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Cc: Bitcoin Protocol Discussion <bitcoin-dev@lists.linuxfoundation.org>
Subject: Re: [bitcoin-dev] cleanstack alt stack & softfork improvements
(Was: Merkle branch verification & tail-call semantics for generalized
MAST)
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--Apple-Mail=_B15E0862-A6D4-4BA1-9E1A-F403AB94707E
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> On Sep 22, 2017, at 1:32 PM, Sergio Demian Lerner =
<sergio.d.lerner@gmail.com> wrote:
>=20
>=20
>=20
> There are other solutions to this problem that could have been taken
> instead, such as committing to the number of items or maximum size of
> the stack as part of the sighash data, but cleanstack was the approach
> taken.=20
>=20
> The lack of signed maximum segwit stack size was one of the objections =
to segwit I presented last year. This together with the unlimited segwit =
stack size.
>=20
> However, committing to the maximum stack size (in bytes) for an input =
is tricky. The only place where this could be packed is in sequence_no, =
with a soft-fork. E.g. when transaction version is 2 and and only when =
lock_time is zero.
>=20
> For transactions with locktime >0, we could soft-fork so transactions =
add a last zero-satoshi output whose scriptPub contains OP_RETURN and =
followed by N VarInts, containing the maximum stack size of each input.=20=
> Normally, for a 400 byte, 2-input transaction, this will add 11 bytes, =
or a 2.5% overhead.
There=E2=80=99s no need to put it in the transaction itself. You put it =
in the witness and it is either committed to as part of the witness (in =
which case it has to hold for all possible spend paths), or at spend =
time by including it in the data signed by CHECKSIG.
--Apple-Mail=_B15E0862-A6D4-4BA1-9E1A-F403AB94707E
Content-Transfer-Encoding: quoted-printable
Content-Type: text/html;
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""><br class=3D""><div><blockquote type=3D"cite" class=3D""><div =
class=3D"">On Sep 22, 2017, at 1:32 PM, Sergio Demian Lerner <<a =
href=3D"mailto:sergio.d.lerner@gmail.com" =
class=3D"">sergio.d.lerner@gmail.com</a>> wrote:</div><br =
class=3D"Apple-interchange-newline"><div class=3D""><blockquote =
class=3D"gmail_quote" style=3D"font-family: Helvetica; font-size: 12px; =
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; margin: 0px 0px 0px 0.8ex; =
border-left-width: 1px; border-left-style: solid; border-left-color: =
rgb(204, 204, 204); padding-left: 1ex;"><br =
class=3D"Apple-interchange-newline"><br class=3D"">There are other =
solutions to this problem that could have been taken<br =
class=3D"">instead, such as committing to the number of items or maximum =
size of<br class=3D"">the stack as part of the sighash data, but =
cleanstack was the approach<br class=3D"">taken.<span =
class=3D"Apple-converted-space"> </span></blockquote><div =
style=3D"font-family: Helvetica; font-size: 12px; 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;" class=3D""><br=
class=3D""></div><div style=3D"font-family: Helvetica; font-size: 12px; =
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;" class=3D"">The lack of =
signed maximum segwit stack size was one of the objections to =
segwit I presented last year. This together with the unlimited segwit =
stack size.</div><div style=3D"font-family: Helvetica; font-size: 12px; =
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;" class=3D""><br class=3D""></div><div =
style=3D"font-family: Helvetica; font-size: 12px; 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;" =
class=3D"">However, committing to the maximum stack size (in bytes) for =
an input is tricky. The only place where this could be packed is =
in sequence_no, with a soft-fork. E.g. when transaction version is =
2 and and only when lock_time is zero.</div><div style=3D"font-family: =
Helvetica; font-size: 12px; 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;" class=3D""><span =
style=3D"background-color: rgb(249, 249, 249); font-family: sans-serif; =
font-size: 14px;" class=3D""><br class=3D""></span></div><span =
style=3D"font-family: Helvetica; font-size: 12px; 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; float: none; =
display: inline !important;" class=3D"">For transactions with locktime =
>0, we could soft-fork so transactions add a last zero-satoshi output =
whose scriptPub contains OP_RETURN and followed by N VarInts, containing =
the maximum stack size of each input.<span =
class=3D"Apple-converted-space"> </span></span><br =
style=3D"font-family: Helvetica; font-size: 12px; 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;" =
class=3D""><span style=3D"font-family: Helvetica; font-size: 12px; =
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; float: none; display: inline =
!important;" class=3D"">Normally, for a 400 byte, 2-input transaction, =
this will add 11 bytes, or a 2.5% overhead.</span></div></blockquote><br =
class=3D""></div><div>There=E2=80=99s no need to put it in the =
transaction itself. You put it in the witness and it is either committed =
to as part of the witness (in which case it has to hold for all possible =
spend paths), or at spend time by including it in the data signed by =
CHECKSIG.</div><br class=3D""></body></html>=
--Apple-Mail=_B15E0862-A6D4-4BA1-9E1A-F403AB94707E--
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