Introduction

The problem is that privacy features are inaccessible. This is the problem that drives our submission. We showcase at least several solutions that stem from the tooling built for this hackathon: (1.) A Starknet & Starknet confidential transfer integration into Zashi (using the Swift SDK we made for confidential transfers and proving) (2.) a privacy maxxing browser extension wallet and confidential transfer network explorer (using the Rust SDK we made for confidential operations and key-management to facilitate a Venmo UX that is privacy maxxing).

What we built!

Swift confidential transfer SDK (Starknet & Tongo) - "Ghost SDK"

Making privacy features manifest in existing products requires tooling specific to that product´s distribution. For integrating Starknet and Starknet confidential transfers into Zashi this requires at least a Swift SDK (it would also require a Kotlin SDK too!) to allow users to derive keys from the same Zashi mnemonic and construct zero knowledge proofs that prove their confidential operations meet the constraints of the confidential transfer Cairo verifiers.

This led to the development of the Swift confidential transfer SDK. Users can derive Starknet account contract address, deploy their OpenZeppelin account and also derive confidential asset addresses to send and receive from. The SDK also has a fast-enough prover; the largest proof (the transfer operation proof) is benchmarked at 1.8 seconds.

With this new confidential Starknet transfer wallet SDK we built a new layer in Zashi which allows Zashi users to create Starknet accounts and perform Starknet confidential transfers. Similarly, it also allows Starknet users access to Zcash while maintaining their ability to re-derive their Starknet account contract and associated Starknet confidential transfer accounts. Distribution of privacy features requires tools that facilitate it and easily manifest in products like Zashi, that´s why we built this SDK and integrated it into Zashi. You can see this work manifest in Zashi in the below image:

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Current zashi demo video: https://www.loom.com/share/fafa1499a6ce458ba5b9d4507cbb

Rust SDK for confidential Transfers: Can we do better than 1.8 second proving? Yes!

While working on the Swift SDK for confidential Starknet transfers, it became apparent that even a 1.8 second prover would not facilitate the best user experience. The last thing we need is to increase a user's cognitive load while accessing privacy features & if privacy is a right, we must do better. This is a secondary problem we solved: can we build a Rust SDK that has blazingly fast provers that eliminate any increase in an end-user's cognitive load? The answer is yes we can and this hackathon's Rust SDK achieves that with a >1,000x improvement in the largest prover's speed (from 1.8 seconds in Swift to ~2 milliseconds in Rust). The following benchmarks of the prover operations demonstrate this:

Venmo Style Browser Extension, Privacy Maxxing Wallet

While the Rust SDK is significantly more performant, it alone does not showcase how we can eliminate cognitive load for end users who require confidentiality. To showcase this for the hackathon, we added a crate to the Rust SDK that created WASM bindings such that the key management, zk-provers, and privacy maxing features can be put to good user in a browser extension.

From there, we built a browser extension wallet to showcase (1.) the speed of the new provers (albeit slightly slower in WASM than Rust but still >100x faster than Swift) and (2.) that a fantastic UX is possible in the style of Venmo peer-to-peer payments. This is shown better in the demo video but there are screenshots below too:

Confidential Transfer Explorer!

Privacy-oriented solutions offer a new paradigm that is under-searched and under-productionised. Part of this is because we label these privacy protocols as "black boxes" when they really are not. Privacy protocols are rich in information, and they are demand as much focus as existing web3 applications. The easiest place to showcase this is with a privacy protocol explorer, which allows anyone to go study, touch, feel, and learn about that protocol. And that is why we built the confidential transfer explorer (which connects to the user's new extension wallet for personal views of the network!)