Smart contract-based methods are used to implement the blockchain applications. While smart contracts have separate pre-deployed steps, which are suitable for applications that are deployed once and invoked many times. However, there are smart contracts that are used only one time (the disposable smart contract) or few times. Pre-deployment requires an additional step and additional transactions, which bring burdens (such as longer waiting time and more transaction fees) to users. In this paper, we propose a new Lifecycle model of smart contracts, which allows combining the pre-deployment with function invocations. This facilitates the usage of the disposable smart contract, as users are only required to send one transaction to perform both the pre-deployment and the function invocation. Together with the smart contract separation, it also allows participants to customize their special smart contracts at the request time. At last, we verify the proposed model and it shows the potential to save additional burden and to facilitate the usage of the smart contract.

Cross-chain exchange swaps assets among different blockchains, which facilitates cooperation among blockchains. A cross-chain exchange contains several transactions from different blockchains. It requires to synchronize asset transfers in those associated blockchains to avoid partial transfers. Current cross-chain methods are divided into two main types. One locks the assets first and transfers the frozen asset to receivers later. The second one is the two-phase or three-phase transaction commit protocol. Those methods require at least two steps, which makes those blockchains coherent to synchronize at different time(steps). Serialization is required as the second step has to wait for the completion of the first step, and even some steps in the same stage are required to be serialized. Meanwhile, their implements are either by smart contracts or special blockchain structures/roles. Smart contract based methods require to pre-deploy a smart contract and cannot change dynamically. Special structure or role-based methods force associated blockchains to have those special requirements. In this paper, we propose a new cross-chain exchange model based on the dependence of associated transactions, which is expressed inside a transaction and can change when sending transactions. It saves the step to lock the asset or perform a pre-commit and has no special requirements for blockchains or pre-deployment of smart contracts. The simulation results show the proposed model exchanges asset effectively among different blockchains.

In cross-chain scenarios, there are different blockchains, which need to cooperate. Cooperation among different blockchains is done by smart contracts that work together to complete cross-chain tasks. When numerous cooperative smart contracts are involved, smart contracts form a complex interaction network, which makes it difficult to evaluate the cooperation. It needs a common model to quantitatively analyze the cross-chain cooperation of associated smart contracts. In this paper, we model the cooperation among smart contracts as conditions and their corresponding actions, the condition-trigger model. Then we propose the method to calculate the cooperation probabilities by the graph weight. As the edge weight lacks the information of interaction probabilities, we introduce the dimension of the edge weight to calculate the probabilities. Finally, we verify the proposed condition-trigger model and its different types. It demonstrates that our proposed methods can effectively analyze the cross-chain cooperation among smart contracts.

In recent years, the number of IoT devices has increased substantially. One of the main concerns is the interaction with high availability. While peer-to-peer (P2P) technology has been used to achieve high availability by software running in P2P hardware, a single software still acts as the center for the interaction. If the software has bugs or is out of service, all devices are affected. Aiming at this issue, this paper proposes a fully decentralized model as a high-availability solution, in which P2P software runs on a P2P hardware environment. P2P software is a set of independent software from respective participants (IoT devices) that can work cooperatively without centralized software. We use blockchain as a P2P platform because it has P2P nodes and a trustless environment, so the P2P software in this paper is P2P smart contracts. To pair cooperative smart contracts, each P2P smart contract has requirements on other smart contracts. If several smart contracts matches the requirements mutually, they are treated as a work group (a topic), and then they process each other’s requests within that group. When a single smart contract fails, the paired P2P software can be re-selected, resulting in high availability. Simulation results show that the proposed model can effectively eliminate the impact of the failure of any single smart contract.