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Author Topic: [NXT] Vitalik B. confirms the NXT algo is secure.  (Read 2660 times)
EvilDave
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April 06, 2015, 10:22:55 PM
 #1

Just taken a look at Vitalik Buterins latest paper, which contains a couple of pages devoted to NXT and its algo:
 
Notes on Scalable Blockchain Protocols (v 0.0.2)

Pages 10 and 11 are interesting for NXT:

Quote
Example 3.0.2. The cryptoeconomically secure entropy source used in
NXT[16] is defined recursively as follows:
E(G) = 0

Quote
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 pro-
duces a block every minute, and so the update

I must admit that most of this paper (and all of its math) go straight over my head, but VB does seem to regard Nxt as being 'cryptoeconomically secure' which sounds like  a good thing to me.... anyone got any more expert input on this paper and it's implications for NXT ?

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April 06, 2015, 10:39:46 PM
 #2

None techies, just read the last line for explanation  Grin

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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April 07, 2015, 02:40:03 AM
 #3

I wonder what J.Garzik has to say.   Grin

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[/]
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April 07, 2015, 02:42:57 AM
 #4


I must admit that most of this paper (and all of its math) go straight over my head, but VB does seem to regard Nxt as being 'cryptoeconomically secure' which sounds like  a good thing to me.... anyone got any more expert input on this paper and it's implications for NXT ?


Someone buy VB a VB! Worth celebrating Smiley


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April 07, 2015, 04:06:06 AM
 #5

I wonder what J.Garzik has to say.   Grin

Hashes don't match.
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April 07, 2015, 07:04:06 AM
 #6

WOW, this is huge people!


     
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From Above
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April 07, 2015, 07:19:30 AM
 #7

I wonder what J.Garzik has to say.   Grin

actually it would be pretty cool if dem garizk dude could say anything other then just spit out utter BS as usual
LOL!!

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April 07, 2015, 08:04:39 AM
 #8

what a relief...Wink
Now all we need to do is gather all the folks in the world and start to use the damned thing.

NXT makes the Difference
My nxtforum account : bitme
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April 07, 2015, 08:47:51 AM
 #9

WOW, this is huge people!

What is so huge in that? Often developers talk about other projects. He even said Monero technology is cool, so what?
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April 07, 2015, 09:03:04 AM
 #10

WOW, this is huge people!

What is so huge in that? Often developers talk about other projects. He even said Monero technology is cool, so what?

You don't see a difference between "cool" and "cryptoeconomically secure"?
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April 07, 2015, 10:02:07 AM
 #11

Recognition from 3rd parties are not usual in cryptoworld. This is BIG NEWS for NXT.
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April 07, 2015, 10:09:16 AM
 #12

Come-from-Beyond seems satisfied too  Grin

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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April 07, 2015, 10:25:21 AM
 #13

haha,POS of Nxt is future. Wink
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April 07, 2015, 11:05:50 AM
 #14

If anybody wants to play with Nxt, I can manage Nxt node for you (for free). Post there or PM me here.

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April 07, 2015, 12:17:53 PM
 #15

Nice, especially when taking into consideration Vitalik's generic (earlier) skepticism towards NXT

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April 07, 2015, 02:34:09 PM
 #16

Wait for peer review (at least in the community). There's this weird reverence towards certain individuals in this community from people who don't understand shit. Let the experts evaluate and criticize and withhold your opinion until something reaches some sort of expert consensus.

Everyone now-days in crypto see a fucking PDF paper in academic format and treat it like a fucking bible. Speaking from a scientific background I've seen plenty of beautiful looking papers which 'look' like they got a lot of good stuff to say only to be complete and utter bullshit. Too bad this isn't my field of expertise.

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April 07, 2015, 02:48:47 PM
 #17

Let the experts evaluate and criticize and withhold your opinion until something reaches some sort of expert consensus.

Isn't this thread a step towards this?
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April 07, 2015, 03:43:30 PM
 #18

Let the experts evaluate and criticize and withhold your opinion until something reaches some sort of expert consensus.

Jeff "HashesDoNotMatch" Garzik is the only expert I know. And he already evaluated Nxt. Do you know any other experts?
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April 07, 2015, 03:49:15 PM
 #19

Let the experts evaluate and criticize and withhold your opinion until something reaches some sort of expert consensus.

Jeff "HashesDoNotMatch" Garzik is the only expert I know. And he already evaluated Nxt. Do you know any other experts?

maybe David Latapie of Munero is a good match

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April 07, 2015, 04:26:30 PM
 #20

Wait for peer review (at least in the community). There's this weird reverence towards certain individuals in this community from people who don't understand shit. Let the experts evaluate and criticize and withhold your opinion until something reaches some sort of expert consensus.

Everyone now-days in crypto see a fucking PDF paper in academic format and treat it like a fucking bible. Speaking from a scientific background I've seen plenty of beautiful looking papers which 'look' like they got a lot of good stuff to say only to be complete and utter bullshit. Too bad this isn't my field of expertise.

No scientist's paper is worth shit unless its been "peer reviewed", which means a big gang of experts all need to have checked it out and agreed with it before it gets published. Most scientific journals are peer reviewed and all the papers in them have been checked by a gang of experts beforehand. We need more experts to check out NXT.
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