Re: [bitcoin-dev] BIP proposal: Increase block size limit to 2 megabytes

[Luke Dashjr <luke@dashjr.org>]

On Sunday, February 07, 2016 2:16:02 PM Gavin Andresen wrote:
> On Sat, Feb 6, 2016 at 3:46 PM, Luke Dashjr via bitcoin-dev <
> bitcoin-dev@lists.linuxfoundation.org> wrote:
> > On Saturday, February 06, 2016 5:25:21 PM Tom Zander via bitcoin-dev 
wrote:
> > > If you have a node that is "old" your node will stop getting new
> > > blocks. The node will essentially just say "x-hours behind" with "x"
> > > getting larger every hour. Funds don't get confirmed. etc.
> > 
> > Until someone decides to attack you. Then you'll get 6, 10, maybe more
> > blocks confirming a large 10000 BTC payment. If you're just a normal end
> > user (or perhaps an automated system), you'll figure that payment is good
> > and irreversibly hand over the title to the house.
> 
> There will be approximately zero percentage of hash power left on the
> weaker branch of the fork, based on past soft-fork adoption by miners (they
> upgrade VERY quickly from 75% to over 95%).

I'm assuming there are literally ZERO miners left on the weaker branch.
The attacker in this scenario simply rents hashing for a few days in advance 
to build his fake chain, then broadcasts the blocks to the unsuspecting 
merchant at ~10 block intervals so it looks like everything is working normal 
again. There are lots of mining rental services out there, and miners quite 
often do not care to avoid selling hashrate to the highest bidder regardless 
of what they're mining. 10 blocks worth costs a little more than 250 BTC - 
soon, that will be 125 BTC.

Luke