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| <pre> | ||
| BIP: TBD | ||
| Layer: Consensus (soft fork) | ||
| Title: INTERNALKEY | ||
| Author: Brandon Black <freedom@reardencode.com> | ||
| Comments-Summary: No comments yet. | ||
| Status: Draft | ||
| Type: Standards Track | ||
| Created: 2023-12-22 | ||
| License: PD | ||
| </pre> | ||
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| ==Abstract== | ||
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| This BIP describes a new tapscript opcode (OP_INTERNALKEY) which pushes the | ||
| taproot internal key to the stack. | ||
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| ==Specification== | ||
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| When verifying taproot script spends having leaf version 0xc0 (as defined in | ||
| BIP342), OP_INTERNALKEY replaces OP_SUCCESS187 (0xbb). OP_INTERNALKEY pushes | ||
| the taproot internal key, as defined in BIP341, to the stack. | ||
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| ==Motivation== | ||
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| ===Key spend with additional conditions=== | ||
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| When building taproot outputs, especially those secured by an aggregate key | ||
| representing more than 1 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 32 bytes of witness space. | ||
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| ===Mitigated control block overhead for scripts using hash locks=== | ||
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| 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 32 witness | ||
| bytes. | ||
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| ==Reference Implementation== | ||
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| A reference implementation is provided here: | ||
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| https://github.com/brandonblack/bitcoin/commit/985e8c788d5e0f91802200044d31f9b86500255c | ||
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| ==Backward Compatibility== | ||
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| 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_SUCCESS187, OP_INTERNALKEY would invalidate their | ||
| spend. | ||
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| ==Deployment== | ||
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| TBD | ||
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| ==Credits== | ||
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| Jeremy Rubin described most of the ideas for OP_INTERNALKEY to me. | ||
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| ==References== | ||
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| [https://github.com/bitcoin/bips/blob/master/bip-0341.mediawiki BIP 341] Taproot | ||
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| [https://github.com/bitcoin/bips/blob/master/bip-0342.mediawiki BIP 342] Tapscript | ||
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| ==Copyright== | ||
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| This document is placed in the public domain. |