Also covering Overt ASICBoost and Covert ASICBoost

ASICBoost is a technique for specially constructing a Bitcoin block header in order to reduce by about 15% the number of operations necessary to find a certain amount of proof of work.

ASICBoost can be implemented in two forms:

  • Overt ASICBoost requires manipulating the nVersion field of a block header. This is clearly visible on the block chain. Miners wishing to use overt ASICBoost are recommended to use the version bits reserved for general purpose use by BIP320.

  • Covert ASICBoost requires manipulating part of the merkle root field of a block header. This can be done undetectably, although naive implementations often leave clues.

    Covert ASICBoost is not compatible with blocks that contain secondary commitments to their transactions, as is the case with any block that contains a segwit transaction. This produced controversy when it was discovered that a mining hardware manufacturer who strongly objected to segwit had secretly designed features into their ASICs to use covert ASICBoost.

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