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MARA already did OFAC transaction censorship. They stopped because their blocks were getting orphaned by other miners, losing them block rewards. Nobody wants that.

Control-Plane Capital 2mo ago

Censoring blocks don't get orphaned. MARA was mining blocks that did not have the highest fee transactions.

If a miner/pool builds a valid block that merely omits certain transactions (OFAC list, "risk-graded" UTXOs, etc.), other miners do not orphan it.

They extend the heaviest valid chain tip. Orphaning a valid-but-omissive block would require:

- A coordination rule (social soft fork) to reject such blocks, or

- A protocol change that makes omission invalid (not happening without civil war).

So a censoring miner's blocks are paid normally. The cost they bear is opportunity cost (they skip some fees) and potentially slightly higher stale risk if their template construction is slower. That's it.

I have not extensively looked into why MARA stopped, but my guess is it was a short-term test for the future. Predictive programming if you will.

Fred Thiel would sacrifice his shareholder base in a nanosecond if it means he gets to sniff Trump's jockstrap.

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Discussion

Jerome Powell 21iQ 40TPW 2mo ago

MARA was doing OFAC and their blocks were getting orphaned. Which is why they eventually were forced to capitulate. It's not about fees but about timing of other blocks being mined. It's wasn't 100% of the time, but enough to hurt their profits. Yes they were concensus valid, but nobody else was doing OFAC, nor does anyone want to. Why do you even care about OFAC?

Control-Plane Capital 2mo ago

Maybe try to read my comment again. Censoring blocks don't get orphaned.

MARA's blocks were valid (just included fewer txs/fees).

They allegedly abandoned the experiment within weeks amid industry backlash and to align with Bitcoin Core 0.21.1/Taproot signaling, saying they would validate like everyone else (no censorship).

Orphan/stale events happen for timing races, not because a miner filters tx by policy if the block is otherwise valid.

So again, none of MARA's OFAC-compliant blocks were orphaned.

BitMEX Research noted one of the OFAC-compliant blocks contained ~0.0033 BTC less in fees than a normal maximized template would have, implying foregone revenue — not invalidity.

Jerome Powell 21iQ 40TPW 2mo ago

I can't find any reference to their blocks being orphaned, so perhaps I'm wrong. In any case, it wasn't effective since they were the only miner doing it. I highly doubt the Chinese miners would do it. Still not sure why it's important since it wasn't effective and isn't happening anymore.

Control-Plane Capital 2mo ago

It being effective or not depends on their true intent, which we don't know for sure.

I'm pretty sure F2Pool (China) was already caught censoring transactions multiple times.

- https://news.bitcoin.com/bitcoin-mining-pool-f2pool-acknowledges-ofac-transaction-censorship-backpedals-after-community-backlash

- https://atlas21.com/f2pool-accused-of-transaction-censorship-and-vulnerability-in-bitcoin-core/

It is important to me because it's an attack vector and I like to know about these things. If it's not important to you, it's all good 🤝

Jerome Powell 21iQ 40TPW 2mo ago

If different pools censor different transactions it can delay them but won't prevent them. I don't think it would have any effect on L2 either.

You're right, it is important to think about. I guess I'm more focused in node implementation centralized and arbitrary data storage attacks right now.

🤝

Control-Plane Capital 2mo ago

And by the way, you maybe got confused because in a separate event, much later, Marathon did mine an invalid block in Sept 2023 due to a transaction-ordering error — unrelated to OFAC filtering and years after they'd stopped the "clean block" trial.