It is mentioned in Tangle's white paper (technology behind IOTA) that

From the above discussion it is important to recognize that the inequality λ > μ should be true for the system to be secure. In other words, the input flow of “honest” transactions should be large compared to the attacker’s computational power.

For this line, refer to second last paragraph, page 19 in here.

It is also mentioned that,

The number of nonces that one needs to check in order to find a suitable hash for issuing a transaction is not unreasonably large. On average, it is around 38.

For this line, refer to last paragraph, page 26 in here.

The TPS or transactions per second in IOTA is ~12 as of today.

Check live TPS at Tangle Live.

Combining all three points, my question is that

Anybody with reasonable amount of power can easily check 38 nonces to produce transactions reasonably larger than the current Transaction Per Second in IOTA. So, does this mean that double spending is possible on IOTA or am I missing something?

  • 2
    You are missing The Coordinator which protects the network in its infancy – mihi Feb 10 '18 at 0:00
  • 1
    @mihi, so it means currently The Coordinator is preventing the system from breaking? Got it. Just one question out of curiosity, how much TPS might they be aiming for befogging shutting down the coordinator? – scipsycho Feb 10 '18 at 8:08

In short: double spending is incredibly unlikely in IOTA.

In IOTA, majority hashpower is insufficient for a double-spend attack. IOTA is unlike proof-of-work based blockchains in this regard. You also need enough neighbors to get your transactions confirmed. IOTA calls this concept omnipresence.

IOTA nodes use mutual tethering rather than automatic peer discovery, which means that it is difficult to become neighbors with the majority of the network. This feature makes double spending orders of magnitudes more difficult in IOTA because the network topology is nearly impossible to know.

For more, see this article.


I think that based on the need for constant overwhelming honest transactions and a complete dependence on the proper functioning of an honest network, that an attack is plausible, feasible and probably even likely when the costs of the double-spend attack will be rewarding enough.


With the Tangle, the majority hashpower must be always honest and always working. As researchers have already outlined, "The number of assiduous honest transactions must ALWAYS be found to be in the majority. In order to guarantee that, they must, by all practical estimations, be constantly generating new honest transactions AT ALL TIMES."

The IOTA Foundation already acknowledges this in their FAQ documentation:

The most critical factor ... is the greater adoption of the IOTA technology increasing the throughput of transactions on the network to meet the fundamental security assumption - that ... honest transactions is large compared to that which an attacker could feasibly produce.

Low Cost Devices and Ternary Chips Help Attackers Too

One problem is that IoT devices might be many (billions even!) but they are low-power devices and cannot be constantly churning out new "honest" transactions. And that assumes too, that the IoT devices are running to spec and also not hacked with malware and/or susceptible to control by malicious actors.

Another problem is that the same technology that is said to allow IoT devices to provide low-cost PoW per transaction on limited electrical and hardware resources (JINN Trinary Chips) is exactly the same technology that a hacker or attacker can use to overpower the network with fake transactions.

What TPS is actually required to thwart an attacker?

The basis of this is an answer that shows that using current Bitcoin hashrates and resources as a benchmark, the IOTA network would need to generate 1.7 billion transactions per second of honest transactions - constantly and without letup.

This rate of honest transactions required is just impossible because even the network at the most optimized state in the next 100 years probably will not allow that many transactions to circulate in a peer-to-peer network per second.

It is also impossible because the amount of 1.7B TPS needed to be produced will ONLY resist against 1% of the current BTC network hashrate in the power of an adversary.

I would like to emphasize that - 1.7B TPS is required to thwart just 1% of the Bitcoin hashrate in the hands of an adversary.

What about Omnipresence?

It is often stated that the concept of "omnipresence" is required for an adversary to efficiently and successfully distribute their dishonest transactions. This is a false argument because it is proven that with 8 neighbors, the entire network can be efficiently permeated with a single double-spend in only 7 gossip generations (sometimes even 6).

What about Tethering Protections?

IOTA nodes also use mutual tethering rather than automatic peer discovery. This means that nodes cannot discover the rest of the network as easily as Bitcoin and other common true peer-to-peer Gossip-based networks.

However, this fact also lends power to the attacker because the honest nodes cannot see each other and have enough network intelligence to see the attacker's initial attack and ensure that honest transactions are properly distributed at all times.

Although it seems that the network topology is nearly impossible to know, an attacker can create many fake peers and then mutually tether them into the network, thereby gaining a more complete network graph because unlike regular users, the attacker is invested in the attack versus regular individually tethered users that are only using the network and any conveniences it may provide.

  • Where do you got these calculations from with the 1,7b TDS? Did I get you right by saying: A simple DDos Attack could outrun the whole tangle and IOTA is just not worth it to be attacked? – Compass Dec 5 '18 at 8:23
  • Figures calculated here: iota.stackexchange.com/questions/48/… The Coordinator protects against all attacks at the moment. – The Coordinator Dec 5 '18 at 20:58
  • BTW - I'm not saying that Bitcoin or any other blockchain is a sound idea. I'm just showing that a very very small percentage of BTC hashpower could out-do the biggest Tangle network imaginable. I'm not advocating Bitcoin at all. – The Coordinator Dec 5 '18 at 21:00
  • Come-From-Beyond discusses this with a random bitcoin-talk member here: bitcointalk.org/index.php?topic=1216479.msg12762128#msg12762128 – The Coordinator Dec 5 '18 at 21:01

Most of the public ledgers are possible to double spending.

In Bitcoin, we have the famous 51% attack, when attacker's hashrate was larger than honest nodes, it may break the consensus on the block (stopping mining new block, rewrite the blockchain...etc)

In IOTA, we face the same problem. When attacker's hashrate greater than honest nodes, it may do the double spending on the tangle. See whitepaper CH4 for how attacker may do the double spending.

  • 1
    You are correct. However, in bitcoin, the hashing power currently required is so much that it is currently implausible to double spend on it. However, IOTA is very less computationally expensive and it focuses more on TPS than hashing power. Currently it's TPS is so low that I think it is possible (now!) with even a high end computer to double spend on it. I want to know if I am correct in this. – scipsycho Feb 9 '18 at 14:08

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