Shanghai Jiao Tong University and Virginia Commonwealth University jointly published a paper: PoW combined with PoS can effectively resist malicious 51% attacks on the Bitcoin network (full text download)

One of the key elements for the success of blockchain, whether it is a public chain or a private chain, is that the executors of the 51% attack (especially miners) must be credible. In theory, the more executors there are, the more credible the 51% attack is. However, a large number of Bitcoin developers (including Gregory Maxwell, Peter Todd, Luke-Jr, etc.) have shown that the Bitcoin mining industry is centralized and the computing power is in the hands of a very few people.

With the invention of professional integrated circuits and the advent of economies of scale, large mining companies have chosen remote areas of China as their locations. This is because electricity is cheap there, which increases mining profits. Obviously, block mining rewards and transaction fees are more profitable than malicious 51% attacks. But as long as the risk of 51% attacks exists, it is not surprising that someone really uses it to do bad things.

Recently, Shanghai Jiao Tong University and Virginia Commonwealth University in the United States jointly published a paper (full text download) aimed at solving malicious 51% attacks. The paper begins: Bitcoin cleverly uses the computing power of miners to ensure the security of the blockchain. Based on this, this paper proposes to use Bitcoin transactions in the hands of users to further improve network security.

In other words, this scheme adds an extra layer of protection to the proof of work (PoW), which can also be called proof of stake (PoS). The paper analyzes the specific implementation methods of PoS and some application concepts, including Ethereum's Casper. The researchers said that the random number generator used by Casper is an extractor based on the previous state of the blockchain, in which the function is derived from the missing block proposition, so its data is controllable.

In addition, researchers said that the current PoS mechanism will lock the currency, which can easily bring potential risks.

The paper suggests not locking in currencies, but letting users choose the best blockchain:

One way to allow trusted users to choose to support the best chain is to include their available blockchain as part of a transaction; this transaction is signed by the user and is bundled with the blockchain selected by the user. When this transaction is broadcast to the entire network, all miners will know which blockchain the user has chosen. After collecting all user transactions, miners can maintain and develop the best chain selected by the user.

The researchers say that combining the two mechanisms could effectively prevent malicious users in PoW and malicious miners in PoS. However, it is unclear whether this solution is actually feasible.