Is double spending possible in IOTA?

Question

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?

Answer 1

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.

Answer 2

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.