From Brave New Coin
On Wednesday afternoon, Bitcoin Core developer Greg Maxwell submitted a Bitcoin Improvement Proposal (BIP), inhibiting a “covert attack on the Bitcoin POW function.” Maxwell discovered patent pending technology being used in an ASIC Bitcoin mining chip, which gives certain Bitcoin miners 20 to 30 percent more mining power.https://bravenewcoin.com/news/covert-attack-on-bitcoin-ends-block-size-debate-stagnation/The technology, AsicBoost, was invented by Timo Hanke in collaboration with Sergio Lerner. "Through clever pre-processing and crafting of the work that is sent to the chip, the ASIC is allowed to re-use about one quarter of the information that would otherwise be created and discarded on a continuous basis internally to the hashing cores,” explains Hanke. “A hashing core adopted for AsicBoost can save up to one quarter of the gates by re-using that information over time or by sharing it with other hashing cores."
While the technology is offered for use under license, Maxwell discovered an ASIC chip with the technology in, which the creators “were completely unaware of.” The BIP to counter the problem does not prevent the attack in general, “but only inhibits covert forms of it which are incompatible with improvements to the Bitcoin protocol.”
“A month ago I was explaining the attack on Bitcoin's SHA2 hashcash which is exploited by ASICBOOST and the various steps which could be used to block it in the network if it became a problem,” states Maxwell. “As I explained one of the approaches to inhibit covert ASICBOOST I realized that my words were pretty much also describing the SegWit commitment structure.”
“An incompatibility would go a long way to explaining some of the more inexplicable behavior from some parties in the mining ecosystem so I began looking for supporting evidence.”
- Greg Maxwell
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