Bitcoin users will soon be able to use zero-knowledge proofs (ZK-proofs) to speed up the process of validating individual blocks and eventually the entire blockchain.
Switzerland-based nonprofit ZeroSync Association is developing a tool that would allow users to verify the state of the Bitcoin network without having to download the blockchain or trust a third party for verification.
ZeroSync was founded to develop and maintain open source software to enable concise ZK proofs on the Bitcoin blockchain. The team used StarkWare’s proprietary Zero-Knowledge Scalable Transparent Argument of Knowledge (zk-STARK) validity proof to generate ZK proofs for the Bitcoin network.
The tool promises to revolutionize the process of validating the Bitcoin blockchain, which still requires node operators to download large amounts of data to synchronize the correct state of the Bitcoin network.
ZeroSync uses ZK-proofs to ultimately generate valid proofs and verify the latest state of the blockchain almost instantly.
ZK proofs have been a revelation to the Ethereum ecosystem, with various proof methods powering multiple layer 2 scaling platforms, including Polygon, Arbitrum, Optimism, and StarkNet.
An announcement from the ZeroSync Association underscores ZK proofs’ commitment to blockchain scalability and privacy by providing “nearly fixed-size” proofs to verify large computations.
The project's work pioneered the use of ZK proofs on the Bitcoin network, and the group describes Bitcoin's relative simplicity and unspent transaction output (UTXO) model as unique value propositions for applying recursive proofs.
ZeroSync noted that the ZK-Proof tool does not require consensus changes or additional trust assumptions on the Bitcoin network and its users. The organization is building a software development kit that allows developers to generate custom validity proofs for specific use cases without requiring deep domain expertise.
ZeroSync is building a client for fast initial block downloads, as well as implementing the first complete proof of Bitcoin consensus. The client will allow users to sync full nodes without making changes to the Bitcoin Core code.
ZeroSync uses the Cairo programming language pioneered by StarkWare to create STARK provable computational programs.
ZeroSync’s tool is currently in a prototype state, but is able to prove the validity of a single assumed-valid block, verifying all Bitcoin rules except scripts. The team also has a working in-browser demo validator for STARK proofs of Bitcoin blocks.
The ZeroSync Association was initially funded by Geometry and StarkWare, but is in the process of establishing a non-profit entity to support continued development and maintenance by stakeholders within the Bitcoin community.
StarkWare president and co-founder Eli Ben-Sasson, who co-invented zk-STARKS, summed up the importance of ZK proofs entering the Bitcoin ecosystem in a statement:
"After becoming frustrated with slow syncing, users will be able to sync with the network much faster and with less computation. It's a technological leap similar to the move from slow dial-up internet to high-speed broadband."
Lightning Labs, the team behind Bitcoin’s Layer 2 Lightning Network payment system, is a contributing partner to the ZeroSync project.
The company intends to use ZeroSync to provide compressed transaction history proof for its Taproot Asset Representation Overlay (Taro) protocol, which is designed to power the issuance of digital assets on the Bitcoin blockchain.