[bitcoin-dev] MATT: [demo] Optimistic execution of arbitrary programs

["Johan Torås Halseth" <johanth@gmail.com>]

Hi, all!

I've been working on an implementation of the original MATT challenge
protocol[0], with a detailed description of how we go from a
"high-level arbitrary program" to something that can be verified
on-chain in Bitcoin Script.

You can find the write-up here, which also includes instructions of
how to run the code and inspect the transactions using a local block
explorer: https://github.com/halseth/mattlab/blob/main/docs/challenge.md

TLDR; Using the proposed opcode OP_CHECKCONTRACTVERIFY and OP_CAT, we
show to trace execution of the program `multiply` [1] and challenge
this computation in O(n logn) on-chain transactions:

func multiply(x int) int {
    i := 0
    while {
        if i < 8 {
            x = x + x
            i = i + 1
        } else {
            break
        }
    }
    return x
}

Next steps would be to make this a generic framework with tools to
automatically compile arbitrary high-level programs down to
MATT-compatible Bitcoin Scripts.

All feedback appreciated!

- Johan

[0] https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2022-November/021182.html
[1] https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2022-November/021205.html