The Bitcoin scaling debate keeps getting more intense everyday with the two predominant scaling solutions, Bitcoin Unlimited and SegWit, competing for miner approval and with supporters from both sides threatening to activate User Activated Forks. However, the situation escalated quickly when members of the Bitcoin community accused Bitmain, one of the most vocal supporters of Bitcoin Unlimited, of blocking SegWit for its own personal gain.
It started when Greg Maxwell, CTO of Blockstream and Bitcoin Core developer made a post to the Bitcoin mailing list in which he claims that Bitmain (not mentioned by name) was secretly using ASICBOOST, an exploit on Bitcoin’s SHA2 hashcash that gives the miner an estimated ~20% advantage. The method was invented by Timo Hanke in collaboration with Sergio Lerner
“An incompatibility would go a long way to explain some of the more inexplicable behavior from some parties in the mining ecosystem so I began looking for supporting evidence.Reverse engineering of a particular mining chip has demonstrated conclusively that ASICBOOST has been implemented in hardware.” Greg Maxwell
The theory is that Bitmain was secretly using this technology in order to boost earnings from its mining pools. This, however, is not the main accusation, as the miners are expected to be competitive. The problem is SegWit and Bitmain’s attitude towards it.
While many have previously suggested that Bitmain opposes SegWit due to the transaction malleability fix, which would allow payment channels like Lightning Network to be implemented and in turn “steal” fees from miners, the accusations have now morphed.
In light of the information presented by Maxwell, in which Bitmain’s mining equipment has a circuit design that supports ASICBOOST, the theory now is that Bitmain is actively opposing SegWit because this performance boost is not compatible with the SegWit upgrade. This accusation has caused outrage throughout the community.
“The thing he’s accused of isn’t violating a patent, or even using asicboost. It’s blocking segwit for disingenuous selfish reasons.” Brian Cohen, creator of Bittorrent
Brian Cohen also criticized Bitmain for for filing a chinese patent application for ASICBOOST without giving credit to its inventors.
Now, Bitmain has responded to these allegations as previously promised. The company claims that they are utterly false and that while their ASIC chips have a circuit design that supports ASICBOOST, they are not using it on the Bitcoin mainnet, although they hold the ASICBOOST patent in China and can legally use it in their mining farms. The company does claim to have tested the tech in the Bitcoin testnet.
Bitmain also reminded the accusers that they have always, as a company, supported the Hong Kong Agreement in which SegWit plus a hard fork to 2MB block size limit was agreed. The company is also a vocal proponent of bigger blocks, which would make the collisions more dificult and damage Bitmain’s gain from the covert use of ASICBOOST.
Although it’s not clear if the post is completely truthful, Bitmain does make some compelling arguments. The company’s development and testing of ASICBOOST is nothing out of the ordinary since Bitmain focuses on advancing mining hardware. But if they have been using this technology in secret or not is still out in the open.