SPOS: The Consensus Mechanism for Secure Sharding
One of the most fundamental aspects of a blockchain is security. For a network to hold true to its immutable nature, maintain intended cryptocurrency supply, and properly maintain the wealth of wallets, it’s imperative that the protocol utilizes a robust consensus mechanism that can thwart attack vectors. For the sake of security, existing blockchains have willing given up security or, to some degree, decentralization. However, decentralization is an important pillar of blockchain technology and therefore it must be preserved. Simultaneously, scalability is of crucial importance else blockchains cannot deliver a tangible utility.
The developers behind Elrond Network have spent over 18 months, focused entirely on research and development, to create a blockchain that encompasses all three factors — scalability, decentralization, and security — that must be present in a blockchain that can truly handle the demands of mass usage. To achieve this, Elrond Network utilizes a novel consensus mechanism called Secure Proof of Stake (SPOS).
What makes Elrond Network so Secure?
Elrond Network is one of the most accessible decentralized networks to date. Anyone with access to a typical household laptop will have the computation power and storage capacity to become an active node on the Elrond blockchain. This is made possible by Elrond Network’s use of Adaptive State Sharding.
Presently, blockchains that are pursuing scalability, e.g. Zilliqa, try to implement transaction sharding (just a subset of nodes validate each transaction) in order to increase the scalability, without the state sharding, which also partitions the storage). Adaptive State Sharding, on the other hand, aggregates the benefits of state sharding, communication sharding, and computation sharding, and allows the network to linearly scale by making the number of shards dynamically adaptive. Through this, Adaptive State Sharding partitions all the resource demands of the blockchain to such a degree that even household computers can become part of the network. Elrond Network leverages this opportunity to offer a scalable throughput capacity. When network usage and number of available nodes grows, the protocol will form new shards to improve its throughput. Thus, as the blockchain’s usage grows Elrond Network scales up as additional shards are formed to provide increased throughput.
The Secure Proof of Stake (SPOS) consensus mechanism ensures that, despite the ease of becoming a node, attackers are kept at bay.
Under Secure Proof of Stake, nodes must maintain a minimum qualifying stake and a positive network reputation to receive eligible candidacy as a block proposer or validator. As the reputation is dependent on the actions of a node, each network participant has the capacity to receive a role be they willing to duly act in the best interest of the network. Thus, rather than delegating nodes, such a mechanism gives everyone the power to control their own fate in the network. Each round, a randomly sampled group of qualified nodes are selected; from a consensus group, one node will act as the block proposer. The proposed block is only approved once 2/3 + 1 of the validators in the consensus group aggregate a signature. Since the selection process is driven by a variable derived from the aggregated signature of the previous block, attackers cannot know which node to attack.
All proposed blocks of every round in every shard will also be notarized in the MetaChain. This is a separate chain in a separate shard, that acts as a notarizer of blocks in the shards. Only after a block header is added to the MetaChain blockchain, can the block be considered finalized.
With such a system, a 1% attack, which is a commonly asserted rebuttal against networks that propose sharding as a scalability solution, is avoided.
In a Proof of Work (PoW) blockchain, each transaction is processed by every node. So, an attack on a PoW network mandates the need to have the controlling share of the network hash rate; due to the incredible cost and difficulty of such an endeavor, attackers are discouraged from even attempting to breach a PoW blockchain. However, as sharding involves parallel transaction processing among shards, overwhelming a single node can result in a network compromise. Elrond Network leaves no room for such an attacker as block proposers and validators are selected from a provably random variable generated from a decentralized function. Thus, the proposer and validator are only known for few instants prior to the generation of a block. To add to this, after each epoch, the random variable is also used to reshuffle up to 1/3 of the validators.
Secure Proof of Stake (SPOS) is a consensus mechanism that is exclusively used by Elrond Network. It ensures the blockchain is able to achieve near linear scalability by allowing eased access to nodes sourced from virtually any household, without compromising network security.