Harmony is a high performance public link project based on state sharding and PoS. Its sharding architecture consists of one beacon chain and several sharding chains. The beacon chain provides services including decentralized random number, verification of shard chain Header, and acceptance of equity mortgage of verified nodes.

It is committed to building a new generation of blockchain network: a blockchain based on sharding architecture with high scalability, security and low energy consumption.

Blockchain technology is seen as a major technology to restructure production relations and improve efficiency in many areas. With its development, more and more people pay attention to this field, bringing a large amount of capital inflow, but the relatively mature public chain has not been applied on a large scale. Blockchain technology has struggled to make headway in mass adoption, and one of its main hurdles has been performance.

Harmony is a fast, secure blockchain for decentralized applications. Harmony's main focus is to achieve scalability by dividing not only network nodes but also blockchain state into multiple fragments, "scaling linearly across all three aspects of machine, transaction, and storage". Verifiable random functions enable Harmony sharding, which enables security and random state sharding. The harmonious consensus mechanism, i.e., effective proof of interest, innovates on the practical Byzantine fault-tolerant consensus mechanism to further reduce centralization while supporting pledge, reward and double punishment.

Harmony's overall architecture is similar to Ethereum 2.0, consisting of beacon chains and shard chains. Harmony has some technical innovations in consensus, sharding, and networking: Consensus: Using BLS multiple signatures to improve PBFT and implement extensible FBFT consensus. Sharding: Improved security of sharding through distributed random generation of VRF and VDF fusion and adaptive PoS. Network: Use erasure codes and Kademlia routing to improve network performance.

Its functional token, ONE, has been running on Harmony's main network since June 2019 and is expected to achieve an annual inflation rate of 3%. The token must be used as collateral for the network validator and is required to initiate the transaction.

Harmony adopts PoS+FBFT consensus mechanism, that is, the nodes participating in the block signature are selected through PoS first, and then the consensus is reached through FBFT. Among them, FBFT is Harmony's innovation based on PBFT. PBFT is a consensus algorithm that allows predefined nodes to agree on certain results. As long as more than 2/3 of them follow the algorithm, PBFT can guarantee all honest nodes to agree on the same result in a limited time, regardless of the malicious behavior of the remaining less than 1/3 of the nodes. PBFT works by electing one of the nodes to be the leader and having the leader coordinate consensus, while the other nodes are selected as validators. In general, each PBFT consensus round has two phases -- preparation and submission. In each phase, the lead node broadcasts the proposal to all the validator nodes, and the validator node itself broadcasts its vote to each other node. The votes of all verifiers need to be counted by other verifiers. In this case, all nodes communicate with network complexity O(n^2), where n is the total number of nodes. O(n^2) complexity means that with the increase of nodes, the communication complexity of PBFT network increases in the form of square. Therefore, PBFT is not scalable and the network can only be consented by fewer nodes. Harmony is optimized for PBFT scalability issues, referred to as FBFT. FBFT achieves O(N) communication complexity and can be linearly extended. Like PBFT, there are roles of leader and verifier in the FBFT algorithm. Instead of requiring all verifiers to broadcast their votes, the leader runs a multi-signed signing process to collect verifier votes. As shown in the figure above, FBFT adopts BLS (Boneh-Lynn-Shacham) multi-signature scheme, which is an improvement of Schnorr signature scheme. On the basis of realizing constant size of multi-signature (complexity O(1)), FBFT also realizes that only one round trip is required to deliver messages (complexity O(n)). In this case, the VERifier of the FBFT only needs to receive a multiple signature, and the complexity of communication is reduced from O(N²) to O(N). In addition to these improvements, Harmony also uses RaptorQ Fountain code to speed up the block broadcast process. Harmony's FBFT is more scalable than PBFT, allowing more nodes to participate in consensus.

Sharding, as an extension of blockchain, was first implemented on Zilliqa. But Zilliqa only implements network sharding and transaction sharding. Zilliqa divides its network into shards with hundreds of nodes each (network shards). This allows different transactions to be processed simultaneously by different shards (transaction shards). However, in order to be able to process transactions, each node in the shard must store the entire blockchain state information. This makes the network have higher requirements on nodes, which prevents hardware resources from joining the network, and is not conducive to the decentralization of the network. Harmony takes state Sharding a step further and calls its Sharding technology Deep Sharding, where Harmony shards not only the transaction layer but also the layer where consensus occurs, which increases the level of parallel processing and improves network throughput. In addition, since none of the nodes need to store the entire blockchain state, general personal computers can also join the network as nodes, making the network more decentralized.

Incentive mechanism is an important factor to maintain the security and stability of blockchain network. The incentive mechanism designed by Harmony mainly includes the following three aspects: 1. Consensus reward. Upon the successful addition of a block, all verifiers participating in the consensus process will split the block award and transfer fee based on the number of votes cast. 2. Pledge and confiscation. All violations detected by the network, such as not issuing blocks on time, double flowers and other malicious acts, will be partially confiscated tokens pledged by the offending node. Confiscated tokens are distributed to nodes that report violations. 3. Withdrawal of pledge. Put in place additional measures during the pledge token withdrawal process to reduce the possibility of a long-range attack.

In view of the difficulty of state sharding, there is still uncertainty in the realization of technological innovation.

Harmony's core team members mostly come from the technical teams of Google, Amazon, Apple and other large high-tech companies, covering a wide range of fields. They have made great innovations in Harmony's consensus mechanism, state sharding and network communication (fast block propagation, cross-sharding routing). In addition to improving performance, Harmony also improves network security and decentralization to some extent, which can be said to solve the "impossible triangle" problem to some extent. However, Harmony does not discuss the mechanism and safety of FBFT activities in the case of evil leaders in the white paper, which is difficult to review. The Harmony code has been open source since the beginning of the year and has been well received in the industry. Compared with other public chains, we can see its advantages in performance and security, but the delayed launch of Harmony's main network also shows how difficult it is to develop. The development of public chains is closely related to ecology. Compared with public chains that have been online for a long time, such as Ethereum and EOS, there is a big gap in ecology. In terms of token economy, Harmony's initial token allocation is reasonable. Binance Lauchpad has made a wide distribution. Meanwhile, certain reserve funds are left for the continued development and ecological operation of the agreement, and the linear unlocking scheme of these funds is also reasonable. Harmony has no obvious problem with the token incentive scheme for verification nodes, which needs to be further verified and improved in practice.