2003/1 6216/3112INT Network Security

1Copyright © Griffith University, 2003

Gold Coast CampusSchool of Information Technology

6216INT / 3112INT6216INT / 3112INTNetwork SecurityNetwork Security

Lecture 7. Web Security

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ReferencesReferences

• Cryptography and Network Security: Principles and Practice, 3rd ed., William Stallings: Chapter 17

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Web SecurityWeb 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

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Web SecurityWeb 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: -

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Web SecurityWeb 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

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Web Security ThreatsWeb 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

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Web SecurityWeb Security

• Network level: IPSec Transparent to end users & applications Only selected traffic need incur the overhead of

IPSec processing• Transport level: SSL/ TLS

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Web SecurityWeb Security

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Web SecurityWeb 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

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SSL (Secure Socket Layer)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

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SSL ArchitectureSSL Architecture

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SSLSSL

• 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

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SSL ArchitectureSSL 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

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SSL Record ProtocolSSL 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

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SSL Record Protocol OperationSSL Record Protocol Operation

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SSL Change Cipher Spec ProtocolSSL 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

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SSL Alert ProtocolSSL 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

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SSL Handshake ProtocolSSL 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

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SSL Handshake ProtocolSSL Handshake Protocol

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TLS (Transport Layer Security)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

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TLS Function P_hash (secret, seed)TLS Function P_hash (secret, seed)

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Secure Electronic Transactions Secure Electronic Transactions (SET)(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

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SET ComponentsSET Components

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SET TransactionSET Transaction1. customer opens account2. customer receives a certificate3. merchants have their own certificates4. customer places an order5. merchant is verified6. order and payment are sent7. merchant requests payment authorization8. merchant confirms order9. merchant provides goods or service10. merchant requests payment

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Dual SignatureDual 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

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Purchase Request – CustomerPurchase Request – Customer

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Purchase Request – MerchantPurchase Request – Merchant

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Purchase Request – MerchantPurchase Request – Merchant

1. verifies cardholder certificates using CA sigs2. 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

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Payment Gateway AuthorizationPayment Gateway Authorization

1. verifies all certificates2. decrypts digital envelope of authorization block to obtain

symmetric key & then decrypts authorization block3. verifies merchant's signature on authorization block4. decrypts digital envelope of payment block to obtain

symmetric key & then decrypts payment block5. verifies dual signature on payment block6. verifies that transaction ID received from merchant matches

that in PI received (indirectly) from customer7. requests & receives an authorization from issuer8. sends authorization response back to merchant

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Payment CapturePayment 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

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SummarySummary

• have considered: need for web security SSL/TLS transport layer security protocols SET secure credit card payment protocols

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Tutorial 12Tutorial 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?