CRYPTO '88 Proceedings of the 8th Annual International Cryptology Conference on Advances in Cryptology
Blinding of Credit Card Numbers in the SET Protocol
FC '99 Proceedings of the Third International Conference on Financial Cryptography
PPay: micropayments for peer-to-peer systems
Proceedings of the 10th ACM conference on Computer and communications security
Making p2p accountable without losing privacy
Proceedings of the 2007 ACM workshop on Privacy in electronic society
PAR: Payment for Anonymous Routing
PETS '08 Proceedings of the 8th international symposium on Privacy Enhancing Technologies
Double spending protection for e-cash based on risk management
ISC'10 Proceedings of the 13th international conference on Information security
Pay as you browse: microcomputations as micropayments in web-based services
Proceedings of the 20th international conference on World wide web
EUROCRYPT'05 Proceedings of the 24th annual international conference on Theory and Applications of Cryptographic Techniques
Design, implementation, and deployment of the iKP secure electronic payment system
IEEE Journal on Selected Areas in Communications
Privacy-friendly tasking and trading of energy in smart grids
Proceedings of the 28th Annual ACM Symposium on Applied Computing
A fistful of bitcoins: characterizing payments among men with no names
Proceedings of the 2013 conference on Internet measurement conference
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Bitcoin is a decentralized payment system that relies on Proof-of-Work (PoW) to verify payments. Nowadays, Bitcoin is increasingly used in a number of fast payment scenarios, where the time between the exchange of currency and goods is short (in the order of few seconds). While the Bitcoin payment verification scheme is designed to prevent double-spending, our results show that the system requires tens of minutes to verify a transaction and is therefore inappropriate for fast payments. An example of this use of Bitcoin was recently reported in the media: Bitcoins were used as a form of \emph{fast} payment in a local fast-food restaurant. Until now, the security of fast Bitcoin payments has not been studied. In this paper, we analyze the security of using Bitcoin for fast payments. We show that, unless appropriate detection techniques are integrated in the current Bitcoin implementation, double-spending attacks on fast payments succeed with overwhelming probability and can be mounted at low cost. We further show that the measures recommended by Bitcoin developers for the use of Bitcoin in fast payments are not always effective in detecting double-spending; we show that if those recommendations are integrated in future Bitcoin implementations, double-spending attacks on Bitcoin will still be possible. Finally, we propose and implement a modification to the existing Bitcoin implementation that ensures the detection of double-spending attacks against fast payments.