Bitcoin Developers,

The Third CTV meeting was held earlier today (Tuesday February 8th, 2022).  You can find the meeting log here: https://gnusha.org/ctv-bip-review/2022-02-08.log

A best-effort summary:

- Not much new to report on the Bounty
- Non Interactive Lightning Channel Opens
  Non interactive lightning Channel opens seems to work!
  There are questions around being able operate a channel in a "unipolar" way for routing with the receiver's key offline, as HTLCs might require sync revocation. This is orthogonal to the opening of the channels.
- DLCs w/ CTV
  DLCs built with CTV does seem to be a "key enabler" for DLCs.
  The non interactivity provides a dramatic speedup (30x - 300x depending on multi-oracle setup)
  Changes the client/server setup enable new use cases to explore, and simplify the spec substantially.
  Backfilling lets clients commit to the DLC faster and lazily backfill at cost of state storage.
  For M-N oracles, precompiling N choose M groups + musig'ing the attestation points can possibly save some witness space because log2(N)*32 + N*32 > log2(N*(N choose M))*32 for many values of N and M.
- Pathcoin
  Not well understood yet concretely.
  Seems like the API of a "a coin that 1-of-N can spend" shared by N is new/unique and not something LN can do (which always requires N online to sign txns)
  Binary expansion of coins could allow arbitrary value transfer (binary expansion can live in a CTV tree too).
  Best way to think of Pathcoin at this point is an important theoretical result that should open up new exploration/improvement
- TXHash
  Main concerns: more complexity, potential for recursion, script size overhead
- Soft Forks, Generally
  Big question: Are the fork processes themselves (e.g., BIP9/8/ST activiations) riskier than the upgrades (CTV)?
  On the one hand, validation rules are something we have to live with forever so they should be riskier. Soft fork rules and coordination might be bad, but after activation they go away.
  On the other hand, we can "prove" a technical upgrade correct, but soft-fork signalling requires unprovable user behavior and coordination (e.g., actually upgrading).
  If you perceive the forking mechanism as high risk, it makes sense to make the upgrades have as much content as possible since you need to justify the high risk.
  If you perceive the forking mechanism as low risk, it is fine to make the upgrades smaller and easier to prove safe since there's not a high cost to forking.
- Elements CTV Emulation
  Seems to be workable.
  Questionable if any of the use cases one might want CTV for (Lightning, DLCs, Vaults) would have much demand on Liquid today.

Feel free to correct me where I've not represented perspectives decently, as always the logs are the only true summary.

Best,

Jeremy