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From: Tao Effect <contact@taoeffect.com>
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Date: Tue, 6 Jun 2017 16:27:33 -0700
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	<20170606232015.GA11830@erisian.com.au>
To: Anthony Towns <aj@erisian.com.au>
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Subject: Re: [bitcoin-dev] Replay attacks make BIP148 and BIP149 untennable
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> CoinJoin works as a method of both improving fungibility and mixing =
with
> coinbase transactions.

My understanding is that the two situations are quite different.

Unlike mixing to coin-split, CoinJoin doesn't create a high demand =
exclusively for coinbase transactions.

However, of the proposed methods, coin-mixing seems the better option, =
because it might be reasonably easy (I don't know) for exchanges to =
obtain 148 coinbase coins, and mix their coins with them, extending the =
coin-splitting capability beyond just miner coins and then using that to =
split incoming coins.

That seems like the most reasonable approach I've heard so far. Whether =
exchanges would be willing to do that is a separate question.

> When it's confirmed on one chain, but not on the other, you
> can then "double-spend" on the lower hashrate chain with a higher fee,
> to end up with different coins on both chains.

This method is time consuming and not guaranteed to work. CPFP can be =
used by an attacker to get your original txn into the 148 chain.

> (also, no double-n in untenable)

Why thank you aj, you're so good at spelling. :-)

Cheers,
Greg

--
Please do not email me anything that you are not comfortable also =
sharing with the NSA.

> On Jun 6, 2017, at 4:20 PM, Anthony Towns via bitcoin-dev =
<bitcoin-dev@lists.linuxfoundation.org =
<mailto:bitcoin-dev@lists.linuxfoundation.org>> wrote:
>=20
> On Tue, Jun 06, 2017 at 03:39:28PM -0700, Tao Effect via bitcoin-dev =
wrote:
>> - Mixing with 148 coinbase txns destroys fungibility.
>=20
> CoinJoin works as a method of both improving fungibility and mixing =
with
> coinbase transactions.
>=20
> You probably don't need to do anything clever to split a coin though:
> if you send a transaction with a standard fee it will get confirmed
> in a normal time on the higher hashrate chain, but won't confirm as
> quickly on the lower hashrate chain (precisely because transactions =
are
> valid on both chains, but blocks are found more slowly with the lower
> hashrate). When it's confirmed on one chain, but not on the other, you
> can then "double-spend" on the lower hashrate chain with a higher fee,
> to end up with different coins on both chains.
>=20
> (also, no double-n in untenable)
>=20
> Cheers,
> aj
>=20
> _______________________________________________
> bitcoin-dev mailing list
> bitcoin-dev@lists.linuxfoundation.org =
<mailto:bitcoin-dev@lists.linuxfoundation.org>
> https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev


--Apple-Mail=_0CD83101-2A35-4251-9FD6-8A17DA62C4EE
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<html><head><meta http-equiv=3D"Content-Type" content=3D"text/html =
charset=3Dus-ascii"><meta http-equiv=3D"Content-Type" content=3D"text/html=
 charset=3Dus-ascii"></head><body style=3D"word-wrap: break-word; =
-webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" =
class=3D""><blockquote type=3D"cite" class=3D"">CoinJoin works as a =
method of both improving fungibility and mixing with<br =
class=3D"">coinbase transactions.</blockquote><div class=3D""><br =
class=3D"webkit-block-placeholder"></div><div class=3D"">My =
understanding is that the two situations are quite different.</div><div =
class=3D""><br class=3D""></div><div class=3D"">Unlike mixing to =
coin-split, CoinJoin doesn't create a high demand exclusively for =
coinbase transactions.</div><div class=3D""><br class=3D""></div><div =
class=3D"">However, of the proposed methods, coin-mixing seems the =
better option, because it might be reasonably easy (I don't know) for =
exchanges to obtain 148 coinbase coins, and mix their coins with them, =
extending the coin-splitting capability beyond just miner coins and then =
using that to split incoming coins.</div><div class=3D""><br =
class=3D""></div><div class=3D"">That seems like the most reasonable =
approach I've heard so far. Whether exchanges would be willing to do =
that is a separate question.</div><div class=3D""><br =
class=3D""></div><div class=3D""><blockquote type=3D"cite" class=3D"">When=
 it's confirmed on one chain, but not on the other, you<br class=3D"">can =
then "double-spend" on the lower hashrate chain with a higher fee,<br =
class=3D"">to end up with different coins on both =
chains.</blockquote><br class=3D""></div><div class=3D"">This method is =
time consuming and not guaranteed to work. CPFP can be used by an =
attacker to get your original txn into the 148 chain.</div><div =
class=3D""><br class=3D""></div><div class=3D""><blockquote type=3D"cite" =
class=3D"">(also, no double-n in untenable)</blockquote><br =
class=3D""></div><div class=3D"">Why thank you aj, you're so good at =
spelling. :-)</div><div class=3D""><br class=3D""></div><div =
class=3D"">Cheers,</div><div class=3D"">Greg</div><div class=3D"">
<span style=3D"color: rgb(0, 0, 0); font-family: Helvetica; font-size: =
14px; font-style: normal; font-variant-caps: normal; font-weight: =
normal; letter-spacing: normal; text-align: start; text-indent: 0px; =
text-transform: none; white-space: normal; word-spacing: 0px; =
-webkit-text-stroke-width: 0px; font-variant-ligatures: normal; =
font-variant-position: normal; font-variant-numeric: normal; =
font-variant-alternates: normal; font-variant-east-asian: normal; =
line-height: normal; orphans: 2; widows: 2;" class=3D""><br =
class=3D"Apple-interchange-newline">--</span><br style=3D"color: rgb(0, =
0, 0); font-family: Helvetica; font-size: 14px; font-style: normal; =
font-variant-caps: normal; font-weight: normal; letter-spacing: normal; =
text-align: start; text-indent: 0px; text-transform: none; white-space: =
normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; =
font-variant-ligatures: normal; font-variant-position: normal; =
font-variant-numeric: normal; font-variant-alternates: normal; =
font-variant-east-asian: normal; line-height: normal; orphans: 2; =
widows: 2;" class=3D""><span style=3D"color: rgb(0, 0, 0); font-family: =
Helvetica; font-size: 14px; font-style: normal; font-variant-caps: =
normal; font-weight: normal; letter-spacing: normal; text-align: start; =
text-indent: 0px; text-transform: none; white-space: normal; =
word-spacing: 0px; -webkit-text-stroke-width: 0px; =
font-variant-ligatures: normal; font-variant-position: normal; =
font-variant-numeric: normal; font-variant-alternates: normal; =
font-variant-east-asian: normal; line-height: normal; orphans: 2; =
widows: 2;" class=3D"">Please do not email me anything that you are not =
comfortable also sharing</span><span style=3D"color: rgb(0, 0, 0); =
font-family: Helvetica; font-size: 14px; font-style: normal; =
font-variant-caps: normal; font-weight: normal; letter-spacing: normal; =
text-align: start; text-indent: 0px; text-transform: none; white-space: =
normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; =
font-variant-ligatures: normal; font-variant-position: normal; =
font-variant-numeric: normal; font-variant-alternates: normal; =
font-variant-east-asian: normal; line-height: normal; orphans: 2; =
widows: 2;" class=3D"">&nbsp;with the NSA.</span>
</div>

<br class=3D""><div><blockquote type=3D"cite" class=3D""><div =
class=3D"">On Jun 6, 2017, at 4:20 PM, Anthony Towns via bitcoin-dev =
&lt;<a href=3D"mailto:bitcoin-dev@lists.linuxfoundation.org" =
class=3D"">bitcoin-dev@lists.linuxfoundation.org</a>&gt; wrote:</div><br =
class=3D"Apple-interchange-newline"><div class=3D""><div class=3D"">On =
Tue, Jun 06, 2017 at 03:39:28PM -0700, Tao Effect via bitcoin-dev =
wrote:<br class=3D""><blockquote type=3D"cite" class=3D"">- Mixing with =
148 coinbase txns destroys fungibility.<br class=3D""></blockquote><br =
class=3D"">CoinJoin works as a method of both improving fungibility and =
mixing with<br class=3D"">coinbase transactions.<br class=3D""><br =
class=3D"">You probably don't need to do anything clever to split a coin =
though:<br class=3D"">if you send a transaction with a standard fee it =
will get confirmed<br class=3D"">in a normal time on the higher hashrate =
chain, but won't confirm as<br class=3D"">quickly on the lower hashrate =
chain (precisely because transactions are<br class=3D"">valid on both =
chains, but blocks are found more slowly with the lower<br =
class=3D"">hashrate). When it's confirmed on one chain, but not on the =
other, you<br class=3D"">can then "double-spend" on the lower hashrate =
chain with a higher fee,<br class=3D"">to end up with different coins on =
both chains.<br class=3D""><br class=3D"">(also, no double-n in =
untenable)<br class=3D""><br class=3D"">Cheers,<br class=3D"">aj<br =
class=3D""><br =
class=3D"">_______________________________________________<br =
class=3D"">bitcoin-dev mailing list<br class=3D""><a =
href=3D"mailto:bitcoin-dev@lists.linuxfoundation.org" =
class=3D"">bitcoin-dev@lists.linuxfoundation.org</a><br class=3D""><a =
href=3D"https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev" =
class=3D"">https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev<=
/a><br class=3D""></div></div></blockquote></div><br =
class=3D""></body></html>=

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