We introduce Harmony, the next generation sharding-based blockchain that is fully scalable, provably secure, and energy efficient. Harmony addresses the problems of existing blockchains by combining the best research results and engineering practice in an optimally tuned system. Specifically, Harmony makes breakthroughs in following aspects:
● Fully Scalable: Harmony shards not only the network communication and transaction validation like Zilliqa, but also shards the blockchain state. This makes Harmony a fully scalable blockchain.
● Secure Sharding: Harmony’s sharding process is provably secure thanks to the distributed randomness generation (DRG) process which is unpredictable, unbiaseable, verifiable and scalable. Harmony also reshards the network in a non-interruptive manner to prevent against slowly adaptive byzantine adversaries.
● Efficient and Fast Consensus: Unlike other sharding-based blockchains which require PoW to select validators, Harmony is based on PoS and thus energy efficient. Consensus is reached with a linearly scalable BFT algorithm that’s 100 times faster than PBFT.
● Adaptive-Thresholded PoS: The threshold of stakes required for a node to join the network is adjusted based on the volume of total staking in a way that malicious stakers cannot concentrate their power in a single shard. Moreover, the threshold is low enough so that small stakers can still participate in the network and earn rewards.
● Scalable Networking Infrastructure: With RaptorQ fountain code, Harmony can propagate blocks quickly within shards or across network by using the Adaptive Information Dispersal Algorithm. Harmony also adopts Kademlia routing  to achieve cross-shard transactions that scale logarithmically with the number of shards.
● Consistent Cross-Shard Transactions: Harmony supports cross-shard transactions with shards directly communicating with each other. An atomic locking mechanism is used to ensure the consistency of cross-shard transactions.