Draft BIP for OP_TXHASH and OP_CHECKTXHASHVERIFY

stevenroose · October 6, 2023, 5:21pm

I added a reference implementation to the BIP and also added an example implementation of a caching strategy in rust-bitcoin:

github.com

stevenroose/rust-bitcoin/blob/c54a09cb2dd334d6cdeec23dda55c6b6e7154d03/bitcoin/src/blockdata/script/txhash.rs


#![allow(missing_docs)]

use std::borrow::Borrow;

use crate::{Transaction, TxOut};
use crate::consensus::encode::Encodable;
use crate::hashes::{sha256, Hash, HashEngine};

pub const TXFS_VERSION: u8 = 1 << 0;
pub const TXFS_LOCKTIME: u8 = 1 << 1;
pub const TXFS_NB_INPUTS: u8 = 1 << 2;
pub const TXFS_NB_OUTPUTS: u8 = 1 << 3;
pub const TXFS_CURRENT_INPUT_IDX: u8 = 1 << 4;
pub const TXFS_CURRENT_INPUT_CONTROL_BLOCK: u8 = 1 << 5;
pub const TXFS_INPUTS: u8 = 1 << 6;
pub const TXFS_OUTPUTS: u8 = 1 << 7;

pub const TXFS_ALL: u8 = TXFS_VERSION
    | TXFS_LOCKTIME

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All large fields are cached individually and there are caches for the leading caches at intervals and caches for “all”. So, like you said, this means that after every large piece of information in the tx has been hashed once, the number of hashed bytes per invocation of TXHASH has clear bounds.