Chair of Network Architectures and Services Department of Informatics Technical University of Munich A Survey of Electronic Micropayment Schemes Lovis J.I. Zenz advised by Richard von Seck Friday 12 th April, 2019 Chair of Network Architectures and Services Department of Informatics Technical University of Munich
Context: Electronic Micropayment Schemes What is a micropayment? • “Payments worth a few pennies” [1] • varying upper bounds • never more than 10$ [6] L. Zenz — Electronic Micropayment Schemes 2
Context: Electronic Micropayment Schemes Where are micropayments relevant? • handling free-riders in P2P anonymity systems [2] • one-time webpage access [7] • other one-time services [3] • access to financial services in developing countries [8] L. Zenz — Electronic Micropayment Schemes 3
Context: Electronic Micropayment Schemes How do micropayment schemes differ from common payment systems like PayPal? • reduced cost • less broker involvement L. Zenz — Electronic Micropayment Schemes 4
Categorization: Basic Characteristics of Micropayment Schemes Based on which properties can micropayment schemes be distinguished? • online vs. offline • centralized vs. decentralized • credit-based vs. debit-based L. Zenz — Electronic Micropayment Schemes 5
Basic Micropayment Scheme: PayWord What is PayWord? • proposed by Rivest & Shamir in 1997 [7] • employs one-dimensional hashing (100 times faster than RSA signature verification) • employs public key encryption • centralized, offline, credit-based • roles: brokers, vendors, and users L. Zenz — Electronic Micropayment Schemes 6
Basic Micropayment Scheme: PayWord How are payments handled by PayWord? 1. user generates PayWord chain (caps maximum amount of payments in prior) 2. vendor receives single PayWords from user 3. vendor provides service 4. repeat 1. - 3. several times during day 5. vendor forwards PayWords to broker at end of day 6. broker verifies PayWords and conducts transactions L. Zenz — Electronic Micropayment Schemes 7
Basic Micropayment Scheme: PayWord How is a PayWord chain generated? 1. define amount of needed PayWords → n ∈ N 2. choose a hash function and a random PayWord appropriately → w n 3. calculate remaining PayWords → ∀ i ∈ N , 0 ≤ i ≤ ( n − 1) : w i = h ( w i +1 ) L. Zenz — Electronic Micropayment Schemes 8
Basic Micropayment Scheme: PayWord How are payments handled by PayWord? 1. user generates PayWord chain (caps maximum amount of payments in prior) 2. vendor receives single PayWords from user 3. vendor provides service 4. repeat 1. - 3. several times during day 5. vendor forwards PayWords to broker at end of day 6. broker verifies PayWords and conducts transactions L. Zenz — Electronic Micropayment Schemes 9
Extensions: Micropayment Schemes that Are Based on PayWord What is PPayWord? • proposed by Mu, Varadharajan, and Lin in 1997 [4] • adds salting techniques to PayWord • third of three schemes that are based on each other L. Zenz — Electronic Micropayment Schemes 10
Extensions: Micropayment Schemes that Are Based on PayWord How does PPayWord extend PayWord? • SPayWord: set of salts → shared secret w i = h ( w i +1 , S i +1 ) with S i = h ( S i +1 , P , g ) where g = h ( g C ( d j ), V ) • UPayWord: reverse generation → unlimited PayWords • PPayWord: shared payment commitment → loss recovery L. Zenz — Electronic Micropayment Schemes 11
Extensions: Micropayment Schemes that Are Based on PayWord How does PPayWord extend PayWord? • SPayWord: set of salts → shared secret • UPayWord: reverse generation → unlimited PayWords w i +1 = h ( w i , S i +1 ) with S i = R i ⊕ h ( P , g ) where R i +1 = h ( R i , P ) and g = h ( g C ( d j ), V ) • PPayWord: shared payment commitment → loss recovery L. Zenz — Electronic Micropayment Schemes 12
Extensions: Micropayment Schemes that Are Based on PayWord How does PPayWord extend PayWord? • SPayWord: set of salts → shared secret • UPayWord: reverse generation → unlimited PayWords • PPayWord: shared payment commitment → loss recovery z i = h ( w i ⊕ X i ) with w i = h ( i , P ) ⊕ Si + 1 and X i = h ( g C ( d j ), V , i ) L. Zenz — Electronic Micropayment Schemes 13
Extensions: Micropayment Schemes that Are Based on PayWord What are MDHC? • proposed by Nguyen in 2006 [5] • multi-dimensional hash chains L. Zenz — Electronic Micropayment Schemes 14
Extensions: Micropayment Schemes that Are Based on PayWord How are MDHC generated? 1. choose/generate a one-way hash chain → x 0 = h 1 ( x 1 ) = ... = h n − 1 ( x n − 1 ) = h n ( x n ) 2. employ one-way accumulators y = h 1 ( h 2 (...( h m − 1 ( h m ( x ))))) to generate a multi-dimensional hash chain: X 0 = h n 1 1 ( h n 2 n m − 1 m − 1 ( h n m 2 (...( h m ( X N ))))) L. Zenz — Electronic Micropayment Schemes 15
Extensions: Micropayment Schemes that Are Based on PayWord How can MDHC improve PayWord? • storage capacity: N − 1 = ( n + 1) m − 1 • storage computational complexity: O ( N ) = O ( nlog n +1 (( n + 1) m ) → O ( log 2 N ) for n = 1 L. Zenz — Electronic Micropayment Schemes 16
Alternatives: Micropayment Schemes that Are Not Based on PayWord What is the Peppercoin method? • proposed by Rivest in 2004 • aggregation of several micropayments in one macropayment L. Zenz — Electronic Micropayment Schemes 17
Alternatives: Micropayment Schemes that Are Not Based on PayWord How does the Peppercoin method work? • session-level aggregation, aggregation by intermediation, and universal aggregation • brokers (banks) as buffers L. Zenz — Electronic Micropayment Schemes 18
Alternatives: Micropayment Schemes that Are Not Based on PayWord What is DAM? • proposed by Chiesa et al. in 2017 • Bitcoin as inspiration L. Zenz — Electronic Micropayment Schemes 19
Alternatives: Micropayment Schemes that Are Not Based on PayWord How does DAM work? • decentralized anonymous payments • probabilistic payments • private coin deposits L. Zenz — Electronic Micropayment Schemes 20
Conclusion: Overview of Advantages and Disadvantages Based on which criteria can micropayment schemes be evaluated? • performance • efficiency • security • anonimity L. Zenz — Electronic Micropayment Schemes 21
Conclusion: Overview of Advantages and Disadvantages How do different micropayment schemes look in comparison? Name Performance Efficiency Security Anonymity Peppercoin + simplified signing + aggregation not in scope not in scope method DAM + offline + offline - decentralized + decentralized + probabilistic - double spending + anonymous payments payments + blacklist require- + private coin ment deposit S2 + offline + offline + centralized - centralized Scheme + MDHC + MDHC - RSA modular ex- ponentiation PPayWord + offline + offline + centralized - centralized + shared secret Table 1: Overview of Different Micropayment Schemes Table 1 shows different micropayment schemes in comparison. L. Zenz — Electronic Micropayment Schemes 22
Bibliography [1] A. Chiesa, M. Green, J. Liu, P . Miao, I. Miers, and P . Mishra. Decentralized Anonymous Micropayments. In J.-S. Coron and J. B. Nielsen, editors, Advances in Cryptology – EUROCRYPT 2017 , pages 609–642, Cham, 2017. Springer International Publishing. [2] D. Figueiredo, J. Shapiro, and D. Towsley. Incentives to Promote Availability in Peer-to-Peer Anonymity Systems. 13th IEEE International Conference on Network Protocols (ICNP’05) , pages 12–121, 2005. [3] D. Gille. A TRANSACTION COST ANALYSIS OF MICROPAYMENTS IN MOBILE COMMERCE. Journal of Information and Organizational Sciences , 29(1):25–31, 2005. [4] Y. Mu, V. Varadharajan, and Y.-X. Lin. New micropayment schemes based on Pay Words. In V. Varadharajan, J. Pieprzyk, and Y. Mu, editors, Information Security and Privacy , pages 283–293, Berlin, Heidelberg, 1997. Springer Verlag. [5] Q. S. Nguyen. Multi-Dimensional Hash Chains and Application to Micropayment Schemes. In Ø. Ytrehus, editor, Coding and Cryptography , pages 218–228, Berlin, Heidelberg, 2006. Springer Berlin Heidelberg. [6] R. L. Rivest. Peppercorn Micropayments. Financial Cryptography , pages 2–8, 2004. [7] R. L. Rivest and A. Shamir. PayWord and MicroMint: Two Simple Micropayment Schemes. Lecture Notes in Computer Science , 1189:69–87, 1997. L. Zenz — Electronic Micropayment Schemes 23
Bibliography [8] N. Wishart. Micro-Payment Systems and Their Application to Mobile Networks . infoDev / World Bank, Washington, DC, 2006. L. Zenz — Electronic Micropayment Schemes 24
Recommend
More recommend
