[BIP Draft] Co-signer Spending Policies

This approach is significant as it aims to unify various existing methods and innovations in the realm of co-signed transactions, such as Halseth's blinded co-signers, Chain Code Delegation, predicate blind signatures, and bonded co-signers, as well as products like Liquidium and Lendasat. These technologies each have their own policies, making interoperability between different wallets and co-signers challenging.

Carriere's proposal includes several types of verification processes: open verification, blinded verification, and enclave verification. These are crucial for ensuring that the conditions for co-signing, whether derived from the transaction itself or from external attestations, are met transparently and securely. The draft mandates that all scripts enforceable by the script must be included, maintaining a direct execution path that does not require a co-signer. Importantly, the policy accommodates Discreet Log Contract (DLC) oracle attestations, allowing existing oracles to serve as unchanged sources of evidence.

The draft is detailed in a BIP (Bitcoin Improvement Proposal) which can be reviewed here. Carriere seeks feedback on several open questions within the draft. These include the choice between canonical JSON and TLV for data representation, the current feasibility of specifying blinded verification, the appropriate placement of the statement attestation format (whether within this policy or the DLC specifications), the adequacy of the output expression language, and the necessity of timelocking the fallback path. These questions are critical for refining the draft and ensuring its practicality and effectiveness in standardizing co-signer policies across various platforms and technologies.