1. Gold Coast Campus School of Information Technology 2003/16216/3112INT Network Security 1Copyright © Griffith University, 2003 6216INT / 3112INT Network Security Lecture 7. Web Security

2. 2003/16216/3112INT Network SecurityLecture 7 – Web Security - 2 References Cryptography and Network Security: Principles and Practice, 3rd ed., William Stallings: Chapter 17

3. 2003/16216/3112INT Network SecurityLecture 7 – Web Security - 3 Web Security Web now widely used by business, government, individuals but Internet & Web are vulnerable have a variety of threats  integrity  confidentiality  denial of service  authentication need added security mechanisms

4. 2003/16216/3112INT Network SecurityLecture 7 – Web Security - 4 Web Security Focus on two standardised schemes:  SSL/ TLS  SET WWW is a client/ server application Security tools discussed so far are relevant But, web presents new challenges not appreciated in the computer & network security: -

5. 2003/16216/3112INT Network SecurityLecture 7 – Web Security - 5 Web Security The Internet is 2 way: the web is vulnerable to attacks on the web servers Reputation can be damaged & money can be lost Although developing web application is easy, underlying s/w is extremely complex => security flaws A web server can be exploited as a launching pad Most clients are untrained & not aware of the risks

6. 2003/16216/3112INT Network SecurityLecture 7 – Web Security - 6 Web Security Threats Threats may be classified as:  Passive attacks Eavesdropping  Active attacks Impersonating Altering messages in transit Altering information on a website Threats can be in:  Web server  computer system security  Web browser  computer system security  Network traffic  network security

7. 2003/16216/3112INT Network SecurityLecture 7 – Web Security - 7 Web Security Network level: IPSec  Transparent to end users & applications  Only selected traffic need incur the overhead of IPSec processing Transport level: SSL/ TLS

8. 2003/16216/3112INT Network SecurityLecture 7 – Web Security - 8 Web Security

9. 2003/16216/3112INT Network SecurityLecture 7 – Web Security - 9 Web Security SSL (or TSL) can be implemented in two ways  As part of the underlying protocol suite => transparent to application  As embedded in specific packages – Netscape, Explorer etc Application specific security services are embedded Can be tailored to the specific needs – eg SET

10. 2003/16216/3112INT Network SecurityLecture 7 – Web Security - 10 SSL (Secure Socket Layer) transport layer security service originally developed by Netscape version 3 designed with public input subsequently became Internet standard known as TLS (Transport Layer Security) uses TCP to provide a reliable end-to-end service SSL has two layers of protocols

11. 2003/16216/3112INT Network SecurityLecture 7 – Web Security - 11 SSL Architecture

12. 2003/16216/3112INT Network SecurityLecture 7 – Web Security - 12 SSL SSL Record Protocol provides basic security services to various higher layer protocols (eg. HTTP) The 3 higher layer protocols are defined as part of SSL  These SSL-specific protocols are used in the management of SSL exchanges Two important SSL concepts are:  SSL Session  SSL Connection

13. 2003/16216/3112INT Network SecurityLecture 7 – Web Security - 13 SSL Architecture SSL session  an association between client & server  created by the Handshake Protocol  define a set of cryptographic parameters  may be shared by multiple SSL connections SSL connection  a transient, peer-to-peer, communications link  associated with 1 SSL session

14. 2003/16216/3112INT Network SecurityLecture 7 – Web Security - 14 SSL Record Protocol confidentiality  using symmetric encryption with a shared secret key defined by Handshake Protocol  IDEA, RC2-40, DES-40, DES, 3DES, Fortezza, RC4-40, RC4-128  message is compressed before encryption message integrity  using a MAC with shared secret key  similar to HMAC but with different padding

15. 2003/16216/3112INT Network SecurityLecture 7 – Web Security - 15 SSL Record Protocol Operation

16. 2003/16216/3112INT Network SecurityLecture 7 – Web Security - 16 SSL Change Cipher Spec Protocol one of 3 SSL specific protocols which use the SSL Record protocol a single message causes pending state to become current hence updating the cipher suite in use

17. 2003/16216/3112INT Network SecurityLecture 7 – Web Security - 17 SSL Alert Protocol conveys SSL-related alerts to peer entity severity warning or fatal specific alert unexpected message, bad record mac, decompression failure, handshake failure, illegal parameter close notify, no certificate, bad certificate, unsupported certificate, certificate revoked, certificate expired, certificate unknown compressed & encrypted like all SSL data

18. 2003/16216/3112INT Network SecurityLecture 7 – Web Security - 18

19. 2003/16216/3112INT Network SecurityLecture 7 – Web Security - 19 SSL Handshake Protocol allows server & client to:  authenticate each other  to negotiate encryption & MAC algorithms  to negotiate cryptographic keys to be used comprises a series of messages in phases  Establish Security Capabilities  Server Authentication and Key Exchange  Client Authentication and Key Exchange  Finish

20. 2003/16216/3112INT Network SecurityLecture 7 – Web Security - 20 SSL Handshake Protocol

21. 2003/16216/3112INT Network SecurityLecture 7 – Web Security - 21 TLS (Transport Layer Security) IETF standard RFC 2246 similar to SSLv3 with minor differences  in record format version number  uses HMAC for MAC  a pseudo-random function expands secrets  has additional alert codes  some changes in supported ciphers  changes in certificate negotiations  changes in use of padding

22. 2003/16216/3112INT Network SecurityLecture 7 – Web Security - 22 TLS Function P_hash (secret, seed)

23. 2003/16216/3112INT Network SecurityLecture 7 – Web Security - 23 Secure Electronic Transactions (SET) open encryption & security specification to protect Internet credit card transactions developed in 1996 by Mastercard, Visa etc not a payment system rather a set of security protocols & formats  secure communications amongst parties  trust from use of X.509v3 certificates  privacy by restricted info to those who need it

24. 2003/16216/3112INT Network SecurityLecture 7 – Web Security - 24 SET Components

25. 2003/16216/3112INT Network SecurityLecture 7 – Web Security - 25 SET Transaction 1.customer opens account 2.customer receives a certificate 3.merchants have their own certificates 4.customer places an order 5.merchant is verified 6.order and payment are sent 7.merchant requests payment authorization 8.merchant confirms order 9.merchant provides goods or service 10.merchant requests payment

26. 2003/16216/3112INT Network SecurityLecture 7 – Web Security - 26 Dual Signature customer creates dual messages  order information (OI) for merchant  payment information (PI) for bank neither party needs details of other but must know they are linked use a dual signature for this  signed concatenated hashes of OI & PI

27. 2003/16216/3112INT Network SecurityLecture 7 – Web Security - 27

28. 2003/16216/3112INT Network SecurityLecture 7 – Web Security - 28 Purchase Request – Customer

29. 2003/16216/3112INT Network SecurityLecture 7 – Web Security - 29 Purchase Request – Merchant

30. 2003/16216/3112INT Network SecurityLecture 7 – Web Security - 30 Purchase Request – Merchant 1.verifies cardholder certificates using CA sigs 2.verifies dual signature using customer's public signature key to ensure order has not been tampered with in transit & that it was signed using cardholder's private signature key 3.processes order and forwards the payment information to the payment gateway for authorization (described later) 4.sends a purchase response to cardholder

31. 2003/16216/3112INT Network SecurityLecture 7 – Web Security - 31 Payment Gateway Authorization 1.verifies all certificates 2.decrypts digital envelope of authorization block to obtain symmetric key & then decrypts authorization block 3.verifies merchant's signature on authorization block 4.decrypts digital envelope of payment block to obtain symmetric key & then decrypts payment block 5.verifies dual signature on payment block 6.verifies that transaction ID received from merchant matches that in PI received (indirectly) from customer 7.requests & receives an authorization from issuer 8.sends authorization response back to merchant

32. 2003/16216/3112INT Network SecurityLecture 7 – Web Security - 32 Payment Capture merchant sends payment gateway a payment capture request gateway checks request then causes funds to be transferred to merchants account notifies merchant using capture response

33. 2003/16216/3112INT Network SecurityLecture 7 – Web Security - 33 Summary have considered:  need for web security  SSL/TLS transport layer security protocols  SET secure credit card payment protocols

34. 2003/16216/3112INT Network SecurityLecture 7 – Web Security - 34 Tutorial 12 Why Web presents new challenges with respect to providing security? What are the advantages of each of the three approaches shown in Fig 17.1? What protocols comprise SSL? What is the difference between an SSL connection and an SSL session? What services are provided by the SSL Record Protocol? List the principal categories of SET participants. Explain the sequence of events involved in a SET transaction. What is a dual signature and what is its purpose?