2

In Bitcoin and Ethereum, the longest chain with the most proof-of-work (POW) invested in it is accepted as the true chain and used to determine balances and history on the network.

Because of this, if an adversary wants to change a block in a blockchain of height at h, he has to solve the POW for all blocks from h up to the current block. This is very difficult.

However, with IOTA, the entire Tangle is not broadcast to the network similar to the way that blocks are mined and broadcast with Bitcoin.

What takes the place of nodes honoring the longest chain?

How does IOTA ensure that the consensus is permanent with an immutable Tangle?

Questioner
  • 552
  • 2
  • 8
  • When you say "unique Blockchain" and "unique Tangle", do you actually mean "unanimous Blockchain" and "unanimous Tangle"? – Zauz Aug 09 '18 at 15:05
  • @Austin Powers I mean for example in Bitcoin to achieve a consensus a miner who creates a new block, he broadcasts his new blockchain (as the longest one) to the network and every node after receiving this longest chain will replace it. Thanks – Questioner Aug 09 '18 at 15:17
  • @Zauz I mean every node in the network keep the same blockchain at every time interval. In other word, the blockchain that every node maintains is the same. (All local blockchain are equal.) Thanks – Questioner Aug 09 '18 at 15:20
  • What do you mean by "removable" i.e. what counts as a "removed" transaction for you? – Zauz Aug 09 '18 at 18:59
  • @Zauz I mean one the main features of the blockchain is immutability, meaning that changing and modifying history of transactions is impossible (or very difficult) in case of Bitcoin the reason is that if an adversary wants to remove a transaction from a previous blocks, then he has to calculate again PoW puzzle for all blocks that are after this modified block that is very difficult. Now, consider in IOTA an adversary wants to remove a transaction from Tangle. Has this action "any cost" for the adversary? And in general, is it possible to delete one of previous transactions from Tangle?Thx – Questioner Aug 09 '18 at 19:31
  • "What takes the place of nodes honoring the longest chain? " no, iota don't follow longest chain win. – Long Field Aug 13 '18 at 08:47
  • "How does IOTA ensure that the consensus is permanent with an immutable Tangle?". confirmed by trx come after it, and it confirms trx before it. Or whole network. Similar as bitcoin/eth but instead of confirm one path from before, a trx here confirms two patches before it – Long Field Aug 13 '18 at 08:55
  • @Long Field The question is about "immutability of Tangle" not consensus. an adversary can change history of Tangle, if he is able to calculate again PoW for all transactions again, meaning that the adversary can replace existing transactions with malicious ones. In Bitcoin the thing support immutability of blockchain and transactions is difficulty of PoW. However, IOTA PoW is calculable in milliseconds. – Questioner Aug 13 '18 at 09:05
  • That is why iota network currently, so small in size is vulnerable, have to wait for it large enough, even milliseconds calculation of Pow is ok. Also, iota protocol will be used not only in the internet but also in other environments(like LiWi), and in that enviroment, PoW perharps not relevent. – Long Field Aug 13 '18 at 09:47

1 Answers1

2

At the moment, we rely on Milestones issued by the Coordinator. In the future we might be able to rely on weight, which is the DAG equivalent of chain length.

I don't know if Iota will need a Coordinator forever. If the honest transaction rate reaches a certain point, I think we could get rid of it entirely, but with current PoW (Proof of Work) and difficulty that point is just too high. Maybe Network bound PoW will change something about this but we know hardly anything about it.

As for immutability, Iota uses the same mechanism as Blockchains:

enter image description here
enter image description here

The block with hash value cof points at the previous block eef. If someone changes the content of eef, the hash value of the block changes as well. It will no longer be eef, in fact eef will no longer exist.

tangle tangle 404

The transactions with hash value PMF and VQT point at the transaction JOE. If someone tries to change the content of JOE, the hash value of the transaction changes as well. It will no longer be JOE, in fact JOE will no longer exist.

Zauz
  • 4,454
  • 15
  • 42
  • Thank you, Yes, but as I mentioned in my question, since IOTA PoW takes only milliseconds, so adversary can calculates the PoW for all vertices (tx) again, such that there will be a new Tangle that nobody is capable of distinguishing correct Tangle from malicious Tangle. – Questioner Aug 13 '18 at 15:09
  • Once the honest transaction rate gets high enough, Iota could *theoretically (!!!)* rely on weight only. With the current PoW system, the number of transaction needed for security without COO would be higher than the amount of transactions the network can handle at all. Migrating to network bound PoW (whatever that is) might help. Also, increasing the MWM would work but then it would be more "expensive" to make transactions which we also don't want. – Zauz Aug 13 '18 at 15:22
  • As many people already pointed out, your number is arbitrary. But yes, the number would probably also be incredibly high. But not 1.2 billion! Maybe higher, maybe lower, probably higher if ternary hardware works as predicted, but not 1.2 billion. – Zauz Aug 13 '18 at 18:05