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Date: Fri, 28 Mar 2025 15:40:13 -0700 (PDT)
From: Javier Mateos <javierpmateos@gmail.com>
To: Bitcoin Development Mailing List <bitcoindev@googlegroups.com>
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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?=
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  The solution of splitting the string and using OP_CAT only works if the=
=20
exact position of the substring is known. How would a case be handled where=
=20
the substring could be in any position? =20

El mi=C3=A9rcoles, 19 de marzo de 2025 a las 22:02:05 UTC-3, Vojt=C4=9Bch S=
trnad=20
escribi=C3=B3:

> Hi Weichu,
>
> You can implement this game by having the user supply in the initial stac=
k=20
> the two parts of their public key with the middle "goodluck" removed, and=
=20
> inserting the "goodluck" as part of the script:
>
>    - script: "goodluck" OP_SWAP OP_CAT OP_CAT OP_CHECKSIG
>    - initial stack: signature pubkey_left pubkey_right
>
> Hope this helps.
>
> Vojt=C4=9Bch
> On Thursday, March 20, 2025 at 1:06:41=E2=80=AFAM UTC+1 weichu deng wrote=
:
>
>> Hi Rijndael,
>>
>> =20
>>
>> Thanks for your example=20
>>
>> [witness: foobar  foo] bar CAT EQ
>>
>> =20
>>
>> Yes, the unfixed string can be checked against a target substring in you=
r=20
>> example. However, if the target substring is located in the middle of th=
e=20
>> unfixed string, how to check it? In other words, how to have the same=20
>> function as =E2=80=9Cfoobar ob ISSUBSTR=E2=80=9D with CAT if =E2=80=9Cfo=
obar=E2=80=9D is unfixed?
>>
>> =20
>>
>> For example, suppose that a lucky draw game has the rule: if anyone has =
a=20
>> publicKey which includes a special substring "goodluck", he/she will be=
=20
>> awarded.=20
>>
>> This game can be easily implemented with OP_ISSUBSTR as follow.
>>
>> - LockScript: OP_DUP goodluck OP_ISSUBSTR...
>>
>> - UnlockScript: signature publicKey
>>
>> How to implement it with OP_CAT?
>>
>> =20
>>
>> *Regards*
>>
>> Weichu deng
>>
>> weich...@stu2024.jnu.edu.cn
>>
>> =20
>>
>> =E5=9C=A82025=E5=B9=B43=E6=9C=8819=E6=97=A5=E6=98=9F=E6=9C=9F=E4=B8=89 U=
TC+8 10:28:25<Rijndael> =E5=86=99=E9=81=93=EF=BC=9A
>>
>>> Stack elements in Taproot are limited to 520 bytes. The current proposa=
l=20
>>> for re-activating OP_CAT includes this restriction: creating a string=
=20
>>> 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=
=20
>>> provide them at spend-time as witness data (and allow them to be unfixe=
d in=20
>>> the script).
>>>
>>> Fixed: FOOBAR BAR ISSUBSTR =3D=3D FOOBAR FOO BAR CAT EQ
>>> Variable: [witness: FOOBAR] BAR ISSUBSTR =3D=3D [witness: FOOBAR FOO] B=
AR=20
>>> CAT EQ
>>>
>>>
>>> rijndael=20
>>>
>>>
>>> On Mar 18, 2025, at 11:32=E2=80=AFAM, weichu deng <weich...@stu2024.jnu=
.edu.cn>=20
>>> wrote:
>>>
>>> Hi, Peter Todd
>>> Thanks for your feedback. I agree that "Bitcoin scripts are about=20
>>> validation. Not computation."
>>> String search and concatenation are equivalent in some cases, such as i=
n=20
>>> the example you provided.
>>> However, it is still necessary to introduce the OP_ISSUBSTR operation=
=20
>>> separately.
>>> One example is converting a non-deterministic signature to a=20
>>> deterministic one.
>>> Another case is when the substring in question is located in the middle=
=20
>>> of the checked string.
>>> CAT cannot replace ISSUBSTR for the following reasons:
>>>
>>>    1. The security of CAT is still controversial. It can easily=20
>>>    generate overly long strings, potentially causing a stack overflow.=
=20
>>>    Additionally, whether OP_CAT will be restored is still under discuss=
ion.
>>>    2. The other substring (bar) must be known in advance.
>>>   =20
>>>
>>> With respect,
>>>
>>> Weichu Deng
>>>
>>> weich...@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:
>>> >=20
>>> >=20
>>> > Dear fellow Bitcoin developers,
>>> >=20
>>> >=20
>>> >=20
>>> > I am pleased to present a new BIP proposal. This proposal introduces =
a=20
>>> new=20
>>> > opcode for Bitcoin scripts: OP_ISSUBSTR.
>>> >=20
>>> >=20
>>> > *Abstract*
>>> >=20
>>> > This BIP introduces two string opcodes, OP_ISSUBSTR and=20
>>> OP_ISSUBSTRVERIFY=20
>>> > (similar to the relationship between OP_EQUAL and OP_EQUALVERIFY), to=
=20
>>> > determine whether one string is a substring of another. As these=20
>>> opcodes do=20
>>> > 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
>>>
>>>
>>> --=20
>>> You received this message because you are subscribed to the Google=20
>>> Groups "Bitcoin Development Mailing List" group.
>>> To unsubscribe from this group and stop receiving emails from it, send=
=20
>>> an email to bitcoindev+...@googlegroups.com.
>>> To view this discussion visit=20
>>> https://groups.google.com/d/msgid/bitcoindev/678d40e3-3e22-4d55-82c0-b2=
5ccafb87ecn%40googlegroups.com=20
>>> <https://groups.google.com/d/msgid/bitcoindev/678d40e3-3e22-4d55-82c0-b=
25ccafb87ecn%40googlegroups.com?utm_medium=3Demail&utm_source=3Dfooter>
>>> .
>>>
>>>
>>>

--=20
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=C2=A0 The solution of splitting the string and using OP_CAT only works if =
the exact position of the substring is known. How would a case be handled w=
here the substring could be in any position?=C2=A0=C2=A0<br /><br /><div cl=
ass=3D"gmail_quote"><div dir=3D"auto" class=3D"gmail_attr">El mi=C3=A9rcole=
s, 19 de marzo de 2025 a las 22:02:05 UTC-3, Vojt=C4=9Bch Strnad escribi=C3=
=B3:<br/></div><blockquote class=3D"gmail_quote" style=3D"margin: 0 0 0 0.8=
ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;"><div>Hi =
Weichu,</div><div><br></div><div>You can implement this game by having the =
user supply in the initial stack the two parts of their public key with the=
 middle &quot;goodluck&quot; removed, and inserting the &quot;goodluck&quot=
; as part of the script:</div><div><ul><li>script: &quot;goodluck&quot; OP_=
SWAP OP_CAT OP_CAT OP_CHECKSIG</li><li>initial stack: signature pubkey_left=
 pubkey_right</li></ul></div><div>Hope this helps.</div><div><br></div><div=
>Vojt=C4=9Bch</div><div class=3D"gmail_quote"><div dir=3D"auto" class=3D"gm=
ail_attr">On Thursday, March 20, 2025 at 1:06:41=E2=80=AFAM UTC+1 weichu de=
ng wrote:<br></div><blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 =
0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><p><span lan=
g=3D"EN-US">Hi Rijndael,</span></p>

<p><span lang=3D"EN-US">=C2=A0</span></p>

<p><span lang=3D"EN-US">Thanks for your example </span></p>

<p style=3D"text-indent:12pt"><span lang=3D"EN-US">[witness: foobar =C2=A0f=
oo] bar CAT
EQ</span></p>

<p><span lang=3D"EN-US">=C2=A0</span></p>

<p><span lang=3D"EN-US">Yes, the unfixed string can be checked
against a target substring in your example. However, if the target substrin=
g is
located in the middle of the unfixed string, how to check it? In other word=
s,
how to have the same function as =E2=80=9Cfoobar ob ISSUBSTR=E2=80=9D with =
CAT if =E2=80=9Cfoobar=E2=80=9D is
unfixed?</span></p>

<p><span lang=3D"EN-US">=C2=A0</span></p>

<p><span lang=3D"EN-US">For example, suppose that a lucky draw game
has the rule: if anyone has a publicKey which includes a special substring
&quot;goodluck&quot;, he/she will be awarded. </span></p>

<p><span lang=3D"EN-US">This game can be easily implemented with
OP_ISSUBSTR as follow.</span></p>

<p style=3D"text-indent:48pt"><span lang=3D"EN-US">- LockScript: OP_DUP goo=
dluck OP_ISSUBSTR...</span></p>

<p style=3D"text-indent:48pt"><span lang=3D"EN-US">- UnlockScript: signatur=
e publicKey</span></p>

<p><span lang=3D"EN-US">How to implement it with OP_CAT?<b></b></span></p>

<p><b><span lang=3D"EN-US">=C2=A0</span></b></p>

<p><b><span lang=3D"EN-US">Regards</span></b><span lang=3D"EN-US"></span></=
p>

<p><span lang=3D"EN-US">Weichu deng</span></p>

<p><span lang=3D"EN-US"><a rel=3D"nofollow">weich...@stu2024.jnu.edu.cn</a>=
</span></p>

<p><span lang=3D"EN-US">=C2=A0</span></p><br><div class=3D"gmail_quote"><di=
v dir=3D"auto" class=3D"gmail_attr">=E5=9C=A82025=E5=B9=B43=E6=9C=8819=E6=
=97=A5=E6=98=9F=E6=9C=9F=E4=B8=89 UTC+8 10:28:25&lt;Rijndael&gt; =E5=86=99=
=E9=81=93=EF=BC=9A<br></div><blockquote class=3D"gmail_quote" style=3D"marg=
in:0 0 0 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><di=
v dir=3D"ltr"><div dir=3D"auto" style=3D"line-break:after-white-space">Stac=
k 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.<div><br></div><div>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 scr=
ipt).</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 [witn=
ess: FOOBAR FOO] BAR CAT EQ</div><div><br></div><div><br></div><div>rijndae=
l=C2=A0</div><div><br><div style=3D"direction:ltr"><br><blockquote type=3D"=
cite"></blockquote></div></div></div></div><div dir=3D"ltr"><div dir=3D"aut=
o" style=3D"line-break:after-white-space"><div><div style=3D"direction:ltr"=
><blockquote type=3D"cite"><div>On Mar 18, 2025, at 11:32=E2=80=AFAM, weich=
u deng &lt;<a rel=3D"nofollow">weich...@stu2024.jnu.edu.cn</a>&gt; wrote:</=
div><br></blockquote></div></div></div></div><div dir=3D"ltr"><div dir=3D"a=
uto" style=3D"line-break:after-white-space"><div><div style=3D"direction:lt=
r"><blockquote type=3D"cite"><div><div style=3D"font-size:12px;font-style:n=
ormal;font-variant-caps:normal;font-weight:400;text-align:start;text-indent=
:0px;text-transform:none;white-space:pre-wrap;word-spacing:0px;text-decorat=
ion:none;padding:0px;border:0px;font-variant-numeric:inherit;font-variant-e=
ast-asian:inherit;font-variant-alternates:inherit;font-stretch:inherit;line=
-height:24px;font-family:-apple-system,BlinkMacSystemFont,&quot;Helvetica N=
eue&quot;,Helvetica,&quot;Segoe UI&quot;,Arial,Roboto,&quot;PingFang SC&quo=
t;,MIUI,&quot;Hiragino Sans GB&quot;,&quot;Microsoft YaHei&quot;,sans-serif=
;font-size-adjust:inherit;font-kerning:inherit;font-feature-settings:inheri=
t;vertical-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">Hi,=
 <span style=3D"color:rgb(32,33,36);font-family:Roboto,Arial,sans-serif">Pe=
ter Todd</span></div><div style=3D"font-size:12px;font-style:normal;font-va=
riant-caps:normal;font-weight:400;text-align:start;text-indent:0px;text-tra=
nsform:none;white-space:pre-wrap;word-spacing:0px;text-decoration:none;padd=
ing:0px;border:0px;font-variant-numeric:inherit;font-variant-east-asian:inh=
erit;font-variant-alternates:inherit;font-stretch:inherit;line-height:24px;=
font-family:-apple-system,BlinkMacSystemFont,&quot;Helvetica Neue&quot;,Hel=
vetica,&quot;Segoe UI&quot;,Arial,Roboto,&quot;PingFang SC&quot;,MIUI,&quot=
;Hiragino Sans GB&quot;,&quot;Microsoft YaHei&quot;,sans-serif;font-size-ad=
just:inherit;font-kerning:inherit;font-feature-settings:inherit;vertical-al=
ign:baseline;margin:0px 0px 0.859em;letter-spacing:0.25px;max-width:100%;ov=
erflow:auto hidden;color:rgb(6,6,7);word-break:break-word">Thanks for your =
feedback. I agree that &quot;Bitcoin scripts are about validation. Not comp=
utation.&quot;</div><div style=3D"font-size:12px;font-style:normal;font-var=
iant-caps:normal;font-weight:400;text-align:start;text-indent:0px;text-tran=
sform:none;white-space:pre-wrap;word-spacing:0px;text-decoration:none;paddi=
ng:0px;border:0px;font-variant-numeric:inherit;font-variant-east-asian:inhe=
rit;font-variant-alternates:inherit;font-stretch:inherit;line-height:24px;f=
ont-family:-apple-system,BlinkMacSystemFont,&quot;Helvetica Neue&quot;,Helv=
etica,&quot;Segoe UI&quot;,Arial,Roboto,&quot;PingFang SC&quot;,MIUI,&quot;=
Hiragino Sans GB&quot;,&quot;Microsoft YaHei&quot;,sans-serif;font-size-adj=
ust:inherit;font-kerning:inherit;font-feature-settings:inherit;vertical-ali=
gn:baseline;margin:0px 0px 0.859em;letter-spacing:0.25px;max-width:100%;ove=
rflow:auto hidden;color:rgb(6,6,7);word-break:break-word">String search and=
 concatenation are equivalent in some cases, such as in the example you pro=
vided.</div><div style=3D"font-size:12px;font-style:normal;font-variant-cap=
s:normal;font-weight:400;text-align:start;text-indent:0px;text-transform:no=
ne;white-space:pre-wrap;word-spacing:0px;text-decoration:none;padding:0px;b=
order:0px;font-variant-numeric:inherit;font-variant-east-asian:inherit;font=
-variant-alternates:inherit;font-stretch:inherit;line-height:24px;font-fami=
ly:-apple-system,BlinkMacSystemFont,&quot;Helvetica Neue&quot;,Helvetica,&q=
uot;Segoe UI&quot;,Arial,Roboto,&quot;PingFang SC&quot;,MIUI,&quot;Hiragino=
 Sans GB&quot;,&quot;Microsoft YaHei&quot;,sans-serif;font-size-adjust:inhe=
rit;font-kerning:inherit;font-feature-settings:inherit;vertical-align:basel=
ine;margin:0px 0px 0.859em;letter-spacing:0.25px;max-width:100%;overflow:au=
to hidden;color:rgb(6,6,7);word-break:break-word">However, it is still nece=
ssary to introduce the OP_ISSUBSTR operation separately.</div><div style=3D=
"font-size:12px;font-style:normal;font-variant-caps:normal;font-weight:400;=
text-align:start;text-indent:0px;text-transform:none;white-space:pre-wrap;w=
ord-spacing:0px;text-decoration:none;padding:0px;border:0px;font-variant-nu=
meric:inherit;font-variant-east-asian:inherit;font-variant-alternates:inher=
it;font-stretch:inherit;line-height:24px;font-family:-apple-system,BlinkMac=
SystemFont,&quot;Helvetica Neue&quot;,Helvetica,&quot;Segoe UI&quot;,Arial,=
Roboto,&quot;PingFang SC&quot;,MIUI,&quot;Hiragino Sans GB&quot;,&quot;Micr=
osoft YaHei&quot;,sans-serif;font-size-adjust:inherit;font-kerning:inherit;=
font-feature-settings:inherit;vertical-align:baseline;margin:0px 0px 0.859e=
m;letter-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 sign=
ature to a deterministic one.</div><div style=3D"font-size:12px;font-style:=
normal;font-variant-caps:normal;font-weight:400;text-align:start;text-inden=
t:0px;text-transform:none;white-space:pre-wrap;word-spacing:0px;text-decora=
tion:none;padding:0px;border:0px;font-variant-numeric:inherit;font-variant-=
east-asian:inherit;font-variant-alternates:inherit;font-stretch:inherit;lin=
e-height:24px;font-family:-apple-system,BlinkMacSystemFont,&quot;Helvetica =
Neue&quot;,Helvetica,&quot;Segoe UI&quot;,Arial,Roboto,&quot;PingFang SC&qu=
ot;,MIUI,&quot;Hiragino Sans GB&quot;,&quot;Microsoft YaHei&quot;,sans-seri=
f;font-size-adjust:inherit;font-kerning:inherit;font-feature-settings:inher=
it;vertical-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">An=
other case is when the substring in question is located in the middle of th=
e checked 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-t=
ransform:none;white-space:pre-wrap;word-spacing:0px;text-decoration:none;pa=
dding:0px;border:0px;font-variant-numeric:inherit;font-variant-east-asian:i=
nherit;font-variant-alternates:inherit;font-stretch:inherit;line-height:24p=
x;font-family:-apple-system,BlinkMacSystemFont,&quot;Helvetica Neue&quot;,H=
elvetica,&quot;Segoe UI&quot;,Arial,Roboto,&quot;PingFang SC&quot;,MIUI,&qu=
ot;Hiragino Sans GB&quot;,&quot;Microsoft YaHei&quot;,sans-serif;font-size-=
adjust:inherit;font-kerning:inherit;font-feature-settings:inherit;vertical-=
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">CAT cannot rep=
lace ISSUBSTR for the following reasons:</div><ol start=3D"1" style=3D"font=
-size:12px;font-style:normal;font-variant-caps:normal;font-weight:400;text-=
align:start;text-indent:0px;text-transform:none;white-space:normal;word-spa=
cing:0px;text-decoration:none;padding:0px 0px 0px 2em;border:0px;font-varia=
nt-numeric:inherit;font-variant-east-asian:inherit;font-variant-alternates:=
inherit;font-stretch:inherit;line-height:inherit;font-family:-apple-system,=
BlinkMacSystemFont,&quot;Helvetica Neue&quot;,Helvetica,&quot;Segoe UI&quot=
;,Arial,Roboto,&quot;PingFang SC&quot;,MIUI,&quot;Hiragino Sans GB&quot;,&q=
uot;Microsoft YaHei&quot;,sans-serif;font-size-adjust:inherit;font-kerning:=
inherit;font-feature-settings:inherit;vertical-align:baseline;list-style-po=
sition:initial;margin:0.859em 0px 0px;color:rgb(6,6,7);letter-spacing:0.5px=
"><li style=3D"margin:0px;padding:0px;border:0px;font-style:inherit;font-va=
riant-ligatures:inherit;font-variant-caps:inherit;font-variant-alternates:i=
nherit;font-variant-numeric:inherit;font-variant-east-asian:inherit;font-we=
ight:inherit;font-stretch:inherit;font-size:inherit;line-height:24px;font-f=
amily:inherit;font-size-adjust:inherit;font-kerning:inherit;font-feature-se=
ttings:inherit;vertical-align:baseline;letter-spacing:0.25px"><div style=3D=
"padding:0px;border:0px;font-style:inherit;font-variant-ligatures:inherit;f=
ont-variant-caps:inherit;font-variant-alternates:inherit;font-variant-numer=
ic:inherit;font-variant-east-asian:inherit;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;marg=
in:0px;max-width:100%;overflow:visible;word-break:break-word">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.</div></li><li style=3D"margin:0px;paddi=
ng:0px;border:0px;font-style:inherit;font-variant-ligatures:inherit;font-va=
riant-caps:inherit;font-variant-alternates:inherit;font-variant-numeric:inh=
erit;font-variant-east-asian:inherit;font-weight:inherit;font-stretch:inher=
it;font-size:inherit;line-height:24px;font-family:inherit;font-size-adjust:=
inherit;font-kerning:inherit;font-feature-settings:inherit;vertical-align:b=
aseline;letter-spacing:0.25px"><div style=3D"padding:0px;border:0px;font-st=
yle:inherit;font-variant-ligatures:inherit;font-variant-caps:inherit;font-v=
ariant-alternates:inherit;font-variant-numeric:inherit;font-variant-east-as=
ian:inherit;font-weight:inherit;font-stretch:inherit;line-height:24px;font-=
family:inherit;font-size-adjust:inherit;font-kerning:inherit;font-feature-s=
ettings:inherit;vertical-align:baseline;margin:0px;max-width:100%;overflow:=
visible;word-break:break-word">The other substring (bar) must be known in a=
dvance.</div></li></ol><div style=3D"font-family:Helvetica;font-size:12px;f=
ont-style:normal;font-variant-caps:normal;font-weight:400;letter-spacing:no=
rmal;text-align:start;text-indent:0px;text-transform:none;white-space:norma=
l;word-spacing:0px;text-decoration:none"><font color=3D"#060607" face=3D"-a=
pple-system, BlinkMacSystemFont, Helvetica Neue, Helvetica, Segoe UI, Arial=
, Roboto, 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-cap=
s:normal;font-weight:400;letter-spacing:normal;text-align:start;text-indent=
:0px;text-transform:none;white-space:normal;word-spacing:0px;text-decoratio=
n:none"><p><span lang=3D"EN-US">With respect,</span></p><p><span lang=3D"EN=
-US">Weichu Deng</span></p><p><span lang=3D"EN-US"><a rel=3D"nofollow">weic=
h...@stu2024.jnu.edu.cn</a></span></p></div><div style=3D"font-family:Helve=
tica;font-size:12px;font-style:normal;font-variant-caps:normal;font-weight:=
400;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:n=
one;white-space:normal;word-spacing:0px;text-decoration:none"><div dir=3D"a=
uto">=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><blo=
ckquote style=3D"margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left=
-style:solid;border-left-color:rgb(204,204,204);padding-left:1ex">On Mon, M=
ar 17, 2025 at 09:14:05AM -0700, weichu deng wrote:<br>&gt;<span>=C2=A0</sp=
an><br>&gt;<span>=C2=A0</span><br>&gt; Dear fellow Bitcoin developers,<br>&=
gt;<span>=C2=A0</span><br>&gt;<span>=C2=A0</span><br>&gt;<span>=C2=A0</span=
><br>&gt; I am pleased to present a new BIP proposal. This proposal introdu=
ces a new<span>=C2=A0</span><br>&gt; opcode for Bitcoin scripts: OP_ISSUBST=
R.<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 t=
he relationship between OP_EQUAL and OP_EQUALVERIFY), to<span>=C2=A0</span>=
<br>&gt; determine whether one string is a substring of another. As these o=
pcodes do<span>=C2=A0</span><br>&gt; not alter any blockchain state, they a=
re secure.<br><br>Bitcoin scripts are about validation. Not computation.<br=
><br>This means that substring search and concatenation are equivalent. For=
<br>every script that validates a substring search, you can instead<br>conc=
atenate the substring with the rest of the string, and validate<br>equality=
 instead.<br><br>Basically speaking:<br><br>foobar foo IsSubStr<br><br>is e=
quivalent to:<br><br>foobar foo bar Cat Equal<br><br>A real-world example w=
ould be more complex. But I hope that illustrates<br>my point sufficiently.=
<br><br>--<span>=C2=A0</span><br><a href=3D"https://petertodd.org/" rel=3D"=
nofollow" target=3D"_blank" data-saferedirecturl=3D"https://www.google.com/=
url?hl=3Des&amp;q=3Dhttps://petertodd.org/&amp;source=3Dgmail&amp;ust=3D174=
3287600558000&amp;usg=3DAOvVaw1Ik2DvB3qmfvCC6WNopIcs">https://petertodd.org=
</a><span>=C2=A0</span>&#39;peter&#39;[:-1]@<a href=3D"http://petertodd.org=
/" rel=3D"nofollow" target=3D"_blank" data-saferedirecturl=3D"https://www.g=
oogle.com/url?hl=3Des&amp;q=3Dhttp://petertodd.org/&amp;source=3Dgmail&amp;=
ust=3D1743287600558000&amp;usg=3DAOvVaw3q9sFCwjUyG-epYef9h89z">petertodd.or=
g</a><br></blockquote></div><div style=3D"font-family:Helvetica;font-size:1=
2px;font-style:normal;font-variant-caps:normal;font-weight:400;letter-spaci=
ng:normal;text-align:start;text-indent:0px;text-transform:none;white-space:=
normal;word-spacing:0px;text-decoration:none"><br></div></div></blockquote>=
</div></div></div></div><div dir=3D"ltr"><div dir=3D"auto" style=3D"line-br=
eak:after-white-space"><div><div style=3D"direction:ltr"><blockquote type=
=3D"cite"><div><span 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;float:none;display:inline!important">--<sp=
an>=C2=A0</span></span><br style=3D"font-family:Helvetica;font-size:12px;fo=
nt-style:normal;font-variant-caps:normal;font-weight:400;letter-spacing:nor=
mal;text-align:start;text-indent:0px;text-transform:none;white-space:normal=
;word-spacing:0px;text-decoration:none"><span style=3D"font-family:Helvetic=
a;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;float:none;displa=
y:inline!important">You received this message because you are subscribed to=
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text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;tex=
t-decoration:none"><span style=3D"font-family:Helvetica;font-size:12px;font=
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on:none"><span style=3D"font-family:Helvetica;font-size:12px;font-style:nor=
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s discussion visit<span>=C2=A0</span></span><a href=3D"https://groups.googl=
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</blockquote></div></blockquote></div></blockquote></div>

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