Proof of stake

Proof-of-stake is term referring to the use of currency itself (ownership) to achieve certain goals. In the NovaCoin proof-of-stake is used to provide mining and transaction processing on a par with proof-of-work.

Novacoin uses the mixed Coin-Age/CoinDayWeight approach to provide proofs of the stake. The proof-of-stake difficulty is adjusted so as to limit the rate at which new blocks can be generated by the network to 10 minutes target spacing rate. Due to the very low probability of successful proof generation, this makes it unpredictable which computer in the network will be able to generate the next solution.

How it's supposed to work?

It's performed through scanning all available inputs in order to find lucky one that satisfies following condition:

SHA256(SHA256(KERNEL)) < CoinDayWeight *  NetworkTarget

Miner has to find a SHA256 hash that is under the target value. Target is derived from network target using CoinDayWeight parameter. The proof is presented by kernel hash and header signature.

Kernel structure

Coinstake kernel it's a virtual structure which created during proof-of-stake block validation attempt. This structure exists in database and memory, but not on the network. The kernel parameters are described in the following table.

Field	Type	sizeof	Description
nStakeModifier	unsigned long int	8	Deterministic [[modifier
nTimeBlockFrom	unsigned int	4	Timestamp for block which provided previous transaction, prevent nodes from guessing a good timestamp to generate transaction for future advantage.
nTxPrevOffset	unsigned int	4	Offset of previous transaction inside the block, used to reduce the chance of nodes generating kernel coinstake at the same time.
nTxPrevTime	unsigned int	4	Timestamp of previous transaction, used to reduce the chance of nodes generating coinstake kernel at the same time.
nPrevoutNum	unsigned int	4	Output number of previous transaction, used to reduce the chance of nodes generating coinstake kernel at the same time.
nTimeTx	unsigned int	4	Current timestamp

How long will it take me to generate a proof-of-stake?

Just like with proof-of-work, no-one can say exactly. But there is an estimation of how long it might take. Calculations are quite similar with proof-of-work, but instead of hash we have coin-day-second here. So, at difficulty 1.0 we need ~ 4294967297 coin-day-seconds to find a block.

Probability of successful block generation during one day could be calculated from available CoinDayWeight using formula:

P = CoinDayWeight * 86400 / (4294967297 * difficulty)

Let's estimate probability for current difficulty (0.23482093):

P	Age	<= 30	45	60	90	120	∞
Sum	-
1		0	0.0013	0.0026	0.0051	0.0077	0.0077
10		0	0.0128	0.0257	0.0514	0.0771	0.0771
100		0	0.1285	0.257	0.514	0.771	0.771

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