Outline

1. Outline • Announcement • Authentication • Cryptography • Authentication • Quiz #3 at the end of today’s class

2. Announcement • You must do your demo before 4:30pm, April 29, 2003 • Name server: program1 • Prefix table Logical Prefix Server IP Server Port Remote directory / 128.186.120.34 1281 /tmp/XXX/cop5611-DFS /program1 128.186.120.53 1282 /tmp/XXX/cop5611-DFS /linprog1 128.186.120.33 1280 /tmp/liux/cop5611-DFS /program3 128.186.120.55 1285 /tmp/XXX/cop5611-DFS • You need to have your servers running before you come to my office • I will test your system through your client program and based on your report COP 5611 - Operating Systems

3. Introduction • The fundamental problem to security in distributed systems is the use of cryptographic techniques • Access matrix model can be used to prevent unauthorized accesses if the users that claimed to be are true • However, in distributed systems, the user authentication becomes a big problem COP 5611 - Operating Systems

4. Introduction – cont. COP 5611 - Operating Systems

5. Potential Threats • A threat to a system in which an intruder can have access to only the ciphertext is called a ciphertext-only attack • A threat to a system in which an intruder can have access to both ciphertext and a considerable amount of corresponding plaintext is called a known-plaintext attack • A threat to a system in which an intruder can obtain ciphertext corresponding to plaintext of his choice is referred to as a chosen-plaintext attack COP 5611 - Operating Systems

6. Design Principles • Shannon’s principle • Shannon’s principle of diffusion – Spread the correlation and dependencies among key-string variables over substrings as much as possible • Shannon’s principle of confusion – Change a piece of information so that the output has no obvious relation to the input • Exhaustive search principle • The determination of the key requires an exhaustive search of the an extremely large space COP 5611 - Operating Systems

7. Private Key Cryptography • Data encryption standard (DES) • It is a block cipher that crypts 64-bit data blocks using a 56-bit key • Two basic operations • Permutation • Substitution • Three stages • Initial permutation stage • Complex transformation stage • Final permutation stage COP 5611 - Operating Systems

8. Private Key Cryptography – cont. COP 5611 - Operating Systems

9. Private Key Cryptography – cont. COP 5611 - Operating Systems

10. Private Key Cryptography – cont. COP 5611 - Operating Systems

11. Public Key Cryptography • Private key cryptography and conventional cryptographic techniques require the distribution of secret keys • Known as the key distribution problem • Public key cryptography solves the key distribution problem by making the encryption procedure and the associated key available in the public domain COP 5611 - Operating Systems

12. Public Key Cryptography – cont. • Now it is possible for two users to have a secure communication even they have not communicated before • Implementation issues • One-way functions COP 5611 - Operating Systems

13. RSA Method • The encryption key is a pair (e, n) • The decryption key is a pair (d, n) COP 5611 - Operating Systems

14. RSA Method – cont. • Generating the private and public key requires four steps • Choose two very large prime numbers, p and q • Compute n = p x q and z = (p – 1) x (q – 1) • Choose a number d that is relatively prime to z • Compute the number e such that e x d = 1 mod z COP 5611 - Operating Systems

15. Authentication • In distributed systems, authentication means verifying the identity of communicating entities to each other • The assumption is that the communication network is not secure in that an intruder can copy and play back a message on the network • The textbook called it “interactive secure connections” COP 5611 - Operating Systems

16. Authentication – cont. • Authentication based on a shared secret key. COP 5611 - Operating Systems

17. Authentication – cont. • Authentication based on a shared secret key, but using three instead of five messages. COP 5611 - Operating Systems

18. Authentication – cont. • The reflection attack. COP 5611 - Operating Systems

19. Authentication Using a Key Distribution Center • The principle of using a KDC. COP 5611 - Operating Systems

20. Authentication Using a Key Distribution Center – cont. • Using a ticket and letting Alice set up a connection to Bob. COP 5611 - Operating Systems

21. Authentication Using a Key Distribution Center – cont. • The Needham-Schroeder authentication protocol. COP 5611 - Operating Systems

22. Authentication Using a Key Distribution Center – cont. • Protection against malicious reuse of a previously generated session key in the Needham-Schroeder protocol. COP 5611 - Operating Systems

23. Authentication Using Public-Key Cryptography • Mutual authentication in a public-key cryptosystem. COP 5611 - Operating Systems

24. Message Integrity and Confidentiality • Message integrity means that messages are protected against modification • Confidentiality ensures that messages cannot be intercepted and read by eavesdroppers • Digital signatures • A user cannot forge the signature of other users • A sender of a signed message cannot deny the validity of his signature on the message • A recipient of a signed message cannot modify the signature in the message COP 5611 - Operating Systems

25. Digital Signatures • Digital signing a message using public-key cryptography. COP 5611 - Operating Systems

26. Digital Signatures – cont. COP 5611 - Operating Systems

27. Digital Signatures – cont. • Digitally signing a message using a message digest. COP 5611 - Operating Systems

28. Key Establishment • The principle of Diffie-Hellman key exchange. COP 5611 - Operating Systems

29. Key Distribution COP 5611 - Operating Systems

30. Key Distribution – cont. COP 5611 - Operating Systems

31. Kerberos COP 5611 - Operating Systems

32. Kerberos – cont. • Setting up a secure channel in Kerberos. COP 5611 - Operating Systems

33. Electronic Payment Systems • Payment systems based on direct payment between customer and merchant. • Paying in cash. • Using a check. • Using a credit card. COP 5611 - Operating Systems

34. Electronic Payment Systems – cont. • Payment systems based on money transfer between banks. • Payment by money order. • Payment through debit order. COP 5611 - Operating Systems

35. E-cash COP 5611 - Operating Systems

36. Secure Electronic Transactions COP 5611 - Operating Systems

37. Summary • Cryptography is a fundamental problem in security of distributed systems • Based on private keys • Based on public keys • Authentication in distributed systems • There are still a lot of challenges and research issues in this area COP 5611 - Operating Systems