The solutions to attacks proposed by IOTA white paper seems unclear, in particular, in case of double-spending, it remains unclear what stops a computationally powerful adversary from conducting a double spending attack as follows:

Adversary can use its coin and wait until it receives the goods, then it can make a second transaction with the same coin and confirm it by making many small transaction, perhaps under multiple different accounts. Attacks of this type where adversary floods the systems with new accounts are sometimes called Sybil attacks.

While other consensus algorithms have a clear answer to this problem, e.g. in PoW blockchains the adversary should have more computational power than rest of the system. Similarly in proof of stake blockchains adversary should obtain majority of stake (currency). And permissioned consensus protocols simply restrict the adversary from adding new nodes to the system.

The tangle blog actually leaves the impression that double spending is theoretically possible, but just technically difficult to do in practice.

(1) Do you agree with this assertion?

(2) Does it mean that although it is difficult to do; but eventually it's feasible?

up vote -1 down vote accepted

Re: the impression that double spending is theoretically possible, but just technically difficult to do in practice.

(1) Do you agree with this opinion?

No. It is both theoretically possible and also technically easy.

(2) Does it mean that although it is difficult to do; but eventually it's feasible?

It is easy to do. IOTA just isn't worth enough financially for people to try. For the moment, The Coordinator protects it from malfeasance.

Obviously, the proofs required to back up my opinions on these matters requires a lot of work and more than available on any stack exchange Q & A site.

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    We do require objective answers that go beyond bold claims. If it's easy to do, it's easy to describe. You'll be surprised what energy people put in SE answers. The way this currently looks it has the quality of a comment, not an answer. – Helmar Nov 26 at 19:22
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    @Helmar, maybe the simplest reason would be persisting in using a Coordinator without introducing an elaborated alternative and not to determine an approximate date to remove this central Coo. If IOTA can be resilient to such attacks, why it is not replaced by a decentralized approach? In my opinion, denying to remove Coo can be interpreted that IOTA currently is relied on it seriously. We hear too much about replacing Coo with an alternative without any clear explanation on the alternative approach. Thanks – sas Nov 29 at 14:00
  • If you read the Iota blog you will see they have published detailed updates on the progress to remove the Coo. The IF has setup a research council with leading industry experts and the removal of the Coo is their number one priority. – Spamalot Dec 4 at 10:44

Iota requires PoW on individual transactions. An attacker could double spend but they would need more hashing power than the rest of the honest users.

The hashing power of the current tangle is fairly low hence the need for the protection of the Coo. Unlike other PoW systems the hashing is not used in a competitive manner by miners but by the users themselves. It does however require the activity of the tangle to be high for the natural resilience to arise.

The Foundation is also researching additional security measures that would give the same protection that the coordinator now gives but in a decentralize way.

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    Any reference for the research the foundation is doing? – Helmar Nov 26 at 19:22

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