Proof of stake
Proof-of-stake (PoS) is a consensus mechanism used by blockchain networks to secure and validate transactions. Proof of stake consensus mechanism is more energy efficient than the proof of work consensus mechanism. However, the lower computational requirement also makes PoS more vulnerable to certain attacks.
Use
Biggest blockchain that uses proof-of-stake is the Ethereum blockchain. Other blockchains that use proof-of-stake are Cardano, Solana, and Tron.
Vulnerabilities
Long-range attacks
One type of attack that is possible in PoS but not in PoW is a long-range attack. In a long-range attack, an attacker would attempt to rewrite a significant portion of the blockchain history. This is possible because PoS does not require validators to expend a significant amount of computing power to add blocks to the chain. As a result, an attacker could potentially gain control of the network by rewriting the history and then mining blocks on top of their own version of the chain.
Nothing-at-stake attacks
Another type of attack that is possible in PoS is a nothing-at-stake attack. In a nothing-at-stake attack, an attacker would attempt to gain control of the network by creating a large number of validator nodes. Since validators do not need to expend a significant amount of computing power in PoS, this is a relatively easy task. Once the attacker has control of a majority of the validator nodes, they can then approve blocks that they create, regardless of whether those blocks are valid or not.
Bribery attacks
PoS is also vulnerable to bribery attacks. In a bribery attack, an attacker would attempt to gain control of the network by bribing validators to approve blocks that they create. Since validators are rewarded for approving blocks, they are susceptible to bribery.
Mitigating PoS Vulnerabilities
There are a number of ways to mitigate the vulnerabilities of PoS. One way is to use a consensus mechanism that is based on Byzantine Fault Tolerance (BFT). BFT protocols are designed to be resistant to attacks, even if a majority of the nodes in the network are malicious.
Another way to mitigate PoS vulnerabilities is to design the reward system in such a way that there is no economic incentive for validators to engage in attacks. For example, the reward system could be designed so that validators are only rewarded for approving blocks that are valid.