•   When: Wednesday, November 16, 2016 from 01:15 PM to 02:15 PM
  •   Speakers: Foteini Baldimtsi, Computer Science Department, George Mason University
  •   Location: ENGR 4201
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 Abstract

TumbleBit is a new anonymous payments scheme that addresses two major technical challenges faced by Bitcoin today: (1) scaling Bitcoin to meet increasing use, and (2) protecting the privacy of payments made via Bitcoin. Tumble bit serves as a unidirectional unlinkable payment hub  that uses an untrusted intermediary, the “Tumbler", to enhance anonymity. Every payment made via TumbleBit is backed by bitcoins. We use cryptographic techniques to guarantee that the Tumbler  can neither violate anonymity, nor steal bitcoins, nor "print money" by issuing payments to itself. TumbleBit allows a payer Alice A to send fast off-blockchain payments (of denomination one bitcoin) to a set of payees of her choice. Because payments are performed off the blockchain, TumbleBit also serves to scale the volume and velocity of bitcoin-backed payments. Today, on-blockchain bitcoin transactions suffer a latency of 10 minutes. Meanwhile, TumbleBit payments are sent off-blockchain, via the Tumbler, and complete in seconds.

 In this talk we will walk through the motivation and the design of TumbleBit, and explain how it achieves the following three important features:

 (1) Scalability.  TumbleBit payments are processed off of the Bitcoin blockchain, helping Bitcoin scale to higher transaction velocity and volume. Like Bitcoins on-blockchain transactions, the safety and security of payments sent via TumbleBit do not require trust in any third party. The TumbleBit payment hub can not steal a user’s bitcoins.

(2) Anonymity.  TumbleBit provides anonymity for its off-blockchain payments even against the  TumbleBit service. The exact property we guarantee is unlinkability.

(3) Bitcoin Compatibility.  TumbleBit works with todays Bitcoin protocol. No changes to Bitcoin are required.

 We have implemented TumbleBit and have used it to mix payments from 800 users. Our implementation is open source and publicly available.

Posted 1 year ago