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From: Johnson Lau <jl2012@xbt.hk>
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To: Jeremy <jlrubin@mit.edu>,
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Cc: Steve Davis <steven.charles.davis@gmail.com>
Subject: Re: [bitcoin-dev] Script Abuse Potential?
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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:
>=20
> 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 to (10000-520*2)*520*2 bytes ~=3D~ 10 MB.
>=20
> =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 :)
>=20
>=20
>=20
> --
> @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 =
<mailto:bitcoin-dev@lists.linuxfoundation.org>> wrote:
> Hi all,
>=20
> Suppose someone were to use the following pk_script:
>=20
> [op_2dup, op_2dup, op_2dup, op_2dup, op_2dup, ...(to limit)..., =
op_2dup, op_hash160, <addr_hash>, op_equalverify, op_checksig]
>=20
> This still seems to be valid AFAICS, and may be a potential attack =
vector?
>=20
> Thanks.
>=20
>=20
> _______________________________________________
> bitcoin-dev mailing list
> bitcoin-dev@lists.linuxfoundation.org =
<mailto:bitcoin-dev@lists.linuxfoundation.org>
> https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev =
<https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev>
>=20
>=20
> _______________________________________________
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Content-Transfer-Encoding: quoted-printable
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charset=utf-8
<html><head><meta http-equiv=3D"Content-Type" content=3D"text/html =
charset=3Dutf-8"></head><body style=3D"word-wrap: break-word; =
-webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" =
class=3D""><div class=3D"">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</div><div class=3D""><br class=3D""></div><div =
class=3D"">For OP_CAT, just check if the returned item is within the 520 =
bytes limit.</div><br class=3D""><div><blockquote type=3D"cite" =
class=3D""><div class=3D"">On 3 Jan 2017, at 11:27, Jeremy via =
bitcoin-dev <<a href=3D"mailto:bitcoin-dev@lists.linuxfoundation.org" =
class=3D"">bitcoin-dev@lists.linuxfoundation.org</a>> wrote:</div><br =
class=3D"Apple-interchange-newline"><div class=3D""><div dir=3D"ltr" =
class=3D""><div class=3D"gmail_default" style=3D"font-family: arial, =
helvetica, sans-serif; font-size: small;"><span =
style=3D"font-family:arial,sans-serif;color:rgb(34,34,34);font-size:12.800=
000190734863px" class=3D"">It is an unfortunate script, but can't =
actually </span><div class=3D"gmail_default" =
style=3D"display:inline">=E2=80=8Bdo</div><span =
style=3D"font-family:arial,sans-serif;color:rgb(34,34,34);font-size:12.800=
000190734863px" class=3D""> that much</span><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:12.800=
000190734863px" class=3D"">. The MAX_SCRIPT_ELEMENT_SIZE =3D 520 =
Bytes.</span><div class=3D"gmail_default" =
style=3D"font-family:arial,sans-serif;color:rgb(34,34,34);font-size:12.800=
000190734863px;display:inline"><font face=3D"arial, helvetica, =
sans-serif" class=3D"">=E2=80=8B Thus, it would seem the worst you could =
do with this would be to </font>(10000-520*2)*520*2 bytes ~=3D~=
10 MB.</div></div><div style=3D"font-size:12.800000190734863px" =
class=3D""><br class=3D""></div><div =
style=3D"font-size:12.800000190734863px" class=3D""><div =
class=3D"gmail_default" style=3D"font-family: arial, helvetica, =
sans-serif; font-size: small;">=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 :)</div><div class=3D""><br =
class=3D""></div></div></div><div class=3D"gmail_extra"><br clear=3D"all" =
class=3D""><div class=3D""><br clear=3D"all" class=3D""><div =
class=3D""><div class=3D"gmail_signature" =
data-smartmail=3D"gmail_signature"><div dir=3D"ltr" class=3D"">--<br =
class=3D""><a href=3D"https://twitter.com/JeremyRubin" target=3D"_blank" =
class=3D"">@JeremyRubin</a><a href=3D"https://twitter.com/JeremyRubin" =
target=3D"_blank" class=3D""></a></div></div></div>
</div>
<br class=3D""><div class=3D"gmail_quote">On Mon, Jan 2, 2017 at 4:39 =
PM, Steve Davis via bitcoin-dev <span dir=3D"ltr" class=3D""><<a =
href=3D"mailto:bitcoin-dev@lists.linuxfoundation.org" target=3D"_blank" =
class=3D"">bitcoin-dev@lists.linuxfoundation.org</a>></span> =
wrote:<br class=3D""><blockquote class=3D"gmail_quote" style=3D"margin:0 =
0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div =
style=3D"word-wrap:break-word" class=3D""><div class=3D""><div =
style=3D"color:rgb(34,34,34);font-family:arial,sans-serif;font-size:12.800=
000190734863px" class=3D"">Hi all,</div><div =
style=3D"color:rgb(34,34,34);font-family:arial,sans-serif;font-size:12.800=
000190734863px" class=3D""><br class=3D""></div><div =
style=3D"color:rgb(34,34,34);font-family:arial,sans-serif;font-size:12.800=
000190734863px" class=3D"">Suppose someone were to use the following =
pk_script:</div><div =
style=3D"color:rgb(34,34,34);font-family:arial,sans-serif;font-size:12.800=
000190734863px" class=3D""><br class=3D""></div><div =
class=3D"m_-8615729711671762748m_8591747901013163489gmail_signature" =
style=3D"color:rgb(34,34,34);font-family:arial,sans-serif;font-size:12.800=
000190734863px"><div dir=3D"ltr" class=3D"">[op_2dup, op_2dup, op_2dup, =
op_2dup, op_2dup, ...(to limit)..., op_2dup, op_hash160, =
<addr_hash>, op_equalverify, op_checksig]</div><div dir=3D"ltr" =
class=3D""><br class=3D""></div><div class=3D"">This still seems to be =
valid AFAICS, and may be a potential attack vector?</div><div =
class=3D""><br class=3D""></div><div =
class=3D"">Thanks.</div></div></div><div class=3D""><br =
class=3D""></div></div><br class=3D"">______________________________<wbr =
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.<wbr class=3D"">linuxfoundation.org</a><br =
class=3D"">
<a href=3D"https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev"=
rel=3D"noreferrer" target=3D"_blank" =
class=3D"">https://lists.linuxfoundation.<wbr =
class=3D"">org/mailman/listinfo/bitcoin-<wbr class=3D"">dev</a><br =
class=3D"">
<br class=3D""></blockquote></div><br class=3D""></div>
_______________________________________________<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"">https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev<=
br class=3D""></div></blockquote></div><br class=3D""></body></html>=
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