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Bitcoin Cash Protocol Upgrades
layout: specification title: 2019-NOV-15 Network Upgrade Specification date: 2019-10-23 category: spec activation: 1573819200 version: 0.4
When the median time past  of the most recent 11 blocks (MTP-11) is greater than or equal to UNIX timestamp 1573819200, 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 for OP_CHECKMULTISIG(VERIFY).
- Enforce minimal push and minimal number encoding rules in Script.
The following are not consensus changes, but are recommended changes for Bitcoin Cash implementations:
- Automatic replay protection for future upgrade
Schnorr Signatures for OP_CHECKMULTISIG(VERIFY)
Use of Schnorr signatures is enabled in OP_CHECKMULTISIG(VERIFY). The dummy element is repurposed to flag Schnorr mode when it is non-null, and the order of signatures in Schnorr mode is constrained according to the bitfield encoded in the repurposed dummy element.
Details can be found in the full specification: 2019-11-15-schnorrmultisig.
NOTE: The repurposing of the dummy element as a flag and bitfield supersedes the need for NULLDUMMY.
Enforce MINIMALDATA in Script.
Enforce existing standardness checks that all executed data pushes use minimal push operators, and all numbers are encoded minimally, together known as the “MINIMALDATA” rule. This goes into effect at the consensus layer.
Details can be found in the full specification: 2019-11-15-minimaldata.
Automatic Replay Protection
The purpose of Automatic Replay Protection is to serve as a full node version-deprecation mechanism. It is intended to cause full validating nodes which do not upgrade, to automatically separate themselves from the main network after the next upgrade on 15 May 2020. Nodes which implement the next upgrade will remove this automatic replay protection, and thus all regular wallets can continue using the default ForkID with no change to follow the main upgraded chain.
When the median time past  of the most recent 11 blocks (MTP-11) is less than UNIX timestamp 1589544000 (May 2020 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 1589544000 (May 2020 upgrade) Bitcoin Cash full nodes implementing the Nov 2019 consensus rules SHOULD enforce the following change:
forkid to be equal to
XXXXis some arbitrary hex value. 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.