descriptor: Expose key expression parsing #35918

pull pseudoramdom wants to merge 3 commits into bitcoin:master from pseudoramdom:parse-key-expression-v2 changing 3 files +302 −86

pseudoramdom commented at 6:44 PM on August 6, 2026: contributor
This PR exposes a utility function to parse and validate a standalone descriptor key expression. This is particularly useful in GUI multisig setup flows where the UI accepts a pasted key expression. The GUI can use this parser to validate input, inspect the parsed key, and apply setup-specific policy i.e. reject private keys, uncompressed keys etc. (Multisig Wizard tracking issue: #35645)

PubkeyProvider is the existing internal representation of a parsed key expression. This PR exposes its interface in descriptor.h and adds a public ParsePubkey() overload that returns the providers produced by the existing parser.

Key changes
- public overload uses P2TR key rules, permitting compressed, x-only, extended, and MuSig key expressions while rejecting uncompressed keys.
- Add GetOriginInfo() for retrieving explicitly provided key origin information.
Also, while I'm here, I noticed that musig parser accepted trailing characters apart from /.
- Add a fix & test to reject unexpected trailing characters after a musig() expression
DrahtBot added the label Descriptors on Aug 6, 2026
DrahtBot commented at 6:44 PM on August 6, 2026: contributor


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Code Coverage & Benchmarks

For details see: https://corecheck.dev/bitcoin/bitcoin/pulls/35918.



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Conflicts

Reviewers, this pull request conflicts with the following ones:
- #35742 (descriptors: check duplicate keys in all multipath Miniscript branches by yashbhutwala)
- #35445 (wallet, descriptor: Revert StringType::COMPAT for Miniscript expressions and drop the concept of a Descriptor ID that can be validated by achow101)
- #34697 (descriptor: fix musig() duplicate key checks and doubled PSBT origin paths by shuv-amp)
If you consider this pull request important, please also help to review the conflicting pull requests. Ideally, start with the one that should be merged first.
DrahtBot closed this on Aug 7, 2026
DrahtBot reopened this on Aug 7, 2026
DrahtBot added the label Needs rebase on Aug 11, 2026

Type	Reviewers
ACK	w0xlt

descriptor: Reject trailing text after musig()

The musig() parser split the input at the closing parenthesis without
validating the remaining text. This allowed unexpected characters after
the expression to be ignored.
Add a requirement for nonempty char after musig() to begin with '/'.

33af6fdbc1

descriptor: move PubkeyProvider to descriptor.h

Expose the abstract interface by moving to descriptor.h to allow other
modules to consume parsed key expressions.
Mostly a move-only commit. Implementation of operator< is retained in
descriptor.cpp

296898cebd

descriptor: Add public ParsePubKey overload

Add an overload for parsing standalone key expressions using P2TR key
rules.
Also, expose explicitly provided origin information through GetOriginInfo(),
allowing callers to inspect the fingerprint and derivation path without
re-parsing the expression.

93600f9f03

pseudoramdom force-pushed on Aug 11, 2026
pseudoramdom marked this as ready for review on Aug 11, 2026
DrahtBot removed the label Needs rebase on Aug 11, 2026
w0xlt commented at 8:32 PM on August 13, 2026: contributor

ACK 93600f9f0360bf48a1f616f0f5db3c9ce985ce4b
DrahtBot added the label Needs rebase on Aug 24, 2026
DrahtBot commented at 11:29 AM on August 24, 2026: contributor



🐙 This pull request conflicts with the target branch and needs rebase.

in src/script/descriptor.cpp:2871 in 93600f9f03

2866 | +std::vector<std::unique_ptr<PubkeyProvider>> ParsePubkey(std::string_view key_expression, FlatSigningProvider& out, std::string& error)
2867 | +{
2868 | +    uint32_t key_exp_index{0};
2869 | +    const std::span<const char> expression{key_expression};
2870 | +    return ParsePubkey(key_exp_index, expression, ParseScriptContext::P2TR, out, error);
2871 | +}

uqlidi commented at 5:05 PM on August 28, 2026:

std::vector<std::unique_ptr<PubkeyProvider>> ParsePubkey(std::string_view key_expression, ParseScriptContext ctx, FlatSigningProvider& out, std::string& error)
{
    uint32_t key_exp_index{0};
    const std::span<const char> expression{key_expression};
    return ParsePubkey(key_exp_index, expression, ctx, out, error);
}

I see you hardcoded it for p2tr. shouldn't be for all script types? Why are you making the overload follow the p2tr rules only?

Contributors

Labels

Needs rebase Descriptors

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#35645 Multisig Wizard tracking issue

descriptor: Expose key expression parsing #35918

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Conflicts