1. Security Requirements
Confidentiality
Requires information in a computer system only be accessible for reading by authorized parties
Integrity
Assets can be modified by authorized parties only
Availability
Assets be available to authorized parties
Authenticity
Requires that a computer system be able to verify the identity of a user

2. Threats Confidentiality Integrity Availability Authenticity
Interception
Unauthorized access
wiretapping
Modification
Change or Delete: Data, Messages, Programs
Interruption
Hardware destruction
Disable File Management
Fabrication
Create data, messages ...

3. What it there to protect?
Hardware
Accidental and deliberate damage
Tapping of Network lines
Overload of networks
Software
Threats include deletion, alteration, damage
Data
Involves files
Security concerns for availability, secrecy, and integrity
Stealing of classified information

4. Protection Limit Sharing Limit Communication Encryption of data
Control access
Electronic Signatures
Intrusion detection

5. Examples of Protection
File systems
Access control defined by user
Most system files are not accessible for user
Access control
OS provides access control via Login and Password
User privileges
different user have different status (NT user groups)
Clean Memory Partitioning
Systematic backups

6. Sharing Sharing is the source of all evil!
No sharing: Separation in time or place
Share all or share nothing
Owner of an object declares it public or private
Share via access limitation
Operating system checks the permissibility of each access by a specific user/process to a specific object
Operating system acts as the guard

7. Memory issues Bound registers for processes access to RAM
Delete vs. erase
If you delete a file it is not really gone
OS only “forgot” that it was there
You can still retrieve the content
If you really want to erase thing:
Reformat the device(not always possible)
Delete files and save useless things until drive is full
Beware when your sell you used computer, there may be traces of sensitive information

8. Message encryption: Artistic Math
Encode content x y=F(x,k1) and send y
Receiver decodes the content with a function x=D(x,k2)
Public key & private: 2 different keys are used (PGP)
Secrete Key: k1=k2, D=F-1 ! Illusion of safety
You can only read content if you know k2
Simple letter replacement (Midterm)
has about 4*10^26 possibilities but easy to guess

9. Electronic Signatures
Became very important recently due to e-commerce
Example: You sent and to buy a stock
stock crashes 1 hour later, you deny ever having sent the
Legal issue: How to prove the authenticity of electronic documents
Similar to encryption: You calculate a complex function from the message text, decode it using your private and append it

10. Access Control Authentication
Login
Requires both a user identifier (ID) and a password
Only admit known and matching ID and password
User based or computer based
Problems:
Users can reveal their password to others either intentionally or accidentally
Hackers are skillful at guessing passwords
ID/password file can be obtained (hard to decode)

11. ID Provides Security
Determines whether the user is authorized to gain access to a system
Determines the privileges accorded to the user
Guest or anonymous accounts have mover limited privileges than others
ID is used for discretionary access control
A user may grant permission to files to others by ID

12. Intrusion Techniques Steal Id and Password Circumvent access control
Use a Trojan horse to bypass restrictions on access

13. Techniques for Learning Passwords
Try default password used with standard accounts shipped with computer
Exhaustively try all short passwords license plates
Try words in dictionary or a list of likely passwords
Collect information about users and use these items as passwords
address, names, relatives, SSN, phone numbers
In a study 86% of password could be guessed

14. Techniques for Stealing Passwords
Tap the line between a remote user and the host system
Watch user during login
Intercept s that contain passwords

15. Password Selection Strategies
Computer generated passwords :-(
Hard to remember, user write them down
Reactive password checking strategy :-(
System periodically runs password cracker to find guessable passwords
System cancels passwords that are guessed and notifies user
Consumes resources to do this, can be to late!
Proactive password checker :-)
The system checks at the time of selection if the password is allowable

16. Types of Attacks Intrusion Remote Attack
Somebody unauthorized manages to log into your system
Remote Attack
Somebody changes the behavior of your computer without being logged in

17. Intrusion Prevention Firewalls around network Limit the access type:
telnet, ftp, http, ssh, rsh ….
Limit access location
allow access only from designated machines
Machine ID: IP address

18. Intrusion Detection
Assume the behavior of the intruder differs from the legitimate user
Statistical anomaly detection
Collect data related to the behavior of legitimate users over a period of time
Statistical tests are used to determine if the behavior is not legitimate behavior
Rule-based detection
Rules are developed to detect deviation form previous usage pattern
Expert system searches for suspicious behavior

20. Intrusion Detection Data Collection
Audit record
Native audit records
All operating systems include accounting software that collects information on user activity
Detection-specific audit records
Collection facility can be implemented that generates audit records containing only that information required by the intrusion detection system
Very common for Web services
I can tell exactly what you did on blackboard

21. Remote attacks via Software

22. 2 Types of Malicious Programs
Those that need a host program
Fragments of programs that cannot exist independently of some application program, utility, or system program
Independent
Self-contained programs that can be scheduled and run by the operating system

23. Trojan Horse
Useful program that contains hidden code that when invoked performs some unwanted or harmful function
Can be used to accomplish functions indirectly that an unauthorized user could not accomplish directly
User may set file permission so everyone has access
can do anything the user could do
Example: new exciting freeware game
Does not need illegal access

24. Login Spoofing Setup a screen that looks exactly like login
New user comes and tries to login
Program reads in login information and mails is to intruder
Login fails, user thinks he misspelled and logs in again

25. Logic Bomb
Code embedded in a legitimate program that is set to “explode” when certain conditions are met
Presence or absence of certain files
Particular day of the week
Particular user running application
Example: An employee had a program that checked whether his name appeared on payroll
After he was fired the bomb went off and destroyed important software
Potential of blackmail

26. Worms Use network connections to spread form system to system
Electronic mail facility
A worm mails a copy of itself to other systems
Remote execution capability
A worm executes a copy of itself on another system
Remote log-in capability
A worm logs on to a remote system as a user and then uses commands to copy itself from one system to the other

27. Zombie
Program that secretly takes over another Internet-attached computer
It uses that computer to launch attacks that are difficult to trace to the zombie’s creator
Typical Windows NT problem: Recent case that attacked the White House server

28. Viruses Program that can “infect” other programs by modifying them
Modification includes copy of virus program
The infected program can infect other programs

29. Virus Stages Dormant phase Propagation phase Virus is idle
Virus places an identical copy of itself into other programs or into certain system areas on the disk

30. Virus Stages Triggering phase Execution phase
Virus is activated to perform the function for which it was intended
Caused by a variety of system events
Execution phase
Function is performed

31. Types of Viruses Parasitic Memory-resident
Attaches itself to executable files and replicates
When the infected program is executed, it looks for other executables to infect
Memory-resident
Lodges in main memory as part of a resident system program
Once in memory, it infects every program that executes

32. Types of Viruses Boot sector Stealth Infects boot record
Spreads when system is booted from the disk containing the virus
Stealth
Designed to hide itself form detection by antivirus software
May use compression

33. Types of Viruses Polymorphic
Mutates with every infection, making detection by the “signature” of the virus impossible
Mutation engine creates a random encryption key to encrypt the remainder of the virus
The key is stored with the virus

34. Macro Viruses
A macro is an executable program embedded in a word processing document or other type of file
Autoexecuting macros in Word
Autoexecute
Executes when Word is started
Automacro
Executes when defined event occurs such as opening or closing a document
Command macro
Executed when user invokes a command (e.g., File Save)
Dominantly Windows problem

35. E-mail Virus: Windows Issue
Activated when recipient opens the attachment
Activated by open an that contains the virus
Uses Visual Basic scripting language
Propagates itself to all of the addresses known to the infected host
Protection: Use program that has very limited privileges (Beware Outlook and Explorer)

36. Antivirus Approaches Detection Identification Removal
Your antivirus program from yesterday is useless for today’s virus!
Stern approach: Every time the user logs in to his machine the computer downloads the most current version of antivirus software from the network

37. How does Antivirus software work?
Virus signature scanner
Scan target code looking for known viruses
CPU emulator
Instructions in an executable file are interpreted by the emulator rather than the processor

38. Internet Attacks
One way to attack internet services is to create an overload for the server
Most server have a capacity that reflects normal use requirements
Tojan horse or worms get distributed onto many machines
At a specific time all infected machines start sending requests to the same server
Server goes down
Big problem for online brokerage with time sensitive information

39. Comparison UNIX to WINDOWS
UNIX: targeted by access attacks since it is a
Multi-user environment
High degree of sharing
Constant network access
Sophisticated OS: hard to write malicious programs
WINDOWS: targeted by remote attacks
Singly user environment
Less sophisticated OS: easier to write malicious programs
Switched off most of the time (used to be)

40. Security Design Principles
Public system design
It creates a false illusion if you think nobody knows you architecture
Default: no access
Repetitive checks for current authority
User might have forgotten to lock out, timeout
Give the least privileges possible
Security should be build in the lowest levels of the system, security as add-on does not work well

41. Summary There is no safe system! Business decision
How do I enforce save behavior from employees
Security is very expensive
Security get more expensive, the more flexibility , communication and sharing I allow
Separate physical network for sensitive data
Hire an ex-hacker to break into my system to test security