# IOTA-BT: A P2P File-Sharing System Based on IOTA
## 1 Introduction
The consensus mechanism in the RapidChain system is to form a reference committee by nodes and introduce the concept of epoch to iterate the members of the reference committee. Since the routing protocol between the client and the committee refers to Kad (Kademlia), the composition of the committee is continuously updated to avoid Sybil attacks. Polkadot [20] is aimed at creating a network protocol to solve the isolation of the blockchain. By establishing a multi-chain architecture, all different blockchains connected to this architecture can exchange information. To achieve this goal, Polkadot uses Parachain for data calculation and transaction information processing. Through multiple parallel chains, the horizontal expansion of the blockchain can be achieved to improve the performance of blockchains. On the other hand, Polkadot uses Relaychain to verify the blocks given by each Parachain and provide proof of finality. Omnilayer [21] is a software layer built on top of BitCoin, which provides users with a distributed and peer-to-peer platform for trading. The advantage of Omnilayer is its ability to support user-generated currencies and smart property while its drawback is that it is inherently vulnerable to malicious attacks. Although the previous distributed technologies are useful for improving the performance of blockchains, they are dependent on miners and need pay fees for transaction proof. Therefore, they are not cost-effective for a voluntary file-sharing environment such as BitTorrent. Fortunately, the emergence of IOTA [22] has dramatically improved the efficiency of blockchain transaction verification. It abandoned the chain structure of the previous blockchain and used DAG (Directed Acyclic Graph) to form its Tangle network. Whenever users need to post a transaction, they only need to verify two past transactions to complete the transaction process, which significantly improves the throughput and scalability of the blockchain. More important is that IOTA supports zero transaction fees and does not rely on miners for transaction proof. Therefore, IOTA has been widely used in the Internet of Things. For example, the IOTA Data Market [23] cooperates with many well-known companies for secure storage and transactions. [PERSON] [24] et al. proposed publishing data collected by IoT devices (such as smart meters and smart charging systems) to the Tangle network for enhancing privacy and security. As previously described, we propose an IOTA-based BitTorrent system called IOTA-BT for P2P file sharing in this paper. By replacing the central tracker, it solves a single point of failure and avoidsthe problem of DHTs being vulnerable to cyber-attacks because it inherits the advantages of IOTA. When a BT client attempts to be the seeder of a file, it publishes the seeder information to the IOTA network. When other clients want to download the file, they can query the transaction content on any IOTA node, and then know the seeder and file information. Therefore, the proposed system supports the distributed query and ensures the accuracy of information. In addition, this research tries to add a timestamp when BT clients are seeding so that later other clients can quickly find the latest information about the seeder nodes. The remaining chapters of this paper are organized as follows. Section 2 introduces relevant background knowledge. Section 3 describes the framework of IOTA-BT. Section 4 discusses the efficiency of the proposed system. Section 5 presents the conclusions of this paper and our future work.