Bitcoin Forum

Has there ever been such a thing? And if so, what killed it?

No I don't think that there ever was one, as POS alone doesn't work.
Nobody actually tested it on a live example I think (all coins still on POW). But people are looking for alternatives (look at CGB team).

IS there any potential IMPLEMENTATION of a POS alone coin?

Seriously, I have no idea how it would even work.

ADT is POS only now.

Well there could be, but POS alone is insecure, so I don't know why anyone would want to do that.

CGB (CryptogenicBullion) is POS and is clearly an alternative for long term holding. They are looking into it being fully POS. Most are hybrids.

PPCoin is a fully PoS altcoin. The PoW isn't actually relevant for blockchain validity, only PoS matters. PoW is just used as a marketing device to distribute coins.

A pure PoS altcoin has the following properties:
1) The incentives to attack are the minimum possible achievable for any coin design.
2) The capital cost of attacking is relatively high.
3) The marginal cost of attempting an attack is 0. An attacks can be attempted as many times as you like at this cost.

The first point is ideal for PPCoin. The second point is generally good in all PoS coin designs, but could be much higher than what exists in PPCoin. Interestingly there is a trade off between (1) and (2). Improvements on point (2) have negative effects on point (1). PPC has gone for essentially the absolute extreme on point (1). No coin could do better in this area. I would prefer to trade a little bit of point (1) for some more of point (2).

Point (3) makes people want to include a bit of PoW. I'm not convinced it's necessary, but I think it makes sense to err on the side of caution here.

Another way of putting it is this:
Minimization of attack incentives means that PPCoin is extremely safe from rational attacks relative to a PoW based currency.
The lack of any marginal attack cost means that PPCoin is more exposed to irrational terrorists relative to a PoW based currency.

Irrational terrorism is the traditional threat model in computer science and this makes the core development community very skeptical of PPCoin.
Rational attacks are the traditional threat model in economics. Since I am an economist, I view PPCoin much more favorably. In my opinion, the computer science threat model is ill-suited for analysis of bitcoin mining. It makes more sense for low value systems.

I believe that it is best to use a mixed system (which is simple to do but no one has been motivated to do it), but I also believe that pure PoS is better than pure PoW.

Once the altcoins jump to fully POS, they should be fairly secure, even more secure than a PoW only coin, as the only way to attack a coin would be to own a large percentage of coindays than the rest of the network.  For example, if I had 10,000 coins and owned then for 50 days, someone wanting to 51% attack the network would need to have 500,000 coin days just to overtake me, let alone everyone else on the network.  It can be done, but would be economic suicide, as there is no way you would get your coins out before someone noticed and the currency went belly up.  PoW attack is cheaper, because if you do/don't succeed, you still have all the mining equipment you used to pull off the attack.  PoS attacks leave all your coins stuck in a dead currency.   

PPC is fully PoS. This is a myth. Sunny King is a bit reclusive and this leads to persistent misunderstandings.

False... PoS protocol in it's current state can not stand on it's own... PoW is still needed.

See above.

BTW I first suggested the idea of basing PoS hashing power on coin-age. Sunny is completely right that actually doing stuff is much much harder than coming up with concepts, but I sometimes wish he wasn't so prickly about it. Concepts have a certain value too.  ;)

What about shorting? If shorting becomes possible any seeming loss an attacker would incurr from lowered value of their stake coins ought to be more than made up for by their gains in some shorting system or other oughtn't it?

-MarkM-

People can try to DDOS a PoS only network with fake blocks

Definitely possible in theory. However, if the market believed this type of manipulation was possible, then no one would ever take the other side of the bet. So it would be sort of a one-trick pony at best. 

I'd expect that you could short some, but that you could not purchase enough shorts to cover your capital losses. I think you'd encounter similar problems if you tried to profit by holding a large stock of competing assets (e.g. litecoin).

You'd have to ask Sunny King about this.

By fully POS, I mean that all of the coins are distributed via POS.

There was a thread where this was being discussed. Yes, POS alone is not safe!

ADT is a crapcoin.

PHS is pretty close to PoS only, rarely low difficulty spikes profitability and there is the occasional miner, but PoW blocks are <1% atm ; reward halves every 3 months

Just pick up 5-50k and have some fun

anyway see sig,

NXT is 100% POS: http://www.thenxtwiki.org/wiki/Nxt_Wiki