From: Jeff Garzik <jgarzik@bitpay•com>
To: gabe appleton <gappleto97@gmail•com>
Cc: Bitcoin Dev <bitcoin-development@lists•sourceforge.net>
Subject: Re: [Bitcoin-development] Proposed additional options for pruned nodes
Date: Tue, 12 May 2015 12:38:20 -0700 [thread overview]
Message-ID: <CAJHLa0PDbxuqRHuGNhsyvLpAaDq=ZHSg_u-Sb7FqNVnYrhFkFg@mail.gmail.com> (raw)
In-Reply-To: <CANJO25+qURmDzsMgnm7+tsw7icFO--gWhmKmQPuNQCoh_R2big@mail.gmail.com>
[-- Attachment #1: Type: text/plain, Size: 5183 bytes --]
One general problem is that security is weakened when an attacker can DoS a
small part of the chain by DoS'ing a small number of nodes - yet the impact
is a network-wide DoS because nobody can complete a sync.
On Tue, May 12, 2015 at 12:24 PM, gabe appleton <gappleto97@gmail•com>
wrote:
> 0, 1, 3, 4, 5, 6 can be solved by looking at chunks chronologically. Ie,
> give the signed (by sender) hash of the first and last block in your range.
> This is less data dense than the idea above, but it might work better.
>
> That said, this is likely a less secure way to do it. To improve upon
> that, a node could request a block of random height within that range and
> verify it, but that violates point 2. And the scheme in itself definitely
> violates point 7.
> On May 12, 2015 3:07 PM, "Gregory Maxwell" <gmaxwell@gmail•com> wrote:
>
>> It's a little frustrating to see this just repeated without even
>> paying attention to the desirable characteristics from the prior
>> discussions.
>>
>> Summarizing from memory:
>>
>> (0) Block coverage should have locality; historical blocks are
>> (almost) always needed in contiguous ranges. Having random peers
>> with totally random blocks would be horrific for performance; as you'd
>> have to hunt down a working peer and make a connection for each block
>> with high probability.
>>
>> (1) Block storage on nodes with a fraction of the history should not
>> depend on believing random peers; because listening to peers can
>> easily create attacks (e.g. someone could break the network; by
>> convincing nodes to become unbalanced) and not useful-- it's not like
>> the blockchain is substantially different for anyone; if you're to the
>> point of needing to know coverage to fill then something is wrong.
>> Gaps would be handled by archive nodes, so there is no reason to
>> increase vulnerability by doing anything but behaving uniformly.
>>
>> (2) The decision to contact a node should need O(1) communications,
>> not just because of the delay of chasing around just to find who has
>> someone; but because that chasing process usually makes the process
>> _highly_ sybil vulnerable.
>>
>> (3) The expression of what blocks a node has should be compact (e.g.
>> not a dense list of blocks) so it can be rumored efficiently.
>>
>> (4) Figuring out what block (ranges) a peer has given should be
>> computationally efficient.
>>
>> (5) The communication about what blocks a node has should be compact.
>>
>> (6) The coverage created by the network should be uniform, and should
>> remain uniform as the blockchain grows; ideally it you shouldn't need
>> to update your state to know what blocks a peer will store in the
>> future, assuming that it doesn't change the amount of data its
>> planning to use. (What Tier Nolan proposes sounds like it fails this
>> point)
>>
>> (7) Growth of the blockchain shouldn't cause much (or any) need to
>> refetch old blocks.
>>
>> I've previously proposed schemes which come close but fail one of the
>> above.
>>
>> (e.g. a scheme based on reservoir sampling that gives uniform
>> selection of contiguous ranges, communicating only 64 bits of data to
>> know what blocks a node claims to have, remaining totally uniform as
>> the chain grows, without any need to refetch -- but needs O(height)
>> work to figure out what blocks a peer has from the data it
>> communicated.; or another scheme based on consistent hashes that has
>> log(height) computation; but sometimes may result in a node needing to
>> go refetch an old block range it previously didn't store-- creating
>> re-balancing traffic.)
>>
>> So far something that meets all those criteria (and/or whatever ones
>> I'm not remembering) has not been discovered; but I don't really think
>> much time has been spent on it. I think its very likely possible.
>>
>>
>> ------------------------------------------------------------------------------
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>>
>
>
> ------------------------------------------------------------------------------
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> Widest out-of-the-box monitoring support with 50+ applications
> Performance metrics, stats and reports that give you Actionable Insights
> Deep dive visibility with transaction tracing using APM Insight.
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> _______________________________________________
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>
--
Jeff Garzik
Bitcoin core developer and open source evangelist
BitPay, Inc. https://bitpay.com/
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next prev parent reply other threads:[~2015-05-12 19:38 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <CANJO25J1WRHtfQLVXUB2s_sjj39pTPWmixAcXNJ3t-5os8RPmQ@mail.gmail.com>
2015-05-12 15:26 ` gabe appleton
2015-05-12 16:05 ` Jeff Garzik
2015-05-12 16:56 ` gabe appleton
2015-05-12 17:16 ` Peter Todd
2015-05-12 18:23 ` Tier Nolan
2015-05-12 19:03 ` Gregory Maxwell
2015-05-12 19:24 ` gabe appleton
2015-05-12 19:38 ` Jeff Garzik [this message]
2015-05-12 19:43 ` gabe appleton
2015-05-12 21:30 ` [Bitcoin-development] [Bulk] " gb
2015-05-12 20:02 ` [Bitcoin-development] " Gregory Maxwell
2015-05-12 20:10 ` Jeff Garzik
2015-05-12 20:41 ` gabe appleton
2015-05-12 20:47 ` Gregory Maxwell
[not found] ` <CAFVoEQTdmCSRAy3u26q5oHdfvFEytZDBfQb_fs_qttK15fiRmg@mail.gmail.com>
[not found] ` <CAJHLa0OxxxiVd3JOp8SDvbF8dHj6KHdUNGb9L_GvTe93z3Z8mg@mail.gmail.com>
[not found] ` <CAJHLa0MYSpVBD4VE65LVbADb2daOvE=N83G8F_zDSHy3AQ5DAQ@mail.gmail.com>
2015-05-12 21:17 ` [Bitcoin-development] Fwd: " Adam Weiss
2015-05-12 22:00 ` [Bitcoin-development] " Tier Nolan
2015-05-12 22:09 ` gabe appleton
2015-05-13 5:19 ` Daniel Kraft
2015-05-13 9:34 ` Tier Nolan
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