Quote from: dga on July 05, 2014, 03:24:18 PM

Quote from: dreamspark on July 05, 2014, 03:17:56 PM

Quote from: JorgeStolfi on July 05, 2014, 03:09:32 PM

Could a PoS miner "rent" coins from a hoarder to simulate that he has the required stake, without actually having it?

Pure PoS coins don't have miners in the conventional way, perhaps you know this but I am struggling to therefore see the point of the question. Why would a "hoarder" rent his coins to someone else to stake unless they were paying more than he would make by staking his coins? To that end then, why would a "renter" rent coins from someone to make less than they would by buying some?

That's exactly one of the tricks.

Party A holds 1M coins and earns a 1% annual PoS "stake."

Party B rents those coins from party A at an equivalent of 3% annual return.

Thus, for a cost of only 0.25% * 51% = 0.000125 of the existing money supply (let's take XMR as an example - that's $525 USD right now), an attacker can mount a 51% attack for a month.

Man, with that kind of opportunity, I should go write some code...

(The other person who asked about subtle attacks: Just don't orphan everyone's blocks all the time or hold up transactions for too long. But you could easily do things like stopping all deposits into an exchange for an hour or two in order to manipulate the price, if you were so inclined...)

So you expect people just borrowing you coins worth of millions if you promise to pay back?