Sia is a blockchain-based cloud storage network that facilitates payments and increases security through its P2P file storage network. The platform connects users/renters who need file-storage with hosts who want to offer unused hard drive capacity. Through secure smart contracts between hosts and users, Sia enables secure cloud storage at better economics than centralized solutions.
Sia leverages a custom, proof-of-work blockchain designed for facilitating payments and file contracts. Using the Sia blockchain, renters form file contracts (a type of smart contract) with hosts, setting pricing, uptime commitments, and other aspects of the relationship between the renters and the hosts. File contracts allow Sia users to create cryptographic service level agreements (SLAs) that are stored on the Sia blockchain. Since file contracts are automatically enforced by the Sia network, there is no need for intermediaries or trusted third parties.
Sia launched as an entirely functioning decentralized storage platform in 2015 with two digital assets. The first is the Sia coin, used to rent storage on the Sia network. The second is the Siafund token, a digital asset that entitles the holder to a portion of the Siacoins exchanged each time a file contract is created on the Sia network.