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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

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A Comparison of Threats on the Web

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Relative Location of Security Facilities in the TCP/IP Protocol

Stack

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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

– Provides a secure communications amongst parties– Provides trust from use of X.509v3 certificates– Ensures privacy by restricted info to those who need it

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Requisiti di sicurezza forniti dallo standard SET

• Confidenzialità dell’informazione– Encryption DES

• Integrità dei dati– Firma digitale RSA (using SHA-1)

• Autenticazione del possessore di una carta di pagamento o del mercante– Firma digitale RSA + certificato X.509v3

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SET Components

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SET Transaction

1. 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 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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Construction of Dual Signature

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11

Purchase Request Transaction

Initiate Request• The costumer requests the

certificates• The message includes other

informations

Initiate Response• The merchant includes the

certificates• The message includes other

informations

Purchase Request

•Verifies the merchant and gateway certificates•Creates the purchase request message (described later)

Purchase Response•(described later)

costumer merchant

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Purchase Request – Customer

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1)verifies cardholder certificates using CA signs2)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 key3)processes order and forwards the payment information to the payment gateway for authorization (described later)4)sends a purchase response(*) to cardholder

PurchaseRequest - Merchant

(*) Includes a response block that acknowledges the order and references the corresponding transaction number (signed using merchant’s private signature key)

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Payment Gateway Authorization Transaction

Authorization Request• Purchase-related

information (obtained from the costumer)

• Authorization-related information (generated by the merchant)

• Certificates

AuthorizationResponse• (described later)

merchant payment gateway

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Tasks performed by Payment Gateway

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

(*) - Authorization-related information

- Capture token information (to effect payment later)

- Certificate

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Payment Capture Transaction

• merchant sends to payment gateway a payment capture request

• gateway checks request

• then causes funds to be transferred to merchants account

• notifies merchant using capture response