We are observing an unprecedented growth of decentralized crypto-currencies (e.g., Bitcoin), payment networks (e.g., Ripple), and commercial blockchain solutions (e.g., Hyperledger). Many now believe that these technologies are here to stay.
Through our several projects, we are not only improving security, privacy, and reliability of these inherently decentralized systems, but also exploring applications of these technologies to supply chain systems, smart contracts and beyond.
Our work is currently supported by NSF, Northrop Grumman, Intel, and the German Universities Excellence Initiative.
Practical Decentralized Coin Mixing for Bitcoin
CoinShuffle is a completely decentralized Bitcoin mixing protocol that allows users to utilize Bitcoin in a truly anonymous manner. CoinShuffle is inspired by the accountable anonymous group communication protocol Dissent and enjoys several advantages over its predecessor Bitcoin mixing protocols. It does not require any (trusted, accountable or untrusted) third party and it is perfectly compatible with the current Bitcoin system. [Paper]
— DiceMix and CoinShuffle++
P2P Mixing and Unlinkable Bitcoin Transactions
In this work, we show that a P2P Mixing protocol cannot simultaneously provide anonymity, termination and support mixing of fixed messages. Given that, our P2P mixing protocol DiceMix only supports fresh messages while ensuring anonymity and termination. Additionally, Dicemix is asymptotically and practically more efficient than all other P2P mixing protocols. Finally, DiceMix is an ideal privacy-enhancing primitive for crypto-currencies such as Bitcoin. As a representative example, we use DiceMix to define CoinShuffle++, a coin mixing protocol for Bitcoin. [Paper]
Mixing Confidential Transactions: Comprehensive Transaction Privacy for Bitcoin
Previous privacy-enhacing technologies used in Bitcoin address only specific issues. For instance, coin mixing protocols focus on unlinkability between sender and receiver while the transacted values remain public. ValueShuffle provides for the first time comprehensive privacy: ValueShuffle ensures the anonymity of mixing participants as well as the confidentiality of their payment values even against otehr possibly malicious mixing participants. [Paper]
— Other Links
— Listening to Whispers of Ripple
Linking Wallets and Deanonymizing Payments in the Ripple Network
We have performed the first privacy study in the currently deployed Ripple network. Listening the Whisphers of Ripple shows two heuristics that allow to determine accounts that belong to the same owner and describes how to employ them to deanonymize wallets in the Ripple network. [Paper]
Privacy Preserving Payments in Credit Networks
We have designed Privpay, the first provably secure privacy-preserving payment protocol for credit networks. PrivPay allows to perform transactions without revealing the sender or the receiver, nor the transacted amount. We implemented PrivPay and demonstrated its practicality by privately emulating transactions performed in the Ripple payment system over a period of four months. [Paper]
Enforcing Security and Privacy in Decentralized Credit Networks
We have also designed SilentWhispers, the first decentralized, privacy-preserving credit network that does not require any ledger to protect the integrity of transactions. Yet, SilentWhispers guarantees integrity and privacy of link values and transactions even in the presence of distrustful users and malicious neighbors, whose misbehavior in changing link values is detected and such users can be held accountable. SilentWhispers can handle concurrent transactions, network churn, and it is efficient as demonstrated with a prototype implementation evaluated using payments data extracted from the currently deployed Ripple payment system. [Paper]
Mixing Credit Paths for Anonymous Transactions in Ripple
PathShuffle is the first path mixing protocol for credit networks that is fully compatible with the Ripple network. As an essential building block, we develop PathJoin, a novel protocol to perform atomic transactions in the Ripple network. Using PathJoin and the P2P mixing protocol DiceMix, PathShuffle provides a fully distributed yet fast solution for anonymizing Ripple transaction requiring no trusted or untrusted third party. We demonstrate the practicality of PathShuffle by performing path mixing among five users in the currently deployed Ripple network. [Paper]
— Other Links
Listening to Whispers of Ripple
— External Collaborators
— Liar, Liar, Coins on Fire!
Penalizing Equivocation By Loss of Bitcoins
We have designed completely decentralized non-equivocation contracts, which make it possible to penalize an equivocating party by the loss of its money. At the core of these contracts, there is a novel cryptographic primitive called accountable assertions, which reveals the party’s Bitcoin credentials if it equivocates. [Paper]
Realizing Non-Disclosure Agreement using Bitcoin Penalty
Non-Disclosure agreements between two parties are created to set the actions to be taken when confidential information is disclosed. Today, when an unauthorized disclosure occurs, the involved parties usually go to court, a really slow and costly process in most of the cases. SmartNDA is a smart contract based on the Bitcoin blockchain that allows two parties to set a non-disclosure agreement in such a manner that the unauthorized disclosure of information results in an immediate loss of Bitcoins for the misbehaving party. [Poster]
Detection of Unauthorized Supply Chain Tampering using Blockchain Technology
Currently, every player in a supply chain locally maintains its own copy of the activity log. This leads to high management costs and security problems such as equivocation and counterfeit of products. In DUST-BT, we use the Hyperledger blockchain technology to maintain a distributed and yet single source of shared truth for supply chains. We have encoded rich business logics into smart contracts (or chaincode in Hyperledger terms) that allow a set of mutually distrusting players/companies to collaborate with a secure set of rules. [Poster]
— External Collaborators