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“Implementation of Fair Exchange

Protocol” 

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In an e-commerce environment, the merchant and thecustomer are unlikely to trust each other. This problem hasmotivated researchers to propose fair-exchange protocolsbased on using an on-line trusted third party.

We have implemented a fair exchange protocol whichensures:

i. Fair exchange.

ii. Not requiring manual dispute resolution in case of unfair behavior by any party 

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The customer The merchant &

The Trusted Third Party (Administrator)

CustomerMerchant

Administrator

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Every party involved in the transaction has togenerate their keys-

Public Key

Private Key

Keys will be generated using the tools thatcan be downloaded from the web-site.

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The Merchant encrypts his product with theAdvanced Encryption Standard(AES)Encryption tool provided by the site.

The merchant hides the encrypted product inan image.

Then he uploads the image to the site andalso provides the encrypted product key to

the admin.Admin keeps this product key to give it to the

customer in case of any dispute.

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The administrator then verifies the product.After verification of the product the admin

makes the product available for downloading.

Website

Merchant

Uploadsproduct

Administrator

Verifiesproduct

Makes availablefor downloading

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The fair exchange protocol begins when thecustomer downloads the product. Afterdownloading he gets a Transaction Number.

A series of messages are exchanged between the

customer and the merchant.

Customer

WebsiteDownloadsproduct

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  Customer (C) initiates the e-commerce transaction by

sending Merchant(M) three things:

a purchase order, PO

the public key of C Transaction number

Customer Merchant

{Purchase orderPublic Key &Transaction No.}

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M after receiving Message 1 checks if the purchase order is tohis satisfaction. If M is not satisfied, he sends an abortmessage to C and aborts the transaction.

If M is happy with the purchase order and wants to continuewith the protocol he sends the following things to C :

Encrypted account information &   Merchant’s public key. 

Merchant Customer

If not satisfied, M sends abort msg

Else M sends, Encrypted a/c info& his public key

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After receiving Message 2 from M , C checks to see if it is anabort message or the encrypted account information.

If it is an abort, C aborts the transaction.

If C has received the encrypted account information then heprepares a payment token for the specified account number

and send it to merchant.

Customer Merchant

If it is an abort, C aborts thetransaction.

Prepares & sends payment token forspecified a/c no.

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  If merchant’s account is successfully credited

he sends the product key  else he sends anabort message.

Merchant Customer

Sends product key

Else sends abort message

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The customer cannot cheat as he wont begetting the product key until the merchant’saccount gets credited successfully.

The only possible fraud is from themerchant’s side & that is, he gets thepayment from the customer and he refuses tosend him the product key.

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Now the trusted third party comes intopicture.

The administrator acts as the TTP.

He then sees the messages that were sentduring the transaction and checks whetherthe customer is been cheated, if so then theadmin sends the product key to the

customer.

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  The various possible enhancements of our

project are-

The number of messages exchanged pertransaction can be reduced.

Automation of certain tasks is possible.

This protocol can be used in the ecommerceextensively to provide fair transaction.

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