Missing CheckMinimalPush check in MatchMultisig: largest IsStandard multisig n-of-3 is 12 bytes too large? #23285

1. 
   practicalswift commented at 9:44 am on October 15, 2021: contributor

   The following four equivalent scripts all pass standardness check (IsStandard):

   • 1 0x21 0x020000000000000000000000000000000000000000000000000000000000000000 1 CHECKMULTISIG
   • 1 0x4c21 0x020000000000000000000000000000000000000000000000000000000000000000 1 CHECKMULTISIG
   • 1 0x4d2100 0x020000000000000000000000000000000000000000000000000000000000000000 1 CHECKMULTISIG
   • 1 0x4e21000000 0x020000000000000000000000000000000000000000000000000000000000000000 1 CHECKMULTISIG

   Where 0x4c == OP_PUSHDATA1, 0x4d == OP_PUSHDATA2 and 0x4e == OP_PUSHDATA4.

   Only the first one would pass the standardness check if minimal representation was enforced.

   AFAICT we check for minimal representation in all other IsStandard standardness checks. Is there any particular reason we’re not doing it for CHECKMULTISIG in MatchMultisig? :)

2. 
   theStack commented at 11:39 am on October 19, 2021: contributor

   Good find! As far as I can see there is no reason to not enforce minimal representation also on multisig scripts to be considered as IsStandard. Happy to open a PR which fixes (and tests) this if there are no objections.
3. 
   darosior commented at 9:32 am on November 11, 2021: member

   Probably want to check if some (admittedly broken) application doesn’t rely on it before tightening the rules as it’s still in use. This seems like a good place to start looking for such outputs.
4. willcl-ark added the label Validation on Jan 16, 2026
5. willcl-ark added the label Needs Conceptual Review on Jan 16, 2026

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practicalswift theStack darosior

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Validation Needs Conceptual Review