The Chinese pool F2pool recently began censoring certain transactions originating from bitcoin addresses placed on the United States blacklist.
What is a pool?
We must start by remembering that miners participate in securing Bitcoin by providing energy in the form of electricity. These electrons power ASICs designed to hash with the SHA-256 algorithm. This process is called “Proof of Work”.
In short, miners hash a block header hundreds of billions of billions of times per second. Whoever finds a valid hash gains the right to validate a block of transactions. In exchange for their energy, miners receive 6.25 BTC per block.
That said, miners who find a block don’t really receive 6.35 BTC (apart from solo miners) don’t receive 6.25 BTC ruby on the nail. The reason being that they pool their hashrate via pools to smooth out revenue. Otherwise, a small miner would have to wait years before seeing the color of a bitcoin.
And the fact is that it is the pools which are responsible for selecting the transactions inserted into the blocks. As the latter cannot weigh more than 1 MB, it is naturally the transactions offering the highest fees per byte which have priority.
If this is not the case, it is because the pool has consciously decided to leave certain transactions aside.
Possible reasons for missing a transaction in a block
Before being inserted into a block, transactions wait in “the mempool”. Truth be told, talking about “a” mempool is an abuse of language. Each node has its own “mempool”. Pending transactions may differ slightly from node to node for a few seconds.
Clearly, a pool that has not inserted a particular transaction is not necessarily guilty of censorship. The transaction may simply not have had time to propagate to the pool.
Additionally, some pools may prioritize their own transactions to their clients (the miners). A pool may also be paid for a transaction through a channel other than transaction fees.
More problematically – and what interests us in this article – some pools can filter transactions due to government regulations. OFAC (Office of Foreign Assets Control) The US Treasury Department maintains a long blacklist of bitcoin addresses.
The submission of pools to OFAC is a threat to the uncensorable nature of bitcoin transactions. The threat is all the greater as miners tend to cluster in a handful of pools.
All this to say that F2Pool co-founder Mr. Chun admitted the facts. The pool has indeed censored transactions. Faced with popular vindictiveness, the pool removed its filter, ” for the moment “.
Who unmasked F2Pool?
The information was revealed by the anonymous account @0xB10C :
What the founder of F2Pool responded to in a tweet today deleted :
“Why are you surprised that I refuse to confirm the transactions of these criminals, dictators and terrorists? I have every right not to confirm the transactions of Vladimir Putin and Xi Jinping, right? »
Developer @0xB10C discovered the deception thanks to his project miningpool-observer whose purpose is precisely to detect pools which do not select certain transactions.
It turns out that the fourth largest pool in the world, F2Pool, has censored four transactions in recent weeks. We can therefore ask ourselves why a pool of Asian origin filters transactions on the basis of sanctions imposed by the United States?
The miner Marathon (which manages its own pool) had already been ostracized two years ago for the same reasons before immediately reversing course.
Note that a single pool filtering transactions does not affect the censorship resistance of the Bitcoin network. Unless all the pools get involved.
It is up to minors to leave a pool engaging in censorship. Hence the need to increase the number of medium-sized pools in different jurisdictions.
Note also that the company Brainins launched the software Stratum V2 which allows miners to choose transactions themselves. Since miners are more decentralized than pools, this would result in greater resistance to censorship.
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