International Association for Cryptologic Research

International Association
for Cryptologic Research

IACR News item: 05 July 2015

Ahmed Kosba, Andrew Miller, Elaine Shi, Zikai Wen, Charalampos Papamanthou
ePrint Report ePrint Report
Emerging smart contract systems over decentralized cryp-

tocurrencies allow mutually distrustful parties to transact

safely with each other without trusting a third-party inter-

mediary. In the event of contractual breaches or aborts, the

decentralized blockchain ensures that other honest parties

obtain commesurate remuneration. Existing systems, how-

ever, lack transactional privacy. All transactions, including

flow of money between pseudonyms and amount trasacted,

are exposed in the clear on the blockchain.

We present Hawk, a decentralized smart contract system

that does not store financial transactions in the clear on

the blockchain, thus retaining transactional privacy from the

public\'s view. A Hawk programmer can write a private smart

contract in an intuitive manner without having to implement

cryptography, and our compiler automatically generates an

efficient cryptographic protocol where contractual parties in-

teract with the blockchain, using cryptographic primitives

such as succint zero-knowledge proofs.

To formally define and reason about the security of our

protocols, we are the first to formalize the blockchain model

of secure computation. The formal modeling is of indepen-

dent interest. We advocate the community to adopt such a

formal model when designing interesting applications atop

decentralized blockchains.

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