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From: "Russell O'Connor" <roconnor@blockstream.io>
Date: Tue, 3 Jan 2017 00:04:50 -0500
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To: Bitcoin Protocol Discussion <bitcoin-dev@lists.linuxfoundation.org>
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Subject: Re: [bitcoin-dev] Script Abuse Potential?
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OP_2DUP?  Why not OP_3DUP?

On Mon, Jan 2, 2017 at 10:39 PM, Johnson Lau via bitcoin-dev <
bitcoin-dev@lists.linuxfoundation.org> wrote:

> No, there could only have not more than 201 opcodes in a script. So you
> may have 198 OP_2DUP at most, i.e. 198 * 520 * 2 =3D 206kB
>
> For OP_CAT, just check if the returned item is within the 520 bytes limit=
.
>
> On 3 Jan 2017, at 11:27, Jeremy via bitcoin-dev <bitcoin-dev@lists.
> linuxfoundation.org> wrote:
>
> It is an unfortunate script, but can't actually
> =E2=80=8Bdo
>  that much
> =E2=80=8B it seems=E2=80=8B
> . The MAX_SCRIPT_ELEMENT_SIZE =3D 520 Bytes.
> =E2=80=8B Thus, it would seem the worst you could do with this would be t=
o (10000-520*2)*520*2
> bytes  ~=3D~ 10 MB.
>
> =E2=80=8BMuch more concerning would be the op_dup/op_cat style bug, which=
 under a
> similar script =E2=80=8Bwould certainly cause out of memory errors :)
>
>
>
> --
> @JeremyRubin <https://twitter.com/JeremyRubin>
> <https://twitter.com/JeremyRubin>
>
> On Mon, Jan 2, 2017 at 4:39 PM, Steve Davis via bitcoin-dev <
> bitcoin-dev@lists.linuxfoundation.org> wrote:
>
>> Hi all,
>>
>> Suppose someone were to use the following pk_script:
>>
>> [op_2dup, op_2dup, op_2dup, op_2dup, op_2dup, ...(to limit)...,
>> op_2dup, op_hash160, <addr_hash>, op_equalverify, op_checksig]
>>
>> This still seems to be valid AFAICS, and may be a potential attack vecto=
r?
>>
>> Thanks.
>>
>>
>> _______________________________________________
>> bitcoin-dev mailing list
>> bitcoin-dev@lists.linuxfoundation.org
>> https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
>>
>>
> _______________________________________________
> bitcoin-dev mailing list
> bitcoin-dev@lists.linuxfoundation.org
> https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
>
>
>
> _______________________________________________
> bitcoin-dev mailing list
> bitcoin-dev@lists.linuxfoundation.org
> https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
>
>

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<div dir=3D"ltr">OP_2DUP?=C2=A0 Why not OP_3DUP?<br></div><div class=3D"gma=
il_extra"><br><div class=3D"gmail_quote">On Mon, Jan 2, 2017 at 10:39 PM, J=
ohnson Lau via bitcoin-dev <span dir=3D"ltr">&lt;<a href=3D"mailto:bitcoin-=
dev@lists.linuxfoundation.org" target=3D"_blank">bitcoin-dev@lists.linuxfou=
ndation.org</a>&gt;</span> wrote:<br><blockquote class=3D"gmail_quote" styl=
e=3D"margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div st=
yle=3D"word-wrap:break-word"><div>No, there could only have not more than 2=
01 opcodes in a script. So you may have 198 OP_2DUP at most, i.e. 198 * 520=
 * 2 =3D 206kB</div><div><br></div><div>For OP_CAT, just check if the retur=
ned item is within the 520 bytes limit.</div><div><div class=3D"h5"><br><di=
v><blockquote type=3D"cite"><div>On 3 Jan 2017, at 11:27, Jeremy via bitcoi=
n-dev &lt;<a href=3D"mailto:bitcoin-dev@lists.linuxfoundation.org" target=
=3D"_blank">bitcoin-dev@lists.<wbr>linuxfoundation.org</a>&gt; wrote:</div>=
<br class=3D"m_4247512162626257208Apple-interchange-newline"><div><div dir=
=3D"ltr"><div class=3D"gmail_default" style=3D"font-family:arial,helvetica,=
sans-serif;font-size:small"><span style=3D"font-family:arial,sans-serif;col=
or:rgb(34,34,34);font-size:12.800000190734863px">It is an unfortunate scrip=
t, but can&#39;t actually=C2=A0</span><div class=3D"gmail_default" style=3D=
"display:inline">=E2=80=8Bdo</div><span style=3D"font-family:arial,sans-ser=
if;color:rgb(34,34,34);font-size:12.800000190734863px">=C2=A0that much</spa=
n><div class=3D"gmail_default" style=3D"display:inline">=E2=80=8B it seems=
=E2=80=8B</div><span style=3D"font-family:arial,sans-serif;color:rgb(34,34,=
34);font-size:12.800000190734863px">. The MAX_SCRIPT_ELEMENT_SIZE =3D 520 B=
ytes.</span><div class=3D"gmail_default" style=3D"font-family:arial,sans-se=
rif;color:rgb(34,34,34);font-size:12.800000190734863px;display:inline"><fon=
t face=3D"arial, helvetica, sans-serif">=E2=80=8B Thus, it would seem the w=
orst you could do with this would be to=C2=A0</font>(10000-520*2)*520*2 byt=
es =C2=A0~=3D~ 10 MB.</div></div><div style=3D"font-size:12.800000190734863=
px"><br></div><div style=3D"font-size:12.800000190734863px"><div class=3D"g=
mail_default" style=3D"font-family:arial,helvetica,sans-serif;font-size:sma=
ll">=E2=80=8BMuch more concerning would be the op_dup/op_cat style bug, whi=
ch under a similar script =E2=80=8Bwould certainly cause out of memory erro=
rs :)</div><div><br></div></div></div><div class=3D"gmail_extra"><br clear=
=3D"all"><div><br clear=3D"all"><div><div class=3D"m_4247512162626257208gma=
il_signature" data-smartmail=3D"gmail_signature"><div dir=3D"ltr">--<br><a =
href=3D"https://twitter.com/JeremyRubin" target=3D"_blank">@JeremyRubin</a>=
<a href=3D"https://twitter.com/JeremyRubin" target=3D"_blank"></a></div></d=
iv></div>
</div>
<br><div class=3D"gmail_quote">On Mon, Jan 2, 2017 at 4:39 PM, Steve Davis =
via bitcoin-dev <span dir=3D"ltr">&lt;<a href=3D"mailto:bitcoin-dev@lists.l=
inuxfoundation.org" target=3D"_blank">bitcoin-dev@lists.<wbr>linuxfoundatio=
n.org</a>&gt;</span> wrote:<br><blockquote class=3D"gmail_quote" style=3D"m=
argin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div style=3D=
"word-wrap:break-word"><div><div style=3D"color:rgb(34,34,34);font-family:a=
rial,sans-serif;font-size:12.800000190734863px">Hi all,</div><div style=3D"=
color:rgb(34,34,34);font-family:arial,sans-serif;font-size:12.8000001907348=
63px"><br></div><div style=3D"color:rgb(34,34,34);font-family:arial,sans-se=
rif;font-size:12.800000190734863px">Suppose someone were to use the followi=
ng pk_script:</div><div style=3D"color:rgb(34,34,34);font-family:arial,sans=
-serif;font-size:12.800000190734863px"><br></div><div class=3D"m_4247512162=
626257208m_-8615729711671762748m_8591747901013163489gmail_signature" style=
=3D"color:rgb(34,34,34);font-family:arial,sans-serif;font-size:12.800000190=
734863px"><div dir=3D"ltr">[op_2dup, op_2dup, op_2dup, op_2dup, op_2dup, ..=
.(to limit)..., op_2dup,=C2=A0op_hash160, &lt;addr_hash&gt;, op_equalverify=
, op_checksig]</div><div dir=3D"ltr"><br></div><div>This still seems to be =
valid AFAICS, and may be a potential attack vector?</div><div><br></div><di=
v>Thanks.</div></div></div><div><br></div></div><br>_______________________=
_______<wbr>_________________<br>
bitcoin-dev mailing list<br>
<a href=3D"mailto:bitcoin-dev@lists.linuxfoundation.org" target=3D"_blank">=
bitcoin-dev@lists.linuxfoundat<wbr>ion.org</a><br>
<a href=3D"https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev" =
rel=3D"noreferrer" target=3D"_blank">https://lists.linuxfoundation.<wbr>org=
/mailman/listinfo/bitcoin-d<wbr>ev</a><br>
<br></blockquote></div><br></div>
______________________________<wbr>_________________<br>bitcoin-dev mailing=
 list<br><a href=3D"mailto:bitcoin-dev@lists.linuxfoundation.org" target=3D=
"_blank">bitcoin-dev@lists.<wbr>linuxfoundation.org</a><br><a href=3D"https=
://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev" target=3D"_blank=
">https://lists.linuxfoundation.<wbr>org/mailman/listinfo/bitcoin-<wbr>dev<=
/a><br></div></blockquote></div><br></div></div></div><br>_________________=
_____________<wbr>_________________<br>
bitcoin-dev mailing list<br>
<a href=3D"mailto:bitcoin-dev@lists.linuxfoundation.org">bitcoin-dev@lists.=
<wbr>linuxfoundation.org</a><br>
<a href=3D"https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev" =
rel=3D"noreferrer" target=3D"_blank">https://lists.linuxfoundation.<wbr>org=
/mailman/listinfo/bitcoin-<wbr>dev</a><br>
<br></blockquote></div><br></div>

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