Skip to content

2020-MAY-15 Network Upgrade Specification

Version 1.0, 2020-03-04

Summary

When the median time past [1] of the most recent 11 blocks (MTP-11) is greater than or equal to UNIX timestamp 1589544000, 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:

  • Bitcoin Cash's SigOps counting and limiting system is replaced with a new system, referred to as SigChecks.
  • A new opcode called OP_REVERSEBYTES has been added to the script system.

The following are not consensus changes, but are recommended policy changes for Bitcoin Cash implementations:

  • The default for max number of in-mempool ancestors is changed from 25 to 50.
  • The default for max number of in-mempool descendants is changed from 25 to 50.
  • Automatic replay protection for future upgrade.

SigChecks

Enforcement of sigops limits is removed, and replaced with new limits based on the number of signature checks that are actually executed when running a script. This new system is called SigChecks.

Details can be found in the full specification: SigChecks.

OP_REVERSEBYTES

This new opcode reverses the order of bytes in a string. It can be used to change endianness.

Details can be found in the full specification: OP_REVERSEBYTES.

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 [1] of the most recent 11 blocks (MTP-11) is less than UNIX timestamp 1605441600 (Nov 2020 upgrade) Bitcoin Cash full nodes MUST enforce the following rule:

  • forkid [2] to be equal to 0.

When the median time past [1] of the most recent 11 blocks (MTP-11) is greater than or equal to UNIX timestamp 1605441600 (Nov 2020 upgrade) Bitcoin Cash full nodes implementing the May 2020 consensus rules SHOULD enforce the following change:

  • Update forkid [2] to be equal to 0xFFXXXX, where XXXX is 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.

References

[1] Median Time Past is described in bitcoin.it wiki. It is guaranteed by consensus rules to be monotonically increasing.

[2] The forkId is defined as per the replay protected sighash specification.

License of this document

The MIT License (MIT)

Copyright (c) 2017-2020 bitcoincash.org

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.