CarteZcash

About CarteZcash​

The Zcash shielded pool is one of the most trusted private cryptocurrency protocols that has stood the test of time. Actually obtaining and using Zcash however is a poor user experience that generally requires the use of a centralized exchange.

What if you could shield your Eth assets directly from Ethereum by depositing them into a Zcash L2? That is what CarteZcash allows you to do!

CarteZcash takes parts of the Zebra Zcash client and uses them to build a mini version of the protocol called we call TinyCash. This runs inside the Cartesi Machine which handles deposits and withdrawals via Portals. The result is a fully functioning ZCash that allows privately sending wrapped Eth

How It Works​

Architecture​

CarteZcash takes parts of the Zebra Zcash client and uses them to build a mini version of the protocol called we call. This is similar to how Optimism uses minigeth for the Ethereum state transition.

TinyCash is Zcash but with the following changes:

• All network upgrades up to NU5 are applied in the first block
• Each block contains only a single coinbase transaction and up to one user transaction
• No checking of proof-of-work
• No miner rewards
• Transaction fees not enforced

TinyCash then runs inside the Cartesi machine to produce a fully functional rollup.

All interactions with the L2 are done via the Cartesi contracts. Deposits, transactions and withdrawals are all supported.

Deposits​

Using Portals it is possible to deposit Eth into the rollup and have it minted as CarteZcash Coins into a transparent Zcash address.

This works by using the coinbase transaction functionality that was previously used for issuing mining rewards. Upon receiving an AdvanceState message that matches an Eth deposit action, CarteZcash instructs TinyCash to mine a new block with a coinbase that mints coins to the wallet address decoded from the execLayerData field. These new minted coins are transparent (not shielded) but can be made anonymous by making another transaction into the shielded pool.

Transfers​

CarteZcash is able to process regular Zcash transactions produced and signed by any Zcash wallet. This includes private shielded transactions!

The prepared transactions just need to be serialized and then sent to CarteZcash via the InputBox contract.

Withdrawals​

To withdraw from the CarteZcash L2 and get your coins back on L1 you simply cast your coins into the fires of Mt Doom!

What this means is you make a transparent transaction sending your coins to the Mt Doom address t1Hsc1LR8yKnbbe3twRp88p6vFfC5t7DLbs. This address has no private key so the coins can never be spent again.

CarteZcash watches for transaction to this address and when it observes one will issue a voucher to release the corresponding number of coins on L1.

Wallet Interface​

CarteZcash integrates with existing Zcash wallets via the cartezcash-proxy component. The proxy exposes a GRPC interface that matches the lightwalletd specification. This allows any complaint wallet to read the blockchain state and request the require info to update the wallet balances.

The proxy is essentially an indexer that runs the same program as the Cartesi machine but with additional data storage and interfaces. Having the proxy allows the program running in the Cartesi machine to aggressively prune old block data which is no longer needed for verification but wallets might need for updating their balance. It also avoids having to use the inspect HTTP API to retrieve state and allows for using GRPC instead.

What's next​

Looking for contributors to take this from a hackathon project to a PoC

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