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[206.125.169.165]) by gmr-mx.google.com with ESMTPS id w6-20020a25ac06000000b00dcc3d9efcb7si1776262ybi.3.2024.04.24.22.22.20 for (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 24 Apr 2024 22:22:20 -0700 (PDT) Received-SPF: pass (google.com: domain of freedom@reardencode.com designates 206.125.169.165 as permitted sender) client-ip=206.125.169.165; Date: Wed, 24 Apr 2024 22:22:13 -0700 From: Brandon Black To: bitcoindev@googlegroups.com Subject: [bitcoindev] BIP for OP_INTERNALKEY Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline X-Operating-System: Linux 6.1.74 x86_64 X-Original-Sender: freedom@reardencode.com X-Original-Authentication-Results: gmr-mx.google.com; dkim=pass header.i=@reardencode.com header.s=mail header.b=nAQXcDBk; spf=pass (google.com: domain of freedom@reardencode.com designates 206.125.169.165 as permitted sender) smtp.mailfrom=freedom@reardencode.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=reardencode.com 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: -0.8 (/) Hello list, I'm currently failing to find the original reference discussion for adding OP_INTERNALKEY to tapscript. I believe it was in the context of the SIGHASH_ANYPREVOUT proposal which opted instead to access the internalkey as a special key with value `0x01`. Regardless, here[0] is a BIP for adding OP_INTERNALKEY to tapscript to allow access to the taproot internal key. As noted below, this helps certain classes of script come closer to matching segwitv0 in byte efficiency, which can be particularly useful for protocols such as Lightning where the same signers may need to sign a script path in some cases, and a key path in others. ------------ ## Abstract This BIP describes a new tapscript opcode (`OP_INTERNALKEY`) which pushes the taproot internal key to the stack. ## Specification When verifying taproot script spends having leaf version `0xc0` (as defined in [BIP 342]), `OP_INTERNALKEY` replaces `OP_SUCCESS203` (0xcb). `OP_INTERNALKEY` pushes the taproot internal key, as defined in [BIP 341], to the stack. ## Motivation ### Key spend with additional conditions When building taproot outputs, especially those secured by an aggregate key representing more than one signer, the parties may wish to collaborate on signing with the taproot internal key, but only with additional script restrictions. In this case, `OP_INTERNALKEY` saves 8 vBytes. ### Mitigated control block overhead for scripts using hash locks In cases where script path spending is not desired, the internal key may be set to a NUMS point whose bytes would otherwise be required in a tapscript. This could be used with any hash locked transaction, for example, to save 8 vBytes. Note: The internal key must be the X coordinate of a point on the SECP256K1 curve, so any such hash must be checked and modified until it is such an X coordinate. This will typically take approximately 2 attempts. ## Reference Implementation A reference implementation is provided here: https://github.com/bitcoin/bitcoin/pull/29269 ## Backward Compatibility By constraining the behavior of an OP_SUCCESS opcode, deployment of the BIP can be done in a backwards compatible, soft-fork manner. If anyone were to rely on the OP_SUCCESS behavior of `OP_SUCCESS203`, `OP_INTERNALKEY` would invalidate their spend. ## Deployment TBD ## Copyright This document is licensed under the 3-clause BSD license. [BIP 341]: https://github.com/bitcoin/bips/blob/master/bip-0341.mediawiki [BIP 342]: https://github.com/bitcoin/bips/blob/master/bip-0342.mediawiki ------------ [0]: https://github.com/bitcoin/bips/pull/1534 -- --Brandon -- 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 on the web visit https://groups.google.com/d/msgid/bitcoindev/Zinohf1n8-aWN6G9%40console.