Zcash's first network update will go live on June 26 to strengthen the protocol for future network upgrades ahead of privacy-upgrade Sapling. It will prepare the network for regular upgrades and will add an expiry time to transactions which will undo transactions made to incorrect addresses.
Zcash will move from current network stage Sprout to Overwinter at 02:20 UTC+01:00 Tuesday morning. It will occur at block 347500 and estimates are based on a block time of 150 seconds per block. It will begin Zcash's plan for network upgrades to happen twice a year.
In a post, Zcash said: "Overwinter is the first network upgrade for Zcash. Its purpose is strengthening the protocol for future network upgrades. It includes versioning, replay protection for network upgrades, performance improvements for transparent transactions, a new feature of transaction expiry, and more."
The main function Overwinter adds is replay protection. This means that if some users continue to use the old chain and do not recognize the upgrade, their transactions will not be repeated on the new chain. Overwinter will also include 'signature verification performance' which will fix a bug inherited from Bitcoin, which Zcash is forked from.
These changes will help the network prepare for new upgrades, including the upcoming Sapling stage in October. This will focus on making it easier to use the privacy features of Zcash. At present, fully shielded transactions have higher processing requirements.
Unlike Monero which uses obfuscation techniques, Zcash uses cryptography including zero-knowledge proofs (zk-SNARKs) which confirm transactions without revealing the transaction data. Private transactions are made using shielded addresses. At present, only 13% of Zcash transactions include one shielded address and for fully private transactions, both addresses need to be shielded.
The network upgrade will not be a hard fork as most nodes are expected to accept it. This means it will not result in a separate blockchain that will continue to be used. According to their website, 12 exchanges and wallet providers have already committed to the fork.
One of these exchanges said: "The Lykke Exchange will handle the activation of Zcash’s Overwinter upgrade, scheduled for June 2018, entirely in the background. Lykke users will not be required to prepare their accounts for the upgrade or to do anything differently after it has gone into effect."