The effort to bring the privacy features of zcash to ethereum took a step forward today during testing for the upcoming Byzantium upgrade.

A zero-knowledge succinct non-interactive arguments of knowledge, or zkSNARK, is used to prove that data is valid without actually revealing what that data is. The technology sits at the heart of the zcash network, and recent months have seen developers moving to integrate the privacy tech into ethereum.

Earlier today, the zkSNARK part of a zcash transaction was verified on the Byzantium testnet. While only a trial, the development is a critical step toward bringing that kind of functionality to the public ethereum network.

As previously reported, testing on Byzantium is expected to continue into October. Byzantium’s formal introduction will then introduce the gas-subsidised pairing checks and elliptic curve operations that make this kind of verification possible.

This means that once Byzantium becomes the law of the land, a cryptographically privatized transaction can be verified on the network.

However, computations for zkSNARKs are costly. The transaction, which is viewable on the test network here, cost a total of 1,933,895 gas. To put this in some context – a non-private transaction currently costs around 21,000 gas, tiny compared to the zcash equivalent.

Beyond the verification, there is still work to be done before private transactions are possible on ethereum.

Christian Reitwiessner, leading zkSNARKs developer for ethereum, told CoinDesk:

“What is missing after that is basically everything that was missing on top of the Ethereum Virtual Machine in the early times of Ethereum: We need practical implementations of all the other components of a zkSNARK system (apart from the verification).”

Disclaimer: CoinDesk is a subsidiary of Digital Currency Group, which has an ownership in the Zerocoin Electric Coin Company, developer of zcash.

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