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Cc: Bitcoin Dev <bitcoin-development@lists.sourceforge.net>
Subject: Re: [Bitcoin-development] Proposal for extra nonce in block header
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On 27 April 2014 09:07, Timo Hanke <timo.hanke@web.de> wrote:

> I'd like to put the following draft of a BIP up for discussion.
>
> Timo
>
> # Abstract
> There are incentives for miners to find cheap, non-standard ways to
> generate new work, which are not necessarily in the best interest of the
> protocol.
> In order to reduce these incentives this proposal re-assigns 2 bytes from
> the version field of the block header to a new extra nonce field.
> # Copyright
> # Specification
> The block version number field in the block header is reduced in size from
> 4 to 2 bytes.
> The third and fourth byte in the block header are assigned to the new
> extra nonce field inside the block header.
> # Motivation
> The motivation of this proposal is to provide miners with a cheap
> constant-complexity method to create new work that does not require
> altering the transaction tree.
>
> Furthermore, the motivation is to protect the version and timestamp fields
> in the block header from abuse.
> # Rationale
> Traditionally, the extra nonce is part of the coinbase field of the
> generation transaction, which is always the very first transaction of a
> block.
> After incrementing the extra nonce the minimum amount of work a miner has
> to do to re-calculate the block header is a) to hash the coinbase
> transaction and b) to re-calculate the left-most branch of the merkle tree
> all the way to the merkle root.
> This is necessary overhead a miner has to do besides hashing the block
> header itself.
> We shall call the process that leads to a new block header from the same
> transaction set the _pre-hashing_.
>
> First it should be noted that the relative cost of pre-hashing in its
> traditional form depends
> on the block size, which may create an unwanted incentive for miners
> to keep the block size small. However, this is not the main motivation for
> the current proposal.
>
> While the block header is hashed by ASICs, pre-hashing typically happens
> on a CPU because of the greater flexibility required.
> Consequently, as ASIC cost per hash performance drops the relative cost of
> pre-hashing increases.
>
> This creates an incentive for miners to find cheaper ways to create new
> work than by means of pre-hashing.
> An example of this currently happening is the on-device rolling of the
> timestamp into the future.
> These ways of creating new work are unlikely to be in the best interest of
> the protocol.
> For example, rolling the timestamp faster than the real time is unwanted
> (more so on faster blockchains).
>
> The version number in the block header is a possible target for alteration
> with the goal of cheaply creating new work.
> Currently, blocks with arbitrarily large version numbers get relayed and
> accepted by the network.
> As this is unwanted behaviour, there should not exist any incentive for a
> miner to abuse the version number in this way.
>
> The solution is to reduce the range of version numbers from 2^32 to 2^16
> and to declare the third and forth bytes of the block header as legitimate
> space for an extra nonce.
> This will reduce the incentive for a miner to abuse the shortened version
> number by a factor in the order of 2^16.
>
> As a side effect, this proposal greatly reduces the bandwidth requirements
> of a blind pool protocol by only submitting the block header to the miner.
> # Backwards Compatibility
> Old versions of the client will accept blocks of this kind but will throw
> an alert at the user to upgrade.
> The only code change would be a cast of the version number to a short.
> Besides the upgrade alert, old and new versions of the client can co-exist
> and there is no need to introduce a new block version number or to
> phase-out old block versions.
> # Reference Implementation
> # Final implementation
>

If changing the structure of the block header, wouldnt you also need to
increment the version number to 3?


>
> --
> Timo Hanke
> PGP 1EFF 69BC 6FB7 8744 14DB  631D 1BB5 D6E3 AB96 7DA8
>
>
> ------------------------------------------------------------------------------
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--001a1134563058ad8104f801d31c
Content-Type: text/html; charset=UTF-8
Content-Transfer-Encoding: quoted-printable

<div dir=3D"ltr"><br><div class=3D"gmail_extra"><br><br><div class=3D"gmail=
_quote">On 27 April 2014 09:07, Timo Hanke <span dir=3D"ltr">&lt;<a href=3D=
"mailto:timo.hanke@web.de" target=3D"_blank">timo.hanke@web.de</a>&gt;</spa=
n> wrote:<br>
<blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-left:1p=
x #ccc solid;padding-left:1ex">I&#39;d like to put the following draft of a=
 BIP up for discussion.<br>
<br>
Timo<br>
<br>
# Abstract<br>
There are incentives for miners to find cheap, non-standard ways to generat=
e new work, which are not necessarily in the best interest of the protocol.=
<br>
In order to reduce these incentives this proposal re-assigns 2 bytes from t=
he version field of the block header to a new extra nonce field.<br>
# Copyright<br>
# Specification<br>
The block version number field in the block header is reduced in size from =
4 to 2 bytes.<br>
The third and fourth byte in the block header are assigned to the new extra=
 nonce field inside the block header.<br>
# Motivation<br>
The motivation of this proposal is to provide miners with a cheap constant-=
complexity method to create new work that does not require altering the tra=
nsaction tree.<br>
<br>
Furthermore, the motivation is to protect the version and timestamp fields =
in the block header from abuse.<br>
# Rationale<br>
Traditionally, the extra nonce is part of the coinbase field of the generat=
ion transaction, which is always the very first transaction of a block.<br>
After incrementing the extra nonce the minimum amount of work a miner has t=
o do to re-calculate the block header is a) to hash the coinbase transactio=
n and b) to re-calculate the left-most branch of the merkle tree all the wa=
y to the merkle root.<br>

This is necessary overhead a miner has to do besides hashing the block head=
er itself.<br>
We shall call the process that leads to a new block header from the same tr=
ansaction set the _pre-hashing_.<br>
<br>
First it should be noted that the relative cost of pre-hashing in its tradi=
tional form depends<br>
on the block size, which may create an unwanted incentive for miners<br>
to keep the block size small. However, this is not the main motivation for<=
br>
the current proposal.<br>
<br>
While the block header is hashed by ASICs, pre-hashing typically happens on=
 a CPU because of the greater flexibility required.<br>
Consequently, as ASIC cost per hash performance drops the relative cost of =
pre-hashing increases.<br>
<br>
This creates an incentive for miners to find cheaper ways to create new wor=
k than by means of pre-hashing.<br>
An example of this currently happening is the on-device rolling of the time=
stamp into the future.<br>
These ways of creating new work are unlikely to be in the best interest of =
the protocol.<br>
For example, rolling the timestamp faster than the real time is unwanted (m=
ore so on faster blockchains).<br>
<br>
The version number in the block header is a possible target for alteration =
with the goal of cheaply creating new work.<br>
Currently, blocks with arbitrarily large version numbers get relayed and ac=
cepted by the network.<br>
As this is unwanted behaviour, there should not exist any incentive for a m=
iner to abuse the version number in this way.<br>
<br>
The solution is to reduce the range of version numbers from 2^32 to 2^16 an=
d to declare the third and forth bytes of the block header as legitimate sp=
ace for an extra nonce.<br>
This will reduce the incentive for a miner to abuse the shortened version n=
umber by a factor in the order of 2^16.<br>
<br>
As a side effect, this proposal greatly reduces the bandwidth requirements =
of a blind pool protocol by only submitting the block header to the miner.<=
br>
# Backwards Compatibility<br>
Old versions of the client will accept blocks of this kind but will throw a=
n alert at the user to upgrade.<br>
The only code change would be a cast of the version number to a short.<br>
Besides the upgrade alert, old and new versions of the client can co-exist =
and there is no need to introduce a new block version number or to phase-ou=
t old block versions.<br>
# Reference Implementation<br>
# Final implementation<br></blockquote><div><br></div><div>If changing the =
structure of the block header, wouldnt you also need to increment the versi=
on number to 3?<br></div><div>=C2=A0</div><blockquote class=3D"gmail_quote"=
 style=3D"margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">

<br>
--<br>
Timo Hanke<br>
PGP 1EFF 69BC 6FB7 8744 14DB =C2=A0631D 1BB5 D6E3 AB96 7DA8<br>
<br>
---------------------------------------------------------------------------=
---<br>
Start Your Social Network Today - Download eXo Platform<br>
Build your Enterprise Intranet with eXo Platform Software<br>
Java Based Open Source Intranet - Social, Extensible, Cloud Ready<br>
Get Started Now And Turn Your Intranet Into A Collaboration Platform<br>
<a href=3D"http://p.sf.net/sfu/ExoPlatform" target=3D"_blank">http://p.sf.n=
et/sfu/ExoPlatform</a><br>
_______________________________________________<br>
Bitcoin-development mailing list<br>
<a href=3D"mailto:Bitcoin-development@lists.sourceforge.net">Bitcoin-develo=
pment@lists.sourceforge.net</a><br>
<a href=3D"https://lists.sourceforge.net/lists/listinfo/bitcoin-development=
" target=3D"_blank">https://lists.sourceforge.net/lists/listinfo/bitcoin-de=
velopment</a><br>
</blockquote></div><br></div></div>

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