Blockchain的鱼和熊掌系列（17）Privacy Protection

Figure 2 shows the privacy-protecting scheme for Blockchain. Most research works focus on the peers (users) privacy-protecting problems as shown above, of which a classical solution to protect users’ privacy is to providing methods for communicating through encrypted data.

Hawk. The Hawk is originally proposed and implemented in their work [Hawk: The blockchain model of cryptography and privacy-preserving smart contracts]. Since the problem of lacking transactional privacy in existing Bitcoin systems, makes all transaction data, including payee, payer, transaction amount etc, visible and exposed to publics. What the Hawk actually does is to solve such a safety issue, where it functionally serves as a security suite in Bitcoin network, and allows programmers to write smart contracts without needing to implement cryptography primitives. The underlying security model of Hawk is based on Prof. Szabo’s work[Formalizing and securing relationships on public networks].

Darkcoin. The Darkcoin [Darkcoin: Peer­to­Peer Crypto­Currency with Anonymous Blockchain Transactions and an Improved Proof­of­Work System], similar to Zcash [A blockchain currency that beat s bitcoin on privacy], is a privacy centric cryptographic currency based on Bitcoin. A problem in Bitcoin is that all transactions are traceable, resulting a high possibility for leaking user information. To solve such a problem of privacy is the goal of Darkcoin. A key component in Darkcoin is a transactional pool based on the blind signature mechanism [Blind signatures for untraceable payments]. In this transactional pool, all participants know nothing about which transactional output belongs to which output. So, in this way, users in Darkcoin can achieve a higher level of anonymity, and can better protect their personal information and privacy.

Cosigning. The Cosigning [Keeping authorities” honest or bust” with decentralized witness cosigning] is a protocol to protect user’s privacy on a distributed open network. In such a protocol, any individual cannot personally sign a statement in behalf of a collective will. By ensuring that, attackers who steal a specific victim’s secret keys cannot able to individually sign a group statement without exposing the statement to all members of a group for cosigning. The cosigning protocol also has been applied to Bitcoin’s applications, a typical example of which is the ByzCoin [Enhancing Bitcoin Security and Performance with Strong Consistency via Collective Signing], it is based on the cosigning protocol, reconfigures Bitcoin’s backbone, and achieves a considerable performance optimization result.