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From: Matias Alejo Garcia <matias@bitpay.com>
Date: Mon, 5 Oct 2015 15:04:44 -0300
Message-ID: <CA+vKqYcqYS4_0aDK_=TtVsEDVMhJzDmtHvzm6YRdNFX2mhztgg@mail.gmail.com>
To: Jean-Pierre Rupp <root@haskoin.com>
Content-Type: multipart/alternative; boundary=047d7b10c9cb44e83c05215f5ac3
Cc: bitcoin-dev@lists.linuxfoundation.org
Subject: Re: [bitcoin-dev] [Bitcoin-development] New BIP32 structure for
 P2SH multisig wallets [BIP-45]
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On Mon, Oct 5, 2015 at 9:18 AM, Jean-Pierre Rupp <root@haskoin.com> wrote:
>
> Perhaps Pedro wants to also participate in a 2-of-2 cosigning
> arrangement with a merchant that will deliver a laptop to him, so Pedro
> provides this merchant with the same extended public key derived from
> path m/45', and the merchant provides Pedro with his own:
>
> Pedro: xpub456...
> ElCheapoPC: xpub987...
>


Thanks for the explanation. OK, maybe that should be stated on BIP45, but
it was never the idea that you reuse your xpub for different wallet, as I
mention
on the original reply. The only implementation of BIP45 I am aware of
(Copay),
use completely different xprivs for each wallet.



>
> On 05/10/15 07:57, Matias Alejo Garcia wrote:
> >
> > Hi,
> >
> > Sorry the late response. Going back to the original message:
> >
> >
> >     > On 03/10/15 13:42, Jean-Pierre Rupp via bitcoin-dev wrote:
> >     >> I have been reviewing BIP-45 today.  There is a privacy problem
> >     with it
> >     >> that should at least be mentioned in the document.
> >     >>
> >     >> When using the same extended public key for all multisig
> >     activity, and
> >     >> dealing with different cosigners in separate multisig accounts,
> >     reuse of
> >     >> the same set of public keys means that all cosigners from all
> >     accounts
> >     >> will be able to monitor multisig activity from every other
> >     cosigner, in
> >     >> every other account.
> >
> >
> > I am not completely sure what you mean by 'account' and 'mutisig
> > activity'. You seem to imply
> > that the same set of extended public keys will be used in more that one
> > wallet, which it is
> > not required (and certainly not recommended) by BIP45.
> >
> > According to BIP45, a singing party, in order to generate a wallet
> > address, needs the extended public keys of all the other parties, so
> > each party will be able to see the transaction history of the wallet
> > they are sharing, but if the party has other wallets with other copayer=
s
> > the xpub should be completely different.
> >
> > mat=C3=ADas
> >
> >
> >
> > --
> > BitPay.com
>



--=20
BitPay.com

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<div dir=3D"ltr"><br><div class=3D"gmail_extra"><br><div class=3D"gmail_quo=
te">On Mon, Oct 5, 2015 at 9:18 AM, Jean-Pierre Rupp <span dir=3D"ltr">&lt;=
<a href=3D"mailto:root@haskoin.com" target=3D"_blank">root@haskoin.com</a>&=
gt;</span> wrote:<blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8=
ex;border-left:1px #ccc solid;padding-left:1ex">
Perhaps Pedro wants to also participate in a 2-of-2 cosigning<br>
arrangement with a merchant that will deliver a laptop to him, so Pedro<br>
provides this merchant with the same extended public key derived from<br>
path m/45&#39;, and the merchant provides Pedro with his own:<br>
<br>
Pedro: xpub456...<br>
ElCheapoPC: xpub987...<br></blockquote><div><br></div><div><br></div><div>T=
hanks for the explanation. OK, maybe that should be stated on BIP45, but</d=
iv><div>it was never the idea that you reuse your xpub for different wallet=
, as I mention</div><div>on the original reply. The only implementation of =
BIP45 I am aware of (Copay),</div><div>use completely different xprivs for =
each wallet.</div><div><br></div><div>=C2=A0</div><blockquote class=3D"gmai=
l_quote" style=3D"margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left=
:1ex">
<div class=3D"HOEnZb"><div class=3D"h5"><br>
On 05/10/15 07:57, Matias Alejo Garcia wrote:<br>
&gt;<br>
&gt; Hi,<br>
&gt;<br>
&gt; Sorry the late response. Going back to the original message:<br>
&gt;<br>
&gt;<br>
&gt;=C2=A0 =C2=A0 =C2=A0&gt; On 03/10/15 13:42, Jean-Pierre Rupp via bitcoi=
n-dev wrote:<br>
&gt;=C2=A0 =C2=A0 =C2=A0&gt;&gt; I have been reviewing BIP-45 today.=C2=A0 =
There is a privacy problem<br>
&gt;=C2=A0 =C2=A0 =C2=A0with it<br>
&gt;=C2=A0 =C2=A0 =C2=A0&gt;&gt; that should at least be mentioned in the d=
ocument.<br>
&gt;=C2=A0 =C2=A0 =C2=A0&gt;&gt;<br>
&gt;=C2=A0 =C2=A0 =C2=A0&gt;&gt; When using the same extended public key fo=
r all multisig<br>
&gt;=C2=A0 =C2=A0 =C2=A0activity, and<br>
&gt;=C2=A0 =C2=A0 =C2=A0&gt;&gt; dealing with different cosigners in separa=
te multisig accounts,<br>
&gt;=C2=A0 =C2=A0 =C2=A0reuse of<br>
&gt;=C2=A0 =C2=A0 =C2=A0&gt;&gt; the same set of public keys means that all=
 cosigners from all<br>
&gt;=C2=A0 =C2=A0 =C2=A0accounts<br>
&gt;=C2=A0 =C2=A0 =C2=A0&gt;&gt; will be able to monitor multisig activity =
from every other<br>
&gt;=C2=A0 =C2=A0 =C2=A0cosigner, in<br>
&gt;=C2=A0 =C2=A0 =C2=A0&gt;&gt; every other account.<br>
&gt;<br>
&gt;<br>
&gt; I am not completely sure what you mean by &#39;account&#39; and &#39;m=
utisig<br>
&gt; activity&#39;. You seem to imply<br>
&gt; that the same set of extended public keys will be used in more that on=
e<br>
&gt; wallet, which it is<br>
&gt; not required (and certainly not recommended) by BIP45.<br>
&gt;<br>
&gt; According to BIP45, a singing party, in order to generate a wallet<br>
&gt; address, needs the extended public keys of all the other parties, so<b=
r>
&gt; each party will be able to see the transaction history of the wallet<b=
r>
&gt; they are sharing, but if the party has other wallets with other copaye=
rs<br>
&gt; the xpub should be completely different.<br>
&gt;<br>
&gt; mat=C3=ADas<br>
&gt;<br>
&gt;<br>
&gt;<br>
&gt; --<br>
&gt; BitPay.com<br>
</div></div></blockquote></div><br><br clear=3D"all"><div><br></div>-- <br>=
<div class=3D"gmail_signature"><div dir=3D"ltr"><div>BitPay.com</div></div>=
</div>
</div></div>

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