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From: Jeff Garzik <jgarzik@bitpay.com>
Date: Thu, 24 Jul 2014 21:41:19 -0400
Message-ID: <CAJHLa0NhXdhANCY6rk81VYqUR-fPxe8b27Py08OfuyrqHUB-Tg@mail.gmail.com>
To: Ron OHara <ron.ohara54@gmail.com>
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Cc: Bitcoin Dev <bitcoin-development@lists.sourceforge.net>
Subject: Re: [Bitcoin-development] Time
Precedence: list

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@gmail.com> wrote:
>
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> 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
>
> - --
> public identify: https://www.onename.io/ron_ohara
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-- 
Jeff Garzik
Bitcoin core developer and open source evangelist
BitPay, Inc.      https://bitpay.com/