From: Gavin Andresen <gavinandresen@gmail•com>
To: Gregory Maxwell <greg@xiph•org>
Cc: Bitcoin Dev <bitcoin-dev@lists•linuxfoundation.org>
Subject: Re: [bitcoin-dev] Capacity increases for the Bitcoin system.
Date: Tue, 8 Dec 2015 20:09:16 -0500 [thread overview]
Message-ID: <CABsx9T1i50Gvxj18W=n2mYGNpsMrSkDT26CdA3aQqT5FFN86yw@mail.gmail.com> (raw)
In-Reply-To: <CAAS2fgTGYSiAJHZq80rD4UieV8XetS=W0b45b5onWAS9gF-F7g@mail.gmail.com>
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On Tue, Dec 8, 2015 at 6:59 PM, Gregory Maxwell <greg@xiph•org> wrote:
> > We also need to fix the O(n^2) sighash problem as an additional BIP for
> ANY
> > blocksize increase.
>
> The witness data is never an input to sighash, so no, I don't agree
> that this holds for "any" increase.
>
Here's the attack:
Create a 1-megabyte transaction, with all of it's inputs spending
segwitness-spending SIGHASH_ALL inputs.
Because the segwitness inputs are smaller in the block, you can fit more of
them into 1 megabyte. Each will hash very close to one megabyte of data.
That will be O(n^2) worse than the worst case of a 1-megabyte transaction
with signatures in the scriptSigs.
Did I misunderstand something or miss something about the 1-mb transaction
data and 3-mb segwitness data proposal that would make this attack not
possible?
RE: fraud proof data being deterministic: yes, I see, the data can be
computed instead of broadcast with the block.
RE: emerging consensus of Core:
I think it is a huge mistake not to "design for success" (see
http://gavinandresen.ninja/designing-for-success ).
I think it is a huge mistake to pile on technical debt in
consensus-critical code. I think we should be working harder to make things
simpler, not more complex, whenever possible.
And I think there are pretty big self-inflicted current problems because
worries about theoretical future problems have prevented us from coming to
consensus on simple solutions.
--
--
Gavin Andresen
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next prev parent reply other threads:[~2015-12-09 1:09 UTC|newest]
Thread overview: 56+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-12-07 22:02 Gregory Maxwell
2015-12-07 22:54 ` Bryan Bishop
2015-12-08 2:42 ` Anthony Towns
2015-12-08 4:58 ` Anthony Towns
2015-12-08 5:21 ` Gregory Maxwell
2015-12-08 6:54 ` Anthony Towns
2016-01-18 12:02 ` Anthony Towns
2016-01-22 9:46 ` Anthony Towns
2015-12-08 11:07 ` Wladimir J. van der Laan
2015-12-08 11:14 ` Jorge Timón
2015-12-08 15:12 ` Gavin Andresen
2015-12-08 15:55 ` Justus Ranvier
2015-12-08 17:41 ` Mark Friedenbach
2015-12-08 18:43 ` Justus Ranvier
2015-12-08 19:08 ` Tier Nolan
2015-12-08 19:31 ` Gregory Maxwell
2015-12-08 23:40 ` Jonathan Toomim
2015-12-08 23:48 ` Luke Dashjr
2015-12-09 0:54 ` Jonathan Toomim
2015-12-08 23:50 ` Jorge Timón
2015-12-09 0:56 ` Jonathan Toomim
2015-12-08 23:59 ` Gregory Maxwell
2015-12-09 0:58 ` Jorge Timón
2015-12-09 1:02 ` Jorge Timón
2015-12-09 1:09 ` Gavin Andresen [this message]
2015-12-09 1:31 ` Gregory Maxwell
2015-12-09 4:44 ` Ryan Butler
2015-12-09 6:29 ` Gregory Maxwell
2015-12-09 6:36 ` Ryan Butler
2015-12-09 6:59 ` Mark Friedenbach
2015-12-09 7:17 ` Gregory Maxwell
2015-12-09 7:54 ` Jorge Timón
2015-12-09 8:03 ` Gregory Maxwell
2015-12-09 8:46 ` Mark Friedenbach
2015-12-09 11:08 ` Jorge Timón
2015-12-09 16:40 ` Gavin Andresen
2015-12-11 16:18 ` Jorge Timón
2015-12-11 16:43 ` Gavin Andresen
2015-12-12 5:13 ` digitsu
2015-12-12 15:18 ` Mark Friedenbach
2015-12-14 11:21 ` Jonathan Toomim
2015-12-14 12:44 ` Adam Back
2015-12-09 4:51 ` Anthony Towns
2015-12-09 14:51 ` Chris
[not found] ` <CAPWm=eUomq6SBC0ky0WSs5=_G942vigm4RmgYuq0O-yJ-vqC2A@mail.gmail.com>
[not found] ` <CAPg+sBig9O5+he0PWhTkX5iin14QLz5+eCCu6KfwU=DxntKYtg@mail.gmail.com>
2015-12-21 4:33 ` Pieter Wuille
2015-12-21 4:42 ` Justus Ranvier
2015-12-21 4:44 ` Alex Morcos
2015-12-21 4:50 ` Mark Friedenbach
2015-12-21 5:29 ` Douglas Roark
2015-12-21 5:21 ` Btc Drak
2015-12-21 8:07 ` Anthony Towns
2015-12-21 9:56 ` Jorge Timón
2015-12-08 23:48 ` Jonathan Toomim
2015-12-09 0:23 ` Gregory Maxwell
[not found] ` <CAAS2fgRP8bLWZoKR9-iJS-2RKTGQQ9NG-LpAfa2BOdcR=GuB_A@mail.gmail.com>
2015-12-09 0:40 ` Jonathan Toomim
2015-12-09 12:28 Daniele Pinna
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