welcome to cs 395/495 internet security: a measurement-based approach
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Welcome to CS 395/495 Internet 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 - PowerPoint PPT PresentationTRANSCRIPT
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Welcome to CS 395/495Internet Security: A Measurement-based
Approach
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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
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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
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Some slides are in courtesy of J. Kurose and K. Ross
Overview
• Course Administrative Trivia
• What is Internet security?
• Principles of cryptography
• Authentication
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Logistics• Instructor
Yan Chen ([email protected]),
Office Hours: Wed. 2-4pm or by appointment, Rm 330, 1890 Maple Ave.
• TA
Jason A. Skicewicz ([email protected]) Office Hours: Tu. and Th. 3:30-4:30pm, Rm 321, Maple Ave.
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• 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
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• 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)
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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
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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%
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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
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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)
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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
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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
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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!
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Some slides are in courtesy of J. Kurose and K. Ross
Overview
• Course Administrative Trivia
• What is Internet security?
• Principles of cryptography
• Authentication
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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
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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
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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?
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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)
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Some slides are in courtesy of J. Kurose and K. Ross
Overview
• Course Administrative Trivia
• What is Internet security?
• Principles of cryptography
• Authentication
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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
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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.:
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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
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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
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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
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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-
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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
- +
+
-
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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
-
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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
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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:
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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!
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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
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Some slides are in courtesy of J. Kurose and K. Ross
Overview
• Course Administrative Trivia
• What is Internet security?
• Principles of cryptography
• Authentication
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Authentication
Goal: Bob wants Alice to “prove” her identity to him
Protocol ap1.0: Alice says “I am Alice”
Failure scenario??“I am Alice”
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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”
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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
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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
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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
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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
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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
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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
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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!
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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+