From: Johnson Lau <jl2012@xbt.hk>
Message-Id: <A1AB77D7-7F70-4045-BAB1-96625020A988@xbt.hk>
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Date: Sat, 28 Jan 2017 15:28:14 +0800
In-Reply-To: <cfc013e5-2e29-e967-9f7a-fff3e44e14ce@mattcorallo.com>
To: Matt Corallo <lf-lists@mattcorallo.com>
References: <FB8593E6-3CD7-46D5-8FC8-A73A0EF1AE9A@xbt.hk>
	<5CDE542F-204F-4988-838F-F438D30C7D99@xbt.hk>
	<cfc013e5-2e29-e967-9f7a-fff3e44e14ce@mattcorallo.com>
Cc: bitcoin-dev <bitcoin-dev@lists.linuxfoundation.org>
Subject: Re: [bitcoin-dev] Forcenet: an experimental network with a new
 header format
Precedence: list


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> On 28 Jan 2017, at 10:32, Matt Corallo <lf-lists@mattcorallo.com> =
wrote:
>=20
> Looks cool, though I have a few comments inline.
>=20
> One general note - it looks like you're letting complexity run away =
from
> you a bit here. If the motivation for something is only weak, its
> probably not worth doing! A hard fork is something that must be
> undertaken cautiously because it has so much inherent risk, lets not =
add
> tons to it.
>=20

I think the following features are necessary for a hardfork. The rest =
are optional:

1. A secondary header
2. Anti-replay
3. SigHash limit for old scripts
4. New tx weight accounting

Optional:
1. New coinbase format is nice but not strictly needed. But this can=E2=80=
=99t be reintroduced later with softfork due to the 100 block maturity =
requirement
2. Smooth halving: could be a less elegant softfork
3. Mekle sum tree: definitely could be a softfork

> Matt
>=20
> On 01/14/17 21:14, Johnson Lau via bitcoin-dev wrote:
>> I created a second version of forcenet with more experimental =
features
>> and stopped my forcenet1 node.
>>=20
>> 1. It has a new header format: Height (4), BIP9 signalling field (4),
>> hardfork signalling field (2), Hash TMR (32), Hash WMR (32), Merkle =
sum
>> root (32), number of tx (4), prev hash (32), timestamp (4), nBits =
(4),
>> nonce1 (4), nonce2 (4), nonce3 (compactSize + variable), merkle =
branches
>> leading to header C (compactSize + 32 bit hashes)
>=20
> In order of appearance:
>=20
> First of all lets try to minimize header size. We really dont want any
> more space taken up here than we absolutely need to.
>=20
> I'm super unconvinced that we need more than one merkle tree for
> transactions. Lets just have one merkle tree who's leaves are
> transactions hashed 2 ways (without witnesses and only witnesses).
>=20
> Why duplicate the nBits here? shouldn't the PoW proof be the
> responsibility of the parent header?
>=20

Without nBits in the header, the checking of PoW become contextual and I =
think that may involve too much change. The saving of these 4 bytes, if =
it is really desired, might be done on a p2p level=20

> I have to agree with Tadge here, variable-length header fields are =
evil,
> lets avoid them.
>=20
> Why have merkle branches to yet another header? Lets just leave it as =
an
> opaque commitment header (32).
>=20
> Finally, lets not jump through hoops here - the transaction merkle =
root
> of the "old-style" (now PoW) header should simply be the hash of the =
new
> header. No coinbase transaction, just the hash of the secondary =
header.
> This saves space without giving up utility - SPV nodes are already not
> looking at the coinbase transaction, so no harm in not having one to =
give.


Regarding the header format, a big question we never came into consensus =
is the format of the hardfork. Although I designed forcenet to be a =
soft-hardfork, I am now more inclined to suggest a simple hardfork, =
given that the warning system is properly fixed (at the minimum: =
https://github.com/bitcoin/bitcoin/pull/9443 =
<https://github.com/bitcoin/bitcoin/pull/9443>)

Assuming a simple hardfork is made, the next question is whether we want =
to keep existing light wallets functioning without upgrade, cheating =
them by hiding the hash of the new header somewhere in the transaction =
merkle tree.

We also need to think about the Stratum protocol. Ideally we should not =
require firmware upgrade.

For the primary 80 bytes header, I think it will always be a fixed size. =
But for the secondary header, I=E2=80=99m not quite sure. Actually, one =
may argue that we already have a secondary header (i.e. coinbase tx), =
and it is not fixed size.

>>=20
>> 4. A totally new way to define tx weight. Tx weight is the maximum of
>> the following metrics:
>> a. SigHashSize (see the bip in point 3)
>> b. Witness serialised size * 2 * 90
>> c. Adjusted size * 90. Adjusted size =3D tx weight (BIP141) + (number =
of
>> non-OP_RETURN outputs - number of inputs) * 41 * 4
>> d. nSigOps * 50 * 90. All SigOps are equal (no witness scaling). For
>> non-segwit txs, the sigops in output scriptPubKey are not counted, =
while
>> the sigops in input scriptPubKey are counted.
>=20
> This is definitely too much. On the one hand its certainly nice to be
> able to use max() for limits, and nice to add all the reasonable =
limits
> we might want to, but on the other hand this can make things like coin
> selection super complicated - how do you take into consideration the 4
> different limits? Can we do something much, much simpler like
> max(serialized size with some input discount, nSigOps * X) (which is
> what we effectively already have in our mining code)?
>=20

The max() is at transaction level, not block level. Unless your wallet =
is full of different types of UTXOs, coin selection would not be more =
difficult than current.

Among the 4 limits, the SigHash limit is mostly a safety limit that will =
never be hit by a tx smaller than 100kB. As part of the replay attack =
fix, a linear SigHash may be optionally used. So wallets may just ignore =
this limit in coin selection

Similarly, the SigOp limit is also unlikely to be hit, unless you are =
using a very big multi-sig. Again, this is very uncommon and wallets =
primarily dealing with signal sig may safely ignore this

Finally, an important principle here is to encourage spending of UTXO, =
and limiting creation of UTXO. This might be a bit difficult to fully =
optimise for this, but I think this is necessary evil.

More discussion at: =
https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2017-January/01350=
4.html =
<https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2017-January/0135=
04.html>

>>=20
>>=20
>> 5. Smooth halving: the reward of the last 2016 blocks in a halving =
cycle
>> will be reduced by 25%, which is contributed to the first 2016 blocks =
of
>> the new halving cycle. (different parameters for forcenet) This makes =
a
>> more graceful transition but we will lose some fun around halving.
>=20
> Hum, not sure this is sufficient. Its still stair-stepping at big =
enough
> jumps that we could conceivably see super slow block times around
> halvings in the distant future. Maybe instead of 100%-75%-75%-50% (I
> believe that's what you're proposing here?),
> 100%-87.5%-75%-75%-62.5%-50% might be smoother?
>=20

Yes, but maybe we just don=E2=80=99t need this at all. This could also =
be done with a softfork using OP_CSV, just a bit ugly.

>> 6. A new coinbase tx format. BIP34 is removed. Coinbase tx may have =
more
>> than 1 input. The prevout hash of first input must be the hash of
>> previous block, and index must be 0xffffffff.
>=20
> I'm not necessarily opposed to this, but what is the justification for =
it?

This allows people to sign an input, to be part of a coinbase tx, but =
limited to a particular previous block hash. This is currently not =
possible, but through a later softfork we could introduce a new SigHash =
function that allows something between SIGHASH_ALL and =
SIGHASH_ANYONECANPAY, so people may sign its own input and another =
input, while ignoring the rests of input. (in other words: change the =
name SIGHASH_ANYONECANPAY to SIGHASH_SINGLE_INPUT, and we introduce =
SIGHASH_DUAL_INPUT. But we don=E2=80=99t need to do this in this =
hardfork)


>> The other inputs (if any)
>> must come from UTXOs with valid signatures. Spending of previous
>> coinbase outputs in a coinbase tx is exempted from the 100 block
>> maturity requirement. Therefore, miners of an earlier block may pay
>> other miners to convince them to confirm their blocks.
>=20
> Sounds good.
>=20
>> 7. Merkle sum tree: it allows generating of fraud-proof for fee and
>> weight. A special softfork (bit 15) is defined. When this softfork is
>> activated, the full node will not validate the sum tree. This is =
needed
>> because when the definition of tx weight is changed through a =
softfork
>> (e.g. a new script version introducing new sigop), olds nodes won=E2=80=
=99t know
>> the new rules and will find the sum tree invalid. Disabling the sum =
tree
>> validation won=E2=80=99t degrade the security of a full node by more =
than an
>> usual softfork, because the full node would still validate all other
>> known rules.
>>=20
>> However, it is still not possible to create fraud proof for spending =
of
>> non-existing UTXO. This requires commitment of the block height of
>> inputs, and the tx index in the block. I=E2=80=99m not quire sure how =
this could
>> be implemented because a re-org may change such info (I think =
validation
>> is easy but mining is more tricky)
>=20
> If we cant build wholesale proofs, then lets not jump through hoops =
and
> add special bits to build partial ones? Its not clear to me that it
> would be any reduction in soft-fork-ability later down the road to not
> have this - if you're changing the definition of tx weight, you're
> likely doing something like segwit where you're adding something else,
> not trying to re-adjust weights.

This is just a demo, and I agree this could be added through a softfork =
later. But even if we add this as a softfork, we have to have the =
ability to disable it through a special softfork. I think I have =
explained the reason but let me try again.

Here, when I talking about =E2=80=9Ctx weight=E2=80=9D, it=E2=80=99s the =
=E2=80=9Ctx weight=E2=80=9D defined in point 4, which covers not only =
size, but also other limits like SigOp. For a fraud proof to be really =
useful, it has to cover every type of block level limits. One feature of =
segwit is the script versioning, which allows introduction of new =
scripts. In the process, we will change the definition of SigOp: =
previous 0 SigOp scripts now carries some amount of SigOp. This is by =
itself a softfork (we did this type of softfork twice already: P2SH and =
segwit). However, if we have a merkle sum root covering the SigOp, old =
nodes won=E2=80=99t count these new SigOps, and they will fail to =
validate the sum root.

Without a backdoor to disable the sum tree validation in old nodes, the =
only way would be keeping the original sum tree untouched, while create =
another sum tree, every time we have a new script version. This is not =
acceptable at all.

But even such backdoor would not be harmful to the security of full =
nodes because they will still fully verify the tx and witness merkle =
root.

I=E2=80=99d argue that any fraud proof related commitment: sum tree, =
delayed UTXO commitment etc will require such a backdoor to disable. =
Maybe we should just remove this from here and make this a new topic. We =
could even do this as a softfork today.



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<html><head><meta http-equiv=3D"Content-Type" content=3D"text/html =
charset=3Dutf-8"></head><body style=3D"word-wrap: break-word; =
-webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" =
class=3D""><br class=3D""><div><blockquote type=3D"cite" class=3D""><div =
class=3D"">On 28 Jan 2017, at 10:32, Matt Corallo &lt;<a =
href=3D"mailto:lf-lists@mattcorallo.com" =
class=3D"">lf-lists@mattcorallo.com</a>&gt; wrote:</div><br =
class=3D"Apple-interchange-newline"><div class=3D""><span =
style=3D"font-family: Helvetica; font-size: 12px; font-style: normal; =
font-variant-caps: normal; font-weight: normal; letter-spacing: normal; =
orphans: auto; text-align: start; text-indent: 0px; text-transform: =
none; white-space: normal; widows: auto; word-spacing: 0px; =
-webkit-text-stroke-width: 0px; float: none; display: inline =
!important;" class=3D"">Looks cool, though I have a few comments =
inline.</span><br style=3D"font-family: Helvetica; font-size: 12px; =
font-style: normal; font-variant-caps: normal; font-weight: normal; =
letter-spacing: normal; orphans: auto; text-align: start; text-indent: =
0px; text-transform: none; white-space: normal; widows: auto; =
word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=3D""><br =
style=3D"font-family: Helvetica; font-size: 12px; font-style: normal; =
font-variant-caps: normal; font-weight: normal; letter-spacing: normal; =
orphans: auto; text-align: start; text-indent: 0px; text-transform: =
none; white-space: normal; widows: auto; word-spacing: 0px; =
-webkit-text-stroke-width: 0px;" class=3D""><span style=3D"font-family: =
Helvetica; font-size: 12px; font-style: normal; font-variant-caps: =
normal; font-weight: normal; letter-spacing: normal; orphans: auto; =
text-align: start; text-indent: 0px; text-transform: none; white-space: =
normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; =
float: none; display: inline !important;" class=3D"">One general note - =
it looks like you're letting complexity run away from</span><br =
style=3D"font-family: Helvetica; font-size: 12px; font-style: normal; =
font-variant-caps: normal; font-weight: normal; letter-spacing: normal; =
orphans: auto; text-align: start; text-indent: 0px; text-transform: =
none; white-space: normal; widows: auto; word-spacing: 0px; =
-webkit-text-stroke-width: 0px;" class=3D""><span style=3D"font-family: =
Helvetica; font-size: 12px; font-style: normal; font-variant-caps: =
normal; font-weight: normal; letter-spacing: normal; orphans: auto; =
text-align: start; text-indent: 0px; text-transform: none; white-space: =
normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; =
float: none; display: inline !important;" class=3D"">you a bit here. If =
the motivation for something is only weak, its</span><br =
style=3D"font-family: Helvetica; font-size: 12px; font-style: normal; =
font-variant-caps: normal; font-weight: normal; letter-spacing: normal; =
orphans: auto; text-align: start; text-indent: 0px; text-transform: =
none; white-space: normal; widows: auto; word-spacing: 0px; =
-webkit-text-stroke-width: 0px;" class=3D""><span style=3D"font-family: =
Helvetica; font-size: 12px; font-style: normal; font-variant-caps: =
normal; font-weight: normal; letter-spacing: normal; orphans: auto; =
text-align: start; text-indent: 0px; text-transform: none; white-space: =
normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; =
float: none; display: inline !important;" class=3D"">probably not worth =
doing! A hard fork is something that must be</span><br =
style=3D"font-family: Helvetica; font-size: 12px; font-style: normal; =
font-variant-caps: normal; font-weight: normal; letter-spacing: normal; =
orphans: auto; text-align: start; text-indent: 0px; text-transform: =
none; white-space: normal; widows: auto; word-spacing: 0px; =
-webkit-text-stroke-width: 0px;" class=3D""><span style=3D"font-family: =
Helvetica; font-size: 12px; font-style: normal; font-variant-caps: =
normal; font-weight: normal; letter-spacing: normal; orphans: auto; =
text-align: start; text-indent: 0px; text-transform: none; white-space: =
normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; =
float: none; display: inline !important;" class=3D"">undertaken =
cautiously because it has so much inherent risk, lets not add</span><br =
style=3D"font-family: Helvetica; font-size: 12px; font-style: normal; =
font-variant-caps: normal; font-weight: normal; letter-spacing: normal; =
orphans: auto; text-align: start; text-indent: 0px; text-transform: =
none; white-space: normal; widows: auto; word-spacing: 0px; =
-webkit-text-stroke-width: 0px;" class=3D""><span style=3D"font-family: =
Helvetica; font-size: 12px; font-style: normal; font-variant-caps: =
normal; font-weight: normal; letter-spacing: normal; orphans: auto; =
text-align: start; text-indent: 0px; text-transform: none; white-space: =
normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; =
float: none; display: inline !important;" class=3D"">tons to =
it.</span><br style=3D"font-family: Helvetica; font-size: 12px; =
font-style: normal; font-variant-caps: normal; font-weight: normal; =
letter-spacing: normal; orphans: auto; text-align: start; text-indent: =
0px; text-transform: none; white-space: normal; widows: auto; =
word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=3D""><br =
style=3D"font-family: Helvetica; font-size: 12px; font-style: normal; =
font-variant-caps: normal; font-weight: normal; letter-spacing: normal; =
orphans: auto; text-align: start; text-indent: 0px; text-transform: =
none; white-space: normal; widows: auto; word-spacing: 0px; =
-webkit-text-stroke-width: 0px;" class=3D""></div></blockquote><div><br =
class=3D""></div><div>I think the following features are necessary for a =
hardfork. The rest are optional:</div><div><br class=3D""></div><div>1. =
A secondary header</div><div>2. Anti-replay</div><div>3. SigHash limit =
for old scripts</div><div>4. New tx weight accounting</div><div><br =
class=3D""></div><div>Optional:</div><div>1. New coinbase format is nice =
but not strictly needed. But this can=E2=80=99t be reintroduced later =
with softfork due to the 100 block maturity requirement</div><div>2. =
Smooth halving: could be a less elegant softfork</div><div>3. Mekle sum =
tree: definitely could be a softfork</div><br class=3D""><blockquote =
type=3D"cite" class=3D""><div class=3D""><span style=3D"font-family: =
Helvetica; font-size: 12px; font-style: normal; font-variant-caps: =
normal; font-weight: normal; letter-spacing: normal; orphans: auto; =
text-align: start; text-indent: 0px; text-transform: none; white-space: =
normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; =
float: none; display: inline !important;" class=3D"">Matt</span><br =
style=3D"font-family: Helvetica; font-size: 12px; font-style: normal; =
font-variant-caps: normal; font-weight: normal; letter-spacing: normal; =
orphans: auto; text-align: start; text-indent: 0px; text-transform: =
none; white-space: normal; widows: auto; word-spacing: 0px; =
-webkit-text-stroke-width: 0px;" class=3D""><br style=3D"font-family: =
Helvetica; font-size: 12px; font-style: normal; font-variant-caps: =
normal; font-weight: normal; letter-spacing: normal; orphans: auto; =
text-align: start; text-indent: 0px; text-transform: none; white-space: =
normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: =
0px;" class=3D""><span style=3D"font-family: Helvetica; font-size: 12px; =
font-style: normal; font-variant-caps: normal; font-weight: normal; =
letter-spacing: normal; orphans: auto; text-align: start; text-indent: =
0px; text-transform: none; white-space: normal; widows: auto; =
word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: =
inline !important;" class=3D"">On 01/14/17 21:14, Johnson Lau via =
bitcoin-dev wrote:</span><br style=3D"font-family: Helvetica; font-size: =
12px; font-style: normal; font-variant-caps: normal; font-weight: =
normal; letter-spacing: normal; orphans: auto; text-align: start; =
text-indent: 0px; text-transform: none; white-space: normal; widows: =
auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" =
class=3D""><blockquote type=3D"cite" style=3D"font-family: Helvetica; =
font-size: 12px; font-style: normal; font-variant-caps: normal; =
font-weight: normal; letter-spacing: normal; orphans: auto; text-align: =
start; text-indent: 0px; text-transform: none; white-space: normal; =
widows: auto; word-spacing: 0px; -webkit-text-size-adjust: auto; =
-webkit-text-stroke-width: 0px;" class=3D"">I created a second version =
of forcenet with more experimental features<br class=3D"">and stopped my =
forcenet1 node.<br class=3D""><br class=3D"">1. It has a new header =
format: Height (4), BIP9 signalling field (4),<br class=3D"">hardfork =
signalling field (2), Hash TMR (32), Hash WMR (32), Merkle sum<br =
class=3D"">root (32), number of tx (4), prev hash (32), timestamp (4), =
nBits (4),<br class=3D"">nonce1 (4), nonce2 (4), nonce3 (compactSize + =
variable), merkle branches<br class=3D"">leading to header C =
(compactSize + 32 bit hashes)<br class=3D""></blockquote><br =
style=3D"font-family: Helvetica; font-size: 12px; font-style: normal; =
font-variant-caps: normal; font-weight: normal; letter-spacing: normal; =
orphans: auto; text-align: start; text-indent: 0px; text-transform: =
none; white-space: normal; widows: auto; word-spacing: 0px; =
-webkit-text-stroke-width: 0px;" class=3D""><span style=3D"font-family: =
Helvetica; font-size: 12px; font-style: normal; font-variant-caps: =
normal; font-weight: normal; letter-spacing: normal; orphans: auto; =
text-align: start; text-indent: 0px; text-transform: none; white-space: =
normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; =
float: none; display: inline !important;" class=3D"">In order of =
appearance:</span><br style=3D"font-family: Helvetica; font-size: 12px; =
font-style: normal; font-variant-caps: normal; font-weight: normal; =
letter-spacing: normal; orphans: auto; text-align: start; text-indent: =
0px; text-transform: none; white-space: normal; widows: auto; =
word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=3D""><br =
style=3D"font-family: Helvetica; font-size: 12px; font-style: normal; =
font-variant-caps: normal; font-weight: normal; letter-spacing: normal; =
orphans: auto; text-align: start; text-indent: 0px; text-transform: =
none; white-space: normal; widows: auto; word-spacing: 0px; =
-webkit-text-stroke-width: 0px;" class=3D""><span style=3D"font-family: =
Helvetica; font-size: 12px; font-style: normal; font-variant-caps: =
normal; font-weight: normal; letter-spacing: normal; orphans: auto; =
text-align: start; text-indent: 0px; text-transform: none; white-space: =
normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; =
float: none; display: inline !important;" class=3D"">First of all lets =
try to minimize header size. We really dont want any</span><br =
style=3D"font-family: Helvetica; font-size: 12px; font-style: normal; =
font-variant-caps: normal; font-weight: normal; letter-spacing: normal; =
orphans: auto; text-align: start; text-indent: 0px; text-transform: =
none; white-space: normal; widows: auto; word-spacing: 0px; =
-webkit-text-stroke-width: 0px;" class=3D""><span style=3D"font-family: =
Helvetica; font-size: 12px; font-style: normal; font-variant-caps: =
normal; font-weight: normal; letter-spacing: normal; orphans: auto; =
text-align: start; text-indent: 0px; text-transform: none; white-space: =
normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; =
float: none; display: inline !important;" class=3D"">more space taken up =
here than we absolutely need to.</span><br style=3D"font-family: =
Helvetica; font-size: 12px; font-style: normal; font-variant-caps: =
normal; font-weight: normal; letter-spacing: normal; orphans: auto; =
text-align: start; text-indent: 0px; text-transform: none; white-space: =
normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: =
0px;" class=3D""><br style=3D"font-family: Helvetica; font-size: 12px; =
font-style: normal; font-variant-caps: normal; font-weight: normal; =
letter-spacing: normal; orphans: auto; text-align: start; text-indent: =
0px; text-transform: none; white-space: normal; widows: auto; =
word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=3D""><span =
style=3D"font-family: Helvetica; font-size: 12px; font-style: normal; =
font-variant-caps: normal; font-weight: normal; letter-spacing: normal; =
orphans: auto; text-align: start; text-indent: 0px; text-transform: =
none; white-space: normal; widows: auto; word-spacing: 0px; =
-webkit-text-stroke-width: 0px; float: none; display: inline =
!important;" class=3D"">I'm super unconvinced that we need more than one =
merkle tree for</span><br style=3D"font-family: Helvetica; font-size: =
12px; font-style: normal; font-variant-caps: normal; font-weight: =
normal; letter-spacing: normal; orphans: auto; text-align: start; =
text-indent: 0px; text-transform: none; white-space: normal; widows: =
auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=3D""><span=
 style=3D"font-family: Helvetica; font-size: 12px; font-style: normal; =
font-variant-caps: normal; font-weight: normal; letter-spacing: normal; =
orphans: auto; text-align: start; text-indent: 0px; text-transform: =
none; white-space: normal; widows: auto; word-spacing: 0px; =
-webkit-text-stroke-width: 0px; float: none; display: inline =
!important;" class=3D"">transactions. Lets just have one merkle tree =
who's leaves are</span><br style=3D"font-family: Helvetica; font-size: =
12px; font-style: normal; font-variant-caps: normal; font-weight: =
normal; letter-spacing: normal; orphans: auto; text-align: start; =
text-indent: 0px; text-transform: none; white-space: normal; widows: =
auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=3D""><span=
 style=3D"font-family: Helvetica; font-size: 12px; font-style: normal; =
font-variant-caps: normal; font-weight: normal; letter-spacing: normal; =
orphans: auto; text-align: start; text-indent: 0px; text-transform: =
none; white-space: normal; widows: auto; word-spacing: 0px; =
-webkit-text-stroke-width: 0px; float: none; display: inline =
!important;" class=3D"">transactions hashed 2 ways (without witnesses =
and only witnesses).</span><br style=3D"font-family: Helvetica; =
font-size: 12px; font-style: normal; font-variant-caps: normal; =
font-weight: normal; letter-spacing: normal; orphans: auto; text-align: =
start; text-indent: 0px; text-transform: none; white-space: normal; =
widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" =
class=3D""><br style=3D"font-family: Helvetica; font-size: 12px; =
font-style: normal; font-variant-caps: normal; font-weight: normal; =
letter-spacing: normal; orphans: auto; text-align: start; text-indent: =
0px; text-transform: none; white-space: normal; widows: auto; =
word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=3D""><span =
style=3D"font-family: Helvetica; font-size: 12px; font-style: normal; =
font-variant-caps: normal; font-weight: normal; letter-spacing: normal; =
orphans: auto; text-align: start; text-indent: 0px; text-transform: =
none; white-space: normal; widows: auto; word-spacing: 0px; =
-webkit-text-stroke-width: 0px; float: none; display: inline =
!important;" class=3D"">Why duplicate the nBits here? shouldn't the PoW =
proof be the</span><br style=3D"font-family: Helvetica; font-size: 12px; =
font-style: normal; font-variant-caps: normal; font-weight: normal; =
letter-spacing: normal; orphans: auto; text-align: start; text-indent: =
0px; text-transform: none; white-space: normal; widows: auto; =
word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=3D""><span =
style=3D"font-family: Helvetica; font-size: 12px; font-style: normal; =
font-variant-caps: normal; font-weight: normal; letter-spacing: normal; =
orphans: auto; text-align: start; text-indent: 0px; text-transform: =
none; white-space: normal; widows: auto; word-spacing: 0px; =
-webkit-text-stroke-width: 0px; float: none; display: inline =
!important;" class=3D"">responsibility of the parent header?</span><br =
style=3D"font-family: Helvetica; font-size: 12px; font-style: normal; =
font-variant-caps: normal; font-weight: normal; letter-spacing: normal; =
orphans: auto; text-align: start; text-indent: 0px; text-transform: =
none; white-space: normal; widows: auto; word-spacing: 0px; =
-webkit-text-stroke-width: 0px;" class=3D""><br style=3D"font-family: =
Helvetica; font-size: 12px; font-style: normal; font-variant-caps: =
normal; font-weight: normal; letter-spacing: normal; orphans: auto; =
text-align: start; text-indent: 0px; text-transform: none; white-space: =
normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: =
0px;" class=3D""></div></blockquote><div><br class=3D""></div><div>Without=
 nBits in the header, the checking of PoW become contextual and I think =
that may involve too much change. The saving of these 4 bytes, if it is =
really desired, might be done on a p2p level&nbsp;</div><br =
class=3D""><blockquote type=3D"cite" class=3D""><div class=3D""><span =
style=3D"font-family: Helvetica; font-size: 12px; font-style: normal; =
font-variant-caps: normal; font-weight: normal; letter-spacing: normal; =
orphans: auto; text-align: start; text-indent: 0px; text-transform: =
none; white-space: normal; widows: auto; word-spacing: 0px; =
-webkit-text-stroke-width: 0px; float: none; display: inline =
!important;" class=3D"">I have to agree with Tadge here, variable-length =
header fields are evil,</span><br style=3D"font-family: Helvetica; =
font-size: 12px; font-style: normal; font-variant-caps: normal; =
font-weight: normal; letter-spacing: normal; orphans: auto; text-align: =
start; text-indent: 0px; text-transform: none; white-space: normal; =
widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" =
class=3D""><span style=3D"font-family: Helvetica; font-size: 12px; =
font-style: normal; font-variant-caps: normal; font-weight: normal; =
letter-spacing: normal; orphans: auto; text-align: start; text-indent: =
0px; text-transform: none; white-space: normal; widows: auto; =
word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: =
inline !important;" class=3D"">lets avoid them.</span><br =
style=3D"font-family: Helvetica; font-size: 12px; font-style: normal; =
font-variant-caps: normal; font-weight: normal; letter-spacing: normal; =
orphans: auto; text-align: start; text-indent: 0px; text-transform: =
none; white-space: normal; widows: auto; word-spacing: 0px; =
-webkit-text-stroke-width: 0px;" class=3D""><br style=3D"font-family: =
Helvetica; font-size: 12px; font-style: normal; font-variant-caps: =
normal; font-weight: normal; letter-spacing: normal; orphans: auto; =
text-align: start; text-indent: 0px; text-transform: none; white-space: =
normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: =
0px;" class=3D""><span style=3D"font-family: Helvetica; font-size: 12px; =
font-style: normal; font-variant-caps: normal; font-weight: normal; =
letter-spacing: normal; orphans: auto; text-align: start; text-indent: =
0px; text-transform: none; white-space: normal; widows: auto; =
word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: =
inline !important;" class=3D"">Why have merkle branches to yet another =
header? Lets just leave it as an</span><br style=3D"font-family: =
Helvetica; font-size: 12px; font-style: normal; font-variant-caps: =
normal; font-weight: normal; letter-spacing: normal; orphans: auto; =
text-align: start; text-indent: 0px; text-transform: none; white-space: =
normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: =
0px;" class=3D""><span style=3D"font-family: Helvetica; font-size: 12px; =
font-style: normal; font-variant-caps: normal; font-weight: normal; =
letter-spacing: normal; orphans: auto; text-align: start; text-indent: =
0px; text-transform: none; white-space: normal; widows: auto; =
word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: =
inline !important;" class=3D"">opaque commitment header (32).</span><br =
style=3D"font-family: Helvetica; font-size: 12px; font-style: normal; =
font-variant-caps: normal; font-weight: normal; letter-spacing: normal; =
orphans: auto; text-align: start; text-indent: 0px; text-transform: =
none; white-space: normal; widows: auto; word-spacing: 0px; =
-webkit-text-stroke-width: 0px;" class=3D""><br style=3D"font-family: =
Helvetica; font-size: 12px; font-style: normal; font-variant-caps: =
normal; font-weight: normal; letter-spacing: normal; orphans: auto; =
text-align: start; text-indent: 0px; text-transform: none; white-space: =
normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: =
0px;" class=3D""><span style=3D"font-family: Helvetica; font-size: 12px; =
font-style: normal; font-variant-caps: normal; font-weight: normal; =
letter-spacing: normal; orphans: auto; text-align: start; text-indent: =
0px; text-transform: none; white-space: normal; widows: auto; =
word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: =
inline !important;" class=3D"">Finally, lets not jump through hoops here =
- the transaction merkle root</span><br style=3D"font-family: Helvetica; =
font-size: 12px; font-style: normal; font-variant-caps: normal; =
font-weight: normal; letter-spacing: normal; orphans: auto; text-align: =
start; text-indent: 0px; text-transform: none; white-space: normal; =
widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" =
class=3D""><span style=3D"font-family: Helvetica; font-size: 12px; =
font-style: normal; font-variant-caps: normal; font-weight: normal; =
letter-spacing: normal; orphans: auto; text-align: start; text-indent: =
0px; text-transform: none; white-space: normal; widows: auto; =
word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: =
inline !important;" class=3D"">of the "old-style" (now PoW) header =
should simply be the hash of the new</span><br style=3D"font-family: =
Helvetica; font-size: 12px; font-style: normal; font-variant-caps: =
normal; font-weight: normal; letter-spacing: normal; orphans: auto; =
text-align: start; text-indent: 0px; text-transform: none; white-space: =
normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: =
0px;" class=3D""><span style=3D"font-family: Helvetica; font-size: 12px; =
font-style: normal; font-variant-caps: normal; font-weight: normal; =
letter-spacing: normal; orphans: auto; text-align: start; text-indent: =
0px; text-transform: none; white-space: normal; widows: auto; =
word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: =
inline !important;" class=3D"">header. No coinbase transaction, just the =
hash of the secondary header.</span><br style=3D"font-family: Helvetica; =
font-size: 12px; font-style: normal; font-variant-caps: normal; =
font-weight: normal; letter-spacing: normal; orphans: auto; text-align: =
start; text-indent: 0px; text-transform: none; white-space: normal; =
widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" =
class=3D""><span style=3D"font-family: Helvetica; font-size: 12px; =
font-style: normal; font-variant-caps: normal; font-weight: normal; =
letter-spacing: normal; orphans: auto; text-align: start; text-indent: =
0px; text-transform: none; white-space: normal; widows: auto; =
word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: =
inline !important;" class=3D"">This saves space without giving up =
utility - SPV nodes are already not</span><br style=3D"font-family: =
Helvetica; font-size: 12px; font-style: normal; font-variant-caps: =
normal; font-weight: normal; letter-spacing: normal; orphans: auto; =
text-align: start; text-indent: 0px; text-transform: none; white-space: =
normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: =
0px;" class=3D""><span style=3D"font-family: Helvetica; font-size: 12px; =
font-style: normal; font-variant-caps: normal; font-weight: normal; =
letter-spacing: normal; orphans: auto; text-align: start; text-indent: =
0px; text-transform: none; white-space: normal; widows: auto; =
word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: =
inline !important;" class=3D"">looking at the coinbase transaction, so =
no harm in not having one to give.</span><br style=3D"font-family: =
Helvetica; font-size: 12px; font-style: normal; font-variant-caps: =
normal; font-weight: normal; letter-spacing: normal; orphans: auto; =
text-align: start; text-indent: 0px; text-transform: none; white-space: =
normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: =
0px;" class=3D""></div></blockquote><div><br class=3D""></div><div><br =
class=3D""></div><div>Regarding the header format, a big question we =
never came into consensus is the format of the hardfork. Although I =
designed forcenet to be a soft-hardfork, I am now more inclined to =
suggest a simple hardfork, given that the warning system is properly =
fixed (at the minimum:&nbsp;<a =
href=3D"https://github.com/bitcoin/bitcoin/pull/9443" =
class=3D"">https://github.com/bitcoin/bitcoin/pull/9443</a>)</div><div><br=
 class=3D""></div><div>Assuming a simple hardfork is made, the next =
question is whether we want to keep existing light wallets functioning =
without upgrade, cheating them by hiding the hash of the new header =
somewhere in the transaction merkle tree.</div><div><br =
class=3D""></div><div>We also need to think about the Stratum protocol. =
Ideally we should not require firmware upgrade.</div><div><br =
class=3D""></div><div>For the primary 80 bytes header, I think it will =
always be a fixed size. But for the secondary header, I=E2=80=99m not =
quite sure. Actually, one may argue that we already have a secondary =
header (i.e. coinbase tx), and it is not fixed size.</div><br =
class=3D""><blockquote type=3D"cite" class=3D""><div =
class=3D""><blockquote type=3D"cite" style=3D"font-family: Helvetica; =
font-size: 12px; font-style: normal; font-variant-caps: normal; =
font-weight: normal; letter-spacing: normal; orphans: auto; text-align: =
start; text-indent: 0px; text-transform: none; white-space: normal; =
widows: auto; word-spacing: 0px; -webkit-text-size-adjust: auto; =
-webkit-text-stroke-width: 0px;" class=3D""><br class=3D"">4. A totally =
new way to define tx weight. Tx weight is the maximum of<br class=3D"">the=
 following metrics:<br class=3D"">a. SigHashSize (see the bip in point =
3)<br class=3D"">b. Witness serialised size * 2 * 90<br class=3D"">c. =
Adjusted size * 90. Adjusted size =3D tx weight (BIP141) + (number of<br =
class=3D"">non-OP_RETURN outputs - number of inputs) * 41 * 4<br =
class=3D"">d. nSigOps * 50 * 90. All SigOps are equal (no witness =
scaling). For<br class=3D"">non-segwit txs, the sigops in output =
scriptPubKey are not counted, while<br class=3D"">the sigops in input =
scriptPubKey are counted.<br class=3D""></blockquote><br =
style=3D"font-family: Helvetica; font-size: 12px; font-style: normal; =
font-variant-caps: normal; font-weight: normal; letter-spacing: normal; =
orphans: auto; text-align: start; text-indent: 0px; text-transform: =
none; white-space: normal; widows: auto; word-spacing: 0px; =
-webkit-text-stroke-width: 0px;" class=3D""><span style=3D"font-family: =
Helvetica; font-size: 12px; font-style: normal; font-variant-caps: =
normal; font-weight: normal; letter-spacing: normal; orphans: auto; =
text-align: start; text-indent: 0px; text-transform: none; white-space: =
normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; =
float: none; display: inline !important;" class=3D"">This is definitely =
too much. On the one hand its certainly nice to be</span><br =
style=3D"font-family: Helvetica; font-size: 12px; font-style: normal; =
font-variant-caps: normal; font-weight: normal; letter-spacing: normal; =
orphans: auto; text-align: start; text-indent: 0px; text-transform: =
none; white-space: normal; widows: auto; word-spacing: 0px; =
-webkit-text-stroke-width: 0px;" class=3D""><span style=3D"font-family: =
Helvetica; font-size: 12px; font-style: normal; font-variant-caps: =
normal; font-weight: normal; letter-spacing: normal; orphans: auto; =
text-align: start; text-indent: 0px; text-transform: none; white-space: =
normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; =
float: none; display: inline !important;" class=3D"">able to use max() =
for limits, and nice to add all the reasonable limits</span><br =
style=3D"font-family: Helvetica; font-size: 12px; font-style: normal; =
font-variant-caps: normal; font-weight: normal; letter-spacing: normal; =
orphans: auto; text-align: start; text-indent: 0px; text-transform: =
none; white-space: normal; widows: auto; word-spacing: 0px; =
-webkit-text-stroke-width: 0px;" class=3D""><span style=3D"font-family: =
Helvetica; font-size: 12px; font-style: normal; font-variant-caps: =
normal; font-weight: normal; letter-spacing: normal; orphans: auto; =
text-align: start; text-indent: 0px; text-transform: none; white-space: =
normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; =
float: none; display: inline !important;" class=3D"">we might want to, =
but on the other hand this can make things like coin</span><br =
style=3D"font-family: Helvetica; font-size: 12px; font-style: normal; =
font-variant-caps: normal; font-weight: normal; letter-spacing: normal; =
orphans: auto; text-align: start; text-indent: 0px; text-transform: =
none; white-space: normal; widows: auto; word-spacing: 0px; =
-webkit-text-stroke-width: 0px;" class=3D""><span style=3D"font-family: =
Helvetica; font-size: 12px; font-style: normal; font-variant-caps: =
normal; font-weight: normal; letter-spacing: normal; orphans: auto; =
text-align: start; text-indent: 0px; text-transform: none; white-space: =
normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; =
float: none; display: inline !important;" class=3D"">selection super =
complicated - how do you take into consideration the 4</span><br =
style=3D"font-family: Helvetica; font-size: 12px; font-style: normal; =
font-variant-caps: normal; font-weight: normal; letter-spacing: normal; =
orphans: auto; text-align: start; text-indent: 0px; text-transform: =
none; white-space: normal; widows: auto; word-spacing: 0px; =
-webkit-text-stroke-width: 0px;" class=3D""><span style=3D"font-family: =
Helvetica; font-size: 12px; font-style: normal; font-variant-caps: =
normal; font-weight: normal; letter-spacing: normal; orphans: auto; =
text-align: start; text-indent: 0px; text-transform: none; white-space: =
normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; =
float: none; display: inline !important;" class=3D"">different limits? =
Can we do something much, much simpler like</span><br =
style=3D"font-family: Helvetica; font-size: 12px; font-style: normal; =
font-variant-caps: normal; font-weight: normal; letter-spacing: normal; =
orphans: auto; text-align: start; text-indent: 0px; text-transform: =
none; white-space: normal; widows: auto; word-spacing: 0px; =
-webkit-text-stroke-width: 0px;" class=3D""><span style=3D"font-family: =
Helvetica; font-size: 12px; font-style: normal; font-variant-caps: =
normal; font-weight: normal; letter-spacing: normal; orphans: auto; =
text-align: start; text-indent: 0px; text-transform: none; white-space: =
normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; =
float: none; display: inline !important;" class=3D"">max(serialized size =
with some input discount, nSigOps * X) (which is</span><br =
style=3D"font-family: Helvetica; font-size: 12px; font-style: normal; =
font-variant-caps: normal; font-weight: normal; letter-spacing: normal; =
orphans: auto; text-align: start; text-indent: 0px; text-transform: =
none; white-space: normal; widows: auto; word-spacing: 0px; =
-webkit-text-stroke-width: 0px;" class=3D""><span style=3D"font-family: =
Helvetica; font-size: 12px; font-style: normal; font-variant-caps: =
normal; font-weight: normal; letter-spacing: normal; orphans: auto; =
text-align: start; text-indent: 0px; text-transform: none; white-space: =
normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; =
float: none; display: inline !important;" class=3D"">what we effectively =
already have in our mining code)?</span><br style=3D"font-family: =
Helvetica; font-size: 12px; font-style: normal; font-variant-caps: =
normal; font-weight: normal; letter-spacing: normal; orphans: auto; =
text-align: start; text-indent: 0px; text-transform: none; white-space: =
normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: =
0px;" class=3D""><br style=3D"font-family: Helvetica; font-size: 12px; =
font-style: normal; font-variant-caps: normal; font-weight: normal; =
letter-spacing: normal; orphans: auto; text-align: start; text-indent: =
0px; text-transform: none; white-space: normal; widows: auto; =
word-spacing: 0px; -webkit-text-stroke-width: 0px;" =
class=3D""></div></blockquote><div><br class=3D""></div><div>The max() =
is at transaction level, not block level. Unless your wallet is full of =
different types of UTXOs, coin selection would not be more difficult =
than current.</div><div><br class=3D""></div><div>Among the 4 limits, =
the SigHash limit is mostly a safety limit that will never be hit by a =
tx smaller than 100kB. As part of the replay attack fix, a linear =
SigHash may be optionally used. So wallets may just ignore this limit in =
coin selection</div><div><br class=3D""></div><div>Similarly, the SigOp =
limit is also unlikely to be hit, unless you are using a very big =
multi-sig. Again, this is very uncommon and wallets primarily dealing =
with signal sig may safely ignore this</div><div><br =
class=3D""></div><div>Finally, an important principle here is to =
encourage spending of UTXO, and limiting creation of UTXO. This might be =
a bit difficult to fully optimise for this, but I think this is =
necessary evil.</div><div><br class=3D""></div><div>More discussion =
at:&nbsp;<a =
href=3D"https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2017-Janua=
ry/013504.html" =
class=3D"">https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2017-Ja=
nuary/013504.html</a></div><div><br class=3D""></div><blockquote =
type=3D"cite" class=3D""><div class=3D""><blockquote type=3D"cite" =
style=3D"font-family: Helvetica; font-size: 12px; font-style: normal; =
font-variant-caps: normal; font-weight: normal; letter-spacing: normal; =
orphans: auto; text-align: start; text-indent: 0px; text-transform: =
none; white-space: normal; widows: auto; word-spacing: 0px; =
-webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px;" =
class=3D""><br class=3D""><br class=3D"">5. Smooth halving: the reward =
of the last 2016 blocks in a halving cycle<br class=3D"">will be reduced =
by 25%, which is contributed to the first 2016 blocks of<br class=3D"">the=
 new halving cycle. (different parameters for forcenet) This makes a<br =
class=3D"">more graceful transition but we will lose some fun around =
halving.<br class=3D""></blockquote><br style=3D"font-family: Helvetica; =
font-size: 12px; font-style: normal; font-variant-caps: normal; =
font-weight: normal; letter-spacing: normal; orphans: auto; text-align: =
start; text-indent: 0px; text-transform: none; white-space: normal; =
widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" =
class=3D""><span style=3D"font-family: Helvetica; font-size: 12px; =
font-style: normal; font-variant-caps: normal; font-weight: normal; =
letter-spacing: normal; orphans: auto; text-align: start; text-indent: =
0px; text-transform: none; white-space: normal; widows: auto; =
word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: =
inline !important;" class=3D"">Hum, not sure this is sufficient. Its =
still stair-stepping at big enough</span><br style=3D"font-family: =
Helvetica; font-size: 12px; font-style: normal; font-variant-caps: =
normal; font-weight: normal; letter-spacing: normal; orphans: auto; =
text-align: start; text-indent: 0px; text-transform: none; white-space: =
normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: =
0px;" class=3D""><span style=3D"font-family: Helvetica; font-size: 12px; =
font-style: normal; font-variant-caps: normal; font-weight: normal; =
letter-spacing: normal; orphans: auto; text-align: start; text-indent: =
0px; text-transform: none; white-space: normal; widows: auto; =
word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: =
inline !important;" class=3D"">jumps that we could conceivably see super =
slow block times around</span><br style=3D"font-family: Helvetica; =
font-size: 12px; font-style: normal; font-variant-caps: normal; =
font-weight: normal; letter-spacing: normal; orphans: auto; text-align: =
start; text-indent: 0px; text-transform: none; white-space: normal; =
widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" =
class=3D""><span style=3D"font-family: Helvetica; font-size: 12px; =
font-style: normal; font-variant-caps: normal; font-weight: normal; =
letter-spacing: normal; orphans: auto; text-align: start; text-indent: =
0px; text-transform: none; white-space: normal; widows: auto; =
word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: =
inline !important;" class=3D"">halvings in the distant future. Maybe =
instead of 100%-75%-75%-50% (I</span><br style=3D"font-family: =
Helvetica; font-size: 12px; font-style: normal; font-variant-caps: =
normal; font-weight: normal; letter-spacing: normal; orphans: auto; =
text-align: start; text-indent: 0px; text-transform: none; white-space: =
normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: =
0px;" class=3D""><span style=3D"font-family: Helvetica; font-size: 12px; =
font-style: normal; font-variant-caps: normal; font-weight: normal; =
letter-spacing: normal; orphans: auto; text-align: start; text-indent: =
0px; text-transform: none; white-space: normal; widows: auto; =
word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: =
inline !important;" class=3D"">believe that's what you're proposing =
here?),</span><br style=3D"font-family: Helvetica; font-size: 12px; =
font-style: normal; font-variant-caps: normal; font-weight: normal; =
letter-spacing: normal; orphans: auto; text-align: start; text-indent: =
0px; text-transform: none; white-space: normal; widows: auto; =
word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=3D""><span =
style=3D"font-family: Helvetica; font-size: 12px; font-style: normal; =
font-variant-caps: normal; font-weight: normal; letter-spacing: normal; =
orphans: auto; text-align: start; text-indent: 0px; text-transform: =
none; white-space: normal; widows: auto; word-spacing: 0px; =
-webkit-text-stroke-width: 0px; float: none; display: inline =
!important;" class=3D"">100%-87.5%-75%-75%-62.5%-50% might be =
smoother?</span><br style=3D"font-family: Helvetica; font-size: 12px; =
font-style: normal; font-variant-caps: normal; font-weight: normal; =
letter-spacing: normal; orphans: auto; text-align: start; text-indent: =
0px; text-transform: none; white-space: normal; widows: auto; =
word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=3D""><br =
style=3D"font-family: Helvetica; font-size: 12px; font-style: normal; =
font-variant-caps: normal; font-weight: normal; letter-spacing: normal; =
orphans: auto; text-align: start; text-indent: 0px; text-transform: =
none; white-space: normal; widows: auto; word-spacing: 0px; =
-webkit-text-stroke-width: 0px;" class=3D""></div></blockquote><div><br =
class=3D""></div><div>Yes, but maybe we just don=E2=80=99t need this at =
all. This could also be done with a softfork using OP_CSV, just a bit =
ugly.</div><div><br class=3D""></div><blockquote type=3D"cite" =
class=3D""><div class=3D""><blockquote type=3D"cite" style=3D"font-family:=
 Helvetica; font-size: 12px; font-style: normal; font-variant-caps: =
normal; font-weight: normal; letter-spacing: normal; orphans: auto; =
text-align: start; text-indent: 0px; text-transform: none; white-space: =
normal; widows: auto; word-spacing: 0px; -webkit-text-size-adjust: auto; =
-webkit-text-stroke-width: 0px;" class=3D"">6. A new coinbase tx format. =
BIP34 is removed. Coinbase tx may have more<br class=3D"">than 1 input. =
The prevout hash of first input must be the hash of<br class=3D"">previous=
 block, and index must be 0xffffffff.<br class=3D""></blockquote><br =
style=3D"font-family: Helvetica; font-size: 12px; font-style: normal; =
font-variant-caps: normal; font-weight: normal; letter-spacing: normal; =
orphans: auto; text-align: start; text-indent: 0px; text-transform: =
none; white-space: normal; widows: auto; word-spacing: 0px; =
-webkit-text-stroke-width: 0px;" class=3D""><span style=3D"font-family: =
Helvetica; font-size: 12px; font-style: normal; font-variant-caps: =
normal; font-weight: normal; letter-spacing: normal; orphans: auto; =
text-align: start; text-indent: 0px; text-transform: none; white-space: =
normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; =
float: none; display: inline !important;" class=3D"">I'm not necessarily =
opposed to this, but what is the justification for it?</span><br =
style=3D"font-family: Helvetica; font-size: 12px; font-style: normal; =
font-variant-caps: normal; font-weight: normal; letter-spacing: normal; =
orphans: auto; text-align: start; text-indent: 0px; text-transform: =
none; white-space: normal; widows: auto; word-spacing: 0px; =
-webkit-text-stroke-width: 0px;" class=3D""></div></blockquote><div><br =
class=3D""></div><div>This allows people to sign an input, to be part of =
a coinbase tx, but limited to a particular previous block hash. This is =
currently not possible, but through a later softfork we could introduce =
a new SigHash function that allows something between SIGHASH_ALL and =
SIGHASH_ANYONECANPAY, so people may sign its own input and another =
input, while ignoring the rests of input. (in other words: change the =
name SIGHASH_ANYONECANPAY to SIGHASH_SINGLE_INPUT, and we introduce =
SIGHASH_DUAL_INPUT. But we don=E2=80=99t need to do this in this =
hardfork)</div><div><br class=3D""></div><br class=3D""><blockquote =
type=3D"cite" class=3D""><div class=3D""><blockquote type=3D"cite" =
style=3D"font-family: Helvetica; font-size: 12px; font-style: normal; =
font-variant-caps: normal; font-weight: normal; letter-spacing: normal; =
orphans: auto; text-align: start; text-indent: 0px; text-transform: =
none; white-space: normal; widows: auto; word-spacing: 0px; =
-webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px;" =
class=3D"">The other inputs (if any)<br class=3D"">must come from UTXOs =
with valid signatures. Spending of previous<br class=3D"">coinbase =
outputs in a coinbase tx is exempted from the 100 block<br =
class=3D"">maturity requirement. Therefore, miners of an earlier block =
may pay<br class=3D"">other miners to convince them to confirm their =
blocks.<br class=3D""></blockquote><br style=3D"font-family: Helvetica; =
font-size: 12px; font-style: normal; font-variant-caps: normal; =
font-weight: normal; letter-spacing: normal; orphans: auto; text-align: =
start; text-indent: 0px; text-transform: none; white-space: normal; =
widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" =
class=3D""><span style=3D"font-family: Helvetica; font-size: 12px; =
font-style: normal; font-variant-caps: normal; font-weight: normal; =
letter-spacing: normal; orphans: auto; text-align: start; text-indent: =
0px; text-transform: none; white-space: normal; widows: auto; =
word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: =
inline !important;" class=3D"">Sounds good.</span><br =
style=3D"font-family: Helvetica; font-size: 12px; font-style: normal; =
font-variant-caps: normal; font-weight: normal; letter-spacing: normal; =
orphans: auto; text-align: start; text-indent: 0px; text-transform: =
none; white-space: normal; widows: auto; word-spacing: 0px; =
-webkit-text-stroke-width: 0px;" class=3D""><br style=3D"font-family: =
Helvetica; font-size: 12px; font-style: normal; font-variant-caps: =
normal; font-weight: normal; letter-spacing: normal; orphans: auto; =
text-align: start; text-indent: 0px; text-transform: none; white-space: =
normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: =
0px;" class=3D""><blockquote type=3D"cite" style=3D"font-family: =
Helvetica; font-size: 12px; font-style: normal; font-variant-caps: =
normal; font-weight: normal; letter-spacing: normal; orphans: auto; =
text-align: start; text-indent: 0px; text-transform: none; white-space: =
normal; widows: auto; word-spacing: 0px; -webkit-text-size-adjust: auto; =
-webkit-text-stroke-width: 0px;" class=3D"">7. Merkle sum tree: it =
allows generating of fraud-proof for fee and<br class=3D"">weight. A =
special softfork (bit 15) is defined. When this softfork is<br =
class=3D"">activated, the full node will not validate the sum tree. This =
is needed<br class=3D"">because when the definition of tx weight is =
changed through a softfork<br class=3D"">(e.g. a new script version =
introducing new sigop), olds nodes won=E2=80=99t know<br class=3D"">the =
new rules and will find the sum tree invalid. Disabling the sum tree<br =
class=3D"">validation won=E2=80=99t degrade the security of a full node =
by more than an<br class=3D"">usual softfork, because the full node =
would still validate all other<br class=3D"">known rules.<br =
class=3D""><br class=3D"">However, it is still not possible to create =
fraud proof for spending of<br class=3D"">non-existing UTXO. This =
requires commitment of the block height of<br class=3D"">inputs, and the =
tx index in the block. I=E2=80=99m not quire sure how this could<br =
class=3D"">be implemented because a re-org may change such info (I think =
validation<br class=3D"">is easy but mining is more tricky)<br =
class=3D""></blockquote><br style=3D"font-family: Helvetica; font-size: =
12px; font-style: normal; font-variant-caps: normal; font-weight: =
normal; letter-spacing: normal; orphans: auto; text-align: start; =
text-indent: 0px; text-transform: none; white-space: normal; widows: =
auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=3D""><span=
 style=3D"font-family: Helvetica; font-size: 12px; font-style: normal; =
font-variant-caps: normal; font-weight: normal; letter-spacing: normal; =
orphans: auto; text-align: start; text-indent: 0px; text-transform: =
none; white-space: normal; widows: auto; word-spacing: 0px; =
-webkit-text-stroke-width: 0px; float: none; display: inline =
!important;" class=3D"">If we cant build wholesale proofs, then lets not =
jump through hoops and</span><br style=3D"font-family: Helvetica; =
font-size: 12px; font-style: normal; font-variant-caps: normal; =
font-weight: normal; letter-spacing: normal; orphans: auto; text-align: =
start; text-indent: 0px; text-transform: none; white-space: normal; =
widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" =
class=3D""><span style=3D"font-family: Helvetica; font-size: 12px; =
font-style: normal; font-variant-caps: normal; font-weight: normal; =
letter-spacing: normal; orphans: auto; text-align: start; text-indent: =
0px; text-transform: none; white-space: normal; widows: auto; =
word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: =
inline !important;" class=3D"">add special bits to build partial ones? =
Its not clear to me that it</span><br style=3D"font-family: Helvetica; =
font-size: 12px; font-style: normal; font-variant-caps: normal; =
font-weight: normal; letter-spacing: normal; orphans: auto; text-align: =
start; text-indent: 0px; text-transform: none; white-space: normal; =
widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" =
class=3D""><span style=3D"font-family: Helvetica; font-size: 12px; =
font-style: normal; font-variant-caps: normal; font-weight: normal; =
letter-spacing: normal; orphans: auto; text-align: start; text-indent: =
0px; text-transform: none; white-space: normal; widows: auto; =
word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: =
inline !important;" class=3D"">would be any reduction in =
soft-fork-ability later down the road to not</span><br =
style=3D"font-family: Helvetica; font-size: 12px; font-style: normal; =
font-variant-caps: normal; font-weight: normal; letter-spacing: normal; =
orphans: auto; text-align: start; text-indent: 0px; text-transform: =
none; white-space: normal; widows: auto; word-spacing: 0px; =
-webkit-text-stroke-width: 0px;" class=3D""><span style=3D"font-family: =
Helvetica; font-size: 12px; font-style: normal; font-variant-caps: =
normal; font-weight: normal; letter-spacing: normal; orphans: auto; =
text-align: start; text-indent: 0px; text-transform: none; white-space: =
normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; =
float: none; display: inline !important;" class=3D"">have this - if =
you're changing the definition of tx weight, you're</span><br =
style=3D"font-family: Helvetica; font-size: 12px; font-style: normal; =
font-variant-caps: normal; font-weight: normal; letter-spacing: normal; =
orphans: auto; text-align: start; text-indent: 0px; text-transform: =
none; white-space: normal; widows: auto; word-spacing: 0px; =
-webkit-text-stroke-width: 0px;" class=3D""><span style=3D"font-family: =
Helvetica; font-size: 12px; font-style: normal; font-variant-caps: =
normal; font-weight: normal; letter-spacing: normal; orphans: auto; =
text-align: start; text-indent: 0px; text-transform: none; white-space: =
normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; =
float: none; display: inline !important;" class=3D"">likely doing =
something like segwit where you're adding something else,</span><br =
style=3D"font-family: Helvetica; font-size: 12px; font-style: normal; =
font-variant-caps: normal; font-weight: normal; letter-spacing: normal; =
orphans: auto; text-align: start; text-indent: 0px; text-transform: =
none; white-space: normal; widows: auto; word-spacing: 0px; =
-webkit-text-stroke-width: 0px;" class=3D""><span style=3D"font-family: =
Helvetica; font-size: 12px; font-style: normal; font-variant-caps: =
normal; font-weight: normal; letter-spacing: normal; orphans: auto; =
text-align: start; text-indent: 0px; text-transform: none; white-space: =
normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; =
float: none; display: inline !important;" class=3D"">not trying to =
re-adjust weights.</span><br style=3D"font-family: Helvetica; font-size: =
12px; font-style: normal; font-variant-caps: normal; font-weight: =
normal; letter-spacing: normal; orphans: auto; text-align: start; =
text-indent: 0px; text-transform: none; white-space: normal; widows: =
auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" =
class=3D""></div></blockquote><div><br class=3D""></div><div>This is =
just a demo, and I agree this could be added through a softfork later. =
But even if we add this as a softfork, we have to have the ability to =
disable it through a special softfork. I think I have explained the =
reason but let me try again.</div><div><br class=3D""></div><div>Here, =
when I talking about =E2=80=9Ctx weight=E2=80=9D, it=E2=80=99s the =E2=80=9C=
tx weight=E2=80=9D defined in point 4, which covers not only size, but =
also other limits like SigOp. For a fraud proof to be really useful, it =
has to cover every type of block level limits. One feature of segwit is =
the script versioning, which allows introduction of new scripts. In the =
process, we will change the definition of SigOp: previous 0 SigOp =
scripts now carries some amount of SigOp. This is by itself a softfork =
(we did this type of softfork twice already: P2SH and segwit). However, =
if we have a merkle sum root covering the SigOp, old nodes won=E2=80=99t =
count these new SigOps, and they will fail to validate the sum =
root.</div><div><br class=3D""></div><div>Without a backdoor to disable =
the sum tree validation in old nodes, the only way would be keeping the =
original sum tree untouched, while create another sum tree, every time =
we have a new script version. This is not acceptable at =
all.</div><div><br class=3D""></div><div>But even such backdoor would =
not be harmful to the security of full nodes because they will still =
fully verify the tx and witness merkle root.</div><div><br =
class=3D""></div><div>I=E2=80=99d argue that any fraud proof related =
commitment: sum tree, delayed UTXO commitment etc will require such a =
backdoor to disable. Maybe we should just remove this from here and make =
this a new topic. We could even do this as a softfork =
today.</div><div><br class=3D""></div></div><br class=3D""></body></html>=

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