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From: Stephen <stephencalebmorse@gmail.com>
In-Reply-To: <CAGH37SK0k1YUvadetyHcBGjzW+OHNFRmRwqsUDeHBGejUacigQ@mail.gmail.com>
Date: Fri, 5 Jun 2015 23:20:38 -0400
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To: Kristov Atlas <kristovatlas.lists@gmail.com>
Cc: Bitcoin development mailing list
	<bitcoin-development@lists.sourceforge.net>
Subject: Re: [Bitcoin-development] Lexicographical Indexing of Transaction
	Inputs and Outputs
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Hi Kristov,

I like the idea. Mainly because having a standard reminds developers to cons=
ider this issue. In addition, we would have visibility into the portion of t=
he network that adopts this strategy to enhance privacy. A few points of fee=
dback:

 - I think your explanation of sorting could be significantly shortened and c=
larified by simply saying that the TXIDs of inputs should be compared as uin=
t256 integers.=20
 - The malleability of input TXIDs, as mentioned in the proposal, could caus=
e inputs to be ordered in a non-standard way. Reordering then them would inv=
alidate the signatures (assuming SIGHASH_ALL), so the transaction would be l=
eft with improperly ordered inputs. While not a huge issue, it's not ideal. I=
 think the best way to get around this would be to use normalized TXIDs, but=
 you might also be able to sort based on the previous outputs that each of t=
he inputs are spending? These both require information that may not be readi=
ly available, however, and use of normalized transaction IDs is not fully de=
veloped yet.=20

Best,
Stephen=20


> On Jun 5, 2015, at 8:12 PM, Kristov Atlas <kristovatlas.lists@gmail.com> w=
rote:
>=20
> Hello all,
>=20
> I have written a draft of a BIP to standardize the sorting of tx inputs an=
d outputs for privacy and security reasons. A few colleagues have reviewed t=
his and provided feedback privately, but now it's ready for feedback from a w=
ider audience.
>=20
> If there is positive sentiment about the proposal after feedback is integr=
ated, I aim for a bip number to be assigned and have it accepted into https:=
//github.com/bitcoin/bips=20
>=20
> Link: https://github.com/kristovatlas/rfc/blob/master/bips/bip-li01.mediaw=
iki
>=20
> For your convenience, here's the abstract:
>=20
> "Currently there is no standard for bitcoin wallet clients when ordering t=
ransaction inputs and outputs. As a result, wallet clients often have a disc=
ernible blockchain fingerprint, and can leak private information about their=
 users. By contrast, a standard for non-deterministic sorting could be diffi=
cult to audit. This document proposes deterministic lexicographical sorting,=
 using hashes of previous transactions and output indices to sort transactio=
n inputs, as well as value and locking scripts to sort transaction outputs."=

>=20
> Thanks,
>=20
> Kristov Atlas
> Open Bitcoin Privacy Project Contributor, Blockchain.info Security Enginee=
r, etc.
> Twitter: @kristovatlas
> Blog: kristovatlas.com
> --------------------------------------------------------------------------=
----
> _______________________________________________
> Bitcoin-development mailing list
> Bitcoin-development@lists.sourceforge.net
> https://lists.sourceforge.net/lists/listinfo/bitcoin-development

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<html><head><meta http-equiv=3D"content-type" content=3D"text/html; charset=3D=
utf-8"></head><body dir=3D"auto"><div>Hi Kristov,</div><div><br></div><div>I=
 like the idea. Mainly because having a standard reminds developers to consi=
der this issue. In addition, we would have visibility into the portion of th=
e network that adopts this strategy to enhance privacy. A few points of feed=
back:</div><div><br></div><div>&nbsp;- I think your explanation of sorting c=
ould be significantly shortened and clarified by simply saying that the TXID=
s of inputs should be compared as uint256 integers.&nbsp;</div><div>&nbsp;- T=
he malleability of input TXIDs, as mentioned in the proposal, could cause in=
puts to be ordered in a non-standard way. Reordering then them would invalid=
ate the signatures (assuming SIGHASH_ALL), so the transaction would be left w=
ith improperly ordered inputs. While not a huge issue, it's not ideal. I thi=
nk the best way to get around this would be to use normalized TXIDs, but you=
 might also be able to sort based on the previous outputs that each of the i=
nputs are spending? These both require information that may not be readily a=
vailable, however, and use of normalized transaction IDs is not fully develo=
ped yet.&nbsp;</div><div><br></div><div>Best,</div><div>Stephen&nbsp;</div><=
div><br><br></div><div><br>On Jun 5, 2015, at 8:12 PM, Kristov Atlas &lt;<a h=
ref=3D"mailto:kristovatlas.lists@gmail.com">kristovatlas.lists@gmail.com</a>=
&gt; wrote:<br><br></div><blockquote type=3D"cite"><div><div dir=3D"ltr"><di=
v><div><div><div><div><div><div><div>Hello all,<br><br></div>I have written a=
 draft of a BIP to standardize the sorting of tx inputs and outputs for priv=
acy and security reasons. A few colleagues have reviewed this and provided f=
eedback privately, but now it's ready for feedback from a wider audience.<br=
><br></div>If there is positive sentiment about the proposal after feedback i=
s integrated, I aim for a bip number to be assigned and have it accepted int=
o <a href=3D"https://github.com/bitcoin/bips">https://github.com/bitcoin/bip=
s</a> <br><br>Link: <a href=3D"https://github.com/kristovatlas/rfc/blob/mast=
er/bips/bip-li01.mediawiki">https://github.com/kristovatlas/rfc/blob/master/=
bips/bip-li01.mediawiki</a><br><br></div>For your convenience, here's the ab=
stract:<br><br>"Currently there is no standard for bitcoin wallet clients wh=
en ordering transaction inputs and outputs. As a result, wallet clients ofte=
n have a discernible blockchain fingerprint, and can leak private informatio=
n about their users. By contrast, a standard for non-deterministic sorting c=
ould be difficult to audit. This document proposes deterministic lexicograph=
ical sorting, using hashes of previous transactions and output indices to so=
rt transaction inputs, as well as value and locking scripts to sort transact=
ion outputs."<br><br></div>Thanks,<br><br></div>Kristov Atlas<br></div>Open B=
itcoin Privacy Project Contributor, Blockchain.info Security Engineer, etc.<=
br></div>Twitter: @kristovatlas<br></div>Blog: <a href=3D"http://kristovatla=
s.com">kristovatlas.com</a><br></div>
</div></blockquote><blockquote type=3D"cite"><div><span>--------------------=
----------------------------------------------------------</span><br></div><=
/blockquote><blockquote type=3D"cite"><div><span>___________________________=
____________________</span><br><span>Bitcoin-development mailing list</span>=
<br><span><a href=3D"mailto:Bitcoin-development@lists.sourceforge.net">Bitco=
in-development@lists.sourceforge.net</a></span><br><span><a href=3D"https://=
lists.sourceforge.net/lists/listinfo/bitcoin-development">https://lists.sour=
ceforge.net/lists/listinfo/bitcoin-development</a></span><br></div></blockqu=
ote></body></html>=

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