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CS 54001 -1: Large-Scale Networked Systems Professor: Ian Foster TAs: Xuehai Zhang, Yong Zhao CS 54001 -1: Large-Scale Networked Systems Professor: Ian Foster TAs: Xuehai Zhang, Yong Zhao Lecture 4 www. classes. cs. uchicago. edu/classes/archive/2003/winter/54001 -1

Week 1: Internet Design Principles & Protocols l An introduction to the mail system Week 1: Internet Design Principles & Protocols l An introduction to the mail system l An introduction to the Internet l Internet design principles and layering l Brief history of the Internet l Packet switching and circuit switching l Protocols l Addressing and routing l Performance metrics l A detailed FTP example CS 54001 -1 Winter Quarter 2

Week 2: Routing and Transport l Routing techniques – Flooding – Distributed Bellman Ford Week 2: Routing and Transport l Routing techniques – Flooding – Distributed Bellman Ford Algorithm – Dijkstra’s Shortest Path First Algorithm l Routing in the Internet – Hierarchy and Autonomous Systems – Interior Routing Protocols: RIP, OSPF – Exterior Routing Protocol: BGP l Transport: achieving reliability l Transport: achieving fair sharing of links CS 54001 -1 Winter Quarter 3

Week 3: Measurement & Characterization l What does the Internet look like? l What Week 3: Measurement & Characterization l What does the Internet look like? l What does Internet traffic look like? l How do I measure such things? l How do such characteristics evolve? l l What Internet characteristics are shared with other networks? Are all those Faloutsos’ related? CS 54001 -1 Winter Quarter 4

Week 4: Security l Context: Attacks, services, & mechanisms l Message encryption l Public Week 4: Security l Context: Attacks, services, & mechanisms l Message encryption l Public key cryptography l Authentication protocols l Message integrity l Public key infrastructure l Firewalls CS 54001 -1 Winter Quarter 5

Attacks, Services and Mechanisms l l l Security Attack: Any action that compromises the Attacks, Services and Mechanisms l l l Security Attack: Any action that compromises the security of information. Security Mechanism: A mechanism that is designed to detect, prevent, or recover from a security attack. Security Service: A service that enhances the security of data processing systems and information transfers. A security service makes use of one or more security mechanisms. CS 54001 -1 Winter Quarter 6

Security Attacks CS 54001 -1 Winter Quarter 7 Security Attacks CS 54001 -1 Winter Quarter 7

Security Attacks l l Interruption: This is an attack on availability Interception: This is Security Attacks l l Interruption: This is an attack on availability Interception: This is an attack on confidentiality Modification: This is an attack on integrity Fabrication: This is an attack on authenticity CS 54001 -1 Winter Quarter 8

Active and Passive Threats CS 54001 -1 Winter Quarter 9 Active and Passive Threats CS 54001 -1 Winter Quarter 9

Methods of Defense l l Encryption Software Controls (access limitations in a data base, Methods of Defense l l Encryption Software Controls (access limitations in a data base, in operating system protect each user from other users) l Hardware Controls (smartcard) l Policies (frequent changes of passwords) l Physical Controls CS 54001 -1 Winter Quarter 10

Security Algorithms & Services Security Cryptography algorithms Secret key (e. g. , DES) CS Security Algorithms & Services Security Cryptography algorithms Secret key (e. g. , DES) CS 54001 -1 Public key (e. g. , RSA) Security services Message digest (e. g. , MD 5) Winter Quarter Privacy Chapter 8, Figure 3 Authentication Message integrity 11

Security Services l Confidentiality (privacy) l Authentication (who created or sent the data) l Security Services l Confidentiality (privacy) l Authentication (who created or sent the data) l Integrity (has not been altered) l Non-repudiation (the order is final) l Access control (prevent misuse of resources) l Availability (permanence, non-erasure) – Denial of Service Attacks – Virus that deletes files CS 54001 -1 Winter Quarter 12

CS 54001 -1 Winter Quarter 13 CS 54001 -1 Winter Quarter 13

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Week 4: Security l Context: Attacks, services, & mechanisms l Message encryption l Public Week 4: Security l Context: Attacks, services, & mechanisms l Message encryption l Public key cryptography l Authentication protocols l Message integrity l Public key infrastructure l Firewalls CS 54001 -1 Winter Quarter 15

Conventional Encryption Principles l An encryption scheme has five ingredients: – Plaintext – Encryption Conventional Encryption Principles l An encryption scheme has five ingredients: – Plaintext – Encryption algorithm – Secret Key – Ciphertext – Decryption algorithm l Security depends on the secrecy of the key, not the secrecy of the algorithm CS 54001 -1 Winter Quarter 16

Conventional Encryption Principles CS 54001 -1 Winter Quarter 17 Conventional Encryption Principles CS 54001 -1 Winter Quarter 17

Cryptography l Classified along three independent dimensions: – The type of operations used for Cryptography l Classified along three independent dimensions: – The type of operations used for transforming plaintext to ciphertext – The number of keys used > symmetric (single key) > asymmetric (two-keys, or public-key encryption) – The way in which the plaintext is processed CS 54001 -1 Winter Quarter 18

Average time required for exhaustive key search Key Size (bits) Number of Alternative Keys Average time required for exhaustive key search Key Size (bits) Number of Alternative Keys Time required at 106 Decryption/µs 32 232 = 4. 3 x 109 2. 15 milliseconds 56 256 = 7. 2 x 1016 10 hours 128 2128 = 3. 4 x 1038 5. 4 x 1018 years 168 2168 = 3. 7 x 1050 5. 9 x 1030 years CS 54001 -1 Winter Quarter 19

Conventional Encryption Algorithms l Data Encryption Standard (DES) – The most widely used encryption Conventional Encryption Algorithms l Data Encryption Standard (DES) – The most widely used encryption scheme – The algorithm is reffered to the Data Encryption Algorithm (DEA) – DES is a block cipher – The plaintext is processed in 64 -bit blocks – The key is 56 -bits in length CS 54001 -1 Winter Quarter 20

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CS 54001 -1 Winter Quarter 22 CS 54001 -1 Winter Quarter 22

Expansion Phase of DES 4 -bit chunk … … Expanded to 6 bits by Expansion Phase of DES 4 -bit chunk … … Expanded to 6 bits by stealing a bit from left and right chunks CS 54001 -1 Winter Quarter Chapter 8, Figure 6 23

Cipher Block Chaining Block 1 Block 4 + + DES DES Cipher 1 CS Cipher Block Chaining Block 1 Block 4 + + DES DES Cipher 1 CS 54001 -1 Block 3 DES IV Block 2 Cipher 3 Cipher 4 Winter Quarter Chapter 8, Figure 7 24

Time to break a code (106 decryptions/µs) CS 54001 -1 Winter Quarter 25 Time to break a code (106 decryptions/µs) CS 54001 -1 Winter Quarter 25

Week 4: Security l Context: Attacks, services, & mechanisms l Message encryption l Public Week 4: Security l Context: Attacks, services, & mechanisms l Message encryption l Public key cryptography l Authentication protocols l Message integrity l Public key infrastructure l Firewalls CS 54001 -1 Winter Quarter 26

Public-Key Cryptography CS 54001 -1 Winter Quarter 27 Public-Key Cryptography CS 54001 -1 Winter Quarter 27

Applications for Public-Key Cryptosystems l Three categories: – Encryption/decryption: The sender encrypts a message Applications for Public-Key Cryptosystems l Three categories: – Encryption/decryption: The sender encrypts a message with the recipient’s public key – Digital signature: The sender ”signs” a message with its private key – Key exchange: Two sides cooperate to exhange a session key CS 54001 -1 Winter Quarter 28

Requirements for Public-Key Cryptography l l l Computationally easy for a party B to Requirements for Public-Key Cryptography l l l Computationally easy for a party B to generate a pair (public key KUb, private key KRb) Easy for sender to generate ciphertext Easy for the receiver to decrypt ciphertect using private key CS 54001 -1 Winter Quarter 29

Requirements for Public-Key Cryptography l l l Computationally infeasible to determine private key (KRb) Requirements for Public-Key Cryptography l l l Computationally infeasible to determine private key (KRb) knowing public key (KUb) Computationally infeasible to recover message M, knowing KUb and ciphertext C Either of the two keys can be used for encryption, with the other used for decryption CS 54001 -1 Winter Quarter 30

Public-Key Cryptographic Algorithms l l RSA and Diffie-Hellman RSA - Ron Rives, Adi Shamir Public-Key Cryptographic Algorithms l l RSA and Diffie-Hellman RSA - Ron Rives, Adi Shamir and Len Adleman at MIT, in 1977. – RSA is a block cipher – The most widely implemented l Diffie-Hellman – Exchange a secret key securely – Compute discrete logarithms CS 54001 -1 Winter Quarter 31

The RSA Algorithm – Key Generation 1. Select p, q 2. Calculate n = The RSA Algorithm – Key Generation 1. Select p, q 2. Calculate n = p x q 3. Calculate 4. Select integer e 5. Calculate d 6. Public Key KU = {e, n} 7. Private key KR = {d, n} CS 54001 -1 Winter Quarter p and q both prime 32

Example of RSA Algorithm CS 54001 -1 Winter Quarter 33 Example of RSA Algorithm CS 54001 -1 Winter Quarter 33

The RSA Algorithm - Encryption l Plaintext: M<n l Ciphertext: C = Me (mod The RSA Algorithm - Encryption l Plaintext: M

The RSA Algorithm - Decryption l Ciphertext: C l Plaintext: M = Cd (mod The RSA Algorithm - Decryption l Ciphertext: C l Plaintext: M = Cd (mod n) CS 54001 -1 Winter Quarter 35

Key Management Public-Key Certificate Use CS 54001 -1 Winter Quarter 36 Key Management Public-Key Certificate Use CS 54001 -1 Winter Quarter 36

Week 4: Security l Context: Attacks, services, & mechanisms l Message encryption l Public Week 4: Security l Context: Attacks, services, & mechanisms l Message encryption l Public key cryptography l Authentication protocols l Message integrity l Public key infrastructure l Firewalls CS 54001 -1 Winter Quarter 37

Authentication Protocols l Simple three-way handshake – Assume two parties share a secret key Authentication Protocols l Simple three-way handshake – Assume two parties share a secret key l Trusted third party – E. g. , Kerberos l Public key authentication CS 54001 -1 Winter Quarter 38

Simple Three-Way Handshake E(m, k) denotes encryption of message m with key k CS Simple Three-Way Handshake E(m, k) denotes encryption of message m with key k CS 54001 -1 Winter Quarter Chapter 8, Figure 9 39

Trusted Third Party S A B A, B E((T , L, K , B), Trusted Third Party S A B A, B E((T , L, K , B), KA ), L, K , A), KB ) E((A , T), E((T K), , L, K , A ), KB ) + 1, K E (T ) Ka and Kb are secret keys shared with server S T=timestamp, L=lifetime, K=session key CS 54001 -1 Winter Quarter Chapter 8, Figure 10 40

Public Key Cryptography CS 54001 -1 Winter Quarter Chapter 8, Figure 11 41 Public Key Cryptography CS 54001 -1 Winter Quarter Chapter 8, Figure 11 41

Message Integrity l Requirements - must be able to verify that: – Message came Message Integrity l Requirements - must be able to verify that: – Message came from apparent source or author, – Contents have not been altered, – Sometimes, it was sent at a certain time or sequence. l Protection against active attack (falsification of data and transactions) CS 54001 -1 Winter Quarter 42

Approaches to Message Integrity l Conventional encryption – Only the sender and receiver should Approaches to Message Integrity l Conventional encryption – Only the sender and receiver should share a key l Message integrity without message encryption – An authentication tag is generated and appended to each message l Message Authentication Code – Calculate the MAC as a function of the message and the key. MAC = F(K, M) CS 54001 -1 Winter Quarter 43

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One-way HASH function CS 54001 -1 Winter Quarter 45 One-way HASH function CS 54001 -1 Winter Quarter 45

One-way HASH function l Secret value is added before the hash and removed before One-way HASH function l Secret value is added before the hash and removed before transmission. CS 54001 -1 Winter Quarter 46

Secure HASH Functions l l Purpose of the HASH function is to produce a Secure HASH Functions l l Purpose of the HASH function is to produce a ”fingerprint. Properties of a HASH function H : 1. 2. 3. 4. 5. 6. CS 54001 -1 H can be applied to a block of data at any size H produces a fixed length output H(x) is easy to compute for any given x. For any given block x, it is computationally infeasible to find x such that H(x) = h For any given block x, it is computationally infeasible to find with H(y) = H(x). It is computationally infeasible to find any pair (x, y) such that H(x) = H(y) Winter Quarter 47

Simple Hash Function l One-bit circular shift on the hash value after each block Simple Hash Function l One-bit circular shift on the hash value after each block is processed would improve CS 54001 -1 Winter Quarter 48

Message Digest Generation Using SHA-1 CS 54001 -1 Winter Quarter 49 Message Digest Generation Using SHA-1 CS 54001 -1 Winter Quarter 49

SHA-1 Processing of single 512 -Bit Block CS 54001 -1 Winter Quarter 50 SHA-1 Processing of single 512 -Bit Block CS 54001 -1 Winter Quarter 50

Sender identity and message integrity confirmed if checksums match Calculate MD 5 checksum over Sender identity and message integrity confirmed if checksums match Calculate MD 5 checksum over message contents Sign checksum using RSA with sender’ s private key Calculate MD 5 checksum on received message and compare against received value Decrypt signed checksum with sender’ s public key Transmitted message CS 54001 -1 Winter Quarter Chapter 8, Figure 13 51

Create a random secret key k Original message Encrypt message using DES with secret Create a random secret key k Original message Encrypt message using DES with secret key k Decrypt message using DES with secret key k Encrypt k using RSA with recipient’ s public key Decrypt E(k) using RSA with my private key -> k Encode message + E(k) in ASCII for transmission Convert ASCII message Transmitted message CS 54001 -1 Winter Quarter Chapter 8, Figure 14 52

Week 4: Security l Context: Attacks, services, & mechanisms l Message encryption l Public Week 4: Security l Context: Attacks, services, & mechanisms l Message encryption l Public key cryptography l Authentication protocols l Message integrity l Public key infrastructure l Firewalls CS 54001 -1 Winter Quarter 53

Public-Key Cryptography Principles l l The use of two keys has consequences in: key Public-Key Cryptography Principles l l The use of two keys has consequences in: key distribution, confidentiality and authentication. The scheme has six ingredients – Plaintext – Encryption algorithm – Public and private key – Ciphertext – Decryption algorithm CS 54001 -1 Winter Quarter 54

Encryption using Public-Key system CS 54001 -1 Winter Quarter 55 Encryption using Public-Key system CS 54001 -1 Winter Quarter 55

X. 509 Authentication Service l l Distributed set of servers that maintains a database X. 509 Authentication Service l l Distributed set of servers that maintains a database about users Each certificate contains the public key of a user and is signed with the private key of a CA Is used in S/MIME, IP Security, SSL/TLS and SET RSA is recommended CS 54001 -1 Winter Quarter 56

X. 509 Formats CS 54001 -1 Winter Quarter 57 X. 509 Formats CS 54001 -1 Winter Quarter 57

Typical Digital Signature Approach CS 54001 -1 Winter Quarter 58 Typical Digital Signature Approach CS 54001 -1 Winter Quarter 58

Obtaining a User’s Certificate l Characteristics of certificates generated by CA: – Any user Obtaining a User’s Certificate l Characteristics of certificates generated by CA: – Any user with access to the public key of the CA can recover the user public key that was certified. – No part other than the CA can modify the certificate without this being detected. CS 54001 -1 Winter Quarter 59

IPRA = Internet Policy Registration Authority (root) PCA n= policy certification authority CA = IPRA = Internet Policy Registration Authority (root) PCA n= policy certification authority CA = certification authority IPRA PCA 1 CA User PCA 2 CA User CS 54001 -1 CA CA User PCA 3 CA CA CA User CA User Winter Quarter Chapter 8, Figure 12 60

X. 509 CA Hierarchy CS 54001 -1 Winter Quarter 61 X. 509 CA Hierarchy CS 54001 -1 Winter Quarter 61

Revocation of Certificates l Reasons for revocation: – The users secret key is assumed Revocation of Certificates l Reasons for revocation: – The users secret key is assumed to be compromised. – The user is no longer certified by this CA. – The CA’s certificate is assumed to be compromised. CS 54001 -1 Winter Quarter 62

Week 4: Security l Context: Attacks, services, & mechanisms l Message encryption l Public Week 4: Security l Context: Attacks, services, & mechanisms l Message encryption l Public key cryptography l Authentication protocols l Message integrity l Public key infrastructure l Firewalls CS 54001 -1 Winter Quarter 63

Firewall Design Principles l l The firewall is inserted between the premises network and Firewall Design Principles l l The firewall is inserted between the premises network and the Internet Aims: – Establish a controlled link – Protect the premises network from Internetbased attacks – Provide a single choke point CS 54001 -1 Winter Quarter 64

Firewall Characteristics l Design goals: – All traffic from inside to outside must pass Firewall Characteristics l Design goals: – All traffic from inside to outside must pass through the firewall (physically blocking all access to the local network except via the firewall) – Only authorized traffic (defined by the local security police) will be allowed to pass – The firewall itself is immune to penetration (use of trusted system with a secure operating system) CS 54001 -1 Winter Quarter 65

Four General Techniques l Service control – Determines the types of Internet services that Four General Techniques l Service control – Determines the types of Internet services that can be accessed, inbound or outbound l Direction control – Determines the direction in which particular service requests are allowed to flow l User control – Controls access to a service according to which user is attempting to access it l Behavior control – Controls how particular services are used (e. g. filter e-mail) CS 54001 -1 Winter Quarter 66

Types of Firewalls l Three common types of Firewalls: – Packet-filtering routers – Application-level Types of Firewalls l Three common types of Firewalls: – Packet-filtering routers – Application-level gateways – Circuit-level gateways – (Bastion host) CS 54001 -1 Winter Quarter 67

Types of Firewalls l Packet-filtering Router CS 54001 -1 Winter Quarter 68 Types of Firewalls l Packet-filtering Router CS 54001 -1 Winter Quarter 68

Types of Firewalls l Packet-filtering Router – Applies a set of rules to each Types of Firewalls l Packet-filtering Router – Applies a set of rules to each incoming IP packet and then forwards or discards the packet – Filter packets going in both directions – The packet filter is typically set up as a list of rules based on matches to fields in the IP or TCP header – Two default policies (discard or forward) CS 54001 -1 Winter Quarter 69

Types of Firewalls l Advantages: – Simplicity – Transparency to users – High speed Types of Firewalls l Advantages: – Simplicity – Transparency to users – High speed l Disadvantages: – Difficulty of setting up packet filter rules – Lack of Authentication CS 54001 -1 Winter Quarter 70

Types of Firewalls l Possible attacks and appropriate countermeasures – IP address spoofing – Types of Firewalls l Possible attacks and appropriate countermeasures – IP address spoofing – Source routing attacks – Tiny fragment attacks CS 54001 -1 Winter Quarter 71

Types of Firewalls l Application-level Gateway CS 54001 -1 Winter Quarter 72 Types of Firewalls l Application-level Gateway CS 54001 -1 Winter Quarter 72

Types of Firewalls l Application-level Gateway – Also called proxy server – Acts as Types of Firewalls l Application-level Gateway – Also called proxy server – Acts as a relay of application-level traffic l Advantages: – Higher security than packet filters – Only need to scrutinize a few allowable applications – Easy to log and audit all incoming traffic l Disadvantages: – Additional processing overhead on each connection (gateway as splice point) CS 54001 -1 Winter Quarter 73

Types of Firewalls l Circuit-level Gateway CS 54001 -1 Winter Quarter 74 Types of Firewalls l Circuit-level Gateway CS 54001 -1 Winter Quarter 74

Types of Firewalls l Circuit-level Gateway – Stand-alone system or – Specialized function performed Types of Firewalls l Circuit-level Gateway – Stand-alone system or – Specialized function performed by an Application-level Gateway – Sets up two TCP connections – The gateway typically relays TCP segments from one connection to the other without examining the contents CS 54001 -1 Winter Quarter 75

Types of Firewalls l Circuit-level Gateway – The security function consists of determining which Types of Firewalls l Circuit-level Gateway – The security function consists of determining which connections will be allowed – Typically use is a situation in which the system administrator trusts the internal users – An example is the SOCKS package CS 54001 -1 Winter Quarter 76

Course Outline (Subject to Change) 1. (January 9 th) Internet design principles and protocols Course Outline (Subject to Change) 1. (January 9 th) Internet design principles and protocols 2. (January 16 th) Internetworking, transport, routing 3. (January 23 rd) Mapping the Internet and other networks 4. (January 30 th) Security 5. (February 6 th) P 2 P technologies & applications (Matei Ripeanu) (plus midterm) 6. (February 13 th) Optical networks (Charlie Catlett) 7. *(February 20 th) Web and Grid Services (Steve Tuecke) 8. (February 27 th) Network operations (Greg Jackson) 9. 10. *(March 6 th) Advanced applications (with guest lecturers: Terry Disz, Mike Wilde) (March 13 th) Final exam * Ian Foster is out of town. CS 54001 -1 Winter Quarter 77