Quote from: jonald_fyookball on April 23, 2015, 06:37:15 PM

Quote from: koubiac on April 23, 2015, 04:40:54 PM

Quote from: jonald_fyookball on April 23, 2015, 04:03:37 PM

Haha. Pot calling kettle black.

We did have a debate. You lost imo.

What is that even supposed to mean?!?
What you're basically saying is that you actually haven't thought of any actual attack vector but "in your opinion" NeuCoin is not secure.

In this case, your opinion definitely isn't worth much.

The attack vectors were described in the thread I posted; you either didn't understand them or chose to ignore them.

Here it is again:
https://bitcointalk.org/index.php?topic=1007155.0

To be fair though, these fundamental issues exist with all POS coins.
It is simply a weaker security model than PoW and probably cannot
provide distributed consensus that scales, as others have written about.

However, it is dishonest for NeuCoin to claim they have "solved the issues with PoS" when they haven't.

The most precise you've been in the thread was saying:

Quote

As far as spoofing the time intervals, lets say you want to start a chain "from 200 minutes ago". You can have a computer calculate an alternate chain that supposedly started 200 minutes ago in a few seconds, and broadcast that in realtime right now. Nodes receiving that would not know that the blocks on
the false chain weren't really built 200 minutes ago.

Nodes must accept the longest chain, otherwise you will loose consensus and risk a fork in the blockchain.

You won't always be able to achieve this, but occassionally you will, and since the cost is minimal, why not try it?

Ok so this is the most "precise" attack vector you've cared to give me.
I guess your confusion lies in the fact that "occasionally" doesn't mean anything. Will you succeed once every month? Once every year? Once every billion years?

I'll keep it simple and if you really are interested in the subject and aren't just trolling against PoS, I'll be glad to further our discussion.

So let's say the attacker owns 20% of the mining coins (I'm giving you a pretty substantial amount!) and he tries to fork every two hundred minutes in the past.
For the attacker to have a maximum advantage let's also suppose that the attacker didn't mine on the main chain which means he's competing against 100-20=80% of the mining coins.

Over 200 minutes, in average, the main chain will have created 200*0.8=160 while the attacker will create in average 200*0.2=80
I understand where you're coming from, since there's no cost, the attacker can try many times so you might think that at "some point" he will create more blocks than the rest of the network.
This probability is the probability that a Poisson process of Pois(80) has more occurrences than Pois(160) (http://imgur.com/cYZ1SHE) which is ~10^-46

So now let's go back to what "occasionally" actually means.
You can repeat that every 200 minutes (I'll explain why underneath), so the expected time (in years) before you succeed such an attack is 365*24*60/(200*10^-46)~10^48 years.
How large this number is is hard to fathom, as a comparison, the universe is 13.8 billions years old (~10^9).

So if you try your attack "constantly" you'll never succeed.

I know you think you can try more than once, so let me explain why this is not possible.

Trying more than once means that you need to modify the kernel. The only thing you have control over, as an attacker in such a situation, are the parameters linked to the UTXO.
You can modify them, and to do so, you must at the beginning of the fork send your coins back to yourself. These coins will then not be able to create any block for 1.6 days. All the numbers I'm giving are clock time, not real time, so I completely agree you can "spoof" the clock compared to real time, I've been making this supposition all throughout the attack.
So after 200 minutes, your branch will have created exactly zero blocks, the blocks you would have created would be rejected by the nodes because the UTXOs weren't old enough to mine.

If you have any arguments that aren't based on intuition, I'd be glad to answer them.

koubiac

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