Security

1. Security Yih-Kuen Tsay Dept. of Information Management National Taiwan University Security -- 1

2. Introduction • Security Needs • Secrecy (confidentiality), integrity, etc. • Arise from the desire to share resources • Security Policies • Specify who are authorized to access what resources • Independent of the technology used • Security Mechanisms • Enforce security policies • Security Models • Help understand and analyze the above Security -- 2

3. Components of a Security Model Source: G. Coulouris et al., Distributed Systems: Concepts and Design, Fourth Edition. Security -- 3

4. The Enemy in Network Security Source: G. Coulouris et al., Distributed Systems: Concepts and Design, Fourth Edition. Security -- 4

5. Familiar Names in the Security Literature Source: G. Coulouris et al., Distributed Systems: Concepts and Design, Fourth Edition. Security -- 5

6. Classes of Security Threats • Leakage • Acquisition of information by unauthorized parties • Tampering (Modification) • Unauthorized alteration of information • Vandalism • Interference with the proper operation without gain to the perpetrator Security -- 6

7. Methods of Attack • Eavesdropping • Release of message contents and traffic analysis • Masquerading • Message Tampering (Modification) • Man-in-the-middle attack • Replaying • Denial of Service • Mobile Code Security -- 7

8. Designing Secure Systems • Use best standards available • Informal analysis and checks • Formal validation • Security logs and auditing Security -- 8

9. Security Requirements • Secrecy (Confidentiality) • Data Integrity • Authentication • Non-repudiation • Availability • … Security -- 9

10. The Secret-Key Encryption Model Source: W. Stallings, “Cryptography and Network Security” Security -- 10

11. The Public-Key Encryption Model Source: W. Stallings, “Cryptography and Network Security” Security -- 11

12. The Public-Key Authentication Model Source: W. Stallings, “Cryptography and Network Security” Security -- 12

13. Notational Conventions Source: G. Coulouris et al., Distributed Systems: Concepts and Design, Fourth Edition. Security -- 13

14. Alice’s Bank Account Certificate Source: G. Coulouris et al., Distributed Systems: Concepts and Design, Fourth Edition. Security -- 14

15. A Public Key Certificate of Bob’s Bank Source: G. Coulouris et al., Distributed Systems: Concepts and Design, Fourth Edition. Security -- 15

16. A Scheme of Cipher Block Chaining Source: G. Coulouris et al., Distributed Systems: Concepts and Design, Fourth Edition. Security -- 16

17. A Stream Cipher Source: G. Coulouris et al., Distributed Systems: Concepts and Design, Fourth Edition. Security -- 17

18. Digital Signatures with Secret Keys Source: G. Coulouris et al., Distributed Systems: Concepts and Design, Fourth Edition. Security -- 18

19. Digital Signatures with Public Keys Source: G. Coulouris et al., Distributed Systems: Concepts and Design, Fourth Edition. Security -- 19

20. Key size/hash size Extrapolated PRB optimized (bits) speed (kbytes/s) (kbytes/sec.) TEA 128 700 - DES 56 350 7746 112 120 2842 Triple-DES IDEA 128 700 4469 512 7 - RSA RSA 2048 1 - MD5 128 1740 62425 160 750 25162 SHA Performance of Encryption Algorithms Source: G. Coulouris et al., Distributed Systems: Concepts and Design, Fourth Edition. Security -- 20

21. The Needham-Schroeder Authentication Protocol Source: G. Coulouris et al., Distributed Systems: Concepts and Design, Fourth Edition. Security -- 21

22. Kerberos • Developed at MIT (Project Athena) • For protecting networked services • Based on the Needham-Schroeder protocol • Current version: Kerberos Version 5 • Source code available • Also used in OSF DCE, Windows 2000, ... • Probable extension for the initial authentication of principals Security -- 22

23. Kerberos Architecture Source: G. Coulouris et al., Distributed Systems: Concepts and Design, Fourth Edition. Security -- 23

24. The Kerberos Protocol Source: G. Coulouris et al., Distributed Systems: Concepts and Design, Fourth Edition. Security -- 24

25. The Kerberos Protocol (cont.) auth(C) contains C,t. ticket(C,S) contains C,S,t1,t2,KCS. Source: G. Coulouris et al., Distributed Systems: Concepts and Design, Fourth Edition. Security -- 25

26. Critiques of Kerberos • Synchronization of clients’ and servers’ clocks (Version 4) • Unique timestamps or sequence numbers as nonces • Limited session lifetimes Security -- 26

27. TLS/SSL • The Secure Sockets Layer (SSL) protocol originated from Netscape, now a nonproprietary standard (SSLv3) • An extension of SSL became the Transport Layer Security (TLS) protocol (RFC 2246) • Provides secure end-to-end communications • Operates between TCP/IP (or any other reliable transport protocol) and the application • Built into most browsers and servers Security -- 27

28. TLS TLS Change TLS Alert Handshake HTTP Telnet Cipher Spec Protocol protocol TLS Record Protocol Transport layer (usually TCP) Network layer (usually IP) TLS protocols: Other protocols: The TLS/SSL Protocol Stack Source: G. Coulouris et al., Distributed Systems: Concepts and Design, Fourth Edition. Security -- 28

29. How SSL/TLS Works • Sessions between a client and a server are established by the Handshake Protocol • A session defines a set of security parameters, including peer certificate, cipher spec, and master secret • Multiple connections can be established within a session, each defining further security parameters such as keys for encryption and authentication • Security parameters dictate how application data are processed by the SSL Record Protocol into TCP segments Security -- 29

30. Security Functions of SSL/TLS • Confidentiality: using one of DES, Triple DES, IDEA, RC2, RC4, … • Integrity: using MAC with MD5 or SHA-1 • Authentication: using X.509v3 digital certificates Security -- 30

31. The SSL/TLS Handshake Protocol Security -- 31 Source: G. Coulouris et al., Distributed Systems: Concepts and Design, Fourth Edition.

32. Component Description Example Key exchange the method to be used for RSA with public-key method exchange of a session key certificates Cipher for data the block or stream cipher to be IDEA transfer used for data Message digest for creating message SHA function authentication codes (MACs) SSL/TLS Handshake Configuration Options Source: G. Coulouris et al., Distributed Systems: Concepts and Design, Fourth Edition. Security -- 32

33. The SSL/TLS Record Protocol Source: G. Coulouris et al., Distributed Systems: Concepts and Design, Fourth Edition. Security -- 33

34. Wired Equivalent Privacy (WEP) • Access control by a challenge-response protocol • A single key shared by the base station and all authorized devices • Encryption based on RC4 • The access key also used for encryption Security -- 34

35. RC4 in IEEE 802.11 WEP *Note: The IV is only 24-bit long and is sent in clear. Source: G. Coulouris et al., Distributed Systems: Concepts and Design, Fourth Edition. Security -- 35

36. Weaknesses in WEP • The sharing of a single key • Base stations never authenticated • Inappropriate use of a stream cipher • Key lengths of 40 bits and 64 bits • Weakness of RC4 • The user’s likely lack of awareness Solution: WPA (Wi-Fi Protected Access) and 802.11i WPA2 Security -- 36

37. Micropayments • The price of some goods may be lower than the standard transaction fees • Micropayments offer a way for selling small-value products and services • Technology providers: eCharge (via phone bills), Qpass (monthly bills), Millicent (prepay electronic cash), ... Security -- 37