapter 14: Protection • Goals of Protection • Principles of Protection • Domain of Protection • Access Matrix • Implementation of Access Matrix • Access Control • Revocation of Access Rights • Capability-Based Systems • Language-Based Protection

3. Objectives • Discuss the goals and principles of protection in a modern computer system • Explain how protection domains combined with an access matrix are used to specify the resources a process may access • Examine capability and language-based protection systems

4. Protection • Operating system consists of a collection of objects, hardware or software • Each object has a unique name and can be accessed through a well-defined set of operations. • Protection problem • Ensure that each object is accessed correctly and only by those processes that are allowed to do so. • Guiding principle • principle of least privilege • Programs, users and systems should be given just enough privileges to perform their tasks

5. Domain Structure • Access-right = <object-name, rights-set> • where rights-set is a subset of all valid operations that can be performed on the object. • Domain = set of access-rights

6. Domain Implementation (UNIX) • System consists of 2 domains: • User • Supervisor • UNIX • Domain = user-id • Domain switch accomplished via file system. • Each file has associated with it a domain bit (setuid bit). • When file is executed and setuid = on, • then user-id is set to owner of the file being executed. • When execution completes user-id is reset.

7. Domain Implementation (MULTICS) • Let Di and Djbe any two domain rings. • If j < I Di  Dj

8. Access Matrix • View protection as a matrix (access matrix) • Rows represent domains • Columns represent objects • Access(i, j) is the set of operations that a process executing in Domaini can invoke on Objectj

9. Use of Access Matrix • If a process in Domain Ditries to do “op” on object Oj, • then “op” must be in the access matrix. • Can be expanded to dynamic protection. • Operations to add, delete access rights. • Special access rights: • owner of Oi • copy op from Oi to Oj • control – Di can modify Dj access rights • transfer – switch from domain Di to Dj

10. Use of Access Matrix (Cont.) • Access matrix design separates mechanism from policy • Mechanism • Operating system provides access-matrix + rules • It ensures that the matrix is only manipulated by authorized agents and that rules are strictly enforced • Policy • User dictates policy • Who can access what object and in what mode

11. Implementation of Access Matrix • Each column = Access-control list for one object Defines who can perform what operation. Domain 1 = Read, Write Domain 2 = Read Domain 3 = Read • Each Row = Capability List (like a key)Fore each domain, what operations allowed on what objects. Object 1 – Read Object 4 – Read, Write, Execute Object 5 – Read, Write, Delete, Copy

12. Access Matrix With Domains as Objects Figure B

13. Access Matrix with Copy Rights

14. Access Matrix With Owner Rights

15. Modified Access Matrix of Figure B

16. Access Control • Protection can be applied to non-file resources • Solaris 10 provides role-based access control to implement least privilege • Privilege is right to execute system call or use an option within a system call • Can be assigned to processes • Users assigned roles granting access to privileges and programs

17. Revocation of Access Rights • Access List – Delete access rights from access list. • Simple • Immediate • Capability List – Scheme required to locate capability in the system before capability can be revoked. • Reacquisition • Back-pointers • Indirection • Keys

18. Language-Based Protection • Specification of protection in a programming language allows the high-level description of policies for the allocation and use of resources. • Language implementation can provide software for protection enforcement when automatic hardware-supported checking is unavailable. • Interpret protection specifications to generate calls on whatever protection system is provided by the hardware and the operating system.

19. Protection in Java • Protection is handled by the Java Virtual Machine (JVM) • A class is assigned a protection domain when it is loaded by the JVM. • The protection domain indicates what operations the class can (and cannot) perform. • If a library method is invoked that performs a privileged operation, • the stack is inspected to ensure the operation can be performed by the library.

21. 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

22. 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

23. 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

24. Concern for Security • Explosive growth of desktops started in ‘80s • No emphasis on security • Who wants military security, I just want to run my spreadsheet! • Internet was originally designed for a group of mutually trusting users • By definition, no need for security • Users can send a packet to any other user • Identity (source IP address) taken by default to be true • Explosive growth of Internet in mid ’90s • Security was not a priority until recently • Only a research network, who will attack it?

25. 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

26. 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

27. 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

28. C Program with Buffer-overflow Condition #include <stdio.h> #define BUFFER SIZE 256 int main(int argc, char *argv[]) { char buffer[BUFFER SIZE]; if (argc < 2) return -1; else { strcpy(buffer,argv[1]); return 0; } }

29. Layout of Typical Stack Frame

30. Modified Shell Code #include <stdio.h> int main(int argc, char *argv[]) { execvp(‘‘\bin\sh’’,‘‘\bin \sh’’, NULL); return 0; }

31. Hypothetical Stack Frame After attack Before attack

32. Program Threats (Cont.) • Viruses • Code fragment embedded in legitimate program • Very specific to CPU architecture, operating system, applications • Usually borne via email or as a macro • Visual Basic Macro to reformat hard drive Sub AutoOpen() Dim oFS Set oFS = CreateObject(’’Scripting.FileSystemObject’’) vs = Shell(’’c:command.com /k format c:’’,vbHide) End Sub

33. Program Threats (Cont.) • Virus dropper inserts virus onto the system • Many categories of viruses, literally many thousands of viruses • File • Boot • Macro • Source code • Polymorphic • Encrypted • Stealth • Tunneling • Multipartite • Armored

34. A Boot-sector Computer Virus

35. System and Network 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 • Port scanning • Automated attempt to connect to a range of ports on one or a range of IP addresses • Denial of Service • Overload the targeted computer preventing it from doing any useful work • Distributed denial-of-service (DDOS) come from multiple sites at once

36. The Morris Internet Worm

37. Code-Red Worm • On July 19, 2001, more than 359,000 computers connected to the Internet were infected in less than 14 hours • Spread

38. Sapphire Worm • was the fastest computer worm in history • doubled in size every 8.5 seconds • infected more than 90 percent of vulnerable hosts within 10 minutes.

39. DoS attack on SCO • On Dec 11, 2003 • Attack on web and FTP servers of SCO • a software company focusing on UNIX systems • SYN flood of 50K packet-per-second • SCO responded to more than 700 million attack packets over 32 hours

40. Witty Worm • 25 March 2004 • reached its peak activity after approximately 45 minutes • at which point the majority of vulnerable hosts had been infected • World • USA

41. Nyxem Email Virus • Jan 15, 2006: infected about 1M computers within two weeks • At least 45K of the infected computers were also compromised by other forms of spyware or botware • Spread

42. Security Trends www.cert.org (Computer Emergency Readiness Team)

43. The Cast of Characters • Alice and Bob are the good guys • Trudy is the bad guy • Trudy is our generic “intruder” • Who might Alice, Bob be? • … well, real-life Alices and Bobs • Web browser/server for electronic transactions • on-line banking client/server • DNS servers • routers exchanging routing table updates

44. Alice’s Online Bank • Alice opens Alice’s Online Bank (AOB) • What are Alice’s security concerns? • If Bob is a customer of AOB, what are his security concerns? • How are Alice and Bob concerns similar? How are they different? • How does Trudy view the situation?

45. Alice’s Online Bank • AOB must prevent Trudy from learning Bob’s balance • Confidentiality (prevent unauthorized reading of information) • Trudy must not be able to change Bob’s balance • Bob must not be able to improperly change his own account balance • Integrity (prevent unauthorized writing of information)

46. Alice’s Online Bank • AOB’s information must be available when needed • Availability (data is available in a timely manner when needed) • How does Bob’s computer know that “Bob” is really Bob and not Trudy? • When Bob logs into AOB, how does AOB know that “Bob” is really Bob? • Authentication (assurance that other party is the claimed one) • Bob can’t view someone else’s account info • Bob can’t install new software, etc. • Authorization (allowing access only to permitted resources)

47. Think Like Trudy • Good guys must think like bad guys! • A police detective • Must study and understand criminals • In security • We must try to think like Trudy • We must study Trudy’s methods • We can admire Trudy’s cleverness • Often, we can’t help but laugh at Alice and Bob’s carelessness • But, we cannot act like Trudy