Zero-knowledge proofs use cryptography to prove the validity of information without revealing the information itself. Using a zk-proof to validate the Bitcoin blockchain means nodes can sync almost instantly instead of taking hours (and sometimes days) to download the chain’s current 500 GB of data.
ZeroSync has already produced a working prototype that allows users to validate the state (who owns what right now) and transaction history of the Bitcoin blockchain without downloading the entire chain or trusting a third party.
The prototype can verify Bitcoin consensus rules but not transaction signatures. It’s also a bit clunky and still needs to be optimized for speed and security, so it’s not ready for prime time just yet, but the important thing is it works.
“It's very much in the prototype stage,” ZeroSync co-founder Robin Linus told CoinDesk. “But the grand vision is that you download that one megabyte of proof and that is as good as if you had downloaded the 500 gigabytes.”
Light clients or simple payment verification (SPV) nodes have always existed on the Bitcoin blockchain. In fact, Satoshi Nakamoto mentioned the concept in the Bitcoin white paper. They are critical for small devices like mobile phones that can’t download the entire blockchain.
“It is possible to verify payments without running a full network node,” Satoshi wrote. "Verification is reliable as long as honest nodes control the network, but is more vulnerable if the network is overpowered by an attacker.”
ZeroSync goes a step further by verifying transactions via cryptographic proof rather than merely trusting honest nodes as suggested by Satoshi.
“You don't have to trust. That is the entire point,” said Linus. “The proof proves it to you. That's the great invention.”
A fully functioning zk-proof mechanism can be used to enable a wide range of applications outside of the flagship node syncing use case. ZeroSync has created a developer tool kit to enable applications like proof-of-reserves on exchanges and transaction history compression on second layer protocols like Lightning Labs’ Taro.
Linus and fellow co-founder Lukas George joined forces in July to work on implementing a full chain proof of the Bitcoin blockchain after George’s undergraduate thesis on implementing a proof of Bitcoin's headers caught the attention of Geometry Research.
The team subsequently added Tino Steffens to the mix; all three co-founders have a background in computer science.
Linus was living in Santa Teresa, a remote beach town on Costa Rica's Nicoya Peninsula that has one ATM machine with a 10 p.m. curfew. It drove Linus nuts and forced him to research alternative payment methods. He stumbled upon Bitcoin, befriended the well-respected “Bitcoin sorcerer” Ruben Somsen (who coined the term “ZeroSync”), and the rest, as they say, is history.
“From there, I started to learn more and more about cryptography,” Linus said. “I developed some skills over time and then Ruben recommended me to Geometry Research. They offered me the opportunity to build STARK proofs for Bitcoin and that's also how I got in touch with Lucas.”
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