Bitcoin has a stale chain of length 2 | Hacker News Reader

Bitcoin has a stale chain of length 2

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26 pointsmjlee12 comments

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More intriguing is the stale chain of length 94:

> 94 0000000000000000000821678efe7f53c388fd2c530ef46e6dd2d2f369c346cd 2020-11-11 18:53:37 BTC.com

What does length 94 mean? Surely there is no reorg of length 94.

That's the winning chain, not a stale one.

Looks like that is the active chain.

No I think those are the lengths of the respective chains; one chain is 2 blocks the other is 94 blocks long.

Makes me wonder if it's some sort of weird attempt by Craig Wright or Bitcoin ABC's deadalnix as there is a power struggle between him and the rest of the Bitcoin Cash team.

The title says bitcoin. Bitcoin cash is not bitcoin so you are talking about something else

This is one of the reasons why a transaction is considered valid by en exchange (who will give you € for ₿) only after six’s “confirmations” which means, six blocks.

Could someone explain what a "stale chain" is and what the implication of this is?

Bitcoin requires a linear history (apart from the genesis block and the currently latest block, every block has exactly one parent and one child). If a block has multiple children, the one with the longest chain (of children) is selected in turn. The child (and its subchildren in turn) that is not selected is called "stale", and its transactions are effectively undone.

This could be a used to try do a "double spend" (send X bitcoins to address A, rollback the transaction, send the same bitcoins to B instead). However, according to the OP's analysis that hasn't been attempted (yet), and the active chain is far enough ahead that it seems unlikely that the stale chain would ever catch up and overtake it.

Length 2 seems quite short - I'd expect this to happen more often, surely.

Yeah, I had that same thought. A length of 4 or something seems unlikely to happen because a miner would almost have to be doing something nefarious to build on top of an already stale chain. A length of 2 could be some kind of concurrency/synchronization issue caused by one miner not having seen another miner's block in time to start mining on the "correct" chain.

Two reason why on BTC it doesn't.

1. Longer block times, so it is pretty rare that multiple miners are finding multiple valid consecutive blocks to compete on separate chains

2. It is against their incentives. By being apart of the losing chain, they have used thousands in hash power and missed out on possible tens of thousands that would come from the valid chain.

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