Storage Proofs
Storage proofs are a cryptographic way to track blockchain information so that it can be shared across chains. Similar to oracles, storage proofs provide proof that the information is true. However, unlike oracles, they do not require trust in a third party for this proof; rather, with storage proofs, the trust is built into the storage. Storage proofs allow you to open cryptographic commitments of state, they can be optimized by marrying them with S[N/T]ARKS. These validity proofs prove that a particular state existed and was valid at a particular block in the past.
Fundamentally, blockchains are databases that contain data cryptographically committed using Merkle trees, Merkle Patricia trees, Verkle trees, etc. Since all the data is committed, we can prove that some information is encapsulated in a given state. However, with simple commitment schemes, the size of this proof becomes more prominent as the size of the data it includes becomes larger. Verifying such proofs on-chain becomes too expensive to be practical.
Storage proofs, on the other hand, when used in conjunction with STARKs or SNARKs, can be relatively small, and allow you to verify a specific piece of state, at a specific point in time, and on any domain — without trusting a third party. Instead of third parties, they rely on the security of the underlying chain itself.
Since storage proofs allow us to efficiently “compress” a blockchain and transmit the data elsewhere, they have quite a few applications. The affordable verification cost, an integral property of storage proofs, allows the proof to be validated on the destination chain, minimizing the need to develop cross-chain messaging systems.
Potential use cases include:
- General information access of one chain from another about state and transactions on the blockchain.
- Simplified cross-chain voting systems. Frequently users hold their assets on a slow but more secure chain A, but some token-based voting occurs on a chain B with cheaper transactions. This forces the user to either skip their vote or pay huge transaction fees to bridge their assets from A to B, cast their vote, then bridge them back to A. In such cases, storage proofs enable users to prove their token balance on chain A at a given block and seamlessly cast their vote on chain B.
- Alternative to cross-chain bridges. Currently, cross-chain bridges assume a level of trust in a third party because they typically involve an intermediary, such as a custodian or a decentralized autonomous organization (DAO). This intermediary is responsible for ensuring that a certain amount of tokens are received on the source chain by the intermediary and for holding the assets on the source chain. Afterward, the corresponding tokens are minted on the destination chain. Storage proofs can enable trustless cross-chain bridges since a smart contract application on the destination chain could validate a transaction where assets were transferred to the bridge smart contract on the source chain and mint the bridged assets. However, in many cases the need of transferring assets between chains may be eliminated since ownership of assets on another chain could be simply proven with storage proofs.
- Enhanced UX for Account Abstraction (AA) use cases. AA has been implemented in different chains and is considered a crucial innovation in onboarding the first billion users to the blockchain space. With storage proofs, wallets could include the additional functionality of restoring access only if the wallet did not send any transactions over a long duration. Additional checks that require some data to be used from other chains could also be enforced.
Not all data provided by oracles actually needs to be supplied by a third party. In some cases, the data provided by an oracle was already available on chain (in the form of on-chain storage, or a transaction) and can be retrieved by taking a peek at a previous state of the blockchain. In these cases, a storage proof can replace the need for trust in a third party and the oracle, and allow smart contracts to rely completely on the security of cryptographic commitments.
In other cases, where storage proofs can’t completely replace an oracle, they can often still enhance them.
