PSBT Addition (BIP 174) for authenticating source/output PSBT files

Summary:

The email thread discusses a proposal to improve the security of Partially Signed Bitcoin Transactions (PSBT) by adding signatures to the PSBT structure. The author suggests that this would protect against bugs, such as those found in hardware wallets like the PSBT Signer, by covering all bytes of the original PSBT file up to the last output of the output section. However, some readers argue that this proposal does not address a MitM who can modify both directions of the PSBT.To mitigate this issue, the author proposes using pre-shared public keys between the PSBT Creator and Signer to block the Signer from looking at MitM'ed files. The author values feedback and prefers to start with legitimate key numbers rather than proprietary keys. Some readers suggest that MiTM protection should be done with out-of-band communication, while others argue for checking the signature by an authority on the 'correctness' of the original PSBT.Another proposed feature is to add an additional signature to authenticate the PSBT creator. The proposal suggests using a separate signature area to create and validate the signature without blanking the signature area during the digest step. However, a participant in the discussion argues that this would introduce unnecessary complexity to PSBT, while also pointing out that multiple signatures may not be required.Despite these concerns, the author plans to get two officially-assigned BIP-174 key numbers and add the feature to Coldcard's firmware, as well as write a BIP or make an addition to BIP-174. Another suggestion is to implement the proposed scheme with proprietary keys, document it, and promote it, which could lead to it becoming a de-facto standard with non-proprietary keys assigned.

Updated on: 2023-06-13T23:06:15.557559+00:00