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[84.184.67.119]) by smtp.googlemail.com with ESMTPSA id bd5-20020a05600c1f0500b004030e8ff964sm21346537wmb.34.2023.10.12.00.43.22 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 12 Oct 2023 00:43:22 -0700 (PDT) Sender: Jonas Nick Message-ID: Date: Thu, 12 Oct 2023 07:43:21 +0000 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Content-Language: en-US To: Anthony Towns , Bitcoin Protocol Discussion , Andrew Chow References: From: Jonas Nick In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Mailman-Approved-At: Thu, 12 Oct 2023 19:13:35 +0000 Subject: Re: [bitcoin-dev] Proposed BIP for MuSig2 PSBT Fields X-BeenThere: bitcoin-dev@lists.linuxfoundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Bitcoin Protocol Discussion List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 12 Oct 2023 07:43:26 -0000 It is true that BIP 327 ("MuSig2") does not include adaptor signatures. The rationale behind this decision was as follows: - the BIP is already long and complicated enough without adaptor signatures; it should be possible to propose a separate adaptor signature BIP on top in a modular fashion - as far as I know, there's no security proof except for a hard-to-follow sketch that I wrote a few years ago [0] - at the time, there seemed to be a higher demand for single-signer adaptor signatures In spite of the missing specification, we added some version of adaptor signatures to the libsecp256k1-zkp MuSig2 module in order to allow experimentation. As for standardizing MuSig2 adaptor signatures, it seems noteworthy that there exist alternative designs to the implementation in the libsecp256k1-zkp module: the current libsecp256k1-zkp PR for (single-signer) Schnorr adaptor signatures [1] uses a slightly different API. Instead of sending the adaptor point along with the adaptor signature, the point is extracted from an adaptor signature. This simplifies the API and reduces communication at the cost of making batch verification of multiple adaptor sigs impossible. [0] https://github.com/BlockstreamResearch/scriptless-scripts/pull/24 [1] https://github.com/BlockstreamResearch/secp256k1-zkp/pull/268