2. Atomic Transactions CS523 - Spring 2006 - Brian Schmidt

3. Different Domains On single CPU Multiprocessor Applications Database Systems Electronic Commerce

4. Types of Transactions Money for Electronic Goods Money for non-Electronic Goods Money for Transferred goods Money changing Accounts + auctions + time contraints [Subr]

5. Types of Money Account Transfer Credit Card PayPal Token Money

6. Beyond Databases Not just responsibility to carry out action robust against failures Must include non-repudiation through verifiable transaction atomicity in presence of malicious failures Repudiation is the refusal to acknowledge or pay a debt [Tang]

7. Required and Desired Properties Required –Security –Atomicity Desired –Privacy –Anonymity –Low Overhead [Subr]

8. Threats Merchant not delivering product Merchant over or double charging Customer denying receipt of product Customer not fulfilling payment 3 rd party replay of transaction Privacy violation of customer by tracking purchases

9. Specifications : VMT Verifiable Message Transmision –If the receiver receives the message m, it can not deny the receipt of m, or the content of m –If the sender transmits a message m to the receiver and the receiver receives it, the sender cannot deny the sending of m or the content of m. [Tang]

10. Specifications : AC Atomic Commitment –All non-faulty participants that decide reach the same decision. –If any participant decides commit, then all participants have voted YES. –If all participants vote YES and no failure occurs, then all participants decide Commit. –Each participant decides at most once (that is, a decision is irreversible). [Tang]

11. Specifications : VAC Verifiable atomic commitment –The interactions (communications) and the contents of the interactions among all participants are verifiable (by a third party) if necessary. –If a participant receives a message with which some monetary value is associated, the transaction in which the participant is involved will be committed eventually (even though the participant may abort the transaction unilaterally). [Tang]

12. Example Protocol Based on Public-Private Key encryption Claims to meet all required and desired properties (security, atomicity, privacy, anonymity, low overhead) From [Subr]

13. Notations A stands for the customer, Alice, with public key a and private key 1/a. B stands for the merchant, Bob, with public key b and private key 1/b. T stands for the third party, Tom, with public key t and private key 1/t. E and e are encryption keys with corresponding decryption keys 1/E and 1/e. [Subr]

14. Notations cont… X => Y [message content] 1/x stands for X sends message content to Y signed with Xs private key. X => Y [message content] y/x stands for X sends message content to Y signed with Xs private key and secured with Ys public key. [Subr]

15. a Protocol 1.B => everybody [product description, price] 1/b 2.A => B [[product description, price] 1/b, a, [price] 1/a, payment e ] b 3.B => A [[payment e ] 1/a, b, [product E ] 1/b ] a 4.A => B [[product E ] 1/b, a, [1/e] 1/a ] b 5.B => A [[1/e] 1/a, b, [1/E] 1/b ] a [Subr]

16. Discussion Credit cards, customer authentication, third party support…

17. More on Privacy IP Addresses Email Reuse of public keys [Camp]

18. References [Tang] L. Tang, Verifiable Transaction Atomicity for Electronic Payment Protocols, Proceeding of the 16 th ICDCS – IEEE 96, pp. 261-269. [Subr] S. Subramanian and M. Singhal, Protocols for Secure, Atomic Transaction Execution in Electronic Commerce, Dept. of Computer and Information Science, Ohio State University, 1997. [Camp] L. Jean Camp, An Atomicity-Generating Protocol for Anonymous Currencies, IEEE Transactions on Software Engineering, Vol. 27 No. 3, March 2001.