5 ms·

There is only one valid blockchain at any given time -- the longest one (currently Bitcoin). Any attempt such as this one to create a new blockchain will always

There is only one valid blockchain at any given time -- the longest one (currently Bitcoin). Any attempt such as this one to create a new blockchain will always be shorter than the pre-existing longer blockchain, thereby making this attempt susceptible to a 51% attack from outside its network.

everfree 4y ago
Bitcoin is not the only valid blockchain in existence, if that's what you're implying (your comment is unclear to me). A blockchain's length (or more specifically, total accumulated work), does not play a direct part in determining its susceptibility to 51% attacks. Furthermore, blockchains are only susceptible to cross-chain attacks like this when they use a proof of work consensus mechanism and also share the same hashing algorithm.
throwawaymaths 4y ago
For some definition of "valid". Nobody is stopping you from trusting a different "parallel universe" branch of the Blockchain, you just don't do it because most likely no one else will trust your work and it will be pointless work. Or you do in fact do it because it's a coordinated soft fork (there is a subpopulation that you care about that will together accept this parallel history and reject the mainline history). Construct an appropriate analogy for the bgp use case.
dgellow 4y ago
If you fork, don’t you have the same length (at least at the moment of fork), by definition?
- kayamon 4y ago
  You fork a blockchain by linking new blocks on the end (with bitcoin.pdf forming an implicit start node they all kicked off from). Whichever of the forks persuades enough people to continue mining on it becomes the real blockchain and the people will slowly stop working on the other forks. The shorter blockchain will never find enough people to mine it when there's a larger more lucrative blockchain to mine.
  - FabHK 4y ago
    Except that it has happened multiple times.

everfree 4y ago

Bitcoin is not the only valid blockchain in existence, if that's what you're implying (your comment is unclear to me). A blockchain's length (or more specifically, total accumulated work), does not play a direct part in determining its susceptibility to 51% attacks. Furthermore, blockchains are only susceptible to cross-chain attacks like this when they use a proof of work consensus mechanism and also share the same hashing algorithm.

throwawaymaths 4y ago

For some definition of "valid". Nobody is stopping you from trusting a different "parallel universe" branch of the Blockchain, you just don't do it because most likely no one else will trust your work and it will be pointless work. Or you do in fact do it because it's a coordinated soft fork (there is a subpopulation that you care about that will together accept this parallel history and reject the mainline history). Construct an appropriate analogy for the bgp use case.

dgellow 4y ago

If you fork, don’t you have the same length (at least at the moment of fork), by definition?

kayamon 4y ago
You fork a blockchain by linking new blocks on the end (with bitcoin.pdf forming an implicit start node they all kicked off from). Whichever of the forks persuades enough people to continue mining on it becomes the real blockchain and the people will slowly stop working on the other forks. The shorter blockchain will never find enough people to mine it when there's a larger more lucrative blockchain to mine.
- FabHK 4y ago
  Except that it has happened multiple times.