# AI Agents Meet Blockchain: A Survey on Secure and Scalable Collaboration for Multi-Agents
## 3 Preliminaries
### Web3  
Web3 is an evolution of the internet that leverages decentralized blockchain to create a more secure and user-owned experience. Unlike Web 1.0 (static content) and Web 2.0 (interactive platforms), Web3 leverages blockchain to create a \"read-write-own\" environment. This allows users to retain ownership over their data through public and private keys. As a result, privacy and security are significantly augmented through mechanisms such as encryption and decentralized data storage. As a result, users are empowered with greater control over how their personal data are shared and utilized. Additionally, the shift reduces the risks associated with centralized data breaches and enhances user trust in online interactions [53; 54]. Web3 facilitates the creation of decentralized apps (dApps) in several sectors, such as banking (DeFi) [55], gaming, decentralized storage, and cross-chain interoperability [56; 57]. Non-Fungible Tokens (NFTs) are integral to the Web3 ecosystem, as they facilitate the ownership and transfer of distinct digital assets on decentralized networks [58].  
The following components represent key building blocks of the Web3 ecosystem, each a vital part of its decentralized and user-empowered structure:  
* Distributed Ledger Technology (DLT): The underlying technology of blockchain, DLT refers to a consensus of replicated, shared, and synchronized digital data spread across multiple locations. This ensures data integrity and transparency.
* DAOs: DAOs shift from conventional centralized models to decentralized blockchain-based decision-making systems [54]. They use smart contracts to automate governance protocols and implement decisions based on member involvement by eliminating intermediaries to ensure transparency and efficiency [58]. For example, MakerDAO ([[https://makerdao.com](https://makerdao.com)]([https://makerdao.com](https://makerdao.com)) (accessed on 20 January 2025)) members voted to add new collateral types to support the stability of its DAI stablecoin to demonstrate decentralized governance in action.
* DeFi: DeFi represents a transformation of traditional banking and financial services through dApps to provide lending, borrowing, and trading without intermediaries [55]. It offers benefits such as reduced transaction costs, increased financial accessibility, and the elimination of traditional banking barriers. Examples include Uniswap and Aave.
* Non-Fungible Tokens (NFTs): A mechanism for the ownership and transfer of distinct digital assets on decentralized networks [58]. NFTs play a crucial role in gaming, art, and virtual assets with platforms like OpenSea ([[https://opensea.io/](https://opensea.io/)]([https://opensea.io/](https://opensea.io/)) (accessed on 20 January 2025)) leading the market.
* Decentralized Storage: A system where data are distributed across multiple nodes rather than being stored in a central server. Decentralized storage solutions such as IPFS ([[https://ipfs.tech/](https://ipfs.tech/)]([https://ipfs.tech/](https://ipfs.tech/)) (accessed on 20 January 2025)) and Filecoin ([[https://filecoin.io/](https://filecoin.io/)]([https://filecoin.io/](https://filecoin.io/)) (accessed on 20 January 2025)) help enhance data redundancy and reduce the risk of single points of failure, contributing to the resilience of Web3.
* Oracles: Services that connect blockchain with external data sources, enabling smart contracts to interact with off-chain data. Oracles are critical for Web3 as they expand the utility of blockchain by allowing real-world events to trigger on-chain actions. For example, in a DeFi application, oracles can provide real-time price feeds for assets by allowing automated trading or lending decisions to be made based on current market conditions. Examples include Chainlink ([[https://chain.link/](https://chain.link/)]([https://chain.link/](https://chain.link/)) (accessed on 20 January 2025)).