Bitmain loses $150K after mining an invalid block

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About the word for it is oops. Antpool, the cryptocurrency mining pool owned by Bitmain and “the most advanced bitcoin mining pool on the planet” (so says its website), just lost $150,000 in SegWitCoin (BTC) after a block it had been mined was rejected by the BTC blockchain. The block had been rejected after its transaction data didn’t meet BTC’s specifications.

BitMEX Research pointed out the SNAFU, which centers on a mining reward the pool had expected to collect. Its Twitter post states that “all 8 nodes at forkmonitor.info identified the block as invalid,” adding, “According to @theinstagibbs, the coinbase suggests @AntPoolofficial is the miner of the invalid block.”

The reference to coinbase has nothing to do with the crypto exchange by the same name. Miners are given rewards in crypto after blocks are successfully added to the network. In order to claim the reward, the miner has to add what’s called a “coinbase transaction” to the block. This data has to be equal to the amount established by the BTC protocol—currently at 12.5 BTC—in order for the transaction to be validated. This security feature ensures miners don’t create blocks incorrectly and automatically rejects those that are not properly configured.

Whoever had mined the block sent the reward request with a coinbase transaction amount of 13.26 BTC not the 12.5 BTC expected by the blockchain. As a result, the system kicked it out, resulting in a loss of around $150,000 to Antpool. The coinbase amount reportedly equates to the amount of the correct transaction amount plus the relative transaction fees, which could indicate that someone new was at the controls or the system had a bug in it. BitMex pointed this out in a separate tweet, stating, “The coinbase value was too high, presumably because this included the transaction fees, but due to some error the transactions themselves were not included.”

One respondent in the thread believes that it could have been caused by a bug, stating, “My guess would be that there was a bug in the block template generator that failed to clear out the txn [transaction] fees from the previous template being worked upon.” However, if the coinbase transaction amount is established at a set amount, there shouldn’t be any need for the field to be manipulated.

Regardless of the cause, it’s going to be an expensive lesson learned for Antpool.