1 E-cash Model Ecash Bank Client Wallet Merchant Software stores coins makes payments accepts payments Goods, Receipt Pay coins sells items accepts payments makes payments Withdraw/ Deposit coins New Coins, statement Valid indication Validate +deposit coins signs coins user accounts database

2 Minting Stage Serial number (unknown) Client (known) Deposit Stage Serial number (known) Client (unknown)

3 Withdrawing Coins Many coins of different denominations can be obtained in a single request to the bank Many coins of different denominations can be obtained in a single request to the bank The request is signed by the client with his private key and contains information about the serial nos. to be signed The request is signed by the client with his private key and contains information about the serial nos. to be signed The request is encrypted with a symmetric key and that symmetric key is encrypted with the public key of the bank The request is encrypted with a symmetric key and that symmetric key is encrypted with the public key of the bank The bank signs serial nos. in order to mint coins of requested denominations and forward them to the client/buyer The bank signs serial nos. in order to mint coins of requested denominations and forward them to the client/buyer

4 Payreq={currency,amount,timestamp, merchant_bank ID, merchant_accID, order description} merchant_bank ID, merchant_accID, order description}

5 Hash function and message digest are sent to the e-cash bank Hash Bluesky MD

6 Lost Coins In case network fails or computer crashes during payment transaction, coins might be lost In case network fails or computer crashes during payment transaction, coins might be lost All signed blinded coins from last 16 withdrawals are sent by the bank to the client All signed blinded coins from last 16 withdrawals are sent by the bank to the client Client uses the blinding factor known to its wallet to reveal the serial # Client uses the blinding factor known to its wallet to reveal the serial # It then sends all serial nos. to the bank for its verification whether or not the coins have already been spent It then sends all serial nos. to the bank for its verification whether or not the coins have already been spent After checking its database the bank credits the client’s account with the value of unspent coins After checking its database the bank credits the client’s account with the value of unspent coins

7 E-Cash & the Web Ecash Bank Merchant Software Merchant Software Client Wallet Client Wallet Web Browser Web Server 9.Goods/Acknowledgement 1.Select Order 2. Merchant wallet Starts 8.Send goods 3. Payment Request (Order) 4. Payment (coins,order) 7. Receipt 5. Deposit coins 6. Accepted

8 Secure Socket Layer (SSL) A protocol developed by Netscape Communications A protocol developed by Netscape Communications SSL is built into many browsers SSL is built into many browsers Operates at the TCP/IP layer Operates at the TCP/IP layer Uses a combination of symmetric and asymmertric cryptography Uses a combination of symmetric and asymmertric cryptography Internet Explorer: Tools menu->Internet options-> Internet Explorer: Tools menu->Internet options-> Advanced tab-> Security (use SSL option is given) Advanced tab-> Security (use SSL option is given)

9 Client sends “hello” message Client sends response Session SSL Client (browser) Server responds With “hello” message Session Send encryption algorithms and key length SSL Server Send server certificate containing server’s public key Send client certificate and encrypted private session key Send data between client and server using private shared key Server receives client response and initiates session

10 Debit Card Automated Clearing House Payer’s Bank Acquirer Bank PayerPayee Internet Debit Card Certification Authority Payment Gateway

11 SETCo Card Issuer Bank Customer Card Brand Merchant

12 Buyer/Bidder Merchant or Auction house Acquirer Bank Encrypted message authorizing payment to the auction house if offer is accepted, but no details about what item is bought MD2 and DSMD encrypted with Bidder’s private key 1a Offer for Items 4 Encrypted message includes amount offered on the item, but no account information MD1 encrypted with Bidder’s private key 1b Decrypt message with auction house private key Decrypt MD1 with bidder’s public key Determine whether to accept bid 2 Decrypt account information with acquirer private key Decrypt offer acceptance message with acquirer private key Decrypt MD2 and DSMD with bidder’s public key Decrypt MD1 from step no. 3 with auction house’s public key Concatenate MD1 and MD2 Recompute dual signature and verify against DSMD sent by bidder Encrypted message that offer is accepted from bidder MD1 encrypted with auction house’s private key 3 4

13 MD1 from auction house related to order information MD1 from auction house related to order information Account information in encrypted form Account information in encrypted form MD2 related to account information MD2 related to account information DSMD = MD1 + MD2 DSMD = MD1 + MD2

14 SSL Vs. SET SSL only handles secured transmission of credit card no. but SET is designed to handle the whole transaction in a secured manner using dual signatures SSL only handles secured transmission of credit card no. but SET is designed to handle the whole transaction in a secured manner using dual signatures SSL is a general purpose protocol built into the browser, whereas SET requires software on,both, the client and the merchant side SSL is a general purpose protocol built into the browser, whereas SET requires software on,both, the client and the merchant side SET uses a hierarchy of certificates for authentication SET uses a hierarchy of certificates for authentication SET is complex and distribution of certificates is sometimes not stable SET is complex and distribution of certificates is sometimes not stable SET increases transaction cost SET increases transaction cost SET transactions are slower than SSL SET transactions are slower than SSL SET uses a payment gateway for secured transmission of information SET uses a payment gateway for secured transmission of information

15 Advantages of E-business Personalized service Personalized service High-quality customer service High-quality customer service No inventory cost No inventory cost Worldwide reach of your business Worldwide reach of your business Electronic catalogues (Convenient and quick transaction) Electronic catalogues (Convenient and quick transaction) Bulk transactions Bulk transactions Improved supply chain management Improved supply chain management