On 2011 November 23 Wednesday, Christian Decker wrote: > Just brainstorming here, no idea if this would work: > > - Pick any old block > - Create a chain fork by creating simpler blocks on top of your chosen > one > - The chain will not be accepted by others > - At some point you might find an incredibly hard block that makes your > forked chain the hardest one in the network > - Suddenly all your blocks are valid and you force people to switch to > your forked chain > > If this is possible it would allow you to revoke all transactions and claim > all the mined coins since you forked. My point is that the notion of > hardest chain is not so simple.
The above is a problem in either system (mine or current). If I can make a
"hardest chain", then I have indeed reverted all the existing transactions.
Look at CBlock::AddToBlockIndex(),
if (pindexNew->bnChainWork > bnBestChainWork)
if (!SetBestChain(txdb, pindexNew))
return false;
If the received block has higher total chain work than the current best chain
work; then the new block becomes the head of the best chain. The chain work
being calculated like this (I've abbreviated for the email):
pindexNew->bnChainWork = pprev->bnChainWork + pindexNew->GetBlockWork()
I'm not entirely convinced that this method of totalling chain work is the
best (it's a sum of exponentials I think); but that's a different issue.
> The difficulty of invalidating a chain is dramatically reduced with your
> time window approach, by not requiring a given difficulty, and relying on
> synchronized time windows.
I don't see that it is reduced; it is the same. Hashes are hashes. A given
difficulty isn't required, but a higher difficulty beats a lower difficulty.
So whatever the hashing power of the network at that moment, it's used. That
makes the chain more secure, not less.
Andy
--
Dr Andy Parkins
[email protected]
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