Proof of Stake (PoS) concept states that a person can validate block transactions according to the quantity of coins held. This means that the validating power is proportional to the Bitcoin or altcoin owned or staked by a miner.The proof of stake was created as an alternative to the proof of work (PoW), to tackle issues of power consumption, computing power cost and fairness. In 2015, it was estimated that one Bitcoin transaction needed the amount of electricity needed to power up 1.6 American households per day. Instead of using energy to answer PoW puzzles, a PoS validator is limited to validating a percentage of transactions that is equivalent to the ownership stake. For instance, a miner who owns 5% of the Bitcoin available can theoretically mine only 5% of the blocks.