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Instant transactions with guaranteed confirmation singapore
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Author Topic: Instant transactions with guaranteed confirmation  (Read 5741 times)

ChuckOne

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Instant transactions with guaranteed confirmation
« on: April 24, 2014, 08:31:33 pm »

Original post: https://bitcointalk.org/index.php?topic=316104.0

Any new insights on that?

May be related to https://nxtforum.org/general/instant-transaction-proposal/

Quote
In Bitcoin a payment is made by transferring all coins from input to output addresses with difference between input and output paid as transaction fee.  If someone wants to send only part of the coins they must send the rest back to one of their own addresses.  An attempt to use the same input twice is a double-spending, only one of the transactions will be confirmed even if enough money is sent back.

Unlike Bitcoin and its forks, Nxt uses a single account instead of multiple addresses for each user.  It is possible to send multiple transactions from the same source address (called "account"), all these transactions will be confirmed if the account holds enough coins.  Someone still can attempt a double-spending by paying for something with low fee and then sending all their coins to other account with higher fee, making it impossible to confirm the first payment.

We can counteract a double-spending attack in Nxt by using special accounts.  A special account has certain limits that don't let to create transactions for more than (for example) 1/10th of the balance in total within a 24 hour timeframe.  The network will simply ignore transactions and blocks that violate this rule.

A merchant (or a vending machine) can accept payments from special accounts without waiting for confirmations.  The only thing should be done is checking that a received transaction doesn't violate the rule.

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mczarnek

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Re: Instant transactions with guaranteed confirmation
« Reply #1 on: April 26, 2014, 02:19:59 am »

Yup, the two work side-by-side, probably should have mentioned that in my post.  Basically if you need at least 10 confirmations and time for it to spread throughout the network, then you could be 10 blocks behind.  Therefore, if you allow a person to spend more than 1/10th of their balance, then they could doublespend it without other blocks knowing.  Not sure why he's saying wait 24 hours.. isn't 10+ confirmations supposedly enough?

I intend to first do some bandwidth calculations this weekend and determine how many TPS Nxt can support without worrying about instant transactions and then also do the same for this.  But point is.. still working on it, would love to discuss it with anyone who would like to.

Have a vague idea for a way to get around that 1/10th of your balance per day via instant transactions limit, which I think would be very nice.. will have to think about it before further discussing though.

Anyway, got one other thing or two going on that I should wrap up first but haven't forgotten about this one and would be happy to further discuss it.
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