1. Security 0 The Secure Environment

2. Security 1 The Secure Environment Security goals (C.I.A.) and threats

3. Security 2 Common Categories 1.Casual prying by nontechnical users 2.Snooping by insiders 3.Determined attempt to make money 4.Commercial or military espionage 5.Others (such as cyber wars) Intruders

4. Security 3 Basics of Cryptography

5. Security 4 Network Is NOT Secure A B C D ABC

6. Security 5 A B C D ~!@ Encrypt Your Information

7. Security 6 Data Encryption Process Encryption Decryption Plaintext Ciphertext Network KEY

8. Security 7 (a) Conventional two-way Cryptography Encryption Decryption Plaintext Ciphertext Network KEY Encryption Decryption Plaintext Ciphertext Network (b) Public Key Cryptography KEY1KEY2 Two Types of Cryptography

9. Security 8 Conventional two-way Cryptography Encryption Decryption Plaintext Ciphertext Network KEY treaty impossible wuhdwb lpsrvvleoh treaty impossible abcdefghijklmnopqrstuvwxyz defghijklmnopqrstuvwxyzabc Encryption: c i =E(p i ) = p i + 3 Decryption: p i =D(c i ) = c i - 3 KEY: Caesar Cipher

10. Security 9 Conventional two-way Cryptography Substitution Cipher Caesar Cipher Playfair Cipher Etc.

11. Security 10 Conventional two-way Cryptography: Problems A B C D

12. Security 11 Public Key Cryptography Encryption Decryption Plaintext Ciphertext Network KEY1KEY2 Public Private

13. Security 12 Public Key Cryptography: Advantages A B C D Private key A Private key B Private key D Private key C Public key A Public key B Public key C Public key D

14. Security 13 PKI: Certification Authority What is a certificate? Why do we need Certification Authorities (CA) or trusted third party? A certificate is a digitally signed statement by a CA that provides independent confirmation of an attribute claimed by a person proffering a digital signature. More formally, a certificate is a computer-based record which: (1) identifies the CA issuing it, (2) names, identifies, or describes an attribute of the subscriber, (3) contains the subscriber's public key, and (4) is digitally signed by the CA issuing it.

15. Security 14 Trapdoor function Public Key Cryptography: Some Roads Are One-Way Easy Difficulty N5N5 N 1/5 Prime1 * Prime2 = Composite Composite = Prime1 * Prime2 Trapdoor characteristics: (1) It is easy to compute f(x) from x. (2) Computation of x from f(x) is likely to be intractable.

16. Security 15 An Example : Encryption E B (p) D B (E B (p)) = p Network User AUser B A encrypts message p using B’s public key B decrypts the ciphertext using its own private key

17. Security 16 Another Example : Digital Signature E B (D A (p)) E A (D B (E B (D A (p)))) = E A (D A (p)) = p Network User A User B A signs message p using its own private key and encrypts it using B’s public key B decrypts the ciphertext using its own private key and verifies it using A’s public key

18. Security 17 Hash functions ………. ……….. ………. ……… Hash Message Digest The basic requirements for a cryptographic hash function H(x) are as follows. The input can be of any length. The output has a fixed length. H(x) is relatively easy to compute for any given x. H(x) is one-way. H(x) is collision-free.

19. Security 18 More on Digital Signature ………. ……….. ………. ……… Hash Message Digest Signature Sign (decrypt) Using Private Key ………. ……….. Signature Append

20. Security 19 More on Digital Signature Hash Message Digest Verify (Encrypt operation) Using Public Key ………. ……….. Signature Message Digest

21. Security 20 User Authentication

22. Security 21 Basic Principles. Authentication must identify: 1.Something the user knows 2.Something the user has 3.Something the user is This is done before user can use the system User Authentication

23. Security 22 (a) A successful login (b) Login rejected after name entered (c) Login rejected after name and password typed Authentication Using Passwords Note: be careful when failed several times.

24. Security 23 Authentication Using Passwords How a cracker broke into LBL (source: A.S.Tanenbaum “Modern Operating System” course materials) a U.S. Dept. of Energy research lab

25. Security 24 Login Spoofing % Login: (a) Correct login screen (b) Phony login screen

26. Security 25 Authentication Using Passwords The use of salt to defeat precomputation of encrypted passwords Salt Password,,,,

27. Security 26 Authentication Using a Physical Object Magnetic cards magnetic stripe cards chip cards: stored value cards, smart cards

28. Security 27 Authentication Using Biometrics A device for measuring finger length.

29. Security 28 Countermeasures Limiting times when someone can log in Automatic callback at number prespecified Limited number of login tries A database of all logins Simple login name/password as a trap security personnel notified when attacker bites

30. Security 29 Secure Communications Over Insecure Channels R. C. Merkle’s Puzzle “secure Communications over Insecure Channels” Communications of the ACM, 1978, Vol. 21, No. 4.

31. Security 30 One-way Hash Chain and TESLA Adrian Perrig, Ran Canetti, Dawn Song, and J. D. Tygar. Efficient and secure source authentication for multicast. In Network and Distributed System Security Symposium, NDSS '01, February 2001.