# TrustShare: Secure and Trusted Blockchain Framework for Threat Intelligence Sharing
## 2 Background
### Blockchain Overview
Some significant properties of blockchain are outlined as follows [17]:  
* **Decentralized:** Decentralized systems eliminate the requirement of a central authority to validate transactions, instead relying on a consensus algorithm. This approach mitigates the risk of a single point of failure in the blockchain system. Each node in the network maintains a complete and verified record of transactions, ensuring a high level of data redundancy and availability. * **Immutability:** Once a block is added to the chain, data becomes nearly immutable, ensuring security. Blockchain uniquely allows data ownership to be changed only by the owner, and its origin is traceable, serving as a reliable ledger. The use of the National Institute of Standards and Technology (NIST)-certified cryptographic methods, like SHA-256 and 256-bit ECDSA, enhances user identity security and preserves digital assets effectively. * **Anonymity:** Anonymity within the context of blockchain technology grants participating nodes the capability to engage in transactions and activities without the necessity of revealing their individual identities. This feature allows users to contribute and interact within the blockchain network while maintaining a level of privacy and confidentiality regarding their personal information. * **Auditability:** At any point in time, the blockchain allows for the validation of existing transactions. This involves verifying that a transaction has not been altered over time by examining the cryptographic hashes associated with the preceding blocks. This process ensures the integrity and security of the transaction history recorded on the blockchain. * **Trustless and Transparency:** Nodes can transact without pre-established trust, and all transactions are recorded on the ledger to ensure transparency. Each transaction is recorded on the blockchain, making it visible to every node in the network. * **Use of Smart Contracts:** Smart contracts enable the automation of transactions within the blockchain. The computer code enhances computational efficiencies by facilitating and verifying agreements among nodes. Moreover, the blockchain consensus algorithm operates at a slower pace because nodes need time to agree on adding a new transaction block to the chain. This process is more time-consuming compared to the conventional transaction mechanism in centralized systems. While blockchain provides valuable features, it faces challenges in scalability, censorship, latency, and privacy. To address these concerns, integrating blockchain with compatible technologies like the IPFS and implementing strong security measures, such as encryption techniques, delegated credentials, trusted signing, and smart contracts, can be effective. Blockchain ensures transparent and secure transactions and unmodifiable content by allowing any node in the decentralized network to observe transactions. However, its public nature raises privacy concerns [18]. In contrast, privacy is a focus in other types, using smart contracts to govern rules on specific nodes, as seen in Ethereum and permissioned blockchain platforms. Blockchain types vary based on user authorization and authentication, ranging from private and consortium blockchains to public blockchains. See Table 2 for features of different blockchain classifications.