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From: Rijndael <rot13maxi@gmail.com>
Date: Tue, 18 Mar 2025 17:33:37 -0400
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Subject: =?UTF-8?Q?Re=3A_=5Bbitcoindev=5D_New_Proposal=EF=BC=9AString_Substring_Sea?=
	=?UTF-8?Q?rch_in_Bitcoin_Script_=2D_OP=5FISSUBSTR?=
To: weichu deng <weichudeng@stu2024.jnu.edu.cn>
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Stack elements in Taproot are limited to 520 bytes. The current proposal
for re-activating OP_CAT includes this restriction: creating a string
longer than 520 bytes with CAT will cause the script to fail.

With either CAT or ISSUBSTR, you can either commit to the substrings or
provide them at spend-time as witness data (and allow them to be unfixed in
the script).

Fixed: FOOBAR BAR ISSUBSTR =3D=3D FOOBAR FOO BAR CAT EQ
Variable: [witness: FOOBAR] BAR ISSUBSTR =3D=3D [witness: FOOBAR FOO] BAR C=
AT EQ


rijndael


On Mar 18, 2025, at 11:32=E2=80=AFAM, weichu deng <weichudeng@stu2024.jnu.e=
du.cn>
wrote:

Hi, Peter Todd
Thanks for your feedback. I agree that "Bitcoin scripts are about
validation. Not computation."
String search and concatenation are equivalent in some cases, such as in
the example you provided.
However, it is still necessary to introduce the OP_ISSUBSTR operation
separately.
One example is converting a non-deterministic signature to a deterministic
one.
Another case is when the substring in question is located in the middle of
the checked string.
CAT cannot replace ISSUBSTR for the following reasons:

   1. The security of CAT is still controversial. It can easily generate
   overly long strings, potentially causing a stack overflow. Additionally,
   whether OP_CAT will be restored is still under discussion.
   2. The other substring (bar) must be known in advance.


With respect,

Weichu Deng

weichudeng@stu2024.jnu.edu.cn
=E5=9C=A82025=E5=B9=B43=E6=9C=8818=E6=97=A5=E6=98=9F=E6=9C=9F=E4=BA=8C UTC+=
8 01:01:16<Peter Todd> =E5=86=99=E9=81=93=EF=BC=9A

On Mon, Mar 17, 2025 at 09:14:05AM -0700, weichu deng wrote:
>
>
> Dear fellow Bitcoin developers,
>
>
>
> I am pleased to present a new BIP proposal. This proposal introduces a ne=
w

> opcode for Bitcoin scripts: OP_ISSUBSTR.
>
>
> *Abstract*
>
> This BIP introduces two string opcodes, OP_ISSUBSTR and OP_ISSUBSTRVERIFY
> (similar to the relationship between OP_EQUAL and OP_EQUALVERIFY), to
> determine whether one string is a substring of another. As these opcodes
do
> not alter any blockchain state, they are secure.

Bitcoin scripts are about validation. Not computation.

This means that substring search and concatenation are equivalent. For
every script that validates a substring search, you can instead
concatenate the substring with the rest of the string, and validate
equality instead.

Basically speaking:

foobar foo IsSubStr

is equivalent to:

foobar foo bar Cat Equal

A real-world example would be more complex. But I hope that illustrates
my point sufficiently.

--=20
https://petertodd.org 'peter'[:-1]@petertodd.org


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<div dir=3D"ltr"><div dir=3D"auto" style=3D"line-break:after-white-space">S=
tack elements in Taproot are limited to 520 bytes. The current proposal for=
 re-activating OP_CAT includes this restriction: creating a string longer t=
han 520 bytes with CAT will cause the script to fail.<div><br></div><div>Wi=
th either CAT or ISSUBSTR, you can either commit to the substrings or provi=
de them at spend-time as witness data (and allow them to be unfixed in the =
script).</div><div><br></div><div>Fixed: FOOBAR BAR ISSUBSTR =3D=3D FOOBAR =
FOO BAR CAT EQ</div><div>Variable: [witness: FOOBAR] BAR ISSUBSTR =3D=3D [w=
itness: FOOBAR FOO] BAR CAT EQ</div><div><br></div><div><br></div><div>rijn=
dael=C2=A0</div><div><br id=3D"m_1356653997907207526lineBreakAtBeginningOfM=
essage"><div style=3D"direction:ltr"><br><blockquote type=3D"cite"><div>On =
Mar 18, 2025, at 11:32=E2=80=AFAM, weichu deng &lt;<a href=3D"mailto:weichu=
deng@stu2024.jnu.edu.cn" target=3D"_blank">weichudeng@stu2024.jnu.edu.cn</a=
>&gt; wrote:</div><br><div><div style=3D"font-size:12px;font-style:normal;f=
ont-variant-caps:normal;font-weight:400;text-align:start;text-indent:0px;te=
xt-transform:none;white-space:pre-wrap;word-spacing:0px;text-decoration:non=
e;padding:0px;border:0px;font-variant-numeric:inherit;font-variant-east-asi=
an:inherit;font-variant-alternates:inherit;font-stretch:inherit;line-height=
:24px;font-family:-apple-system,BlinkMacSystemFont,&quot;Helvetica Neue&quo=
t;,Helvetica,&quot;Segoe UI&quot;,Arial,Roboto,&quot;PingFang SC&quot;,MIUI=
,&quot;Hiragino Sans GB&quot;,&quot;Microsoft YaHei&quot;,sans-serif;font-s=
ize-adjust:inherit;font-kerning:inherit;font-feature-settings:inherit;verti=
cal-align:baseline;margin:0px 0px 0.859em;letter-spacing:0.25px;max-width:1=
00%;overflow:auto hidden;color:rgb(6,6,7);word-break:break-word">Hi, <span =
style=3D"color:rgb(32,33,36);font-family:Roboto,Arial,sans-serif">Peter Tod=
d</span></div><div style=3D"font-size:12px;font-style:normal;font-variant-c=
aps:normal;font-weight:400;text-align:start;text-indent:0px;text-transform:=
none;white-space:pre-wrap;word-spacing:0px;text-decoration:none;padding:0px=
;border:0px;font-variant-numeric:inherit;font-variant-east-asian:inherit;fo=
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&quot;Segoe UI&quot;,Arial,Roboto,&quot;PingFang SC&quot;,MIUI,&quot;Hiragi=
no Sans GB&quot;,&quot;Microsoft YaHei&quot;,sans-serif;font-size-adjust:in=
herit;font-kerning:inherit;font-feature-settings:inherit;vertical-align:bas=
eline;margin:0px 0px 0.859em;letter-spacing:0.25px;max-width:100%;overflow:=
auto hidden;color:rgb(6,6,7);word-break:break-word">Thanks for your feedbac=
k. I agree that &quot;Bitcoin scripts are about validation. Not computation=
.&quot;</div><div style=3D"font-size:12px;font-style:normal;font-variant-ca=
ps:normal;font-weight:400;text-align:start;text-indent:0px;text-transform:n=
one;white-space:pre-wrap;word-spacing:0px;text-decoration:none;padding:0px;=
border:0px;font-variant-numeric:inherit;font-variant-east-asian:inherit;fon=
t-variant-alternates:inherit;font-stretch:inherit;line-height:24px;font-fam=
ily:-apple-system,BlinkMacSystemFont,&quot;Helvetica Neue&quot;,Helvetica,&=
quot;Segoe UI&quot;,Arial,Roboto,&quot;PingFang SC&quot;,MIUI,&quot;Hiragin=
o Sans GB&quot;,&quot;Microsoft YaHei&quot;,sans-serif;font-size-adjust:inh=
erit;font-kerning:inherit;font-feature-settings:inherit;vertical-align:base=
line;margin:0px 0px 0.859em;letter-spacing:0.25px;max-width:100%;overflow:a=
uto hidden;color:rgb(6,6,7);word-break:break-word">String search and concat=
enation are equivalent in some cases, such as in the example you provided.<=
/div><div style=3D"font-size:12px;font-style:normal;font-variant-caps:norma=
l;font-weight:400;text-align:start;text-indent:0px;text-transform:none;whit=
e-space:pre-wrap;word-spacing:0px;text-decoration:none;padding:0px;border:0=
px;font-variant-numeric:inherit;font-variant-east-asian:inherit;font-varian=
t-alternates:inherit;font-stretch:inherit;line-height:24px;font-family:-app=
le-system,BlinkMacSystemFont,&quot;Helvetica Neue&quot;,Helvetica,&quot;Seg=
oe UI&quot;,Arial,Roboto,&quot;PingFang SC&quot;,MIUI,&quot;Hiragino Sans G=
B&quot;,&quot;Microsoft YaHei&quot;,sans-serif;font-size-adjust:inherit;fon=
t-kerning:inherit;font-feature-settings:inherit;vertical-align:baseline;mar=
gin:0px 0px 0.859em;letter-spacing:0.25px;max-width:100%;overflow:auto hidd=
en;color:rgb(6,6,7);word-break:break-word">However, it is still necessary t=
o introduce the OP_ISSUBSTR operation separately.</div><div style=3D"font-s=
ize:12px;font-style:normal;font-variant-caps:normal;font-weight:400;text-al=
ign:start;text-indent:0px;text-transform:none;white-space:pre-wrap;word-spa=
cing:0px;text-decoration:none;padding:0px;border:0px;font-variant-numeric:i=
nherit;font-variant-east-asian:inherit;font-variant-alternates:inherit;font=
-stretch:inherit;line-height:24px;font-family:-apple-system,BlinkMacSystemF=
ont,&quot;Helvetica Neue&quot;,Helvetica,&quot;Segoe UI&quot;,Arial,Roboto,=
&quot;PingFang SC&quot;,MIUI,&quot;Hiragino Sans GB&quot;,&quot;Microsoft Y=
aHei&quot;,sans-serif;font-size-adjust:inherit;font-kerning:inherit;font-fe=
ature-settings:inherit;vertical-align:baseline;margin:0px 0px 0.859em;lette=
r-spacing:0.25px;max-width:100%;overflow:auto hidden;color:rgb(6,6,7);word-=
break:break-word">One example is converting a non-deterministic signature t=
o a deterministic one.</div><div style=3D"font-size:12px;font-style:normal;=
font-variant-caps:normal;font-weight:400;text-align:start;text-indent:0px;t=
ext-transform:none;white-space:pre-wrap;word-spacing:0px;text-decoration:no=
ne;padding:0px;border:0px;font-variant-numeric:inherit;font-variant-east-as=
ian:inherit;font-variant-alternates:inherit;font-stretch:inherit;line-heigh=
t:24px;font-family:-apple-system,BlinkMacSystemFont,&quot;Helvetica Neue&qu=
ot;,Helvetica,&quot;Segoe UI&quot;,Arial,Roboto,&quot;PingFang SC&quot;,MIU=
I,&quot;Hiragino Sans GB&quot;,&quot;Microsoft YaHei&quot;,sans-serif;font-=
size-adjust:inherit;font-kerning:inherit;font-feature-settings:inherit;vert=
ical-align:baseline;margin:0px 0px 0.859em;letter-spacing:0.25px;max-width:=
100%;overflow:auto hidden;color:rgb(6,6,7);word-break:break-word">Another c=
ase is when the substring in question is located in the middle of the check=
ed string.</div><div style=3D"font-size:12px;font-style:normal;font-variant=
-caps:normal;font-weight:400;text-align:start;text-indent:0px;text-transfor=
m:none;white-space:pre-wrap;word-spacing:0px;text-decoration:none;padding:0=
px;border:0px;font-variant-numeric:inherit;font-variant-east-asian:inherit;=
font-variant-alternates:inherit;font-stretch:inherit;line-height:24px;font-=
family:-apple-system,BlinkMacSystemFont,&quot;Helvetica Neue&quot;,Helvetic=
a,&quot;Segoe UI&quot;,Arial,Roboto,&quot;PingFang SC&quot;,MIUI,&quot;Hira=
gino Sans GB&quot;,&quot;Microsoft YaHei&quot;,sans-serif;font-size-adjust:=
inherit;font-kerning:inherit;font-feature-settings:inherit;vertical-align:b=
aseline;margin:0px 0px 0.859em;letter-spacing:0.25px;max-width:100%;overflo=
w:auto hidden;color:rgb(6,6,7);word-break:break-word">CAT cannot replace IS=
SUBSTR for the following reasons:</div><ol start=3D"1" style=3D"font-size:1=
2px;font-style:normal;font-variant-caps:normal;font-weight:400;text-align:s=
tart;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0p=
x;text-decoration:none;padding:0px 0px 0px 2em;border:0px;font-variant-nume=
ric:inherit;font-variant-east-asian:inherit;font-variant-alternates:inherit=
;font-stretch:inherit;line-height:inherit;font-family:-apple-system,BlinkMa=
cSystemFont,&quot;Helvetica Neue&quot;,Helvetica,&quot;Segoe UI&quot;,Arial=
,Roboto,&quot;PingFang SC&quot;,MIUI,&quot;Hiragino Sans GB&quot;,&quot;Mic=
rosoft YaHei&quot;,sans-serif;font-size-adjust:inherit;font-kerning:inherit=
;font-feature-settings:inherit;vertical-align:baseline;list-style-position:=
initial;margin:0.859em 0px 0px;color:rgb(6,6,7);letter-spacing:0.5px"><li s=
tyle=3D"margin:0px;padding:0px;border:0px;font-style:inherit;font-variant-l=
igatures:inherit;font-variant-caps:inherit;font-variant-alternates:inherit;=
font-variant-numeric:inherit;font-variant-east-asian:inherit;font-weight:in=
herit;font-stretch:inherit;font-size:inherit;line-height:24px;font-family:i=
nherit;font-size-adjust:inherit;font-kerning:inherit;font-feature-settings:=
inherit;vertical-align:baseline;letter-spacing:0.25px"><div style=3D"paddin=
g:0px;border:0px;font-style:inherit;font-variant-ligatures:inherit;font-var=
iant-caps:inherit;font-variant-alternates:inherit;font-variant-numeric:inhe=
rit;font-variant-east-asian:inherit;font-weight:inherit;font-stretch:inheri=
t;line-height:24px;font-family:inherit;font-size-adjust:inherit;font-kernin=
g:inherit;font-feature-settings:inherit;vertical-align:baseline;margin:0px;=
max-width:100%;overflow:visible;word-break:break-word">The security of CAT =
is still controversial. It can easily generate overly long strings, potenti=
ally causing a stack overflow. Additionally, whether OP_CAT will be restore=
d is still under discussion.</div></li><li style=3D"margin:0px;padding:0px;=
border:0px;font-style:inherit;font-variant-ligatures:inherit;font-variant-c=
aps:inherit;font-variant-alternates:inherit;font-variant-numeric:inherit;fo=
nt-variant-east-asian:inherit;font-weight:inherit;font-stretch:inherit;font=
-size:inherit;line-height:24px;font-family:inherit;font-size-adjust:inherit=
;font-kerning:inherit;font-feature-settings:inherit;vertical-align:baseline=
;letter-spacing:0.25px"><div style=3D"padding:0px;border:0px;font-style:inh=
erit;font-variant-ligatures:inherit;font-variant-caps:inherit;font-variant-=
alternates:inherit;font-variant-numeric:inherit;font-variant-east-asian:inh=
erit;font-weight:inherit;font-stretch:inherit;line-height:24px;font-family:=
inherit;font-size-adjust:inherit;font-kerning:inherit;font-feature-settings=
:inherit;vertical-align:baseline;margin:0px;max-width:100%;overflow:visible=
;word-break:break-word">The other substring (bar) must be known in advance.=
</div></li></ol><div style=3D"font-family:Helvetica;font-size:12px;font-sty=
le:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;te=
xt-align:start;text-indent:0px;text-transform:none;white-space:normal;word-=
spacing:0px;text-decoration:none"><font color=3D"#060607" face=3D"-apple-sy=
stem, BlinkMacSystemFont, Helvetica Neue, Helvetica, Segoe UI, Arial, Robot=
o, PingFang SC, MIUI, Hiragino Sans GB, Microsoft YaHei, sans-serif"><span =
style=3D"letter-spacing:0.25px"><br></span></font></div><div style=3D"font-=
family:Helvetica;font-size:12px;font-style:normal;font-variant-caps:normal;=
font-weight:400;letter-spacing:normal;text-align:start;text-indent:0px;text=
-transform:none;white-space:normal;word-spacing:0px;text-decoration:none"><=
p><span lang=3D"EN-US">With respect,</span></p><p><span lang=3D"EN-US">Weic=
hu Deng</span></p><p><span lang=3D"EN-US"><a href=3D"mailto:weichudeng@stu2=
024.jnu.edu.cn" target=3D"_blank">weichudeng@stu2024.jnu.edu.cn</a></span><=
/p></div><div style=3D"font-family:Helvetica;font-size:12px;font-style:norm=
al;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-alig=
n:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing=
:0px;text-decoration:none"><div dir=3D"auto">=E5=9C=A82025=E5=B9=B43=E6=9C=
=8818=E6=97=A5=E6=98=9F=E6=9C=9F=E4=BA=8C UTC+8 01:01:16&lt;Peter Todd&gt; =
=E5=86=99=E9=81=93=EF=BC=9A<br></div><blockquote style=3D"margin:0px 0px 0p=
x 0.8ex;border-left-width:1px;border-left-style:solid;border-left-color:rgb=
(204,204,204);padding-left:1ex">On Mon, Mar 17, 2025 at 09:14:05AM -0700, w=
eichu deng wrote:<br>&gt;<span>=C2=A0</span><br>&gt;<span>=C2=A0</span><br>=
&gt; Dear fellow Bitcoin developers,<br>&gt;<span>=C2=A0</span><br>&gt;<spa=
n>=C2=A0</span><br>&gt;<span>=C2=A0</span><br>&gt; I am pleased to present =
a new BIP proposal. This proposal introduces a new<span>=C2=A0</span><br>&g=
t; opcode for Bitcoin scripts: OP_ISSUBSTR.<br>&gt;<span>=C2=A0</span><br>&=
gt;<span>=C2=A0</span><br>&gt; *Abstract*<br>&gt;<span>=C2=A0</span><br>&gt=
; This BIP introduces two string opcodes, OP_ISSUBSTR and OP_ISSUBSTRVERIFY=
<span>=C2=A0</span><br>&gt; (similar to the relationship between OP_EQUAL a=
nd OP_EQUALVERIFY), to<span>=C2=A0</span><br>&gt; determine whether one str=
ing is a substring of another. As these opcodes do<span>=C2=A0</span><br>&g=
t; not alter any blockchain state, they are secure.<br><br>Bitcoin scripts =
are about validation. Not computation.<br><br>This means that substring sea=
rch and concatenation are equivalent. For<br>every script that validates a =
substring search, you can instead<br>concatenate the substring with the res=
t of the string, and validate<br>equality instead.<br><br>Basically speakin=
g:<br><br>foobar foo IsSubStr<br><br>is equivalent to:<br><br>foobar foo ba=
r Cat Equal<br><br>A real-world example would be more complex. But I hope t=
hat illustrates<br>my point sufficiently.<br><br>--<span>=C2=A0</span><br><=
a href=3D"https://petertodd.org/" rel=3D"nofollow" target=3D"_blank">https:=
//petertodd.org</a><span>=C2=A0</span>&#39;peter&#39;[:-1]@<a href=3D"http:=
//petertodd.org/" rel=3D"nofollow" target=3D"_blank">petertodd.org</a><br><=
/blockquote></div><div style=3D"font-family:Helvetica;font-size:12px;font-s=
tyle:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;=
text-align:start;text-indent:0px;text-transform:none;white-space:normal;wor=
d-spacing:0px;text-decoration:none"><br></div><span style=3D"font-family:He=
lvetica;font-size:12px;font-style:normal;font-variant-caps:normal;font-weig=
ht:400;letter-spacing:normal;text-align:start;text-indent:0px;text-transfor=
m:none;white-space:normal;word-spacing:0px;text-decoration:none;float:none;=
display:inline!important">--<span>=C2=A0</span></span><br style=3D"font-fam=
ily:Helvetica;font-size:12px;font-style:normal;font-variant-caps:normal;fon=
t-weight:400;letter-spacing:normal;text-align:start;text-indent:0px;text-tr=
ansform:none;white-space:normal;word-spacing:0px;text-decoration:none"><spa=
n style=3D"font-family:Helvetica;font-size:12px;font-style:normal;font-vari=
ant-caps:normal;font-weight:400;letter-spacing:normal;text-align:start;text=
-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;text-de=
coration:none;float:none;display:inline!important">You received this messag=
e because you are subscribed to the Google Groups &quot;Bitcoin Development=
 Mailing List&quot; group.</span><br style=3D"font-family:Helvetica;font-si=
ze:12px;font-style:normal;font-variant-caps:normal;font-weight:400;letter-s=
pacing:normal;text-align:start;text-indent:0px;text-transform:none;white-sp=
ace:normal;word-spacing:0px;text-decoration:none"><span style=3D"font-famil=
y:Helvetica;font-size:12px;font-style:normal;font-variant-caps:normal;font-=
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ant">.</span><br style=3D"font-family:Helvetica;font-size:12px;font-style:n=
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