CommonLounge Archive

IOTA and the double-spending problem

October 20, 2017

IOTA is an asynchronous network. This means that the ledger does not necessarily have to tally at the end of the day. Unlike blockchain, there is no miner who decides which transaction gets to stay in order to make the ledger synchronous. IOTA confuses people because of the double spending problem — how does IOTA avoid two conflicting transactions, where the same IOTA has been double spent?

How does IOTA avoid double spending problem?

Every node has to approve two transactions in Tangle before making its own transaction. Some other node will then approve your transaction to validate it. This gives each transaction a weight, which later helps in validation, in case there is a double spending problem.

Assume there are two conflicting transactions Tx1 and Tx2 recorded in the Tangle ledger. The cumulative weight of these transactions will decide which one gets to stay. If Tx1 has more cumulative weight than Tx2, it will get “approved” and Tx2 will become stagnant and ultimately perish.

As we saw in the in the tutorial on security concerns with IOTA, there is a chance that spammers try to rig the system by working on their own parasitic mini-tangle networks for approving transactions. In theory, at some point, the weight of this rigged transaction network will stagnate and other genuine transactions will take over.

Can merchants handle the double spending problem?

Merchants will have more control over what they can allow and how many transactions they want to handle. They get more power in deciding the number or weight of transactions that they are ready to allow, and consider “approved”. As everything in IOTA works on probability, nothing is 100% “confirmed” or “approved”. Each merchant decides their own threshold and conflicting transactions get sorted by cumulative weight.


IOTA is gaining traction in the tech industry and it’s likely that it is here to stay. It is worth billions of dollars by market valuation and as tech giants like Microsoft continue to work with it, IOTA will gain more precedence in the future.

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