I think there should be standard format to describe constraints for BIP32 paths.
I present a BIP draft that specifies "path templates" for BIP32 paths: https://github.com/dgpv/bip32_template_parse_tplaplus_spec/blob/master/bip-path-templates.mediawiki Matching against these templates allow to easily discern 'valid' paths, that match the constraints, and 'invalid' paths, that exceed the constraints. Extended motivation is given at the end of this message, and in the text of the BIP draft. A formal spec in TLA+ of a finite state machine implementing the parser for the described format (and the matching operation) accompanies this BIP draft: https://github.com/dgpv/bip32_template_parse_tplaplus_spec This formal spec can be used with TLC model checker and a helper script to generate thorough test data for implementations. One (python) implementation of template parsing and matching already exists (linked in the BIP draft). Examples of the templates: "m/[44,49,84]'/0'/0'/[0-1]/[0-50000]" specifies a full template that matches both external and internal chains of BIP44, BIP49 and BIP84 paths, with a constraint that the address index cannot be larger than 50000 "[0-2,33,123]/*" specifies a partial template that matches non-hardened values 0, 1, 2, 33, 123 as first index, and any non-hardened value at second index "*h/0" specifies a partial template that matches any hardened index followed by any non-hardened index Motivation: BIP32 derivation path format is universal, and a number of schemes for derivation were proposed in BIP43 and other documents, such as BIPs 44,45,49,84. The flexibility of the format allowed industry participants to implement custom derivation shemes that fit particular purposes, but not necessarily useful in general. Unrestricted derivation path usage might be unsafe in certain contexts. In particular, when "change" outputs of a transaction are sent to the addresses derived via paths unknown to the sender, the sender might loose access to the whole change amount. A simplistic approach of hard-coding the checks for well-known paths into software and firmware leads to reduced interoperability. Vendors cannot choose custom paths that are appropriate for their particular, non-general-purpose applications, and are forced to shoehorn their solutions into using well-known paths, or convince other vendors to support their custom paths. This approach scales poorly. A flexible approach proposed is to define a standard notation for "BIP32 path templates" that succintly describes the constraints to impose on the derivation path. Wide support for these path templates will increase interoperability and flexibility of solutions, and will allow vendors and individual developers to easily define their own custom restrictions. This way, they will be able to deal with the risks of accidental or malicious use of unrestricted derivation paths in a more flexible and precise manner. Well-known path templates can be pre-configured by default on devices and applications, but users can have an option to turn off the templates that are not relevant to their uses. Having standardized format for custom path templates will enable a common approach to be developed to the enforcement of application-specific path restrictions in devices and applications. One example of such approach might be for devices to allow to install application-specific profiles with path templates and possibly other custom parameters. Care must be taken to prevent accidental installation of malicious or incorrect profile, though. _______________________________________________ bitcoin-dev mailing list email@example.com https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev