2.1 KiB
BIP: XXX
Layer: Consensus (soft fork)
Title: OP_INTERNALKEY
Author: Brandon Black <freedom@reardencode.com>, Jeremy Rubin <j@rubin.io>
Comments-URI: https://github.com/bitcoin/bips/wiki/Comments:BIP-XXXX
Status: Draft
Type: Standards Track
Created: 2023-12-22
License: BSD-3-Clause
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
Credits
TODO
Copyright
This document is licensed under the 3-clause BSD license.