How does Proof of Stake choose the forgers?

How does Proof of Stake choose the forgers? 

 

 

While PoS has been already implemented in BlackCoin, Lisk, Nxt and Peercoin, among others, will PoS favor the forgers who have more coins at stake? In other words, are the users who have more wealth (coins) preferred?  And how to PoS address this issue? What are forgers by the way? In PoS the users who validate transactions and create new blocks are referred to as forgers.

The two most popular methods used to address the above issues are

1.      Randomized block selection

A formula which looks for the user with the combination of two lowest hash value and the size of their stake is used to select the next forger. Since the size of the stakes are public, each node is usually able to predict the forger for the next block. Nxt and Blackcoin are the two PoS cryptocurrencies that used randomized block selection method.

2.     Coin Age based selection

The coin age-based system selects the next forger based on the ‘coin age’ of the stake the potential forger has put up. Coin age is calculated by multiplying the number of days the cryptocurrency coins have been held as stake by the number of coins that are being staked. Coins must have been held for a minimum of 30 days before they can compete for a block. Users who have staked older and larger sets of coins have a greater chance of being assigned to forge the next block. Once a user has forged a block, their coin age is reset to zero and then they must wait at least 30 days again before they can sign another block. The user is assigned to forge the next block within a maximum period of 90 days, this prevents users with very old and large stakes from dominating the blockchain thereby making the network more secure. Because a forger’s chance of success goes up the longer they fail to create a block, forgers can expect to create blocks more regularly. This mechanism promotes a healthy, decentralized forging community. Peercoin is a proof-of-stake system based cryptocurrency which uses the coin age selection process combined with the randomized selection method. Peercoin’s developers claim that this makes a malicious attack on the network more difficult, since purchasing more than half of the coins is likely costlier than acquiring 51% of proof-of-work hashing power.