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Coin ShufflingThis feature is based on the paper by Tim Ruffing et al,
http://crypsys.mmci.uni-saarland.de/projects/CoinShuffle/coinshuffle.pdf .
Coin shuffling can be used to perform mixing of NXT, MS currencies (unless created as non-shuffleable), or AE assets. Any account can create a new shuffling, specifying the holding to be shuffled, the shuffle amount, number of participants required, and registration deadline. This is done using the shufflingCreate API. The subsequent shuffling steps can be done either manually, by using the shufflingRegister (for accounts other than the creator), shufflingProcess, shufflingVerify or shufflingCancel APIs, or, much more conveniently, by starting an automated Shuffler, using the startShuffler API. Once started, the Shuffler monitors the blockchain state for transactions relevant to the specified shuffle, and automatically submits the required transactions on behalf of the user, performing shuffle processing, verification, or cancellation as needed. To do this, the Shuffler is required to keep the user secret phrase in memory, therefore it should be run on a trusted local machine only. A restart or a crash of the node requires the shuffler to be started again using the startShuffler API, as it should never save the user secret phrase on disk.
To participate in a shuffling, a deposit of 1000 NXT is needed, in addition to the amount of currency or asset being shuffled. Or if shuffling NXT, the amount of the shuffle must exceed this 1000 NXT minimum. If the shuffling completes successfully, this amount is added to the recipient account balance, to allow it to send outgoing transactions (as it is required that only new, unused accounts are specified as recipients). If the shuffle fails due to a registered participant failing to participate as required, or intentionally submitting false data, the participant responsible for the shuffle cancellation is penalized by retaining this deposit and sending it to the forger of the shuffle finish block instead. If a shuffle is cancelled because the required number of participants is not met, nobody is penalized and all deposits are refunded.
Query APIs to retrieve currently running shufflers, shufflings, and shuffling participants are: getAllShufflings, getAccountShufflings, getAssignedShufflings, getHoldingShufflings, getShufflers, getShuffling, and getShufflingParticipants.
If desired, finished shufflings can be automatically deleted from the database if the nxt.deleteFinishedShufflings property is set to true (default is false).
The fee for creating a shuffling or registering in one is 1 NXT, for the shuffling process or shuffling cancel transactions 10 NXT, and for the verify transaction 1 NXT.
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