Alexander Chepurnoy

The Web of Mind

Phasing Transactions in Nxt Part 1: Introduction, Phasing-Safety

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Two-Phased Transactions are similar a bit to Bitcoin’s multisig transactions implementation in Nxt but different in many aspects as well.

Simplest example: Alice starts a Two-Phased transaction. In the first stage a transaction is included in a blockchain but it isn’t processed immediately and has the status of ‘pending’. For it to be processed, Bob has to complete the second phase of the transaction by approving it. This has to be done before the deadline set by Alice has elapsed.

Please note the biggest difference from Bitcoin’s multisig: phased transaction is going to be included into blockchain immediately.

Use cases

  • Bob approving a transaction of Alice
  • Shareholders voting whether to send another 1M Nxt to a marketing service or not
  • Multisig wallet protected from a hacker(think about BTER case etc) (needs Account Control)
  • Trustless escrows
  • Conditional or unconditional transaction happening in some certain moment in future


  • most types of transaction could be 2-phased (but not all, see “Phasing-Safe Transactions” section)!
  • different consensus types: M-of-N account consensus,shareholders voting with assets, currency holders voting with a Monetary System currency units
  • possible vote threshold setting(e.g. only accounts holding 100+ assets could vote)
  • whitelist of voters
  • transaction could be released only prior to finishHeight(or at the height exactly )

Consensus(Voting) models

  • None - synthetic mode, used for unconditional transaction execution at some height in future
  • By account - 1 account is 1 vote
  • By balance - 1 nqt is 1 vote
  • By asset - 1 qnt(asset’s quant, so non-divisible part) is 1 vote
  • By MS currency - 1 unit is 1 vote
  • By transaction - phasing transaction becomes approved if there are transactions in blockchain with hashes set in phasing transaction
  • By hash - another synthetic mode, used for pay-with-secret

Phasing-safe transactions

Not all transaction types are phaseable, so some of them couldn’t be phased at all. Some phasing transactions are phaseable but not phasing-safe, means they doesn’t make sense as phasing transactions(e.g. message could be phased, but you can read it immediately) or there’s a risk a transaction couldn’t be applied at finish height due to some changes in the outer world’s state. Following table shows phaseable & safe transaction types. Please note unsafe phasing transaction could be pretty safe in some practical case, but that’s not guaranteed by the core.

Transaction Type Is Phaseable ? Is Safe ?
Payment Yes Yes
Arbitrary Message Yes No
Alias Assignment Yes No
Alias Sell Yes No
Alias Buy Yes No
Alias Delete Yes No
Poll Creation Yes No
Vote Casting Yes No
Phasing Vote Casting Yes Yes
Hub Announcement Yes Yes
Account Info Yes Yes
Asset Issuance Yes Yes
Asset Transfer Yes Yes
Ask/Bid Order Placement Yes Yes
Order Cancellation Yes Yes
Dividend Payment Yes Yes
DGS Listing / Delisting Yes Yes
DGS Price Change Yes No
DGS Quantity Change Yes No
DGS Purchase Yes No
DGS Delivery Yes No
DGS Feedback Yes No
DGS Refund Yes No
Forging Balance Leasing Yes Yes
Tagged Data Upload No -
Tagged Data Extend No -