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MICROPAYMENT PROTOCOLS

MICROPAYMENT PROTOCOLS. INTRODUCTION. Overview of MicroPayments Protocols - NetBill - NetPay - PayCash. MICROPAYMENTS. - Fraction of a cent or very small amount that may be charged for online usage of Connection time.

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MICROPAYMENT PROTOCOLS

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  1. MICROPAYMENT PROTOCOLS

  2. INTRODUCTION • Overview of MicroPayments • Protocols - NetBill - NetPay - PayCash

  3. MICROPAYMENTS • - Fraction of a cent or very small amount that may be charged for online usage of Connection time. • - Payments of small sums of money, generally smaller than physical currency.

  4. MICROPAYMENTS OBJECTIVES: • Minimize transaction overheads • To use in place of Credit cards -Security • Pay-per-view or pay-per-use type of commerce.

  5. Efficient Protocols • Anonymous (Privacy Protection) • Tamper-proof records • Integrity • Non-repudiation, Atomicity • Accountability • Multiple currencies

  6. NETPAY • Secure • Economical • Easily implementable • Debit-based protocol for a micropayment system • Derived from Payword protocol • Prevents Double spending

  7. NETPAY PROS • No involvement of third party in every transaction • Minimizes the number of expensive public-key operations • Hash function operations are used

  8. NETPAY Consider a trading community : -Untrusted parties • Customer (C) • Vendor (V) -Trusted parties • Broker (B). --registers customers and Merchants

  9. NETPAY PROTOCOL Broker M1 Vendor1 Customer M1= { IDc, n, IP address of V1 }

  10. NETPAY The Broker does : Debit money from the account of C Creates a payword chain W0, W1, ..., Wn, Wn+1 which satisfy Wi = h(Wi+1). • h(.) is a one way hash function • Seed Wn+1 is a secret with the broker. -- Prevents overspending and forging paywords

  11. NETPAY PROTOCOL Broker M1 M2 Vendor1 Customer M2 = { W1, W2, ..., Wn } PK-customer

  12. NETPAY PROTOCOL Broker M1 M3 M2 Vendor1 Customer M3 = {IDc, W0} SK-broker

  13. NETPAY Transaction 2: Customer – Vendor M4 Vendor 1 Customer M4 = { IDc, P} P = {(Wj, j), ( Wj+1, j+1), ..., (Wj+m-1, j+m-1)} payment P is verified by the vendor by hashing the paywords Wi's in the payment P. Ex:W1 is valid if the hash matches (W0)

  14. NETPAY Transaction 2: Customer – Vendor M4 Vendor 1 Customer M4 = { IDc, P} If payment P is valid Then P will be stored for redemption at a later time with the broker.

  15. NETPAY Transaction 2: Customer – Vendor M4 Vendor 1 Customer M5 M5 = {IDv1, the receipt of the payment}

  16. NETPAY Transaction 3: Vendor-Vendor M6 M7 Customer Vendor 2 Vendor 1 M9 M8 M6 = {IP address of V1, IDc, P, O} M7 = {IDc, IDv2} V1 signs the index Index = {IDv1, IDv2, i}SK-v1 M8 = {IDc, W0, Index} M9 = {IDv2, the receipt of the payment}

  17. NETPAY Transaction 4: Vendor – Broker M10 Broker Vendor M11 M10 = {IDc, IDv, P} M11 = {Statement of the vendor's account}

  18. NETBILL • System for micropayments • For information goods on the Internet PLUS POINT Provides an atomic certified delivery method so that a customer pays if and only if she receives her information goods intact.

  19. NETBILL THIRD PARTY NetBill server Merchant Account Customer Account Financial Institution Financial institution E.g: Banks

  20. NETBILL NetBill server Customer Merchant • Three phases: • Price negotiation---Customer Merchant • Goods delivery--- Customer Merchant • Payment---Merchant NetBill

  21. NETBILL The Transaction Protocol • CÞ M Price request -Customer presents evidence of her identity -Requests a price quote on an item. -The customer may also bid for the item. 2. MÞ C Price quote -The merchant responds with a price offer. • CÞ M Goods request

  22. NETBILL 4. MÞ C Goods, encrypted with a key K -The merchant provisionally delivers the goods, under encryption, but withholds the key. 5. CÞ M Signed Electronic Payment Order -customer constructs, and digitally signs, an electronic payment order (or EPO) and sends it to the merchant. 6. MÞ N Endorsed EPO (including K) -Merchant appends the key to the EPO & digitally signs the EPO, forwarding it to the NetBill server. - Proof of Agreed Terms and Key

  23. NETBILL 7. NÞ M Signed result (including K) - NetBill Debits & Credits Accounts. - Also proof of Transaction by NetBill 8. MÞ C Signed result (including K)

  24. PAYCASH • Designed to offer - Strong security - Privacy protection. • Based on CHAUM’S ELECTRONIC COINS -- first to demonstrate anonymity in electronic coins.

  25. PAYCASH

  26. PAYCASH • COIN = { X, g-1(f(X)) } - f(.) and g(.) are functions that are easy to calculate and hard to invert. • Only Third Party (TP) can mint a coin- apply g-1(.) • For anonymity TP should mint without knowing X or F(X) • The user applies a Blinding Fn before Minting the coin.

  27. PAYCASH • Instead of Serial number X,pair of keys are used - Public Key (P) & Secret key (S). • Two Functions: SIGN(S,Z) & VERIFY(P,Sz)  VERIFY(P,SIGN(S,Z))= Z. • COIN = { P, g-1(f(P)) }. • To send a Coin, we send the four tuple: {record, Sign(S,record), P, g-1(f(P)) }

  28. PAYCASH {record, Sign(S,record), P, g-1(f(P)) } • Check if f(p) = g(g-1(f(P)) ) • Using P, • VERIFY(P,SIGN(S,record)) = record • This verifies the sender because only he knows the secret Key, S • P is stored with the third party after intial payment.

  29. PAYCASH Multiple Value Coin: • For each P, Third Party keeps track of m(P). • COIN : {N, P, g-N(f(P)) } • Tuple : {record, Sign(S,record), n, P, g-n(f(P)) } • Condition : N >= k + m(P)/c. • e.g 10 >=2 +5/1

  30. REFERENCES [1]. Rivest, R., Shamir, A., & Adleman, L. (1978). A method for obtaining Digital Signatures and Public-Key Cryptosystems, Communications of the ACM, Vol. 21, 21(2):120-126. [2]. 7   B. Cox, J. D. Tygar, and M. Sirbu. "NetBill Security and Transaction Protocol." In Proceedings of the First USENIX Workshop on Electronic Commerce, pages 77-88, July 1995. [3]. Jon M Peha and Lldar M. Khamitov. PayCash: a secure efficient Internet payment system. ACM International Conference Proceeding Series Proceedings of the 5th international conference on Electronic commerce

  31. REFERENCES HyperLinks 1.Xiaoling Dai and Bruce W N Lo. Netpay--An efficient protocol for micropayments on the WWW. http://ausweb.scu.edu.au/aw99/papers/dai/paper.html 2.http://citeseer.ist.psu.edu/cache/papers/cs/781/http:zSzzSzwww.ini.cmu.eduzSznetbillzSzpubszSzUsenix.pdf/cox95netbill.pdf/ 3.http://portal.acm.org/citation.cfm?id=948022&coll=ACM&dl=ACM&CFID=20304359&CFTOKEN=79408948

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