DFINITY

What is DFINITY

The Dfinity blockchain computer provides a secure, performant and flexible consensus mechanism. While first defined for a permissioned participation model, the consensus mechanism itself can be paired with any method of Sybil resistance (e.g. proof-of-work or proof-of-stake) to create an open participation model. Dfinity’s greatest strength is unfolded in the most challenging proof-of-stake case.

At its core, Dfinity contains a decentralized randomness beacon which acts as a verifiable random function (VRF) that produces a stream of outputs over time. The novel technique behind the beacon relies on the existence of a unique-deterministic, non-interactive, DKG-friendly threshold signatures scheme. The only known examples of such a scheme are pairing-based and derived from BLS.

The Dfinity blockchain is layered on top of the Dfinity beacon and uses the beacon as its source of randomness for leader selection and leader ranking. A "weight" is attributed to a chain based on the ranks of the leaders who propose the blocks in the chain, and that weight is used to select between competing chains. The Dfinity blockchain is further hardened by a notarization process which dramatically improves the time to finality and eliminates the nothing-at-stake and selfish mining attacks.

Dfinity’s consensus algorithm is made to scale through continuous quorum selections driven by the random beacon. In practice, Dfinity achieves block times of a few seconds and transaction finality after only two confirmations. The system gracefully handles temporary losses of network synchrony including network splits, while it is provably secure under synchrony.

PROLOGUE

DFINITY is a decentralized network design whose protocols generate a reliable "virtual blockchain computer" running on top of a peer-to-peer network upon which software can be installed and can operate in the tamperproof mode of smart contracts. The goal is for the virtual computer to finalize computations quickly (using short block times and by requiring only a small number of blocks as "confirmations"), to provide predictable performance (by keeping the time between confirmations approximately constant), and for computational and storage capacity to scale up without bounds as demand for its services increases (using novel validation mechanisms and sharding systems discussed in our other papers). The protocols must be secure against an adversary controlling less than a certain critical proportion of its nodes, must generate cryptographic randomness (which is required by advanced decentralized applications) and must maintain a decentralized nature as it grows in size to millions of nodes.

Dfinity will be introduced in a series of technology overviews, each highlighting an independent innovation in Dfinity such as the consensus backbone, smart contract language, virtual machine, concurrent contract execution model, daemon contracts, peer-topeer networks and secure broadcast, governance mechanism and scaling techniques. The present document will focus on the consensus backbone and cryptographic randomness.

Dfinity has an unbiasable, verifiable random function (VRF) built-in at the core of its protocol. The VRF not only drives the consensus, it will also be the foundation for scaling techniques such as sharding, validation towers, etc. Moreover, the VRF produced by the consensus layer is available to the application layer, i.e., to the smart contracts and virtual machine. In this way, the consensus backbone is intertwined with many of the other topics.