1. 1 fairCASH: Concepts and Framework Yen Choon Ching Institute of Computer Science, University of Kiel, Germany Ver 3.1 15 Sept 2008

2. 2 fairCASH Characteristics Token-based system –Same denomination as physical cash –Tamper-resistant chip to prevent the copying of e-coins Transferable –Offline payment Unify physical payment with the Internet payment –To be designed for usage with mobile phones, computer, cash register, ATM etc Privacy protected –The transacting information is under the control of the two participating parties

3. 3 Public Key Certificate Purposes 1.To provide trust for the system To whom are you sending the e-coins? Is the e-wallet issued by fairCASH? 2.To investigate multi-spent e-coins To identify the e-wallet that is the source of the fraud 3.To limit an entity’s activity By revoking the certificate No certificate -> no transaction

4. 4 User Level Certificates

5. 5 E-wallet Level Certificates

6. 6 Certificate Verification Structure Production Related Certificates Operation Related Certificates

7. 7 Connection Architecture

8. 8 Transaction Connection Proximity Transaction Remote Transaction RFID Phone number IP/DNS address

9. 9 E-coin Bit string object –Denomination, serial number, expiration/clearing date, issuer name + issuer’s digital signature False Money 1.Counterfeit e-coin Failed digital signature verification No valid e-mint currency certificate or e-mint certificate available 2.Multi-spent e-coin E-wallet has been cracked Inside job Easy to block counterfeit e-coin, but not for multi-spent e-coin

10. 10 E-coin Circulation State Offline databases Online databases

11. 11 Risk Management (1) Protection –Tamper-resistant hardware 1.E-coins 2.E-wallet private key Detection –Short lifetime for e-coins –Online renewal facility –Online multi-spending checking facility Investigation –E-wallet transaction logs

12. 12 Risk Management (2) Prevention –Coin Stop List (CSL) Isolation –E-wallet Certificate Revocation List (CRL) Constant update of CSL & e-wallet CRL Force the attacker to repeat his effort –Unique public-private key pair for each e-wallet –To make the attack to be commercially unviable

13. 13 Privacy Privacy is protected –Transaction information is not available to any third parties Anonymity can be obtained if desired –Use non-identified certificate Fully Anonymous Non- Anonymous fairCASHecashCredit card

14. 14 Conclusion An electronic version of physical cash Rely on tamper-resistant hardware and cryptography to contain fraud A practical system that is fraud tolerant

15. 15 Thank You! Q & A