1 Buyer 2. Account ID Valid? 3. Account OK! 5. Transaction Details 1. Account ID 4. Information Goods 6. Satisfied? 7. Accept/Reject or Fraud Indication Web Server (Selling Goods) Web Server (Selling Goods) First Virtual Internet Payment System Server Buying with First Virtual

2 PayPal PayPal E-gold E-gold Billpoint Billpoint Cybergold Cybergold Yahoo! PayDirect Yahoo! PayDirect Amazon.com Payments Amazon.com Payments etc. etc.

3 User to user payment in centralized account systems User A (Payer) User A (Payer) User B (Payee) User B (Payee) Centralized Account System Account ID Amount($) Payment transfer authorization over SSL 2. payment notification 3. Web payment verification over SSL

4 FSTC Electronic Check Concept Payer’s Bank Payee’s Bank Debit AccountCredit Account ACH Check Clearing Statement Payer Payee Invoice Secure H/W Checkbook (secure H/W) Secure Envelope Certs Sig Check Certs Endorsement Certs Sig check Secure Envelope

5 Payee Payer Payee’s Bank Payee’s Bank Payer’s Bank Payer’s Bank 5. Statement 1. Pay 4. Report 2.Deposit 3. Clear Debit Credit Write Endorse

6 Payee Payer Payee’s Bank Payee’s Bank Payer’s Bank Payer’s Bank 6. Statement 1. Pay 5. Report 2.Cash 3. Notify 4. EFT Debit Credit Write Endorse

7 Payee Payer Payee’s Bank Payee’s Bank Payer’s Bank Payer’s Bank 4. Statement 1. Pay 3. Accounts Receivable Update 2. Clear Debit Endorse & Credit Write

8 Payee Payer Payee’s Bank Payee’s Bank Payer’s Bank Payer’s Bank 4. Statement1. Pay 3. Accounts Receivable Update 2. EFT Debit Credit Write

9 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

10 E-cash Coins Coin = Serial#, keyversion, {Serial #}SK bank’s $1 key

11 How bank signs blindly? Cyberwallet generates a serial # and a blinding factor ‘r’ Cyberwallet generates a serial # and a blinding factor ‘r’ Serial #. r e2 (mod m) Serial #. r e2 (mod m) Public key of the bank consists of modulus ‘m’ and a no. ‘e’ Public key of the bank consists of modulus ‘m’ and a no. ‘e’ Bank signs with its secret key of 2 dollars (d2) Bank signs with its secret key of 2 dollars (d2) (Serial #. r e2 ) d2 (mod m)=Serial# d2.r e2d2 (mod m) (Serial #. r e2 ) d2 (mod m)=Serial# d2.r(mod m)

12 How bank signs blindly? Bank cannot see serial # since it does not know ‘r’ Bank cannot see serial # since it does not know ‘r’ Serail# d2.r(mod m)/r=Serial# d2 (mod m) Serail# d2.r(mod m)/r=Serial# d2 (mod m)

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