In this commit, we add a new function to verify the taproot merkle
commitment of a given tapscript leaf. Along the way we add some helper
functions which can be used to construct a taproot output given the raw
script root.
In this commit, we implement the new BIP 341+342 taproot sighash digest
computation. The digest is similar, but re-orders some fragments and
also starts to commit to the input values of all the transactions in the
SIGHASH_ALL case. A new implicit sighash flag, SIGHASH_DEFAULT has been
added that allows signatures to always be 64-bytes for the common case.
The hashcache has been updated as well to store both the v0 and v1 mid
state hashes. The v0 hashes are a double-sha of the contents, while the
v1 hash is a single sha. As a result, if a transaction spends both v0
and v1 inputs, then we 're able to re-use all the intermediate hashes.
As the sighash computation needs the input values and scripts, we create
an abstraction: the PrevOutFetcher to give the caller flexibility w.r.t
how this is done. We also create a `CannedPrevOutputFetcher` that holds
the information in a map for a single input.
A series of function options are also added to allow re-use of the same
base sig hash calculation for both BIP 341 and 342.
In this commit, we optimize our signature implementation slightly, by
defining pre-computed sha256(tag) variables for the commonly used
values. If a tag matches this, then we'll use that hash value to avoid
an extra round of hashing.
In this commit, we add an implementation of the BIP-340 tagged hash
scheme. This initial version can be optimized quite a bit, for example,
we can hard code the output of frequently used `sha256(tag)` values and
save two `sha256` invocations.
The github markdown interpreter has been changed such that it no longer
allows spaces in between the brackets and parenthesis of links and now
requires a newline in between anchors and other formatting. This
updates all of the markdown files accordingly.
While here, it also corrects a couple of inconsistencies in some of the
README.md files.
This is a backport of the chainhash package made in Decred along with a
few additional things cleaned up, finished test coverage, and rewording
of some documentation to make it more generic.
In particular, the new package provides the definition of the hash type
and associated hashing functions which will allow the rest of the code to be
agnostic to the specific hash algorithm.
This only implements the package and does not change any of the code
base over to use it.
