TXHASH
OP_TXHASH and OP_CHECKTXHASHVERIFY
Links
Introduction
This proposal originated on the bitcoin-dev mailing list where it was combined with
OP_CHECKSIGFROMSTACK to form an alternative to the combination of OP_CHECKTEMPLATEVERIFY
(CTV) and SIGHASH_ANYPREVOUT (APO). For more on the
combination of OP_TXHASH with OP_CHECKSIGFROMSTACK, check out the CATT
proposal.
The OP_TXHASH and OP_CHECKTXHASHVERIFY opcodes themselves can be considered an upgrade or
generalization of OP_CHECKTEMPLATEVERIFY and thus a way of enabling
advanced transaction templating.
Whereas CTV allows a user to commit to an entirely pre-specified spending transaction of a certain transaction output, TXHASH allows the user to specify a range of individual bits of the spending transaction to be included in the transaction template. The added flexibility solves a range of difficulties that protocols face when using CTV (for example related to paying fees for the pre-specified transactions), but it also enables additional independent use cases like equality checking of input and output values or scriptPubkeys.
Specification
A BIP of the opcodes in this proposal is currently in draft status on GitHub.
Potential Extensions
The specification for this proposal defines a construction called a TxFieldSelector that can
directly be adopted to implement other constructions like
OP_TX, an opcode for generalized introspection, or a new
Schnorr sighash flag.
Use Cases
For use cases that are enabled in this proposal, we refer to the more general use case page of
transaction templating, or the summary
table. For usage of OP_TXHASH together with some other opcodes, we refer
to the CATT proposal page.