Introduction
Proof of Stake is a novel consensus algorithm that validates blocks mainly according to a validator’s economic stake in the network rather than the hash power. Regarded as the next generation mainstream consensus mechanism of blockchain technology, it has significant advantages including energy saving, reduced risk of centralization and security.
However, in the early discussion of PoS protocol, it is seem to be more vulnerable due to the fact that it is not aware of anything in reality. That arises nothing at stake problem.
权益证明共识算法根据用户在网络中的权益占比来决定出块的权利，被认为是下一代的主流区块链共识算法，具有节能、减少中心化和安全的优点。
然而，在早期PoS协议的讨论里，许多人认为其由于与现实的事物没有实质性上的“锚定”，容易遭受攻击。而Nothing at Stake问题也由此而来。
Nothing at Stake
Early proof of stake algorithms are facing a serious problem that users will validate blocks on all forking chains they see to pursuit maximum rewards with no penalty because this behavior is rational and do not decrease the probability of being a validator. While in PoW protocol, it is irrational to spilit computational power mint on different branches so the optimal strategy for a miner is always mining on the longest single chain.
Nothing at stake problem makes PoS protocol prone to attacks such as double-spending or other sorts of attacks relying on forking the blockchain. As long as the majority of the users lose nothing or a little and they believe the attack may succeed, they will support it by minting on top of the attacker’s forking chain. While forking attacks will be opposed by users with a large amount of currency who will fear to lose their money, if the currency is evenly distributed among many users, the attack is more likely to succeed.[1]
早期的PoS算法面临一个很严重的问题，即网络中的用户会在他们所看到的所有分叉链里参与出块，由于这种行为没有任何惩罚且不会降低他们在网络里出块的概率，他们为了追求利益最大化的诉求而合理地采取这种行动。但是在PoW协议里，这种行为却是不理智的，因为会导致算力的分散，而最优的行为是在网络中最长的链上挖矿。
Nothing at stake问题使得PoS协议很容易遭受双花攻击或其它基于分叉链的攻击。只要大部分用户认为攻击很有可能发成功且他们的利益没有或者损失很少，他们就会转而支持攻击者，在攻击者的分叉链上进行出块。但是，如果网络中持有大部分权益的用户会拒绝这种攻击行为，因为这会导致他们损失大量的权益。
Conclusion
However, there are several countermeasures to this problem and it is addressed by newly improvement in recent proposed consensus algorithm as shown in [2].
随着近来PoS共识算法的发展，Nothing at Stake问题已经有相应的解决方案。具体的进展可以进一步阅读参考文献。
Reference
[1]Proof of Stake versus Proof of Work
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