On Mon, May 22, 2017 at 5:19 PM, Paul Sztorc via bitcoin-dev <
bitcoin-dev@lists.linuxfoundation.org> wrote:

>
> In the future, when there is no block subsidy, a rich attacker can also do
> that in mainchain Bitcoin.
>

I don't think they are the same.

With Bitcoin, you only get to reverse recent transactions.  If you actually
reversed 2-3 weeks of transactions, then the Bitcoin price would fall,
destroying the value of the additional coins you managed to obtain.  Even
if their was no price fall, you can only get a fraction of the total.

With BMM, you can "buy" the entire reserve of the sidechain by paying
(timeout) * (average tx fees).  If you destroy a side-chain's value, then
that doesn't affect the value of the bitcoins you manage to steal.

The incentive could be eliminated by restricting the amount of coin that
can be transferred from the side chain to the main chain to a fraction of
the transaction fee pay to the bitcoin miners.

If the side chain pays x in fees, then at most x/10 can be transferred from
the side chain to the main chain.  This means that someone who pays for
block creation can only get 10% of that value transferred to the main chain.

Main-chain miners could support fraud proofs.  A pool could easily run an
archive node for the side chain in a different data center.

This wouldn't harm the performance of their main operations, but would
guarantee that the side chain data is available for side chain validators.

The sidechain to main-chain timeout would be more than enough for fraud
proofs to be constructed.

This means that the miners would need to know what the rules are for the
side chain, so that they can process the fraud proofs.  They would also
need to run SPV nodes for the side chain, so they know which sidechain
headers to blacklist.


> In point of fact, the transactions *are* validated...by sidechain full
> nodes, same as Bitcoin proper.
>
>
The big difference is that Bitcoin holds no assets on another chain.  A
side-chain's value is directly linked to the fact that it has 100% reserves
on the Bitcoin main chain.  That can be targeted for theft.


> Paul
>
>
> Regards,
> ZmnSCPxj
>
>