Department of Computer Science

Professor Yashar Ganjali

Department of Computer Science

University of Toronto


yganjali@cs.toronto.edu

http://www.cs.toronto.edu/~yganjali

Announcements


Final project


Intermediate report


Due:
Fri. Nov. 16
th
, 5PM


In class presentations


Wed. Nov. 21
st


We already have 6 teams


Wed. Nov. 28
th


15 minute presentation


Assignment
3


Due:

Fri. Nov. 16
th



Email your solutions to me, or bring to my office (BA 5238)



Volunteer for lecture notes?


Last chance!


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The Story …

•
Introduction to computer networks

•
The science of networks


•
Computer networks and healthcare

•
Computer networks and business

•
Computer networks and entertainment

•
Cloud computing /storage

•
Phishing, spam, and fraud in the Internet

•
Privacy in online social networks


•
This week
: computer networks and security

3

The Problem


Computer networks create interconnectivity


We have seen many examples of good uses



Same connectivity can be used for evil


It is easier to


Access someone’s private information


Spread malicious code


Gain control of somebody’s machine


…



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Viruses, Trojan Horses, and Worms


Viruses


Small pieces of malicious software


Usually piggyback on real programs


Or documents: PDF files, spreadsheets, …


Reproduce by attaching to other programs


Worms


Replicates itself using security
holes


Using computer networks


Without human interaction


Trojan Horses


A program that claims
and appears
to be useful (say a game)


… but in reality can be damaging (e.g. delete files)


Can create backdoors for attackers


Do not replicate


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Life Just Before Slammer

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Life Just After Slammer

A Lesson in Economy


Slammer used an extremely lightweight attack


Entire worm fit in a single packet! (376 bytes)


When scanning, worm could “fire and forget”.


Stateless!


Worm infected 75,000+ hosts in 10 minutes (despite
broken random number generator).


At its peak, doubled every 8.5 seconds.


Progress limited by the Internet’s carrying capacity

(= 55 million scans/sec)

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Why Security?


First victim at 12:45 am


By 1:15 am, transcontinental links starting to fail


300,000 access points downed in Portugal


All cell and Internet in Korea failed (27 million people)


5 root name servers were knocked offline


911 didn’t respond (Seattle)


Flights canceled

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Witty Worm

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Witty Worm
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Cont’d



Attacks firewalls and security products (ISS)


First to use vulnerabilities in security software


ISS announced a vulnerability


B
uffer overflow problem


Attack in just
one day!


Attack started from a small number of compromised
machines


In 30 minutes
12,000 infected machines


90 Gb/s

of traffic

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Network Telescope


Large piece of globally announced network addresses


No legitimate hosts (almost)


Inbound traffic is almost always anomalous


1/256th of the all addresses (IPv4 space)


One packet in every 256 packets if unbiased random
generators used.


Provides global view of the spread of Internet worms.

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Today


Network Security Goals


Security vs. Internet Design


Attacks


Defenses


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Network Security Goals


Availability


Everyone can reach all network resources all the time


Protection


Protect users from interactions they don’t want


Authenticity


Know who you are speaking with


Data Integrity


Protect data en
-
route


Privacy


Protect private data

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Today


Network Security Goals


Security vs. Internet Design


Attacks


Defenses

Internet Design


Destination routing


Packet based (statistical multiplexing)


Global addressing (IP addresses)


Simple to join (as infrastructure)


Power in end hosts (end
-
to
-
end argument)

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Internet Design vs. Security


Destination routing


Makes Internet routers simpler


How
do we know where packets are coming from?


Packet
based (statistical multiplexing)


Global addressing (IP addresses)


Simple to join (as infrastructure)


Power in end
hosts

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Internet Design vs. Security


Destination Routing


Packet Based (statistical multiplexing)


Simple + Efficient


Difficult resource bound per
-
communication


How to keep someone from hogging?

(remember, we can’t rely on source addresses)


Global Addressing (IP addresses)


Simple to
join (as infrastructure)


Power in End Hosts

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Internet Design vs. Security


Destination routing


Packet based (statistical multiplexing)


Global Addressing (IP addresses)


Very democratic


Even people who don’t necessarily want to be talked to


“every psychopath is your next door neighbor”
–

Dan Geer


Simple to join (as infrastructure)


Power in end
hosts

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Internet Design vs. Security


Destination routing


Packet based (statistical multiplexing)


Global addressing (IP addresses)


Simple to join (as infrastructure)


Very democratic


Misbehaving routers can do very bad things


No model of trust between routers


Power in End
Hosts

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Internet Design vs. Security


Destination routing


Packet based (statistical multiplexing)


Global addressing (IP addresses)


Simple to join (as infrastructure)


Power in end
-
hosts


Decouple
hosts and infrastructure = innovation at the edge!


Giving power to least trusted actors


How to guarantee good behavior?


Today


Network Security Goals


Security vs. Internet Design


Attacks


Defenses

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Denial of Service (
DoS
) Attacks


Send many requests to a server


Make the requests look legitimate



Exhaust some of the resources


Processing (CPU)


Bandwidth (uplink/downlink)


Memory


…

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DoS: Via Resource Exhaustion

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Downlink

bandwidth

Uplink

bandwidth

Memory

(e.g. TCP TCB

exhaustion)

CPU

User
-
time

Distributed DoS (DDoS)


Attacker compromises multiple hosts


Installs malicious program to do her biding

(bots)


Bots flood (or otherwise attack) victims on command;
Attack is coordinated


Bot
-
networks of 80k to 100k have been seen in the
wild


Aggregate bandwidth > 20Gbps (probably more)

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Today


Network Security Goals


Security vs. Internet Design


Attacks


Defenses

Firewalls


What is a firewall?


Device
designed to permit or deny network transmissions


E.g. traffic entering or leaving your home network


Works based on
a set of
rules


Used
to protect networks from unauthorized
access


While
permitting legitimate communications to pass.



Can be done in the network (e.g. network perimeter) or
at the host



Configuration is not straight forward


Requires knowledge of the network

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How Can We Prevent Network Attacks?


Without changing current Internet’s design





What if we can change everything?


Clean slate design



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Final Comments


Internet not designed for security


Many, many attacks


Defense is very difficult


Attackers are smart
; broken
network aids them!



The impact can be sever


As we rely more on computer networks over time



Time for new designs/principles?




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