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May 2018 Hardfork Specification

Version 1.1, 2018-04-09

Summary

When the median time past[1] of the most recent 11 blocks (MTP-11) is greater than or equal to UNIX timestamp 1526400000 Bitcoin Cash will execute a hardfork according to this specification. Starting from the next block these consensus rules changes will take effect:

  • Blocksize increase to 32,000,000 bytes
  • Re-enabling of several opcodes

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

  • Automatic replay protection for future hardforks
  • Increase OP_RETURN relay size to 223 total bytes

Blocksize increase

The blocksize hard capacity limit will be increased to 32MB (32000000 bytes).

OpCodes

Several opcodes will be re-enabled per may-2018-reenabled-opcodes

Automatic Replay Protection

When the median time past[1] of the most recent 11 blocks (MTP-11) is greater than or equal to UNIX timestamp 1542300000 (November 2018 hardfork) Bitcoin Cash full nodes implementing the May 2018 consensus rules SHOULD enforce the following change:

  • Update forkid[1] to be equal to 0xFF0001. ForkIDs beginning with 0xFF will be reserved for future protocol upgrades.

This particular consensus rule MUST NOT be implemented by Bitcoin Cash wallet software.

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