MET TC670 B1 Computer Science Concepts in Telecommunication Systems - PowerPoint PPT Presentation

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MET TC670 B1 Computer Science Concepts in Telecommunication Systems

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Lecture 8, November 11, 2003. The security environment. Basics ... Casual prying by non-technical users. Snooping by insiders. Determined attempt to make money ... – PowerPoint PPT presentation

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Title: MET TC670 B1 Computer Science Concepts in Telecommunication Systems


1
MET TC670 B1Computer Science Concepts in
Telecommunication Systems
  • Fall 2003

2
Lecture 8, November 11, 2003
  • The security environment
  • Basics of cryptography
  • User authentication
  • Attacks from inside the system
  • Attacks from outside the system
  • Protection mechanisms

3
The Security Environment
  • Security goals and threats

4
Intruders
  • Common Categories
  • Casual prying by non-technical users
  • Snooping by insiders
  • Determined attempt to make money
  • Commercial or military espionage

5
Accidental Data Loss
  • Common Causes
  • Acts of God
  • fires, floods, wars
  • Hardware or software errors
  • CPU malfunction, bad disk, program bugs
  • Human errors
  • data entry, wrong tape mounted

6
Lecture 8, November 11
  • The security environment
  • Basics of cryptography
  • User authentication
  • Attacks from inside the system
  • Attacks from outside the system
  • Protection mechanisms

7
Basics of Cryptography
  • Relationship between the plaintext and the
    ciphertext

8
Secret-Key Cryptography
  • Mono-alphabetic substitution
  • each letter replaced by different letter
  • Given the encryption key,
  • easy to find decryption key
  • Secret-key crypto called symmetric-key crypto

9
Public-Key Cryptography
  • All users pick a public key/private key pair
  • publish the public key
  • private key not published
  • Public key is the encryption key
  • private key is the decryption key

10
One-Way Functions
  • Function such that given formula for f(x)
  • easy to evaluate y f(x)
  • But given y
  • computationally infeasible to find x

11
Digital Signatures
(b)
  • Computing a signature block
  • What the receiver gets

12
Lecture 8, November 11
  • The security environment
  • Basics of cryptography
  • User authentication
  • Attacks from inside the system
  • Attacks from outside the system
  • Protection mechanisms

13
User Authentication
  • Basic Principles. Authentication must identify
  • Something the user knows
  • Something the user has
  • Something the user is
  • This is done before user can use the system

14
Authentication Using Passwords
  • (a) A successful login
  • (b) Login rejected after name entered
  • (c) Login rejected after name and password typed

15
Authentication Using a Physical Object
  • Magnetic cards
  • magnetic stripe cards
  • chip cards stored value cards, smart cards

16
Authentication Using Biometrics
  • A device for measuring finger length.

17
Countermeasures
  • Limiting times when someone can log in
  • Automatic callback at number prespecified
  • Limited number of login tries
  • A database of all logins
  • Simple login name/password as a trap
  • security personnel notified when attacker bites

18
Lecture 8, November 11
  • The security environment
  • Basics of cryptography
  • User authentication
  • Attacks from inside the system
  • Attacks from outside the system
  • Protection mechanisms

19
Trojan Horses
  • Free program made available to unsuspecting user
  • Actually contains code to do harm
  • Place altered version of utility program on
    victim's computer
  • Trick user into running that program

20
Trap Doors
  • (a) Normal code.
  • (b) Code with a trapdoor inserted

21
Login Spoofing
Any program that represents itself as a login
program in order to steal a password.
  • (a) Correct login screen
  • (b) Phony login screen

22
Buffer Overflow
  • (a) Situation when main program is running
  • (b) After program A called
  • (c) Buffer overflow shown in gray

23
Generic Security Attacks
  • Typical attacks
  • Request memory, disk space, tapes and just read
  • Try illegal system calls
  • Start a login and hit DEL, RUBOUT, or BREAK
  • Try modifying complex OS structures
  • Try to do specified DO NOTs
  • Convince a system programmer to add a trap door
  • Beg admin's secy to help a poor user who forgot
    password

24
Famous Security Flaws
(a)
(b)
(c)
  • The TENEX password problem

25
Design Principles for Security
  • System design should be public
  • Default should be n access
  • Check for current authority
  • Give each process least privilege possible
  • Protection mechanism should be
  • simple
  • uniform
  • in lowest layers of system
  • Scheme should be psychologically acceptable

And keep it simple
26
Lecture 8, November 11
  • The security environment
  • Basics of cryptography
  • User authentication
  • Attacks from inside the system
  • Attacks from outside the system
  • Protection mechanisms

27
Virus Damage Scenarios
  • Blackmail
  • Denial of service as long as virus runs
  • Permanently damage hardware
  • Target a competitor's computer
  • do harm
  • espionage
  • Intra-corporate dirty tricks
  • sabotage another corporate officer's files

28
How Viruses Work (1)
  • Virus written in assembly language
  • Inserted into another program
  • use tool called a dropper
  • Virus dormant until program executed
  • then infects other programs
  • eventually executes its payload

29
How Viruses Work (2)
  • Example
  • Recursive procedure that finds executable files
    on a UNIX system
  • Virus could infect them all

30
How Viruses Work (3)
  • An executable program
  • With a virus at the front
  • With the virus at the end
  • With a virus spread over free space within program

31
How Viruses Work (4)
  • After virus has captured interrupt, trap vectors
  • After OS has retaken printer interrupt vector
  • After virus has noticed loss of printer interrupt
    vector and recaptured it

32
How Viruses Spread
  • Virus placed where likely to be copied
  • When copied
  • infects programs on hard drive, floppy
  • may try to spread over LAN
  • Attach to innocent looking email
  • when it runs, use mailing list to replicate

33
Antivirus and Anti-Antivirus Techniques
  • (a) A program
  • (b) Infected program
  • (c) Compressed infected program
  • (d) Encrypted virus
  • (e) Compressed virus with encrypted compression
    code

34
Antivirus and Anti-Antivirus Techniques
  • Integrity checkers
  • Behavioral checkers
  • Virus avoidance
  • good OS
  • install only shrink-wrapped software
  • use antivirus software
  • do not click on attachments to email
  • frequent backups
  • Recovery from virus attack
  • halt computer, reboot from safe disk, run
    antivirus

35
The Internet Worm
  • Consisted of two programs
  • bootstrap to upload worm
  • the worm itself
  • Worm first hid its existence
  • Next replicated itself on new machines

36
Mobile Code Interpretation
  • Applets can be interpreted by a Web browser

37
Mobile Code from Trusted Sources
  • How code signing works

38
Lecture 8, November 11
  • The security environment
  • Basics of cryptography
  • User authentication
  • Attacks from inside the system
  • Attacks from outside the system
  • Protection mechanisms

39
Protection Domains (1)
  • Examples of three protection domains

40
Protection Domains (2)
  • A protection matrix

41
Protection Domains (3)
  • A protection matrix with domains as objects

42
Access Control Lists (1)
  • Use of access control lists of manage file access

43
Access Control Lists (2)
  • Two access control lists

44
Capabilities (1)
  • Each process has a capability list

45
Capabilities (2)
  • Cryptographically-protected capability
  • Generic Rights
  • Copy capability
  • Copy object
  • Remove capability
  • Destroy object

46
Reading
  • Chapter 9, all sections
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