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REAL-TIME PAYMENT BLOCKCHAIN
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How is Graft real-time authorization (“instant confirmation”) within a few seconds possible with 2 minute block interval?

Unlike most crypto payment systems, and similar to traditional credit/debit card processing, Graft payment is divided into two phases: authorization and settlement. Like in credit/debit card world, Graft authorization happens in real time (hundreds milliseconds to a few seconds, depending on various conditions), while settlement is performed later on, usually within 2 minutes (compare to several hours and even days in traditional payment networks).
Although there are cryptocurrencies with block (settlement) interval less than 2 minutes, there is no specific reason to reduce it, especially with Graft built in “always on” real time authorization system. First, very short interval complicates the block generation and PoW process, as a lot of supernodes must communicate each other and agree on the new block, so with very short interval the network latency will start affecting the process. Second, reducing the interval still does not resolve the real-time authorization (“instant confirmation”) problem. Even with 30 seconds interval, it is still too long for real time payments (credit card authorizations are in a range of hundreds milliseconds to a few seconds), not to mention the fact that 1 confirmation (1 block) is still not enough to mitigate the risk of fork for significant amounts. So special additional technology is still required to resolve the real-time authorization problem. Graft resolves this problem by implementing a scheme called authorization sample, which is a group of supernodes that is selected by special Proof of Work/Proof of Stake algorithm from a larger pool of candidates.
The supernodes in authorization sample must match several criteria in order to prove their loyalty to the network:
Must be an active miner – solve at least one block within last 1440 blocksMust maintain a collateral (“stake”) deposit account with 1000 graftMust be “always on” (99% of the time within last 48 hours)Must have a public IP
The authorization sample supernodes validate the transaction and guarantee that the buyer cannot spend the same money more than once until the transaction is settled (added into the block which is written into the blockchain). The settlement is performed by the mining part of the supernode within 2 minutes.