Allowing Duplicate Keys in BIP 390 musig() Expressions

In a recent discussion initiated by Ava on the Bitcoin Development Mailing List, an important aspect of musig() descriptor expressions was brought to light. Ava pointed out the current complexity in implementing musig() descriptor expressions due to the restriction against duplicating participant public keys. This restriction, while seemingly unnecessary as MuSig2 allows for duplicate participant keys, complicates the implementation process. Ava proposed an amendment to the BIP to remove this limitation, arguing that allowing duplicate keys could simplify the implementation of musig() expressions.

Ava sought feedback from others who have already implemented musig() expressions with the existing restriction, questioning whether removing this restriction would cause any significant breaking changes. The proposal aims to make a change to the BIP in the coming days unless there are substantial objections or concerns raised by the community.

This discussion underscores the ongoing efforts to refine and improve the implementation of musig() descriptor expressions within the framework of Bitcoin development. It reflects the open and collaborative nature of the community, inviting comments and considerations from those with practical experience and insight into the matter at hand.