EECS 700: Network Security

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EECS 700 Network Security

• Weichao Wang
• Assistant Professor
• Jan 22, 2007

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Syllabus

• See attachment
• Homework will usually has 4-5 questions and due
  in two weeks. It is due at the time that the
  class begins.
• Project
• We will have 3 projects
• Security of IP layer
• Security of TCP layer
• IPSec
• Coding, Demonstration, and report
• Midterm and final

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What will be covered

• Review of computer security
• Review of computer networks
• Vulnerability in TCP/IP stack
• Protection mechanisms

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Security overview

• Risks
• Computers have controlled our lives
• Medical, ATM, banking, business
• Air traffic control
• Why there are risks
• Adversaries
• Smart and dedicated
• Many of them
• Hiding in the dark
• From fun to profit (worm ?self-changing ? botnet)

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Security overview

• Physical security is not enough (can you be sure
  that your physical security methods are sound and
  enough? Example in Las Vegas)
• Networked computers can be accessed remotely

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Security overview

• What can go wrong
• Trojan war story (trojan horse)
• Corrupted internal worker
• Vulnerabilities of protocols or security
  mechanisms (security patch has problems too)
• By-passing protection walls (CCS 06)
• Backdoors for systems (Linux password)
• Known attacks ignored (push and poll)

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Security overview

• Defending methods
• Prevention
• Prevent (password, salt, private salt, searching)
• Deter raising the bar (password guessing, login
  slow)
• Deflect making other target more attractive
• Detection
• Monitoring (who, what, and how)
• Intrusion detection (signature based, anomaly
  based)
• IP telephony track

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Security Overview

• Recovery
• Recover data (check point)
• Identify the damage
• Forensics
• Containment
• Tolerance
• Maintain a decent service quality
• Automatically degrade video quality while
  reserving bandwidth for voice

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Security overview

• How prevention works
• Policies
• Encryption
• Digital cash, time-stamp, secure multiparty
  computation, e-voting, e-bidding
• Access control and authorization
• Hardware control
• Software control
• Information disclosure (write prevention)

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Security overview

• What can go wrong with prevention
• Design, implement, configuration
• Mal-code transfer (enterprise level security)
• Attackers are smart and dedicated
• Uncle Tom wants it to be safe against terrorists,
  but not to him

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Security overview

• Some additional methods to improve security
• Least privilege
• Writing good code
• Security testing
• Embed security from beginning instead of as a
  patch

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Meaning of security

• What we mean (CIA)
• Confidentiality
• Integrity
• Availability

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• Confidentiality
• Data contents encryption
• Data existence watermarking, masking traffic,
  onion routing
• Resource hiding OS configuration files
• Identity flooding, onion routing

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• Integrity maintaining records of changes
• Data integrity (hash or keyed hash)
• Program integrity
• System integrity
• Identity integrity non-repudiation
• Source integrity traceback (IP traceback)
• Availability
• DoS attack and DDoS attacks (TCP connections, SMS)

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Network security overview

• The features causing security problems
• Sharing access control for a single system is
  not enough
• Complexity of systems
• Undefined boundary one host may on multiple
  networks
• Multiple-node path before data reaches you
  anonymity of attacker and hard to traceback

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• A typical NFS operation and its security
  features
• A read from B confidentiality
• A write to B Integrity and confidentiality
• Forge communication from A to B integrity
• Block traffic b/w A and B availability
• Impersonation

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• Security problems in network protocols
• ARP cache poisoning
• IP spoofing, fragmentation
• ICMP
• UDP
• TCP session hijacking, SYN flood, DoS
• DNS systems
• Buffer overflow

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• Security methods
• Hiding OS configuration, port,
• Encryption IPSec
• Port protection telnet, ftp, etc
• Authentication
• Data integrity digital signature, checksum
• Firewall block unwanted traffic
• IDS
• Forensics

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Review of networks

• Network consists of
• Hosts
• Network devices
• Links
• Softwares
• The view of Internet
• Users view
• Real topology

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• How routers work
• Look at the destination address of the packet
• Look up in the local routing table
• Determine the exit interface
• The next router will do the same
• Default router
• Route based on sub-network instead of IP address

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• IP address classes
• Class A to C
• Class A can have 16.78 million addresses
• Class B can have 65536 addresses
• Class C can have 256 address
• A decent cooperation needs one to many class B
  addresses (Purdues joke)

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• Special address
• 255.255.255.255 local broadcast
• 0.0.0.0 this host
• 127.-.-.- loopback
• CIDR classless inter-domain routing

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Review of Cryptography

• Two kinds of cryptographic algorithms
• Keep the method secret
• Good safe for low security requirement
• Bad update, proof of correctness, how to
  communicate with outsider
• Make the algorithm public but keep the key secret
• Safety depends on the key only
• Good safety analysis can be conducted

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Introduction (cntd)

• Symmetric algorithms
• The encryption and decryption key can be
  calculated from each other easily (most of the
  time the same).
• Block algorithms and stream algorithms
• Cipher text is same of longer in length Why??
• Good efficient and fast, easy to deploy
• Bad key distribution, scalability, broadcast or
  multicast

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Introduction (cntd)

• Public-key encryption
• First appear in 1970s
• Two keys public key and private key
• Private key cannot be derived from public key
• Everyone can send a packet to Alice
• Only Alice has the private key to recover the
  packet
• If Alice uses the private key to encrypt a
  message, can be viewed as digital signature
• Strong, scalable, easy for broadcast and
  multicast, but very slow

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Introduction (cntd)

• Attack to encryption system
• Cipher-text only attack
• The amount of traffic matters
• Known plaintext attack
• Chosen plaintext attack
• Key point
• Keep the cost to break the system higher than the
  gain of the information

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Introduction (cntd)

• Can you always break an encryption system?
• One time pad
• Brute-force attack Try every possible key

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Introduction (cntd)

• Several old fashion encryption algorithms
• Substitution ciphers
• Replace a character in the plaintext with another
  character
• Example Caesar cipher
• Transposition ciphers
• Shuffle the order of characters
• The frequency of characters does not change
• XOR and one-time pad
• If the random bits repeat in cycle, it is bad
• Synchronization at both side is always a problem

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Block 1 one way functions

• One way function is easy to calculate in one
  direction, but not the other.
• Given x, easy to get f(x)
• Given f(x), even f() is known, still not easy to
  get a x
• Trap door one way function
• Given x, easy to calculate f(x)
• Given f(x), difficult to get x
• Given f(x) and a secret y, easy to get x

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Block 1 one way hash function

• Map a variable-length input string to a fixed
  length string fingerprint the file
• Easy to get Hash(x) when giving x
• Almost impossible to find a x that satisfies
  Hash(x)
• Almost impossible to find two files x and x to
  have the same hash value
• Minor change in x, large changes in Hash(x)
• Since the hash value is shorter, we have
  conflict
• We can easily rule out files, but not guarantee
  this is the origin file
• Still good enough in courts, like DNA tests

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Block 1 one way hash function

• Usage of hash function
• Timestamp a file and prove that you are the
  creator (can be used to timestamp the homework)
• Verify the integrity of the files in a file
  system
• Security problems how and where to save the hash
  values
• Hash(x, k) to prevent change on the computer

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Block 2 communication using symmetric crypto
algorithms

• Steps
• (1) Alice and Bob agree a key k and an encryption
  algorithm
• (2) Alice calculates E_k (message) and sends the
  cipher text to Bob
• (3) Bob decrypts the message and gets the
  plaintext
• Problems
• How to determine the key must in a secret place
• How to convince other people it is from Alice
  instead of Bob
• Number of keys increases fast, not scalable

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Block 3 communication using asymmetric crypto
algorithms

• First appeared in 1976, proposed by Diffie and
  Hellman
• Two keys public key and private key, it is
  almost impossible to get private key from public
  key.
• A certain kind of trap door one way functions
  private key is the secret
• Steps
• Alice and Bob agree a public key encryption
  algorithm
• Bob sends his public key to Alice
• (3) Alice calculates E_pubB (message) and sends
  the cipher text to Bob
• (4) Bob decrypts the message with the private
  key and gets the plaintext

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Block 3 communication using asymmetric crypto
algorithms

• Solve the problem in symmetric crypto methods
  the key can be transferred in public
• More scalable, easy for multicast
• New problems
• How can we know that is Bobs public key
• Trusted Third Party
• Certificate for the public key
• Some story about public key
• NSA says it is unnecessary
• But claims credit for it

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Hybrid crypto systems

• Symmetric methods are fast, easy to implement,
  but require special attention during key
  distribution
• Asymmetric methods are slow, but more secure
• Hybrid
• Using asymmetric method to distribute key
• Using symmetric method to encrypt data

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Communication using hybrid crypto systems

• Steps
• Bob sends Alice his public key
• Alice encrypts the session key with this public
  key and sends to Bob
• Both Alice and Bob know the session key and can
  use it for data traffic

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Dual encryption

• Lets assume that everyone in the network has a
  public-private key pair. Alice wants to send a
  message to Bob and convince that it is from
  Alice.
• Two possible format which is better??

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• Reading Assignment
• Chapter 2, 3, 5, 6 of the text book
• Internetworking With TCP/IP Volume 1 Principles
  Protocols, and Architecture by Douglas Comer
  Chapter 4 Classful Internet Addresses