Hello,

I am working on a draft BIP for a signature and script independent hierarchy for deterministic wallets.

I believe with the implementation of descriptor wallets, the typical use case of of a BIP43 `purpose’` level per script type is redundant. The differentiation of separate BIPs for multisignature derivation paths, with BIP45 and “BIP” 48, is also redundant – with path levels such as `cosigner_index` and `script_type`. Descriptors can set the order of the public keys with `multi` or have them sorted lexicographically with `sortedmulti`.

I don’t believe we should be mixing keys and scripts in the same layer. The wallet should create extended private/public keys independent of the script or signature type, whereas the descriptor language tells wallets to watch (single or multi-sig) outputs with the specified public keys.

The BIP defines the following 5 levels in the BIP32 path:

m / purpose' / coin_type' / account' / change / address_index

It is crucial that the `account’` level is increased for each new wallet joined or private/public keys created; for both privacy and cryptographic purposes. For example, in multisignature wallets, before sending a new key record to a coordinator, the wallet must increment the `account’` level. Before creating it's own single signature wallet, the `account’` level must again be incremented. This prevents key reuse - across single signature and multisignature wallets, across ECDSA and Schnorr signatures, and inbetween the same wallet types.

For full details, please see the BIP here: https://github.com/Rspigler/bips-1/blob/Sane_Mulitisg_deriv/Modern%20Derivation%20Standard.mediawiki

Please see the PR here: https://github.com/Rspigler/bips-1/pull/1

Looking forward to comments.

Thank you,

Robert Spigler

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