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Date: Sat, 7 Jun 2014 00:21:48 +0200
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Cc: Bitcoin Dev <bitcoin-development@lists.sourceforge.net>
Subject: Re: [Bitcoin-development] Possible attack: Keeping unconfirmed
	transactions
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Alice does not intercept the transaction, she only saves it and expect that
it will not be confirmed (because has 0 fee for example).

Also using the Payment Protocol I believe that Alice is the only person
that can relay Bob's transaction.

Source: https://github.com/bitcoin/bips/blob/master/bip-0070.mediawiki

*When the merchant's server receives the Payment message, it must determine
> whether or not the transactions satisfy conditions of payment. If and onl=
y
> if they do, if should broadcast the transaction(s) on the Bitcoin p2p
> network.*
>


2014-06-07 0:11 GMT+02:00 Toshi Morita <toshi@peernova.com>:

> From what I know, Alice does not know to which node Bob will broadcast th=
e
> transaction. Therefore, Alice cannot intercept the transaction and preven=
t
> the rest of the network from seeing it.
>
> Toshi
>
>
>
> On Fri, Jun 6, 2014 at 3:02 PM, Ra=C3=BAl Mart=C3=ADnez <rme@i-rme.es> wr=
ote:
>
>> I dont know if this attack is even possible, it came to my mind and I
>> will try to explain it as good as possible.
>>
>> Some transacions keep unconfirmed forever and finally they are purged by
>> Bitcoin nodes, mostly due to the lack of fees.
>>
>>
>> Example:
>> ---------
>>
>> Alice is selling a pizza to Bob, Bob is now making the payment with
>> Bitcoin.
>> The main goal of this attack is to store a unconfirmed transaction send
>> by Bob for a few days (it will not be included in the blockchain because=
 it
>> has no fee or due to other reason), Bob might resend the payment or migh=
t
>> just cancel the deal with Alice.
>>
>> Bob forgets about that failed trade but a couple of days later, Alice,
>> who has stored the signed transacion, relays the transaction to the netw=
ork
>> (or mines it directly with his own hashpower).
>> Bob does not know what is happening, he believed that that transaction
>> was "canceled forever", he even does not remember the failed pizza deal.
>>
>> Alice has now the bitcoins and Bob does not know what happened with his
>> money.
>>
>> ---------
>>
>> This might also work with the Payment Protocol because when using it Bob
>> does not relay the transaction to the network, its Alices job to do it,
>> Alice stores it and tells Bob to resend the payment, Bob creates another
>> transaction (If has the same inputs as the first TX this does not work)
>> (this one is relayed by Alice to the network).
>>
>> Alice comes back a couple of days later and mines with his hashrate the
>> first transaction (the one she didnt relayed to the network).
>>
>> Alice now has two payments, Bob does not know what happened.
>>
>>
>> -----------
>>
>> I hope that I explained well this possible attack, I dont know if there
>> is already a fix for this problem or if it is simply impossible to execu=
te
>> this kind of attack.
>>
>> Thanks for your time.
>>
>>
>>
>>
>>
>>
>> ------------------------------------------------------------------------=
------
>> Learn Graph Databases - Download FREE O'Reilly Book
>> "Graph Databases" is the definitive new guide to graph databases and the=
ir
>> applications. Written by three acclaimed leaders in the field,
>> this first edition is now available. Download your free book today!
>> http://p.sf.net/sfu/NeoTech
>> _______________________________________________
>> Bitcoin-development mailing list
>> Bitcoin-development@lists.sourceforge.net
>> https://lists.sourceforge.net/lists/listinfo/bitcoin-development
>>
>>
>

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<div dir=3D"ltr">Alice does not intercept the transaction, she only saves i=
t and expect that it will not be confirmed (because has 0 fee for example).=
<div><br></div><div>Also using the Payment Protocol I believe that Alice is=
 the only person that can relay Bob&#39;s transaction.</div>

<div><br></div><div>Source:=C2=A0<a href=3D"https://github.com/bitcoin/bips=
/blob/master/bip-0070.mediawiki">https://github.com/bitcoin/bips/blob/maste=
r/bip-0070.mediawiki</a></div><div><br></div><blockquote class=3D"gmail_quo=
te" style=3D"margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-col=
or:rgb(204,204,204);border-left-style:solid;padding-left:1ex">

<span style=3D"color:rgb(51,51,51);font-family:Helvetica,arial,freesans,cle=
an,sans-serif;font-size:15px;line-height:25.5px"><i>When the merchant&#39;s=
 server receives the Payment message, it must determine whether or not the =
transactions satisfy conditions of payment. If and only if they do, if shou=
ld broadcast the transaction(s) on the Bitcoin p2p network.</i></span><br>

</blockquote></div><div class=3D"gmail_extra"><br><br><div class=3D"gmail_q=
uote">2014-06-07 0:11 GMT+02:00 Toshi Morita <span dir=3D"ltr">&lt;<a href=
=3D"mailto:toshi@peernova.com" target=3D"_blank">toshi@peernova.com</a>&gt;=
</span>:<br>

<blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-left:1p=
x #ccc solid;padding-left:1ex"><div dir=3D"ltr">From what I know, Alice doe=
s not know to which node Bob will broadcast the transaction. Therefore, Ali=
ce cannot intercept the transaction and prevent the rest of the network fro=
m seeing it.<div>

<br></div><div>
Toshi</div><div><br></div></div><div class=3D"gmail_extra"><br><br><div cla=
ss=3D"gmail_quote"><div><div class=3D"h5">On Fri, Jun 6, 2014 at 3:02 PM, R=
a=C3=BAl Mart=C3=ADnez <span dir=3D"ltr">&lt;<a href=3D"mailto:rme@i-rme.es=
" target=3D"_blank">rme@i-rme.es</a>&gt;</span> wrote:<br>


</div></div><blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;bo=
rder-left:1px #ccc solid;padding-left:1ex"><div><div class=3D"h5"><div dir=
=3D"ltr">I dont know if this attack is even possible, it came to my mind an=
d I will try to explain it as good as possible.<div>


<br></div><div>Some transacions keep unconfirmed forever and finally they a=
re purged by Bitcoin nodes, mostly due to the lack of fees.</div>

<div><br></div><div><br></div><div>Example:</div><div>---------</div><div><=
br></div><div>Alice is selling a pizza to Bob, Bob is now making the paymen=
t with Bitcoin.</div><div>The main goal of this attack is to store a unconf=
irmed transaction send by Bob for a few days (it will not be included in th=
e blockchain because it has no fee or due to other reason), Bob might resen=
d the payment or might just cancel the deal with Alice.</div>




<div><br></div><div>Bob forgets about that failed trade but a couple of day=
s later, Alice, who has stored the signed transacion, relays the transactio=
n to the network (or mines it directly with his own hashpower).</div><div>




Bob does not know what is happening, he believed that that transaction was =
&quot;canceled forever&quot;, he even does not remember the failed pizza de=
al.</div><div><br></div><div>Alice has now the bitcoins and Bob does not kn=
ow what happened with his money.</div>




<div><br></div><div>---------</div><div><br></div><div>This might also work=
 with the Payment Protocol because when using it Bob does not relay the tra=
nsaction to the network, its Alices job to do it, Alice stores it and tells=
 Bob to resend the payment, Bob creates another transaction (If has the sam=
e inputs as the first TX this does not work) (this one is relayed by Alice =
to the network).</div>




<div><br></div><div>Alice comes back a couple of days later and mines with =
his hashrate the first transaction (the one she didnt relayed to the networ=
k).</div><div><br></div><div>Alice now has two payments, Bob does not know =
what happened.</div>




<div><br></div><div><br></div><div>-----------</div><div><br></div><div>I h=
ope that I explained well this possible attack, I dont know if there is alr=
eady a fix for this problem or if it is simply impossible to execute this k=
ind of attack.</div>




<div><br></div><div>Thanks for your time.</div><div><br></div><div><br></di=
v><div><br></div><div><br></div></div>
<br></div></div>-----------------------------------------------------------=
-------------------<br>
Learn Graph Databases - Download FREE O&#39;Reilly Book<br>
&quot;Graph Databases&quot; is the definitive new guide to graph databases =
and their<br>
applications. Written by three acclaimed leaders in the field,<br>
this first edition is now available. Download your free book today!<br>
<a href=3D"http://p.sf.net/sfu/NeoTech" target=3D"_blank">http://p.sf.net/s=
fu/NeoTech</a><br>_______________________________________________<br>
Bitcoin-development mailing list<br>
<a href=3D"mailto:Bitcoin-development@lists.sourceforge.net" target=3D"_bla=
nk">Bitcoin-development@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>
<br></blockquote></div><br></div>
</blockquote></div><br></div>

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