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[54.240.9.63]) by gmr-mx.google.com with ESMTPS id 5614622812f47-4c32e623b1esi39317b6e.2.2026.09.10.21.16.47 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 10 Sep 2026 21:16:47 -0700 (PDT) Received-SPF: pass (google.com: domain of 010001a08eaeac21-65cd8340-8efe-45da-9a59-9bf2af00f538-000000@send.cipherscope.io designates 54.240.9.63 as permitted sender) client-ip=54.240.9.63; In-Reply-To: References: From: "'duncan0k' via Bitcoin Development Mailing List" To: bitcoindev@googlegroups.com Cc: 2099999997690000@proton.me Subject: Re: [bitcoindev] [BIP draft] Unspendable Internal Keys for Wallet Policies Message-ID: <010001a08eaeac21-65cd8340-8efe-45da-9a59-9bf2af00f538-000000@email.amazonses.com> Date: Fri, 11 Sep 2026 04:16:47 +0000 MIME-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Feedback-ID: :1.us-east-1.uYze2bwK3SHKKircWy/itkS3vRiPQKZLrl6+y7WCGuRPsvW9ql8MorhNCUOEXf2PGCXNSg8zb4wXghGsSzasI0jj39JRaHKfNZGZIx1mhBBywFYJj0UYJyJnxeFR8KB0PocMWVVGOZzOXWt7Tivy/pn7sTtrfNSfjeDxZfpLwxQ=:1.us-east-1.QSNtDRXSTq9sAuvRl56h5mypgasnQ5yDLNpVzTnziu0=:AmazonSES X-SES-Outgoing: 2026.09.11-54.240.9.63 X-Original-Sender: duncan0k@cipherscope.io X-Original-Authentication-Results: gmr-mx.google.com; dkim=pass header.i=@cipherscope.io header.s=resend header.b=Xijj7PxX; dkim=pass header.i=@amazonses.com header.s=224i4yxa5dv7c2xz3womw6peuasteono header.b=Mw4oE8O4; spf=pass (google.com: domain of 010001a08eaeac21-65cd8340-8efe-45da-9a59-9bf2af00f538-000000@send.cipherscope.io designates 54.240.9.63 as permitted sender) smtp.mailfrom=010001a08eaeac21-65cd8340-8efe-45da-9a59-9bf2af00f538-000000@send.cipherscope.io; dmarc=pass (p=REJECT sp=REJECT dis=NONE) header.from=cipherscope.io X-Original-From: duncan0k Reply-To: duncan0k Precedence: list Mailing-list: list bitcoindev@googlegroups.com; contact bitcoindev+owners@googlegroups.com List-ID: X-Google-Group-Id: 786775582512 List-Post: , List-Help: , List-Archive: , List-Unsubscribe: , X-Spam-Score: -1.0 (-) Hi NTL, One property of this construction that isn't in the Motivation or Security sections, and which I think is worth stating: it makes script-path-only Taproot outputs *provably* so after the fact, to anyone handed the policy -- and that has a post-quantum use. Under current rules a CRQC that solves Q can key-path spend any P2TR output regardless of how Q was built; on-chain, a tweaked NUMS key and a bare untweaked key are indistinguishable. So for rescue mechanisms of the shape "prove the key path was never spendable, then recover via script path", the question is whether the holder can produce evidence the attacker cannot. With an ad-hoc r the holder can show r, but a rescue rule can't specify one uniform verification, and r is one more thing to have kept. With this BIP the evidence is the policy itself: recompute the chain code, derive the internal key from H, rebuild Q. The attacker holds q but not the policy, so cannot produce it. Your Security section already notes that anyone can verify derivation from H; the PQ angle is that the *policy* becomes the secret whose knowledge a rescue rule can demand. The versioned tag leaves room for such a rule to pin a version. It may be worth a sentence in Motivation, since it is a reason to adopt beyond interoperability. This came up in the exposure-classification thread [1], where conduition raised holder-provability for P2TR; the two pieces of work look complementary. duncan0k [1] https://gnusha.org/pi/bitcoindev/010001a06dd4cdd9-b8082042-8750-4e9a-917e-2053c919e4c4-000000@email.amazonses.com/ -- You received this message because you are subscribed to the Google Groups "Bitcoin Development Mailing List" group. To unsubscribe from this group and stop receiving emails from it, send an email to bitcoindev+unsubscribe@googlegroups.com. To view this discussion visit https://groups.google.com/d/msgid/bitcoindev/010001a08eaeac21-65cd8340-8efe-45da-9a59-9bf2af00f538-000000%40email.amazonses.com.