1. Privacy-preserving e-payments using one-time payment details Author:Mafruz Zaman Ashrafi and See Kiong Ng Source: Computer Standards & Interfaces 31 (2009) 321 – 328 Presenter: 林志鴻

2. Outline Introduction Proposed method Adversary scenarios Adversary scenarios Discussion Conclusions

3. Introduction(1/2)

4. Introduction Introduction (2/2) SSL 口 Anonymity 口 Authenticity 口 Non-reusability Customer Acquiring BankPayment GatewayCard Issuing Company MerchantIssuing Bank Process Payment Information Approval/Denial Request Payment Request Authorization Request Make Payment Request Amount deducted from Customer Account

5. Outline Introduction Proposed method Adversary scenarios Adversary scenarios Discussion Conclusions

6. Proposed method Proposed method (1/6) CustomerMerchant Acquiring Bank Payment Gateway Card Issuing Company Card Issuing Bank Initialization request Initialization response Payment request Payment processing Authorization request I Authorization request II Authorization status Authorization approved Authorization status Purchase status

7. Proposed method Proposed method (2/6) 1: Initialization request Request an invoice and the public keys of the merchant and credit card issuing company. 2: Initialization response Reply with a signed message that includes an invoice consisting of a transaction identifier, and two certificates (from the merchant and the card issuing company then verifies the two certificate details. CustomerMerchant Initialization request Initialization response

8. 3: Payment request Generates two packets of a message: (a) payment details (b) common order information Proposed method Proposed method (3/6) CustomerMerchant Payment request a Paymet_request_details { random_no. r, Hash(card_no.), Hash(cardholder_name), Hash(date_of_expire), Hash(security_code), Hash(password), Hash(common_order_info), current_time_and_date, time_to_vaild, } b Common_order_info { size_of_transaction_id:tid, amount_agreed, {time_stamp, time_to_valid} }

9. 4: Payment processing Decrypt the common order details using the merchant ‘ s private key and to confirm the details 5: Authorization request – I Verify the message whether include the pre- generated merchant's authorization message Sends it to the credit card issuing company Proposed method Proposed method (4/6) Merchant Payment Gateway Payment processing Card Issuing Company Authorization request I

10. 6: Authorization request – II Decrypt the payment information using its own private key, Check the timestamp and its expiration. Check the common order details. Sends messages to the issuing bank, to verify whether sufficient funds are available for this transaction and sends back an approval or denial message to the credit card issuing company. Proposed method (5/7) Authorization request II Card Issuing Company Card Issuing Bank

11. Proposed method Proposed method (6/6) CustomerMerchant Acquiring Bank Payment Gateway Card Issuing Company Card Issuing Bank Authorization status Authorization approved Authorization status Purchase status 7: Authorization status RSA cryptosystem Encryption Decryption

12. Proposed method Proposed method (7/7) 口 Anonymity -> hash 口 Authenticity -> Authorization status 口 Non-reusability -> timestamp

13. Outline Introduction Proposed method Adversary scenarios Adversary scenarios Discussion Conclusions

14. Adversary scenarios 11 (i)If a dishonest merchant replays the same payment information of an honest customer Timestamp Random number (ii)An attacker spies on the payment information Timestamp Dynamic hash

15. Adversary scenarios (iii)An attacker obtains the timestamp value and payment details of a customer Card issuing company ’ s public key timestamp (iv)An attacker spies on the approved payment status authorized by a payment gateway. Unique transaction ID timestamp

16. 12 Adversary scenarios (v)A consumer lost his/her card Password (vi)Dishonest customer claims more money then the actual amount debited for the product authorization status (vii)Dishonest merchant claims customer did not purchase a product authorization status

17. Outline Introduction Proposed method Adversary scenarios Adversary scenarios Discussion Conclusions

18. Discussion 13 Proposed methodSETSSL AnonymityFullLimited/No ReusabilityNoYes VerificationPassYesNo KeyNoYesNo ComplexityLowHighLow RegistrationCICCANo CIC – Card Issuing Company CA - Certificate Authority

19. Outline Introduction Proposed method Adversary scenarios Adversary scenarios Discussion Conclusions

20. Conclusions This paper presented a protocol that ensures that the customer is able to minimize their privacy and identity theft risk. The proposed protocol allows consumers to anonymously purchase goods or services from an online merchant, thus achieving the ideal privacy environment in which to shop.