soft-fork block size increase (extension blocks) Re: Proposed alternatives to the 20MB stepfunction

soft-fork block size increase (extension blocks) Re: Proposed alternatives to the 20MB stepfunction
2015-05-30  0:16 ` Gavin Andresen
  
From: Adam Back @ 2015-05-30  0:00 UTC (permalink / raw)
  To: Raystonn .;  Bitcoin Dev

I discussed the extension block idea on wizards a while back and it is
a way to soft-fork an opt-in block-size increase.  Like everything
here there are pros and cons.

The security is better than Raylstonn inferred from Tier's explanation
I think..  It works as Tier described - there is an extension block
(say 10MB) and the existing 1MB block.  The extension block is
committed to in the 1MB chain.  Users can transfer bitcoin into the
extension block, and they can transfer them out.

The interesting thing is this makes block sizes changes opt-in and
gives users choice.  Choice is good.  Bitcoin has a one-size-fits-all
blocksize at present hence the block size debate.  If a bigger
block-size were an opt-in choice, and some people wanted 10MB or even
100MB blocks for low value transactions I expect it would be far
easier a discussion - people who think 100MB blocks are dangerously
centralising, would not opt to use them (or would put only small
values they can afford to lose in them).  There are some security
implications though, so this also is nuanced, and more on that in a
bit.

Fee pressure still exists for blocks of difference size as the
security assurances are not the same.  It is plausible that some
people would pay more for transactions in the 1MB block.

Now there are three choices of validation level, rather than the
normal 2-levels of SPV or full-node, with extension blocks we get a
choice: A) a user could run a full node for both 1MB and 10MB blocks,
and get full security for both 1MB and 10MB block transactions (but at
higher bandwidth cost), or B) a user could run a full node on the 1MB
block, but operate as an SPV node for the 10MB block, or C) run in SPV
mode for both 1MB and 10MB blocks.

Similarly for mining - miners could validate 1MB and 10MB transactions
(solo mine or GBT-style), or they could self-validate 1MB transactions
and pool mine 10MB transactions (have a pool validate those).

1MB full node users who do not upgrade to software that understands
extension blocks, could run in SPV mode with respect to 10MB blocks.
Here lies the risk - this imposes a security downgrade on the 1MB
non-upgraded users, and also on users who upgrade but dont have the
bandwidth to validate 10MB blocks.


We could defend non-upgrade users by making receiving funds that came
via the extension block opt-in also, eg an optional to use new address
version and construct the extension block so that payments out of it
can only go to new version addresses.

We could harden 1MB block SPV security (when receiving weaker
extension block transactions) in a number of ways: UTXO commitments,
fraud proofs (and fraud bounties) for moving from the extension block
to the 1MB block.  We could optionally require coins moving via the
extension block to the 1MB block to be matured (eg 100 blocks delay)


Anyway something else to evaluate.  Not as simple to code as a
hard-fork, but way safer transition than a hard-fork, and opt-in - if
you prefer the higher decentralisation of 1MB blocks, keep using them;
if you prefer 10MB blocks you can opt-in to them.

Adam

On 29 May 2015 at 17:39, Raystonn . <raystonn@hotmail•com> wrote:
> Regarding Tier’s proposal: The lower security you mention for extended
> blocks would delay, possibly forever, the larger blocks maximum block size
> that we want for the entire network.  That doesn’t sound like an optimal
> solution.
>
> Regarding consensus for larger maximum block size, what we are seeing on
> this list is typical of what we see in the U.S. Congress.  Support for
> changes by the stakeholders (support for bills by the citizens as a whole)
> has become irrelevant to the probability of these changes being adopted.
> Lobbyists have all the sway in getting their policies enacted.  In our case,
> I would bet on some lobbying of core developers by wealthy miners.
>
> Someone recently proposed that secret ballots could help eliminate the power
> of lobbyists in Congress.  Nobody invests in that which cannot be confirmed.
> Secret ballots mean the vote you are buying cannot be confirmed.  Perhaps
> this will work for Bitcoin Core as well.
>
>
> From: Tier Nolan
> Sent: Friday, May 29, 2015 7:22 AM
> Cc: Bitcoin Dev
> Subject: Re: [Bitcoin-development] Proposed alternatives to the 20MB
> stepfunction
>
> On Fri, May 29, 2015 at 3:09 PM, Tier Nolan <tier.nolan@gmail•com> wrote:
>>
>>
>>
>> On Fri, May 29, 2015 at 1:39 PM, Gavin Andresen <gavinandresen@gmail•com>
>> wrote:
>>>
>>> But if there is still no consensus among developers but the "bigger
>>> blocks now" movement is successful, I'll ask for help getting big miners to
>>> do the same, and use the soft-fork block version voting mechanism to
>>> (hopefully) get a majority and then a super-majority willing to produce
>>> bigger blocks. The purpose of that process is to prove to any doubters that
>>> they'd better start supporting bigger blocks or they'll be left behind, and
>>> to give them a chance to upgrade before that happens.
>>
>>
>> How do you define that the movement is successful?
>
>
> Sorry again, I keep auto-sending from gmail when trying to delete.
>
> In theory, using the "nuclear option", the block size can be increased via
> soft fork.
>
> Version 4 blocks would contain the hash of the a valid extended block in the
> coinbase.
>
> <block height> <32 byte extended hash>
>
> To send coins to the auxiliary block, you send them to some template.
>
> OP_P2SH_EXTENDED <scriptPubKey hash> OP_TRUE
>
> This transaction can be spent by anyone (under the current rules).  The soft
> fork would lock the transaction output unless it transferred money from the
> extended block.
>
> To unlock the transaction output, you need to include the txid of
> transaction(s) in the extended block and signature(s) in the scriptSig.
>
> The transaction output can be spent in the extended block using P2SH against
> the scriptPubKey hash.
>
> This means that people can choose to move their money to the extended block.
> It might have lower security than leaving it in the root chain.
>
> The extended chain could use the updated script language too.
>
> This is obviously more complex than just increasing the size though, but it
> could be a fallback option if no consensus is reached.  It has the advantage
> of giving people a choice.  They can move their money to the extended chain
> or not, as they wish.



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2015-05-30  0:00 [Bitcoin-development] soft-fork block size increase (extension blocks) Re: Proposed alternatives to the 20MB stepfunction Adam Back

  
From: Gavin Andresen @ 2015-05-30  0:16 UTC ( / )
  To: Adam Back;  Bitcoin Dev



RE: soft-forking an "extension block":

So... go for it, code it up. Implement it in the Bitcoin Core wallet.

Then ask the various wallet developer how long it would take them to update
their software to support something like this, and do some UI mockups of
what the experience would look like for users.

If there are two engineering solutions to a problem, one really simple, and
one complex, why would you pick the complex one?

Especially if the complex solution has all of the problems of the simple
one (20MB extension blocks are just as "dangerous" as 20MB main blocks,
yes? If not, why not?)


-- 
--
Gavin Andresen
2015-05-30  3:27 ` Andrew
  
From: Raystonn @ 2015-05-30  1:36 UTC (permalink / raw)
  To: Gavin Andresen;  Bitcoin Dev

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2015-05-30  1:36 Raystonn

  
From: Andrew @ 2015-05-30  3:27 UTC (permalink / raw)
  To: Raystonn;  Bitcoin Dev

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Hello Adam

First of all, thank you for inventing hashcash, which is basically what
bitcoin is!

Some people have said that my proposal, subject line "Scaling Bitcoin with
Subchains" is essentially the idea of blockchain extensions. Though, I
think there is quite a difference between what I propose and what you
propose. You want to add one optional 10 MB blockchain that synchronizes
with the 1 MB blockchain, while I want to add ten 1 MB
 blockchains that each synchronize with the 1 MB chain (and you can
continue like that). I think, as long as we want to keep using blockchains
for our cryptocurrency, we will need a tree structure of blockchains in
order to scale for an arbitrary number of transactions. With just one 10 MB
blockchain, someone who wants to do the lower valued transactions will need
to validate all 10 MB, while with ten 1 MB chains, they can choose just the
chain or chains that are of interest to them. With a tree structure you get
O(a^(n-1)) MB of transactions in the network while each participant only
has to validate O(n) MB of transactions (a is just the number of children
chains per parent divided by 2, so 5 in the case of 10 children as I
described). With just one child chain, you don't get this scaling, and it
is pretty much equivalent to increasing the blocksize, though with a
soft-fork instead of a hard-fork.

I think the actual way that the blockchains interact can be still worked
out (Recently I was thinking of maybe creating a contract system or even a
decentralized market between chains). But still, everyone should agree that
you need this kind of tree structure. Even if you want to only run a pruned
node, the CPU usage and memory scales just as bad. The tree structure also
has good privacy and miner decentralization properties, as I can write
about later.

But another thing that I recommend is an "exit plan". What if we go with
some kind of soft fork and then in the future some better idea comes along?
Then we should have a way to reverse the soft fork. If people already have
coins tied up in sidechains, it can be problematic. So perhaps, in case
people want to later ditch the soft fork, nodes in the parent chain can
allow only old transactions inside the child chains to be accepted back up,
while new transactions are not recognized anymore. That way you can limit
the amount of useless transaction traffic that results in case we want
something else.

On Sat, May 30, 2015 at 1:36 AM, Raystonn <raystonn@hotmail•com> wrote:

> My fear now is too much unnecessary complexity.  More complex means
> brittle code, but also fewer programmers working on this, which is a risk.
>
> We shouldn't delay forever until every potential solution has been
> explored.  There's always going to be one more thing to explore.
>  On 29 May 2015 5:16 pm, Gavin Andresen <gavinandresen@gmail•com> wrote:
>
> RE: soft-forking an "extension block":
>
> So... go for it, code it up. Implement it in the Bitcoin Core wallet.
>
> Then ask the various wallet developer how long it would take them to
> update their software to support something like this, and do some UI
> mockups of what the experience would look like for users.
>
> If there are two engineering solutions to a problem, one really simple,
> and one complex, why would you pick the complex one?
>
> Especially if the complex solution has all of the problems of the simple
> one (20MB extension blocks are just as "dangerous" as 20MB main blocks,
> yes? If not, why not?)
>
>
> --
> --
> Gavin Andresen
>
>
>
> ------------------------------------------------------------------------------
>
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> Bitcoin-development@lists•sourceforge.net
> https://lists.sourceforge.net/lists/listinfo/bitcoin-development
>
>


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