As part of Ethereum’s Metropolis hard-fork, the second biggest cryptocurrency was set to improve anonymity. Byzantium, the first part of the long-awaited upgrade, recently went live on testnet and part of a Zcash transaction has been verified, bringing it all one step closer to reality. The announcement was published on Reddit by Christian Reitweissner, co-creator of the Solidity programming language.

As stated by Christian Reitweissner:

“What is verified here is the zkSNARK part of some real transaction on the real zCash network. I pulled the data out of the chain some time around January, I think. I have no idea who created the transaction or how much money is sent inside it, but now the Ethereum network knows it is correct :-)”

A zkSNARK, zero-knowledge succinct non-interactive arguments of knowledge, was the part that got verified. It is used to prove that data is valid, without revealing what that data is. zkSNARK’s are known and used in the privacy-centric Zcash network, and while the confirmation on Ethereum’s Byzantium was only part of an experiment, it’s significant to keep it in mind

However, according to Bas van Kervel’s words to The Register, zkSNARKs are computationally heavy to verify if implemented in pure smart contracts, so optimization is needed behind the scenes. In fact, the verified transaction can be seen on the testnet, and cost a total of 1,933,095 gas – an exorbitant cost, given that most transaction cost about 21,000 gas.

When one redditor expressed his concerns over the high cost the transaction would’ve had on the mainnet, Reitweissner clarified that the code is “rather unoptimized”, and that various zkSNARK transactions could be verified in one single Ethereum transaction. He stated:

“Also note that the verification cost of a zkSNARKs is largely independent of the amount of computation done in a zkSNARK. This means you could bundle 10000 zk transactions and verify them in a single Ethereum transaction.”

Given the advantages of zkSNARKs, several proposals to tie them to Ethereum have been made in the past. Byzantium’s development is set to introduce more technology that will make this kind of verifications possible on the mainnet.

Ethereum’s hard-fork is set to enable various significant upgrades other than increased anonymity. For example, smart contracts should become easier to create, and security should improve by allowing users to determine the address they have the private key for. As part of the cryptocurrency’s transition to proof-of-stake (PoS), what’s known as a difficulty bomb, that’ll make mining harder, is also included.

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