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NXT stake-grinding attack? singapore
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Author Topic: NXT stake-grinding attack?  (Read 9137 times)

Come-from-Beyond

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Re: NXT stake-grinding attack?
« Reply #20 on: March 22, 2015, 07:32:27 am »

Again, here's the outstanding paper on that https://eprint.iacr.org/2014/765.pdf

Aye, it's quite good, but it proves my claim about Satoshi.

Regarding 50 years, a link to a whitepaper dated that old would prove your words, do you have one?
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jl777

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Re: NXT stake-grinding attack?
« Reply #21 on: March 22, 2015, 07:48:49 am »

Again, here's the outstanding paper on that https://eprint.iacr.org/2014/765.pdf

Aye, it's quite good, but it proves my claim about Satoshi.

Regarding 50 years, a link to a whitepaper dated that old would prove your words, do you have one?
so this means satoshi didnt prove it, but he did solve it and now this paper is proving it?
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kushti

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Re: NXT stake-grinding attack?
« Reply #22 on: March 22, 2015, 07:54:41 am »

I don't quite follow both of you guys  :)
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Come-from-Beyond

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Re: NXT stake-grinding attack?
« Reply #23 on: March 22, 2015, 08:48:12 am »

so this means satoshi didnt prove it, but he did solve it and now this paper is proving it?

Satoshi solved another problem. If anyone solved Byzantine Generals problem then they would get that 1/3 of rogue entities is enough to conduct a successful attack. 1/3, not 1/2.
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kushti

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Re: NXT stake-grinding attack?
« Reply #24 on: March 22, 2015, 09:01:40 am »

Satoshi solved another problem. If anyone solved Byzantine Generals problem then they would get that 1/3 of rogue entities is enough to conduct a successful attack. 1/3, not 1/2.

There are different Byzantine Agreement solutions around with own tolerance to adversary/honest ratio(I saw 1/3, 1/2, 1/1). And it seems you haven't read Backbone's paper yet, Byzantine Agreement model proposed there allows 1/1 ratio if f -> 0 (so to say very roughly 50+% mining power if block propagation within seconds and block generation every 10 minutes)
« Last Edit: March 22, 2015, 09:06:41 am by kushti »
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Come-from-Beyond

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Re: NXT stake-grinding attack?
« Reply #25 on: March 22, 2015, 09:24:50 am »

There are different Byzantine Agreement solutions around with own tolerance to adversary/honest ratio(I saw 1/4, 1/3, 1/2)...

Now my turn to say "I disagree".

There is only one BGP and it has only 2 scenarios:
- 1/3 of rogue participants is enough to break the system if we don't have a way to verify who signed a message
- Even zillions of rogue participants is not enough to break the system if we do have a way to verify who signed a message
A formal proof of this can be found here - http://research.microsoft.com/en-us/um/people/lamport/pubs/byz.pdf

Solutions that you call "different Byzantine Agreement ... 1/4, 1/3, 1/2" is a combined problem of Byzantine Generals + Sybil attack. PoW and PoS are used as a sybil attack mitigation mechanism based on resource testing. We could imagine Bitcoin that uses proof-of-X, where X allows 50% of miners to trick the system by increasing their "weight" 4-fold (e.g. by splitting identities). In this case we would get Bitcoin vulnerable to 1/5 attack. Have you noticed the trick? I changed only the way how sybil attack is mitigated and reduced 51% attack to 21% one. I didn't change BGP component at all.
« Last Edit: March 22, 2015, 09:27:02 am by Come-from-Beyond »
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kushti

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Re: NXT stake-grinding attack?
« Reply #26 on: March 22, 2015, 09:44:26 am »

Now my turn to say "I disagree".

There is only one BGP and it has only 2 scenarios:
- 1/3 of rogue participants is enough to break the system if we don't have a way to verify who signed a message
- Even zillions of rogue participants is not enough to break the system if we do have a way to verify who signed a message
A formal proof of this can be found here - http://research.microsoft.com/en-us/um/people/lamport/pubs/byz.pdf

Solutions that you call "different Byzantine Agreement ... 1/4, 1/3, 1/2" is a combined problem of Byzantine Generals + Sybil attack. PoW and PoS are used as a sybil attack mitigation mechanism based on resource testing. We could imagine Bitcoin that uses proof-of-X, where X allows 50% of miners to trick the system by increasing their "weight" 4-fold (e.g. by splitting identities). In this case we would get Bitcoin vulnerable to 1/5 attack. Have you noticed the trick? I changed only the way how sybil attack is mitigated and reduced 51% attack to 21% one. I didn't change BGP component at all.

1. See e.g. http://18.7.29.232/bitstream/handle/1721.1/14368/20051076.pdf?sequence=1 for different options
2. Why don't you want just to read the paper instead of writing something strange? If you disagree with paper, write detailed feedback paper please and share with paper authors. I'm going to leave the forum crapgrinding
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Come-from-Beyond

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Re: NXT stake-grinding attack?
« Reply #27 on: March 22, 2015, 10:15:30 am »

1. See e.g. http://18.7.29.232/bitstream/handle/1721.1/14368/20051076.pdf?sequence=1 for different options

Funny joke - linking to a 60-page document that doesn't have search option.  ;D What page are you referring to?


2. Why don't you want just to read the paper instead of writing something strange? If you disagree with paper, write detailed feedback paper please and share with paper authors. I'm going to leave the forum crapgrinding

I did read it. But I expected that if you mention it that often then you share their point of view and can defend their position.
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Come-from-Beyond

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Re: NXT stake-grinding attack?
« Reply #28 on: April 06, 2015, 06:48:39 pm »

I have found out that another person shares my opinion that 50+ year history of distributed consensus research is quite useless when we talk about cryptos - http://www.reddit.com/r/ethereum/comments/31mj2i/my_blockchain_scalability_paper_entering_public/cq32vfr:

Quote
[–]vbuterin Founder 3 очка 2 hours ago
Yeah, I would agree with both those points and my next round of revision will probably focus on ease of reading. As for placing squarely in the 20+ year history of distributed systems research, I tend to be quite skeptical that traditional distributed systems research can be easily applied to blockchains. I'm sure there are insights, but the issue is that the hardest problems are not technical; they are economic, and that is something that previous computer scientists simply have not had to face. I've personally found that the field of law and economics (as described by Posner, Becker, Friedman, etc) actually has greater applicability to blockchain theory than anything else. But would love pointers to anything in either field that I may have missed.

Nice to see some progress done in the right direction.
« Last Edit: April 06, 2015, 06:52:43 pm by Come-from-Beyond »
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gs02xzz

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Re: NXT stake-grinding attack?
« Reply #29 on: April 06, 2015, 08:23:43 pm »

Nice to see some progress done in the right direction.

In the paper - https://raw.githubusercontent.com/vbuterin/scalability_paper/master/scalability.pdf, the authors used Nxt algo as an example. It seems a confirmation of Nxt security (But I am not a expert)

Quote
Example 3.0.2. The cryptoeconomically secure entropy source used in NXT[16] is de ned recursively as follows:
 E(G) = 0
 E( + ) = sha256(E()+V ( )) where V ( ) is the block proposer of
.
Assumption 3.1. For any time internal I, there exists some xed probabil-ity po(I) such that a node randomly selected according to the weight functionused to measure a cryptoeconomic state machine's Byzantine fault tolerancecan be expected to be oine for at least the next I seconds starting from anyparticular point in time with at least probability po.Note. We can derive the above assumption from an altruism assumption bysimply stating in the protocol that nodes \should" randomly drop oinewith low probability; however, in practice it is simpler and cleaner to relyonly on natural faults.Note. Combining the two uninuenceability criteria into one (\it is impos-
sible to increase the probability of P from p to p  (1+k) without expendingat least b L k resources") is likely very dicult; it is hard to avoid having
ways to cheaply multiply the probability of low-probability predicates byonly acting when you are sure that your action will have an inuence on theresult.
......

Lemma 3.0.3. The NXT algorithm described above satis es the conditionsfor being a cryptoeconomically secure entropy source.Proof. To prove unpredictability, we note that the NXT blockchain pro-duces a block every minute, and so the update v   sha256(v; V ( )) takesplace once a minute. During each round of updating, there is a probabil-ity 1 ...........
« Last Edit: April 06, 2015, 08:26:16 pm by gs02xzz »
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Come-from-Beyond

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Re: NXT stake-grinding attack?
« Reply #30 on: April 06, 2015, 08:55:11 pm »

In the paper - https://raw.githubusercontent.com/vbuterin/scalability_paper/master/scalability.pdf, the authors used Nxt algo as an example. It seems a confirmation of Nxt security (But I am not a expert)

Quote
Example 3.0.2. The cryptoeconomically secure entropy source used in NXT[16] is de ned recursively as follows:
 E(G) = 0
 E( + ) = sha256(E()+V ( )) where V ( ) is the block proposer of
.
Assumption 3.1. For any time internal I, there exists some xed probabil-ity po(I) such that a node randomly selected according to the weight functionused to measure a cryptoeconomic state machine's Byzantine fault tolerancecan be expected to be oine for at least the next I seconds starting from anyparticular point in time with at least probability po.Note. We can derive the above assumption from an altruism assumption bysimply stating in the protocol that nodes \should" randomly drop oinewith low probability; however, in practice it is simpler and cleaner to relyonly on natural faults.Note. Combining the two uninuenceability criteria into one (\it is impos-
sible to increase the probability of P from p to p  (1+k) without expendingat least b L k resources") is likely very dicult; it is hard to avoid having
ways to cheaply multiply the probability of low-probability predicates byonly acting when you are sure that your action will have an inuence on theresult.
......

Lemma 3.0.3. The NXT algorithm described above satis es the conditionsfor being a cryptoeconomically secure entropy source.Proof. To prove unpredictability, we note that the NXT blockchain pro-duces a block every minute, and so the update v   sha256(v; V ( )) takesplace once a minute. During each round of updating, there is a probabil-ity 1 ...........

BCNext's idea not to provide the whitepaper to force an independent analysis has finally worked. Good, now this page can be turned.
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Daedelus

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Re: NXT stake-grinding attack?
« Reply #31 on: April 06, 2015, 09:16:18 pm »

Yeay. Does that mean, after months of agony, you can give us the full version of Nxts whitepaper? BCNext would have wanted it..
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Come-from-Beyond

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Re: NXT stake-grinding attack?
« Reply #32 on: April 06, 2015, 09:17:02 pm »

Yeay. Does that mean, after months of agony, you can give us the full version of Nxts whitepaper? BCNext would have wanted it..

I quitted Nxt, you are left on your own.
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Daedelus

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Re: NXT stake-grinding attack?
« Reply #33 on: April 06, 2015, 09:30:50 pm »

Lol, I keep asking. It amuses when you post that for some reason  :D
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jl777

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Re: NXT stake-grinding attack?
« Reply #34 on: April 06, 2015, 10:29:54 pm »

Lemma 3.0.3. The NXT algorithm described above satisfies the conditions
for being a cryptoeconomically secure entropy source.

Proof. To prove unpredictability, we note that the NXT blockchain produces
a block every minute, and so the update v ← sha256(v, V (β)) takes
place once a minute. During each round of updating, there is a probability
1 − po(60) that the primary signer will be online, and po(60) that the
signer will be offline and thus a secondary signer will need to produce the
block. Hence, after 1
−log(po(60)) blocks, there is a probability p ≈
1
2
that the
resulting value will be the “default value” obtained from updating v with
the primary signers’ public keys at each block, and a p ≈
1
2
probability that
the resulting value will be different. We model 512 iterations of this process
as a tree, with all leaves being probability distributions over sequences
of 512 public keys of signers, where all probability distributions are disjoint
(ie. no sequence appears with probability greater than zero in multiple
leaves). By random-oracle assumption of sha256, we thus know that we have
a set of 2512 independently randomly sampled probability distributions from
{0, 1}
256, and so each value will be selected an expected {0, 1}
256 times, with
standard deviation 2128. Hence, the probability distribution is statistically
indistinguishable from a random distribution.
To show that the first uninfluenceability criterion holds true, note that
the only way to manipulate the result is for the block proposer to disappear,
leading to another proposer taking over. However, this action is costly for
the proposer as the proposer loses a block reward. The optimal strategy
is to disappear with probability 0 < q <= 1 only when the predicate will
be unsatisfied with the proposer participating but will be satisfied with
the next proposer partipating; if a predicate has probability p this entails
disappearing p ∗ (1 − p) ∗ q of the time, meaning that the predicate will be
satisfied p + p ∗ (1 − p) ∗ q of the time instead of p of the time, a probability
increment of p∗(1−p)∗q will have a cost of p∗(1−p)∗q∗R if R is the signing
reward (whose real value is proportional to the quantity of transaction fees, a
reasonable metric of economic activity). Hence, the desired condition holds
true with b = 1.
To show that the second uninfluenceability criterion holds true, note that
when one is not the signer, one has no influence on the entropy, and when
one is the signer one has the ability to not sign and instead defer to the
next signer. Hence, an attacker controlling 1
k
of all signing slots will be able
to defer to the second signer 1
k
of the time, to the third signer 1
k
2 of the
time (by being in the first two slots simultaneously), etc, so in total such an
attacker will on average be able to choose between 1 + 1
k−1
values and thus
multiply the probability of a desired predicate by a factor of 1 + 1
k−1
. If the
attacker controls 1
3
of all signing slots, the result will thus be increasing the
probablity by a factor of 3
2
.

***********
it seems vitalik made a proof about NXT algo
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