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Author Topic: Why is there a maximum target?  (Read 1314 times)
Ian Maxwell
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May 20, 2011, 06:14:52 PM
 #1

Or more accurately, why isn't the maximum target 2^256 - 1? The issue of excessively fast block generation would have resolved itself within less than a second after the first client was run. Or the initial difficulty could have just been set to 1,000,000,000.

The scaled-down shares-per-block difficulty may be easier on the eyes, but its interpretation is kind of opaque. Quoting difficulty in Ghash/block at least means something.

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Matt Corallo
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May 20, 2011, 06:30:15 PM
 #2

From a couple days ago: http://forum.bitcoin.org/index.php?topic=8928.0

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Ian Maxwell
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May 20, 2011, 06:53:18 PM
 #3

Ah.... sorry.

They didn't really answer the question, though.

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May 20, 2011, 07:05:57 PM
 #4

I'd guess satoshi chose a maximum target to allow for a. that he didnt get the first 2016 blocks so easily, as that might be looked at even worse than the whole scam stuff now. and b. if there is a major network issue at least there is still some minimum security.

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May 20, 2011, 07:51:00 PM
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I'd guess satoshi chose a maximum target to allow for a. that he didnt get the first 2016 blocks so easily, as that might be looked at even worse than the whole scam stuff now. and b. if there is a major network issue at least there is still some minimum security.

Yes, that's part of it.  Kept it too difficult for one, or even a few, average desktops from reaching 10 minutes between blocks.  Partly as a show of faith that others were desired.

Also, setting a max target also creates the metric that we call the difficulty.  The difficulty number is an estimate of how many times more difficult the target is to achieve statisticly as compared to the minimum difficulty of 1, which is defined as the max target number.  Just having the target doesn't help human beings wrap our heads around the concept, but the difficulty provides a relative metric that humans can get used to.

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May 20, 2011, 08:15:00 PM
 #6

With the 4x rule, wouldn't it take quite a few retargets before the target was properly adjusted?

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May 20, 2011, 08:55:04 PM
 #7

With the 4x rule, wouldn't it take quite a few retargets before the target was properly adjusted?

The 4x rule was not present in the first several months.  It was added as a security defense later.  Even so, this would not have had a large impact upon the max target.

"The powers of financial capitalism had another far-reaching aim, nothing less than to create a world system of financial control in private hands able to dominate the political system of each country and the economy of the world as a whole. This system was to be controlled in a feudalist fashion by the central banks of the world acting in concert, by secret agreements arrived at in frequent meetings and conferences. The apex of the systems was to be the Bank for International Settlements in Basel, Switzerland, a private bank owned and controlled by the world's central banks which were themselves private corporations. Each central bank...sought to dominate its government by its ability to control Treasury loans, to manipulate foreign exchanges, to influence the level of economic activity in the country, and to influence cooperative politicians by subsequent economic rewards in the business world."

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May 20, 2011, 10:58:04 PM
 #8

what is the 4x rule?
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May 20, 2011, 11:04:24 PM
 #9

what is the 4x rule?

Difficulty can rise maximum 4 times or drop to 1/4 of the previous value during difficulty retarget.

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May 20, 2011, 11:10:42 PM
 #10

what is the 4x rule?

The difficulty cannot change by more than a factor of four, either up nor down, in any one re-targeting.  This is to limit the damage of a possible attack vector that has never been attempted.  The attack involves a major hasher with much more power than the whole of the network coming in, and rather than attack the blockchain as in the double-spend attack, he simply hashes honestly with abandon up until the next retarget and then shuts his cluster off.  The result being that, without the factor-of-four rule, the period of time between blocks could be stretched to an unreasonable interval.  With the Fo4 rule, this attack would require that the attacker be willing to hash through several retargets in a row; otherwise his attack would be limited to stretching the interval to about 40 minutes, which would be inconvient but not detrimental to the system.  The rule is probably not needed anymore, as there isn't likely any single entity left on Earth with the power to outhash the running network by more than 4 times anyway.

"The powers of financial capitalism had another far-reaching aim, nothing less than to create a world system of financial control in private hands able to dominate the political system of each country and the economy of the world as a whole. This system was to be controlled in a feudalist fashion by the central banks of the world acting in concert, by secret agreements arrived at in frequent meetings and conferences. The apex of the systems was to be the Bank for International Settlements in Basel, Switzerland, a private bank owned and controlled by the world's central banks which were themselves private corporations. Each central bank...sought to dominate its government by its ability to control Treasury loans, to manipulate foreign exchanges, to influence the level of economic activity in the country, and to influence cooperative politicians by subsequent economic rewards in the business world."

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May 21, 2011, 12:03:35 AM
 #11

I can't imagine the major network issue that would cause difficulty to drop anywhere close to 1. Any modern GPU can easily do that in far less than 10 minutes (more like less than 10 seconds).

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Ian Maxwell
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May 21, 2011, 12:14:45 AM
 #12

I think we were talking about the time to get to difficulty 1 from "difficulty" 1/maxtarget.

Answer: 112 retargets, or 225792 blocks, or 11289600 bitcoins generated.

I guess I can see the reason for a maxtarget. Though I do kind of wish the convention were to call the minimum difficulty "4.295 Ghash/block" rather than "1".

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May 21, 2011, 08:48:39 AM
 #13

It would be trivial to switch the network from 256 bit hashes to 512 bit hashes.  I haven't checked the math, but I think that we'd run out of theoretical computing power in the universe before we needed to.

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