1. CONFIDENTIALY USING CONVENTIONAL ENCRYPTION – Chapter 7 CONFIDENTIALY USING CONVENTIONAL ENCRYPTION – Chapter 7 Historically – Conventional Encryption Recently – Authentication, Integrity, Signature, Public-key Link End-to-End Traffic-Analysis Key Distribution Random Number Generation

2. 2 Points of Vulnerability

3. 3 Link / End-to-End

4. Link - both ends of link - many encryps / decryps - all links use it - decrypt at packet switch (read addr.) - unique key / node pair End- to-End - only at ends - data encrypted, not address (header) - one key pair - traffic pattern insecure - authentication from sender Confidentiality Confidentiality

5. Table 7.1 Characteristics of Link and End-to-End Characteristics of Link and End-to-End

6. - Data secure at nodes - Authentication LINK – low level (physical/link) END-TO-END – network (X.25)  End 0  End 1 (ends separately  End 2 protected) | Both Link and End-to-End

7. Front-End Processor Function

8. E-mail Gateway

9. OSI  email gateway  TCP no end-to-end protocol below appl. layer networks terminate at mail gateway mail gateway sets up new transport/network connections need end-to-end encryp. at appl. Layer - disadvantage: many keys E-mail Gateway E-mail Gateway

10. Various Encryption Strategies

11. Traffic Confidentiality Traffic Confidentiality Identities Message Frequency Message Pattern Event Correlation Covert Channel Link Headers encrypted Traffic padding (Fig 7.6) End-to-End Pad data Null messages

12. Traffic Padding

13. KEY DISTRIBUTION KEY DISTRIBUTION 1.Physically deliver 2.Third party physically select/deliver 3.E K old (K new ) → 4. End-to-End(KDC): A E KA (K new )  C  E KB (K new ) B N hosts → (N)choose(2) keys – Fig 7.7 KDC – Key hierarchy – Fig 7.8 Session Key – temporary : end ↔ end Only N master keys – physical delivery

14. #End-to-End Keys

15. Key Hierarchy

16. 16 KEY DISTRIBUTION SCENARIO

17. KEY DISTRIBUTION KEY DISTRIBUTION User shares Master Key with KDC Steps 1-3 : Key Distribution Steps 3,4,5 : Authentication

18. Key Distribution Centre (KDC) Hierarchy Key Distribution Centre (KDC) Hierarchy LOCAL KDCs KDCX KDCA KDCB A B Key selected by KDCA, KDCB, or KDCX

19. LIFETIME LIFETIME Shorter Lifetime → Highter Security → Reduced Capacity Connection-oriented: - change session key periodically Connectionless: - new key every exchange or #transactions or after time period

20. Key Distribution (connection-oriented) End-to-End (X.25,TCP), FEP obtains session keys

21. Decentralised Key Control Not practical for large networks - avoids trusted third party

22. KEY USAGE KEY USAGE key types : Data, PIN, File key tags : Session/Master/Encryp/Decryp Control Vector: associate session key with control vector (Fig 7.12)

23. Control Vector Encryp. and Decryp.

24. PRNG From Counter

25. ANSI X9.17 PRNG

26. Random Number Generation Linear Congruential Generator X n+1 = (aX n + c) mod m Encryption : DES (OFB) – (Fig 7.14) Blum Blum Shub (BBS) X 0 = s 2 mod n for i = 1 to infinity X i = (X i-1 ) 2 mod n B i = X i mod 2