This post introduces a combination of MuSig2 with Signature Adaptors to enable PTLC (Point-Time-Locked-Contract) in LN channels, which is explicitly rely on option_simple_update.
In the process, I thought I find two things less being discussed:
- When combining signature adaptors with MuSig2 (-like aggregated signatures), the offer of a PTLC must get the partial signature of the receiver in advance, otherwise he have no guarantee to be able to extract the secret from the final aggregated signature. See the "A note about combining MuSig2 with signature adaptors" section.
- Using aggregated signatures to enforce PTLC doesn't allow us to leverage the
SIGASH_SINGLE|SIGHASH_ANYONECANPAYtrick, results in sub-optimal (even unacceptable) fee payment schemes (including the one in this design).
However, after I finish this work, (with some of my friends' help) I find that they ware already discovered by at least two authors. The first problem is found by, e.g. instagibbs[^11] and t-bast[^13]. The second probl