1. OPERATING SYSTEMS CS 3502 Fall 2017
Chapter 11 Security
Dr. Donghyun (David) Kim
Department of Computer Science
College of Computing and Software Engineering
Kennesaw State University

2. Protection Mechanisms to control what an authenticated user can do.
File Protection
Memory Protection
Web Protection

3. Protection
Mechanism to keep unauthorized users from accessing the system
Firewalls
Virus Detection
Spyware Detection

4. Encryption
Scrambles data & messages so that eavesdroppers cannot read what is being transmitted
Also used as part of Authentication to help ensure that someone is not posing as somebody else

5. People Lack of knowledge about security
People will not keep information secure
People can be conned into giving out information they shouldn’t
Poor System Administration

6. Types of Attacks Trojan Horse Trap Door Stack & Buffer Overflow Worm
Virus
Denial of Service

7. Trojan Horse
Program that appears to be a legitimate agent or process but really behaves in a different manner
Viruses and Spyware are often introduced as Trojan Horses

8. Trap Door
Program finds a way to bypass the normal security protections
Often left in applications / systems to help support staff

9. Stack & Buffer Overflow
Send an incorrectly formatted command / message to a system.
If system does not carry out adequate checking, it may execute some action it shouldn’t

10. Stack & Buffer Overflow

11. Stack & Buffer Overflow
How does this happen?
Poorly Programmed Read
Should be read(file,buffer,100)
Instead of read(file,buffer) which reads as much data as the remote system sends
Inadequate checking of the validity of the data that is received

12. Stack & Buffer Overflow
Security Design Rule
Assume any data you receive is incorrectly formatted (until proven otherwise)

13. SQL Injection
Application does inadequate validation of user input before putting it into an SQL statement
Example
SELECT BALANCE FROM ACCTS WHERE ACCT_ID=xxxx
User Input for xxxx
104;UPDATE ACCTS SET BALANCE= WHERE ACCT_ID=104

14. Worm
A program that automatically sends itself to another system

15. Virus
Program that attacks a system to carry out some action the computer user does not want

16. Denial of Service
Typical attack sends so many messages to a system, that system cannot execute anything except respond to those messages

17. Goal of Protection
Ensure that resources (data) is available only to users that are authorized to access those resources
A Protection Policy specifies the details of this goal for a particular system
The Protection Policy is implemented via Protection Mechanisms

18. Example Protection Policies
Access by password knowledge
Teresa can access the Personnel File if she knows a password
Access by User ID
Patty can modify the Personnel File Jonathon can read the file Brandon has no access to the file
Access by Group Membership
The HR dept can modify the Personnel File The Payroll dept can read the file Other employees have no access to the file

19. Protection Policies A Protection Policy says:
How a user can obtain access to a resource (data)
What they can carry out with the resource / data (Access Rights)

20. Owner
Most Protection Policies have the concept of the Owner of the data
The Owner:
Has all access rights to the data
Can delegate Access Rights to other users / groups

21. Typical Access Rights
Read
Write
Execute
Delete

22. File Protection R W E Effect No access allowed 1
No access allowed 1
Execute Only – Program can be executed
Write Only - not really useful
Write-Execute – Not used
Read Only – File can be read / copied
Read-Execute – Program can be executed / copied
Read-Write – Normal data file
Read-Write-Execute – no protection

23. Protection Domains
Defines the set of objects that a process can access and how they can be accessed
Object Granularity
Computer
File
Record in a file
Field in a record

24. Two Protection Mechanisms
File Attributes
Each file specify attributes for Owner, Group, Everyone
Access Control Lists
Associated with each protected resource
Specifies which individuals and/or groups have what access rights

25. File Attributes Can specify Read, Write, Execute allowed
Can specify separately for Owner, Group, Everyone

26. Access Control Lists Each protected object has a list
The user/groups that can access it
What each user/group’s access rights are

27. Access Control List Example
HR dept
Read-Write
Payroll Dept
Read
Others
None

28. MS Windows NTFS File System has support for Access Control Lists
FAT file systems have no support for file protection

29. Unix, Linux Uses Attribute Scheme
Protection can only be controlled to the group level

30. Web Browser Protection
Applet

31. Web Browsers
Web Browsers can execute programs (Applets) that are received from another computer
Browsers can execute:
Java Applets
ActiveX Components (Internet Explorer)

32. Web Browsers Potentially a very untrustworthy situation
Some protection mechanism is required

33. Java Applets
Run in a “sandbox” enforced by the Java Virtual Machine (JVM)
JVM prevents applet from performing “bad” actions
In general, Applets cannot access files or other resources on the browser’s machine – only on the web server that provided the applet
A Signed Applet can access files/resources

34. ActiveX Components Execute native code
No sandbox
Code can carry out any action it wants
One should only allow Signed ActiveX components to run

35. What is a Signed component?
Signed Component includes a Digital Signature of the author of the component
Browsers can verify that the Digital Signature is correct

36. Virus Protection
Current Virus protection programs detect malware by use of a “signature”
Better technology is needed
Requires frequent updates
Virus writers starting to be able to trick the signature detection mechanisms

37. Spyware Similar to Viruses
Detection programs use similar technology to find

38. Firewalls
A Firewall prevents undesirable messages from getting past it
A Hardware firewall can make systems behind the firewall invisible to the outside world
Software firewall can also detect programs unexpectedly accessing internet

39. Trusted Computing Initiative
Rather than trying to detect “bad” programs
Allow system to execute only “good” programs
Uses Digital Signature technology and cryptography embedded into hardware
What is a “good” program?

40. Encryption Two Primary Functions ciphertext = encrypt(plaintext,key1)
plaintext = decrypt(ciphertext,key2)

41. Symmetric Systems Key1 = key2 Both sides must know the key
Both sides MUST keep the key secret
Requires a secure channel to distribute the key(s)

42. Symmetric Systems Examples DES (Data Encryption Standard)
56 bit keys
30 years old
AES (Advanced Encryption Standard)
Keys can be 128, 192, or 256 bits
New standard

43. Asymmetric Systems Key1 ≠ key2 One key is published (to the world)
This a “public key”
The other key is kept private
This a “private key”
Also known as Public Key encryption

44. Asymmetric Systems Examples RSA (Rabin, Shamir, Adelman)
Based on the difficulty of factoring very large numbers
ECC (Elliptic Curve Cryptography)
Based on the difficulty of calculating the coefficients of an ellipse

45. Asymmetric Systems To send a message to Bob:
Encrypt the message with Bob’s public key
Bob can decrypt the message with his private key and read the message
Nobody else can read the message

46. Asymmetric Systems If Alice wants to “sign” a document:
She computes hash of the document
An irreversible computation
Encrypts hash with her private key
Anybody can verify that Alice signed the document by decrypting the hash with her public key

47. Symmetric vs Asymmetric
Flexibility
Asymmetric systems are much more flexible
Speed
Symmetric systems are much faster

48. Public Key Infrastructure (PKI)
A business structure using
Digital Certificates
Certificate Authorities

49. Digital Certificates
A Digital Certificate identifies the author of a Signed Component
Contains name of the author
Public key of the author
The Certificate Authority (CA) that validated the author’s public key
Signed by Certificate Authority

50. Verifying a Digital Certificate
Get name of Certificate Authority
Lookup their public key (comes with OS)
Use CA’s public key to decrypt certificate hash
Verify Hash

51. Verifying Digital CertificateOS
Certificate
CA Name
CA Public Key
Decrypt
Encrypted Hash

52. Hackers & Encryption
The IT Director of a company is quoted in the press as saying:
“Yes, a hacker did break into our system and get a copy of the files containing customer’s credit card numbers. But, those files are encrypted, so he can’t use the information.”
Is he correct?

53. Security of Encryption
At least 1 key must be kept secret
A break in the other security components can allow unauthorized access to the secret key
On some systems, the encryption is done on a separate physical secure device