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 where the substring could be in any position? El miércoles, 19 de marzo de 2025 a las 22:02:05 UTC-3, Vojtěch Strnad escribió: > Hi Weichu, > > You can implement this game by having the user supply in the initial stack > the two parts of their public key with the middle "goodluck" removed, and > 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. > > Vojtěch > On Thursday, March 20, 2025 at 1:06:41 AM UTC+1 weichu deng wrote: > >> Hi Rijndael, >> >> >> >> Thanks for your example >> >> [witness: foobar foo] bar CAT EQ >> >> >> >> Yes, the unfixed string can be checked against a target substring in your >> example. However, if the target substring is located in the middle of the >> unfixed string, how to check it? In other words, how to have the same >> function as “foobar ob ISSUBSTR” with CAT if “foobar” is unfixed? >> >> >> >> For example, suppose that a lucky draw game has the rule: if anyone has a >> publicKey which includes a special substring "goodluck", he/she will be >> awarded. >> >> 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? >> >> >> >> *Regards* >> >> Weichu deng >> >> weich...@stu2024.jnu.edu.cn >> >> >> >> 在2025年3月19日星期三 UTC+8 10:28:25 写道： >> >>> 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 >>> 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 >>> >>> weich...@stu2024.jnu.edu.cn >>> 在2025年3月18日星期二 UTC+8 01:01:16 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 >>> >>> >>> -- >>> You received this message because you are subscribed to the Google >>> Groups "Bitcoin Development Mailing List" group. >>> To unsubscribe from this group and stop receiving emails from it, send >>> an email to bitcoindev+...@googlegroups.com. >>> To view this discussion visit >>> https://groups.google.com/d/msgid/bitcoindev/678d40e3-3e22-4d55-82c0-b25ccafb87ecn%40googlegroups.com >>> >>> . >>> >>> >>> -- You received this message because you are subscribed to the Google Groups "Bitcoin Development Mailing List" group. 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