Introduction

The range of applications where blockchain technology can be applied has been widening. Whereblockchain v1.0 designs (e.g.Bitcoin) providedconsensus for serializing token transfers,blockchainv2.0 designs (e.g.Ethereum) added support forgeneric computation via smart contracts. For nextgeneration blockchains. one of the main goals is toenable priuate computation. The SwiftCloud Blockchain Platform is a Layer 1 Proofof Stake (PoS) smart contract platform that provides scalabilityextensibility, and privacy. The mainfeatures of the platform enable efficient verifable andconfidential smart contract execution. The modulardesign of the platform allows the consensus layer tobe easily changed to use a completely different con-sensus mechanism to benefit from the latest progressin the space: furthermore,the consensus layer accommodates multiple smart contract runtimes simultaneously.

These independent parallel runtimes.orParaTimes”，can use different verifiable computingand confidential computing techniques with little orno changes to the interfaces. Before the consensus layer accepts an update submitted by a ParaTime.it first verifies that the updatevalue, which represents a state change for the sourceParaTime. is correct. This is done using a form of verifable computation; currently we use replicated computation in the ParaTime for verifying smart contracttransaction execution results. Our verifiable computing implementation is called“discrepancy detection”48 incorporating an efficientfast-path optimization that allows us to use smallerParaTime execution committees of size F +1 most ofthe time where F is the number of faulty or Byzantine nodes.This compares well with traditional ByzantincFault Tolerance(BFT) based replicated computationtechniques that require committees of size 3F + 1, olEthereum 1.0 which uses a 2F +1 honest-majoritydesign. This greatly improves scalability for smartcontracts that run on the SwiftCloud Blockchain Platformsince the computing cost for a given desired level of security is reduced.

Our modular layered design makesthis possible because it separates smart contract execution from consensus,and this separation allows the SwiftCloud Blockchain Platform to reduce the replicationfactor for smart contract execution without sacrificing security, separate from the validator replicationin the consensus comnmittee. Note that our architecture does not require the use of discrepancy detectionand ParaTime implementers can choose to use otherverifiable computing techniques for smart contract execution. ParaTimes can be implemented,registered.and operated by anvone, and they can commit arbitrary values,eg., something as simple as documenthashes for timestamping26 .rather than ParaTimestate updates. ParaTimes may implement other confidential computing techniques such as multiparty computation (MPC) encryptionFHE),zero-knowledge proofs (ZKP)etc Our goal is to enable a range of privacy enhancingtechnologies so that different ParaTimes can choosedifferent technologies and make different trade-offs. The SwiftCloud Blockchain Platform was designed andimplemented in conjunction with a reference ParaTime implementation by SwiftCloud.Having a working ParaTime allowed us to exercise the system interfaces. so that the module boundaries were notdesigned in tacuo.

It also provides verifiablecomputing via discrepancy detection. Like for verifiabilitv. our architecture does not require ParaTimesto provide confidentiality. nor does it require (or preclude) the use of any particular confidential comput-ing technique. Indeed, a ParaTime that does not useany confidential computing techniques can easily coexist with a TEE-based ParaTime and provide onlya guarantee of verifable execution The modular nature of the architecture also allowsthe consensus layer implementation to be updated independently of the ParaTimes and vice versa.

NewParaTimes can be easily incorporated without anyimpact on existing ParaTimes.For example. a privateclosed smart contract systemn for use within an enterprise environment can be realized as an independentParaTime that operates in parallel with a public,opensmart contract ParaTime. This paper describes our architecture, the consensuslayer desian,and describes how A relerence temtation of a confidential ParaTimefits into the overalarchitecture It describes the interfaces as currentlydesigned/implemented--they could change as the system further evolyes This paper does not describe an?particular blockchain network built using the SwiftCloud Blockchain Platform. In particular, while this papersuggests some potential areas in which the platformmieht be enhanced or extended in the future.