2019-MAY-15 Network Upgrade Specification
When the median time past  of the most recent 11 blocks (MTP-11) is greater than or equal to UNIX timestamp 1557921600, Bitcoin Cash will execute an upgrade of the network consensus rules according to this specification. Starting from the next block these consensus rules changes will take effect:
- Enable Schnorr signatures.
- Allow Segwit recovery.
The following are not consensus changes, but are recommended changes for Bitcoin Cash implementations:
- Automatic replay protection for future upgrade
Enable Schnorr signatures
Support Schnorr signatures in CHECKSIG and CHECKDATASIG per 2019-05-15-schnorr.md.
Allow Segwit recovery
In the last upgrade, coins accidentally sent to Segwit P2SH addresses were made unspendable by the CLEANSTACK rule. This upgrade will make an exemption for these coins and return them to the previous situation, where they are spendable. This means that once the P2SH redeem script pre-image is revealed (for example by spending coins from the corresponding BTC address), any miner can take the coins.
Automatic Replay Protection
When the median time past  of the most recent 11 blocks (MTP-11) is less than UNIX timestamp 1573819200 (Nov 2019 upgrade) Bitcoin Cash full nodes MUST enforce the following rule:
forkid to be equal to 0.
When the median time past  of the most recent 11 blocks (MTP-11) is greater than or equal to UNIX timestamp 1573819200 (Nov 2019 upgrade) Bitcoin Cash full nodes implementing the May 2019 consensus rules SHOULD enforce the following change:
forkid to be equal to 0xFF0002. ForkIDs beginning with 0xFF will be reserved for future protocol upgrades.
This particular consensus rule MUST NOT be implemented by Bitcoin Cash wallet software. Wallets that follow the upgrade should not have to change anything.
 Median Time Past is described in bitcoin.it wiki. It is guaranteed by consensus rules to be monotonically increasing.
forkId is defined as per the replay protected sighash specification.