Yo can fool a SPV wallet even if it requires a thousands confirmations using this attack, and you don't need a Sybil attack, so yes, it impacts SPV wallets also. The protections a SPV node should have to prevent this attack are different, so it must be considered separately.

It should be said that a SPV node can avoid accepting payments if any Merkle node is at the same time a valid transaction, and that basically almost eliminates the problem.

SPV Wallet would reject valid payments with a astonishingly low probability.

On Sat, Jun 9, 2018 at 2:45 PM Peter Todd <pete@petertodd.org> wrote:

On Sat, Jun 09, 2018 at 02:21:17PM +0200, Sergio Demian Lerner wrote:
> Also it must be noted that an attacker having only 1.3M USD that can
> brute-force 72 bits (4 days of hashing on capable ASICs) can perform the
> same attack, so the attack is entirely feasible and no person should accept
> more than 1M USD using a SPV wallet.

That doesn't make any sense. Against a SPV wallet you don't need that attack;
with that kind of budget you can fool it by just creating a fake block at far
less cost, along with a sybil attack. Sybils aren't difficult to pull off when
you have the budget to be greating fake blocks.

> Also the attack can be repeated: once you create the "extension point"
> block, you can attack more and more parties without any additional
> computation.

That's technically incorrect: txouts can only be spent once, so you'll need to
do 2^40 work each time you want to repeat the attack to grind the matching part
of the prevout again.

--
https://petertodd.org 'peter'[:-1]@petertodd.org