Quote from: TheFascistMind on October 02, 2014, 04:16:08 AM

Quote from: TheFascistMind on October 01, 2014, 09:21:25 AM

Quote from: BitcoinEXpress on September 27, 2014, 06:05:04 AM

...

At some point I am sure the XMR team will realize they do indeed need my help and we may work something out.

But anyway the image below posted by nutildah is interesting. Check the blocks just prior to the circle.

Later guys.

~BCX~

Quote from: JorgeStolfi on September 27, 2014, 06:36:33 AM

Quote from: nutildah on September 27, 2014, 06:20:01 AM

another 4 blocks in the last minute.

By my math, with 1 block per minute mean rate, one should see 4 blocks in the same minute about once every hour or so. Is this correct?

I see 12 blocks in 4 minutes.

We apply the Poisson distribution.

The probability that we will get 4 blocks in 4 minutes when the expected rate is 1 block per minute (4 blocks per 4 minutes) is:

p = 4⁴ / 4!e⁴ ≈ 19.5%, i.e. an occurrence expected roughly every 5 minutes.

The probability that we will get 12 blocks in 4 minutes when the expected rate is 1 block per minute (4 blocks per 4 minutes) is:

p = 4¹² / 12!e⁴ ≈ 0.064%, i.e. an occurrence expected roughly every 1559 minutes which is every 26 hours.

And note that the probably we get 10 - 14 blocks in 4 minutes is going to several times higher because we sum the probabilities for each of 10, 11, 12, 13, and 14, thus an occurrence expected several times per day.

I believe the math above is incorrect, because each 1 minute trial is independent (which is one of the requirements for a Poisson distribution). Thus we have four consecutive events, two are 4 blocks in a minute and two are 2 blocks in a minute. Thus the probability is as follows.

p = (1⁴ / 4!e¹)² × (1² / 2!e¹)² ≈ 0.000795%, i.e. an occurrence expected roughly every 125,794 minutes which is every 87 days!

If my correction is correct, we do have evidence of something rarely occurring.

Thank you for undertaking this.

What we have in that sample is evidence that there are inaccurate clocks in some miners. (This much is clear from a time stamp preceding a block it has hashed as the previous in the chain.)
Those time stamps come from the computers of the miners, they are not the times that blocks are received.
NTP (network time protocol, used for clock syncing on computers) is a UDP protocol, it is not reliable, and miners may not even use it. It also has exploitable holes, MITM vulnerabilities and other issues. So yes, it could be malice (to generate unjustified fear), it could also be laziness, carelessness or even miner caution or tuning (avoiding an unprofitable process). What it isn't is evidence of an attack vector. There is no significant damage resulting from this sort of activity.

I looked at this earlier and wrote a bit more about it up-thread, here: https://bitcointalk.org/index.php?topic=789978.msg9039996#msg9039996

If your curiosity compels you, it may be interesting to analyze this sample against the data set from the rest of the chain to more accurately assess how much of an anomaly it is (though it may not be worth the bother considering the negligible consequences), and so your calculations here, while accurate, start with this mistaken premise.