PPC source isn't closed, it's just not really discussed to any extensive manner by the developer and the vulnerabilities that are suspected to come along with PoS systems also aren't really talked about.

Did Sunny King's difficulty algorithm not fix the chain?  I think he extended it to 12 or 24 hours or something like that, that is, these are the timespans from which to calculate the exponential weight averages from, but that's still a fairly short period of time and you can attack by mining like crazy for a couple hours and then hopping back on a while later.

Yeah.  The 51% problem still exists for PoS systems, but you just need 51% of all the coins available to fork the chains instead of 51% of the network hash power.  The tradeoff is that 51% forks of PoS coins are not readily reversible, eg, if your PoS chain has a 30 day waiting period before claiming PoS blocks and you obtain 51% of all coins then wait, then decide to fork the chain, removing any amount of blocks in the chain up to the last 30 days still leaves you, the original forker, with 51% of the coins and perfectly able to commit the same exploit again.

PoW, by contrast, can just roll back a few hours because sustained 51% attacks appear to be extremely rare and also extremely costly.

But the bigger problem with PoS is double spends by creating short PoS block spams of length six or so.

I've been thinking about the PoS system a lot, and this is what I'm concluding as the most simple mechanism to use for their general generation:

1) Require that every single PoS block be followed by a PoW block and succeeded by a PoW block, limiting the maximum block rate of the network to PoW and preventing PoS blocks from easily making forks so they can double spend.
2) For confirmations, six blocks of any type should be used.  Because of 1), this makes a maximum of 3 stake blocks for any six confirmations (which I think should be safe; PoW durations are twice that of Litecoin and most vendors are okay accepting 6 LTC blocks).
3) Stake blocks will be accepted based on their cumulative coin age as calculated by the sum of the products of (coin quantity from input transaction * coin age aka transaction age).  When faced with two or more PoS blocks at nearly the same time, all will be orphaned except the one with the largest cumulative coin age.

I will work this into the next draft of the whitepaper unless someone thinks it's a terrible idea for whatever reason.

I'm also happy this is garnering so much interest.  I'll create BTC and LTC donation addresses tomorrow, and I'll report what people have given.  I don't really want any money for it myself, so I'll hold it in reserve here and distribute it to any developers who hop onto the project.  What I really need are programmers at this point.

It's a working title, I'm open to suggestions.

I'm not sure this would be the best way to go about things.  The system describe already has a method to promote PoS generation through fees because the 256 inputs in the stakebase transaction are allowed feeless and then become condensed into a single output, avoiding fees later for the user.  The fees included in any PoS blocks are also destroyed, preventing fee competition among easily generated stake blocks and also creating competition with PoW blocks (who desperately want fees).

execute command

No, in which case use the cgminer settings in the other thread in my sig, just don't forget to run "export GPU_MAX_ALLOC_PERCENT=100" first

sig threads

guiminer-scrypt 7950 high usage settings

Blocks are given to you based on obtaining and keeping coins for a certain duration (coin age) rather than by mining competitively to solve blocks through a lottery system (proof of work).

The main problem with it is that it seems to introduce vulnerabilities, and the major advantage is that it's more power efficient and makes a chain somewhat more resistant to a PoW 51% attack.

Depends if I can find people to help develop it.  I'm heavily employed so the implementation of everything in here will basically be impossible in the next few months (this is my weekend/late night hobby).

Edit: I can assure you that a non-botched release will happen when it does, though.  I'll create the genesis block string and make binaries of the miner and qt wallet before release on an offline computer, then upload here encrypted with AES256 and a very long, strong password.  Then after a few weeks has past and it's been well distributed, the password will be revealed and everyone can begin mining at the same time.

No long term incentive to mine it (no block reward halving was implemented)

Time to cut out some windows with an old soldering iron!

Right, but finding a block is exceedingly easy (there are very few restrictions) so long as you have a sufficient number of coins with an old enough coin age.

The voting system is there so that the chain stays inflationary well into the future in addition to the option of fees (which has been academically debated as to whether or not it will function correctly).  Of course, anyone can make their own for and implement voting easily in the way I have specified -- just need to add a couple extra bits to the block header.  Pools could also allow voting by running a few instances of the daemon that sent out work based on variations of these bits in the header.

Well, it's the easiest method when blocks are all the same difficulty and people may all have them at the same time (very unlikely, but possible).  Bitcoin blocks are fine being found close to one another because they actually represent some large amount of work -- all stake coins have is stake to back them.  Regardless of the speed PoS blocks function at, PoW at 15 blocks per hour would be steady.

If you had (12/129600) of the current total number of coins in the network and a merchant who accepted funds after 6 confirmations, you could spam 6-12 blocks quickly after waiting three months and try to attempt to double spend like this.  The probability of such an attack succeeding is extremely high, and the cost to the attacker is virtually nothing.  I'm not sure 100% how PPC deals with this.

So, you need some means of mitigating this.  In the Bitcoin network, the likelihood of getting enough hash power to perform such an attack (one hour of forked blocks) was extremely difficult, but it's very easy with stake blocks.

You also can not protect the network the same way you would with BTC/LTC for stake coins (by difficulty) because someone could simply hoard many coins, wait for the right moment, and engage in the attack.  There's no guarantee stake blocks will be claimed at any particular time under the current system, and I'm not sure how you'd implement them to do so other than restrict the rate at which the network allows them to be generated.

Edit: Another option would be to force stake miners to wait until after a PoW block is mined before sending out a PoS block, so that PoW and PoS blocks are all mined back to back.

2nd edit: If you put PoS blocks back to back with PoW blocks, you can actually more easily attack the network because you now only need half the magnitude of your PoW attack vector.  So, PoS in one sense protects the network, but in another sense destabilizes it with a small percentage PoS, small percentage PoW attack vulnerability.  I haven't really seen this addressed anywhere by PPC, but thinking about it now makes perfect sense.

Yes.  It will probably be a little bit before a GPU miner is released.

Thanks

It's double entendre of this and a reference to my first idea for a coin, Memcoin (which turned out to be a bad idea because you don't want to use high memory scrypt for a blockchain PoW hash).

Thanks.  I think it's best to go over the theory really hard before even trying to put it into code.  I want to try to stick as closely to the original BTC code as possible.

If Sunny King or other PPC folks want to chime in, I'm kind of curious as to how PPC prevents brief forks using rapid bursts of stake blocks.  The network time method seems like the easiest and most foolproof method to implement, but I'm wondering if there's some kind of major problem with it.

Yes.  The PoS system described should be difficulty to game and has an enforced reward below that of PoW, so PoW should always be the dominant source of coins.

One shortcoming with PoS as I described is that if someone buys 40% of all the coins and hoards them, they will be eligible to get a bunch of stake blocks all at the same time.  If they could spam them fast enough they might be able to fork the network briefly, but only for four minutes average at most (and if something weird is going on inside the chain of blocks, clients should reject them anyway).

I should probably add to the whitepaper that (1/129600) * total number of coins is the minimum number of coins required to grab a stake block, but that if you have multiples of that are all the same age you can grab a bunch consecutively if you so want to.  I assumed that the wallet would be implemented to do this automatically, but it may not have been clear from the whitepaper that this happened.

I guess you can also enforce throughout the network to only accept one stake block maximum every two minutes and reject the rest to help even out the distribution of stake blocks over time.

Edit: Yeah, I see a weakness now.  There should be some sort of measure to ensure a minimum time between PoS blocks of 1.5 or 2.0 minutes.  I don't think it'll be that hard to enforce -- just make the network reject the PoS blocks if the timestamp is too close to that of the previous timestamp.