From: Rijndael <rot13maxi@gmail•com>
To: weichu deng <weichudeng@stu2024•jnu.edu.cn>
Cc: Bitcoin Development Mailing List <bitcoindev@googlegroups.com>
Subject: Re: [bitcoindev] New Proposal：String Substring Search in Bitcoin Script - OP_ISSUBSTR
Date: Tue, 18 Mar 2025 17:33:37 -0400 [thread overview]
Message-ID: <CAD2YOAp=ft+pApAwh6CQvwMpujfZ0ysSK+=7zKA64nBeB5w3nA@mail.gmail.com> (raw)
In-Reply-To: <678d40e3-3e22-4d55-82c0-b25ccafb87ecn@googlegroups.com>
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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 == FOOBAR FOO BAR CAT EQ
Variable: [witness: FOOBAR] BAR ISSUBSTR == [witness: FOOBAR FOO] BAR CAT EQ
rijndael
On Mar 18, 2025, at 11:32 AM, weichu deng <weichudeng@stu2024•jnu.edu.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
在2025年3月18日星期二 UTC+8 01:01:16<Peter Todd> 写道：
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 new
> 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.
--
https://petertodd.org 'peter'[:-1]@petertodd.org
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next prev parent reply other threads:[~2025-03-19 2:28 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-03-17 16:14 weichu deng
2025-03-17 16:54 ` Peter Todd
2025-03-18 15:32 ` weichu deng
2025-03-18 21:33 ` Rijndael [this message]
2025-03-18 16:41 ` Erik Aronesty
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