Welcome to CS 395/495Internet Security: A Measurement-based

Approach

Why Internet Security

• Internet attacks are increasing in frequency, severity and sophistication

• Denial of service (DoS) attacks

– Cost $1.2 billion in 2000

– 1999 CSI/FBI survey 32% of respondents detected DoS attacks directed to their systems

– Thousands of attacks per week in 2001

– Yahoo, Amazon, eBay, Microsoft, White House, etc., attacked

Why Internet Security (cont’d)

• Virus and worms

– Melissa, Nimda, Code Red, Code Red II, Slammer …

– Cause over $28 billion in economic losses in 2003, growing to over $75 billion in economic losses by 2007.

– Code Red (2001): 13 hours infected >360K machines - $2.4 billion loss

– Slammer (2003): 10 minutes infected > 75K machines - $1 billion loss

• ……

• Security has become one of the hottest jobs even with downturn of economy

Some slides are in courtesy of J. Kurose and K. Ross

Overview

• Course Administrative Trivia

• What is Internet security?

• Principles of cryptography

• Authentication

Logistics• Instructor

Yan Chen (ychen@cs.northwestern.edu),

Office Hours: Wed. 2-4pm or by appointment, Rm 330, 1890 Maple Ave.

• TA

Jason A. Skicewicz (jskitz@cs.northwestern.edu) Office Hours: Tu. and Th. 3:30-4:30pm, Rm 321, Maple Ave.

• Seminar class: paper reading + a big project

• Start with the basic concepts of security

– Cryptography, access control and protection

• First half focus on large-scale Internet attacks

– Mobile Malcode (virus/worm): characterization, technologies, history and current defense

– Denial of service (DoS) attacks

– Firewall technologies

– Intrusion detection systems (IDS)

Course Overview

• Many new unknown attacks/anomalies remaining

• Second half: Internet anomaly detection

– High-speed network measurement and monitoring

– Network fault diagnostics and root cause analysis

– BGP/routing anomalies

– Network topology discovery

– Measurement-based inference

– Peer-to-peer system measurement and monitoring

Course Overview (cont’d)

Prerequisites and Course Materials

• Required: CS340 (Intro to computer networking)

• Highly Recommended: OS or having some familiarity with Unix systems programming

• No required textbook – paper reading!

• Recommended (see webpage for a complete list)

o Firewalls and Internet Security: Repelling the Wily Hacker, 2nd edition, by William R. Cheswick, Steven M. Bellovin, and Aviel D. Rubin

o Computer Networking: A Top-Down Approach Featuring the Internet, [KR], Second Edition, James Kurose and Keith Ross, Addison Wesley, 2002

Grading• No exams for this class

• Class participation and discussion 10%

• Paper reading summary 10%

• In class paper presentation 15%

• Project 65%

– Proposal and survey 5%

– Design document 5%

– Weekly report and meeting 5%

– Project presentation 25%

– Final report 25%

Paper Reading• Write a very brief summary of each paper, to

be emailed to the TA before the class

• Summary should include:

– Paper title and its author(s)

– Brief one-line summary

– A paragraph of the one or two most significant new insight(s) you took away from the paper

– A paragraph of the one or two most significant flaw(s) of the paper

– A last paragraph where you state the relevance of the ideas today, potential future research suggested by the article

Class Format• Introduction of the basic problems, ideas and

solutions (10 minutes)

• Student presentations of the two papers

– 20 minutes for presentation, and 10 minutes for discussion

• Summarize with the last 10 minutes

• Take turns for presentation (~30 papers, 4 papers/student)

Format of the Presentation• Presentation should include the following

– Motivation

– Classification of related work/background

– Main ideas

– Evaluation and results

– Open issues

• Send the slides to the TA and me for review at least 24 hours ahead of the class

• Guidelines online

Projects• The most important part of class

– Group of 2+ people

• Project list will be online soon

• Proposal – April 8– 3-4 pages with another 1-2 pages references.

• Design Document – April 15– 4-5 pages with a detailed description of the software design,

load distribution among group members.

• Weekly Meeting and Progress Report – 4/13-5/25– Each team will schedule a weekly meeting (30 minutes) with

me. A work-in-progress report (except the 4/13 week) of 1-2 pages is due 24 hours ahead of the meeting.

• Project Presentation – June 1 and 3

• Final Report – June 9

Communication and Policies• Web page:

http://www.cs.nwu.edu/~ychen/classes/cs495/

• Newsgroup (cs.netsec) is available

• Send emails to instructor and TA for questions inappropriate in newsgroup

• No late handins! Will be ignored

• Work division

– Each team member should do similar amount of work

– Survey on work division at the end of quarter

– More contribution, better grade!

Some slides are in courtesy of J. Kurose and K. Ross

Overview

• Course Administrative Trivia

• What is Internet security?

• Principles of cryptography

• Authentication

What is network security?Confidentiality: only sender, intended receiver should

“understand” message contents

– sender encrypts message

– receiver decrypts message

Authentication: sender, receiver want to confirm identity of each other

Message Integrity: sender, receiver want to ensure message not altered (in transit, or afterwards) without detection

Access and Availability: services must be accessible and available to users

Friends and enemies: Alice, Bob, Trudy• well-known in network security world

• Bob, Alice (lovers!) want to communicate “securely”

• Trudy (intruder) may intercept, delete, add messages

securesender

securereceiver

channel data, control messages

data data

Alice Bob

Trudy

Who might Bob, Alice be?

• … well, real-life Bobs and Alices!

• Web browser/server for electronic transactions (e.g., on-line purchases)

• on-line banking client/server

• DNS servers

• routers exchanging routing table updates

• other examples?

There are bad guys (and girls) out there!

Q: What can a “bad guy” do?

A: a lot!

– eavesdrop: intercept messages

– actively insert messages into connection

– impersonation: can fake (spoof) source address in packet (or any field in packet)

– hijacking: “take over” ongoing connection by removing sender or receiver, inserting himself in place

– denial of service: prevent service from being used by others (e.g., by overloading resources)

Some slides are in courtesy of J. Kurose and K. Ross

Overview

• Course Administrative Trivia

• What is Internet security?

• Principles of cryptography

• Authentication

The language of cryptography

symmetric key crypto: sender, receiver keys identical

public-key crypto: encryption key public, decryption key secret (private)

plaintext plaintextciphertext

KA

encryptionalgorithm

decryption algorithm

Alice’s encryptionkey

Bob’s decryptionkey

KB

Symmetric key cryptography

substitution cipher: substituting one thing for another

– monoalphabetic cipher: substitute one letter for another

plaintext: abcdefghijklmnopqrstuvwxyz

ciphertext: mnbvcxzasdfghjklpoiuytrewq

Plaintext: bob. i love you. aliceciphertext: nkn. s gktc wky. mgsbc

E.g.:

Symmetric key cryptography

symmetric key crypto: Bob and Alice share know same (symmetric) key: K

• e.g., key is knowing substitution pattern in mono alphabetic substitution cipher

• Q: how do Bob and Alice agree on key value?

plaintextciphertext

KA-B

encryptionalgorithm

decryption algorithm

A-B

KA-B

plaintextmessage, m

K (m)A-B

K (m)A-Bm = K ( )

A-B

Symmetric key crypto: DES and AES

DES: Data Encryption Standard

• US encryption standard [NIST 1993]

• 56-bit symmetric key, 64-bit plaintext input

• How secure is DES?

– DES Challenge: 56-bit-key-encrypted phrase (“Strong cryptography makes the world a safer place”) decrypted (brute force) in 4 months. Most recent record – 22 hours.

AES: Advanced Encryption Standard

• new (Nov. 2001) symmetric-key NIST standard, replacing DES

• processes data in 128 bit blocks

• brute force decryption (try each key) taking 1 sec on DES, takes 149 trillion years for AES

Public Key Cryptography

symmetric key crypto

• requires sender, receiver know shared secret key

• Q: how to agree on key in first place (particularly if never “met”)?

public key cryptography

• radically different approach [Diffie-Hellman76, RSA78]

• sender, receiver do not share secret key

• public encryption key known to all

• private decryption key known only to receiver

Public key cryptography

plaintextmessage, m

ciphertextencryptionalgorithm

decryption algorithm

Bob’s public key

plaintextmessageK (m)

B+

K B+

Bob’s privatekey

K B-

m = K (K (m))B+

B-

Public key encryption algorithms

need K ( ) and K ( ) such thatB B. .

given public key K , it should be impossible to compute private key K

B

B

Requirements:

1

2

RSA: Rivest, Shamir, Adelson algorithm

+ -

K (K (m)) = m BB

- +

+

-

RSA: Choosing keys

1. Choose two large prime numbers p, q. (e.g., 1024 bits each)

2. Compute n = pq, z = (p-1)(q-1)

3. Choose e (with e<n) that has no common factors with z. (e, z are “relatively prime”).

4. Choose d such that ed-1 is exactly divisible by z. (in other words: ed mod z = 1 ).

5. Public key is (n,e). Private key is (n,d).

K B+ K B

-

RSA: Encryption, decryption0. Given (n,e) and (n,d) as computed above

1. To encrypt bit pattern, m, compute

c = m mod n

e (i.e., remainder when m is divided by n)e

2. To decrypt received bit pattern, c, compute

m = c mod n

d (i.e., remainder when c is divided by n)d

m = (m mod n)

e mod n

dMagichappens!

c

Why secure? No quick factorizing algorithm

RSA example:

Bob chooses p=5, q=7. Then n=35, z=24.e=5 (so e, z relatively prime).d=29 (so ed-1 exactly divisible by z.

letter m me c = m mod ne

l 12 1524832 17

c m = c mod nd

17 481968572106750915091411825223071697 12

cdletter

l

encrypt:

decrypt:

RSA: another important property

K (K (m)) = m BB

- +K (K (m))

BB+ -

=

use public key first, followed

by private key

use private key first,

followed by public key

Result is the same!

Symmetric (DES) vs. Public Key (RSA)

• Exponentiation of RSA is expensive !

• AES and DES are much faster

– 100 times faster in software

– 1,000 to 10,000 times faster in hardware

• RSA often used in combination in AES and DES

– Pass the session key with RSA

Some slides are in courtesy of J. Kurose and K. Ross

Overview

• Course Administrative Trivia

• What is Internet security?

• Principles of cryptography

• Authentication

Authentication

Goal: Bob wants Alice to “prove” her identity to him

Protocol ap1.0: Alice says “I am Alice”

Failure scenario??“I am Alice”

Authentication

Goal: Bob wants Alice to “prove” her identity to him

Protocol ap1.0: Alice says “I am Alice”

in a network,Bob can not “see”

Alice, so Trudy simply declares

herself to be Alice“I am Alice”

Authentication: another try

Protocol ap2.0: Alice says “I am Alice” in an IP packetcontaining her source IP address

Failure scenario??

“I am Alice”Alice’s

IP address

Authentication: another try

Protocol ap2.0: Alice says “I am Alice” in an IP packetcontaining her source IP address

Trudy can createa packet

“spoofing”Alice’s address“I am Alice”

Alice’s IP address

Authentication: another try

Protocol ap3.0: Alice says “I am Alice” and sends her secret password to “prove” it.

Failure scenario??

“I’m Alice”Alice’s IP addr

Alice’s password

OKAlice’s IP addr

Authentication: another try

Protocol ap3.0: Alice says “I am Alice” and sends her secret password to “prove” it.

playback attack: Trudy records Alice’s

packetand later

plays it back to Bob

“I’m Alice”Alice’s IP addr

Alice’s password

OKAlice’s IP addr

“I’m Alice”Alice’s IP addr

Alice’s password

Authentication: yet another try

Protocol ap3.1: Alice says “I am Alice” and sends her encrypted secret password to “prove” it.

Failure scenario??

“I’m Alice”Alice’s IP addr

encrypted password

OKAlice’s IP addr

Authentication: another try

Protocol ap3.1: Alice says “I am Alice” and sends her encrypted secret password to “prove” it.

recordand

playbackstill works!

“I’m Alice”Alice’s IP addr

encrypptedpassword

OKAlice’s IP addr

“I’m Alice”Alice’s IP addr

encryptedpassword

Authentication: yet another try

Goal: avoid playback attack

Failures, drawbacks?

Nonce: number (R) used only once –in-a-lifetime

ap4.0: to prove Alice “live”, Bob sends Alice nonce, R. Alice

must return R, encrypted with shared secret key“I am Alice”

R

K (R)A-B

Alice is live, and only Alice knows key to encrypt

nonce, so it must be Alice!

Authentication: ap5.0

ap4.0 requires shared symmetric key

• can we authenticate using public key techniques?

ap5.0: use nonce, public key cryptography

“I am Alice”

RBob computes

K (R)A-

“send me your public key”

K A+

(K (R)) = RA

-K A

+

and knows only Alice could have the

private key, that encrypted R such that

(K (R)) = RA-

K A+