bitcoin-dev

A proposal for a "PSBT for descriptors" format

A proposal for a "PSBT for descriptors" format

Original Postby SeedHammer Team

Posted on: November 23, 2023 22:25 UTC

SeedHammer is actively working on developing a standard, compact output descriptor aimed at enabling self-contained metal engraved backups.

The company has put forward a proposed descriptor format that leverages the PSBT binary encoding, though this proposal is still in the early stages and has not yet achieved a consensus or adoption within the community. The proposed format draws upon the binary BIP174 PSBT format and utilizes its efficient PSBT_GLOBAL_XPUB encoding for representing extended keys.

The textual encoding of the descriptor is consistent with the standards outlined in BIPs 380-386 and BIP 389. It employs wallet-policies format for key references and supports Miniscript with some restrictions; inline keys are prohibited, and pk(NAME) expressions must be substituted with indexed key references. Additional metadata like labels and birthdate blocks is incorporated using PSBT map entries. Some of the issues raised in the discussion include the choice between CBOR and PSBT encoding methods. Blockchain Commons advocates for CBOR, citing it as a more established binary encoding standard. However, SeedHammer contends that the complexity of CBOR does not offer enough benefits to outweigh the simplicity and existing wallet software support for PSBT encoding. There's also a question about whether the proposed format should introduce a separate header and magic number or if it should be integrated as an extension of the existing PSBT format.

To explore the proposal further, SeedHammer invites comments and feedback before moving to formalize it through the Bitcoin Improvement Proposal (BIP) process. Details and examples can be found at the provided links: [proposal], [implementation], and [playground].