From aj at erisian.com.au Thu Sep 21 01:56:10 2023 From: aj at erisian.com.au (Anthony Towns) Date: Thu, 21 Sep 2023 11:56:10 +1000 Subject: [Lightning-dev] Practical PTLCs, a little more concretely In-Reply-To: References: Message-ID: <828BFB6D-812A-44DD-AE40-BB894241DD39@erisian.com.au> On 21 September 2023 11:44:47 am AEST, Lloyd Fournier wrote: >Hi AJ, > >On Wed, 20 Sept 2023 at 17:19, Anthony Towns wrote: > >> >> I think: >> >> https://github.com/BlockstreamResearch/scriptless-scripts/pull/24 >> >> describes (w/ proof sketch) how to do a single-signer adaptor with musig2; >> might need some updates, to match the final musig2 API, but I think it's >> fundamentally okay: ie, you get the "single-sig adaptor" approach, but >> can just use the musig2 api, so best of both worlds. >> >> > Can you explain the distinction here? What is a MuSig2 adaptor signature >vs single-singer adaptor with MuSig2. > >Cheers, > >LL You can do ptlcs scriptlessly by having a 2-of-2 musig pubkey that the payer signs with an adaptor signature - this can be done via the key path, but then requires nonce exchanges leading to extra communication rounds. Alternatively, you can do them via the script path, replacing "hash160 equalverify b checksig" with "a checksigverify b checksig" where Alice gives Bob an adaptor sig which Bob completes when claiming the output. The question is how to do this latter approach, and I think it works fine to have Alice do a "single party musig2" calculation for it, rather than needing a separate api. Cheers, aj -- Sent from my phone.