The authors introduce Sia, a platform for decentralized storage. Sia enables the formation of storage contracts between peers. Contracts are agreements between a storage provider and their client, defining what data will be stored and at what price. They require the storage provider to prove, at regular intervals, that they are still storing their client’s data. Contracts are stored in a blockchain, making them publicly auditable. In this respect, Sia can be viewed as a Bitcoin derivative that includes support for such contracts. Sia will initially be implemented as an altcoin, and later financially connected to Bitcoin via a two-way peg.
Sia is a decentralized cloud storage platform that in- tends to compete with existing storage solutions, at both the P2P and enterprise level. Instead of renting storage from a centralized provider, peers on Sia rent storage from each other. Sia itself stores only the stor- age contracts formed between parties, defining the terms of their arrangement. A blockchain, similar to Bitcoin [1, 12], is used for this purpose.
By forming a contract, a storage provider (also known as a host) agrees to store a client’s data, and to periodically submit proof of their continued stor- age until the contract expires. The host is compen- sated for every proof they submit, and penalized for missing a proof. Since these proofs are publicly veri- fiable (and are publicly available in the blockchain),
network consensus can be used to automatically en- force storage contracts. Importantly, this means that clients do not need to personally verify storage proofs; they can simply upload their file and let the network do the rest.
We acknowledge that storing data on a single un- trusted host guarantees little in the way of availabil- ity, bandwidth, or general quality of service. Instead, we recommend storing data redundantly across mul- tiple hosts. In particular, the use of erasure codes can enable high availability without excessive redundancy.
Sia will initially be implemented as a blockchain- based altcoin. Future support for a two-way peg with Bitcoin is planned, as discussed in “Enabling Blockchain Innovations with Pegged Sidechains” [5]. The Sia protocol largely resembles Bitcoin except for the changes noted below.
sia white paper