[Bitcoin-development] Time

Jeff Garzik jgarzik at bitpay.com
Fri Jul 25 01:41:19 UTC 2014

Miners are free to set the block's timestamp to whatever they please,
within a certain +/- time window.  Time might even go backwards a tiny
bit from the last block to the next block.

On Thu, Jul 24, 2014 at 9:14 PM, Ron OHara <ron.ohara54 at gmail.com> wrote:
> Hash: SHA1
> I thought I should shortcut my research by asking a direct question here.
> As I understand it, the blockchain actually provides an extra piece of
> reliable data that is not being exploited by applications.
> Which data?  The time.   In this case 'the time' as agreed by >50% of
> the participants, where those participants have a strong financial
> incentive to keep that 'time' fairly accurate. (+/- about 10 minutes)
> Is this a reasonable understanding of 'time'? ... aka timestamps on the
> block
> Ok... 'time' on the blockchain could be 'gamed' ... but with great
> difficulty. An application presented with a fake blockchain can use
> quite a few heuristics to test the 'validity' of the block chain.
> It can review the usual cryptographic proofs, and check that difficulty
> is growing/declining only in a realistic manner up to the most recent
> block. Even use some arbitrary test like difficulty > 10,000,000,000
> ... on the presumption that any less means that the Bitcoin system has
> failed massively from where it currently is and has become an unreliable
> time source.
> Reliable 'time' has been impossible up until now - because you need to
> trust the time source, and that can always be faked.  Using the
> blockchain as an approximate time source gives you a world wide
> consensus without direct trust of any player.
> So if this presumption is correct, then we can now build time capsule
> applications that can not be tricked into exposing their contents too
> early by running them in a virtual environment with the wrong system time.
> Is this right? or did miss I something fundamental?
> Ron
> - --
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> =T5fw
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Jeff Garzik
Bitcoin core developer and open source evangelist
BitPay, Inc.      https://bitpay.com/

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