mflaxman

Separately, I'm now conflicted on whether the first address should be encoded in some non-address format, so that there is no ambiguity for end-users.

Here's one imperfect solution that would be trivial for any bitcoin wallet developer to implement:
1. Fetch receive address 2,147,483,647 (`2^31 -1`) for the descriptor record, let's call this address X
2. Calculate the double-sha256 digest of X in hex
3. Truncate to something more reasonable, perhaps 160 bits (40 characters in hex)
4. Prepend some identifier for UX, I suggest `MW-` (multisig wallet).

I find code much clearer as a way to communicate, here is what that looks like in python:
```

mflaxman

from hashlib import sha256

# https://bitcoin.stackexchange.com/questions/92056/what-is-the-max-allowed-depth-for-bip32-derivation-paths
MAX_BIP32 = 2 ** 31 - 1


def encode(num, base=MAX_BIP32):
    result = []
    while num > 0:
        num, remainder = divmod(num, base)

mflaxman

from bitmerchant.wallet import Wallet
from mnemonic import Mnemonic

# put in whatever Trezor generates for you here (or backup from this empty/insecure one as a test)
mnemonic = 'clean health food open blood network differ female lion eagle rough upon update zone antique defense venture uncover mobile charge actress film vocal enough'
passphrase = ''  # empty string or whatever you actually choose
path = "m/44'/0'/0'/0/0"  # whatever shows up on the UI for that account (everything will start with m/44'/0' since it's bip44)

child = Wallet.from_master_secret(Mnemonic('english').to_seed(mnemonic, passphrase)).get_child_for_path(path)
child.to_address()  # '18K9axbPpwqZgngB58nuwsYevL2z6ey4YG' (confirm this matches what Trezor is showing you)

mflaxman

╔══════════════╦══════════════════════════════════════╗
║  BTC Amount  ║                Wallet                ║
╠══════════════╬══════════════════════════════════════╣
║ < $1k USD    ║ Trusted Service                      ║
║ < $50k USD   ║ Breadwallet App                      ║
║ < $250k USD  ║ Hardware Wallet                      ║
║ < $2 MM USD  ║ Electrum on Tails OS (with Airgap)   ║
║ > $2 MM USD  ║ Bitcoin Core Full Node (with Airgap) ║
╚══════════════╩══════════════════════════════════════╝

mflaxman

from pycoin.tx.tx_utils import create_signed_tx
from pycoin.services.blockcypher import BlockcypherProvider

# inspect your spendables
spendables = [x.as_text() for x in BlockcypherProvider().spendables_for_address(address=FROM_ADDRESS)]

# sign TX
signed_tx = create_signed_tx(
    spendables=spendables,
    payables=[TO_ADDRESS],