| Blockchain applications have expanded from the digital currency to all aspects of social life and economy,including medical care,supply chain,finance,government affairs,and traceability.The types of digital assets are also expanded from currency to assets with more complex states and relationships,such as certificates,bills,real estate,and health records（complex assets）.Application scenarios cover the whole life cycle of issuance,use,alteration,and destruction of assets.Based on UTXO and Account model,existing blockchains effectively express the simple state of digital currency,such as the balance,spent,and unspent.Existing blockchains use Pow and other consensus mechanisms to ensure the consistency of digital currency,which effectively avoids the occurrence of inconsistent issues,such as double-spending.Account and UTXO model can only express the simple state,a single stakeholder,and temporal or state association of an asset,but can not express complex states and complex reference or ownership associations between assets.Complex assets put forward higher requirements for the consistency assurance capability of blockchain.This thesis analyzes the characteristics,application scenarios of complex assets and existing blockchain technologies and identifies the critical issues,including the following points:（1）The existing blockchains regard complex states,diverse associations as unrecognized binary data.Existing blockchains use smart contracts and chaincodes to define,interpret and execute complex assets.The blockchain layer regards complex states,diverse associations as unrecognized binary data,resulting in the interpretation and control of complex assets relying too much on the application.（2）Transaction sequencing and execution strategies are not aware of the semantics of complex assets,leading to inconsistent problems such as state change loss and state conflict.The existing blockchain can not identify and explain the association and complex state of complex assets,and stakeholders can trade the same complex asset concurrently,and the transaction between different complex assets can be executed in parallel.Existing blockchains can only sort transactions of complex assets according to digital currency’s temporal and state association.However,they cannot sort transactions according to the association of complex assets,which reduces the security of blockchain and leads to more serious inconsistencies than double-spending and forks.（3）The cross-chain transfer process of complex assets can not deal with the cascading and dynamic relationship,resulting in cross-chain double flowers,cross-chain conflicts,and other inconsistent problems.Existing blockchains transfer assets across the chain or exchange them across the chain through a "freeze-submit" approach to ensure the atomicity and completeness of the cross-chain transfer.Ignoring the influence of associated assets,exiting solutions lead to the incomplete transfer process of assets across the chain,resulting in cross-chain double-spending,cross-chain conflict,and other inconsistent problems.This thesis studies complex assets’ completeness,self-interpretation,and consistency,mainly including the following contents:（1）Complex asset model.（2）Transaction certainty and correctness assurance for the concurrent transaction of the same asset.（3）Security and consistency assurance for concurrent execution of complex assets.（4）The integrity and atomicity of complex assets transfer across the chain.The main contributions of this thesis are as follows:1.Aiming at the problem of poor self-interpretation and data independence of complex assets,this paper proposes a blockchain native complex asset model.Subjects,contracts,and assets are the blockchain native objects,which the blockchain layer can define,explain and execute these objects.By combining the UTXO and Account model,this paper constructs the express model and execution mechanism of associations between objects,such as temporal,state,ownership,and reference association.The state linear transition mechanism is constructed based on finite state machines to avoid the double-spending problem caused by diversified states.This paper constructs a parallel and horizontally expandable world state storage structure based on flattening and reverse MPT data structures on the premise that the world state can be verifiable.This mechanism can achieve O（1）retrieval efficiency and support parallel transaction processing and largescale asset storage.2.Aiming at the uncertain and unpredictable problem of transaction execution results caused by random ordering,this paper proposes a transaction consistency guarantee mechanism based on partial order.This paper constructs the global unique deterministic execution sequence by introducing the partial order between transactions to ensure the deterministic and non-reentrant transactions execution results.Based on the state transfer path,the concurrency transaction serialization mechanism can reduce the transaction conflict rate.3.Aiming at the inconsistent problems caused by the random division of transactions with associations into different groups,this paper proposes a dynamic parallel consensus mechanism.On the premise of ensuring the correctness and certainty of the execution results of blocks and transactions in the parallel process,this paper constructs a parallel linear blockchain ledger structure and multi-nodes collaborative consensus mechanism.This paper can use the number of consensus nodes and server CPU cores to improve blockchain performance.Therefore,this paper can support the parallel construction and execution of blocks and transactions.By introducing and basic blocks,the parallel transaction sequence is divided into different transaction blocks,and the finality of blockchain is guaranteed by connecting multiple transaction blocks through the main block.By dynamically dividing consensus groups,transaction blocks are allocated to multiple groups.Based on coded computing,this paper constructs a cross-group consensus mechanism to ensure the security and liveness of consensus.4.Aiming at the inconsistent problems caused by the incomplete process of cross-chain transfer,this paper proposes a three-stage consistency guarantee mechanism for the cross-chain transfer of assets.Without freezing associated assets,the three-stage dynamic asset cross-chain transfer mechanism makes the starting and ending positions synchronize the changes of assets and ensure the integrity of the cross-chain transfer.Through multi-group message aggregation,the dynamic inter-chain message delivery mechanism is designed to ensure the reachability and integrity of cross-chain messages.This mechanism can prevent malicious nodes from blocking or tampering with cross-chain messages.Aiming at the inadequacy of existing blockchains in the expression and consistency of complex assets,this paper studies the digital object representation model and consistency guarantee mechanism,respectively.The proposed mechanism can express complex assets more comprehensively and correctly,realizing the independence and self-interpretation of complex assets and ensuring the correctness,certainty,predictability,and integrity of transaction execution results.Based on consistency proofs and security analysis,the proposed mechanism can guarantee the consistency of asset status without introducing new security risks and resist security attacks,such as TOD attacks and RV attacks.Experiments results demonstrate that our mechanism does not reduce the performance and can use the number of cores and number of nodes to improve the performance.The transaction execution speed can achieve up to 60,000 transactions per second. |
