[Bitcoin-development] Request For Discussion / BIP number - Multi-Currency Hierarchy For Use In Multisignature Deterministic Wallets

William Swanson swansontec at gmail.com
Fri Apr 10 02:02:32 UTC 2015

Hello Alan,
Your scheme is basically the same as the BIP45 scheme, except that you
have collapsed the "cosigner_index" and "change" fields into a single
field with the formula:

    combined = 2*cosigner_index + change

This removes one level from the hierarchy, but ultimately produces the
same number and type of chains as BIP45 (just addressed differently).

I kinda like the BIP45's approach of giving each field has its own
dedicated purpose. What is the motivation behind flattening the

I ask because the wallet I work on, Airbitz, will be adding multi-sig
at some point in the future, and we need to figure out what kind of HD
tree structure we will be using. Our ideal structure would basically
be BIP 44 plus some "no-collision" logic:

    m / purpose' / coin_type' / wallet' / cosigner_index / change /

I feel like interoperability with Copay would be worth the extra HD
branch. Assuming Kefkius adds similar no-collision logic, his proposal
is pretty close to our ideal:

    m / purpose' / wallet' / coin_type / cosigner_index / change / address_index

Of course, I am open to hearing your thoughts on this as well.


On Thu, Apr 9, 2015 at 3:37 PM, Alan Reiner <etotheipi at gmail.com> wrote:
> BTW, I had originally proposed a "no-collision" scheme for
> multi-signature wallets, which doesn't require modifying the key tree
> structure at all, except for adding new internal and external chains
> (2*N chains).  All siblings watch all chains, but only generate
> receiving and change addresses on their two chains.
> The original document is here, which might be educational for the
> purposes of understand precisely the problem that needs a solution (and
> mine is a different solution than BIP45).
> https://www.dropbox.com/s/58poxi60d8nfj5w/MultisigWalletNoCollide.pdf
> I prefer not adding even more levels to the key tree, and (IMO) it makes
> more sense to add more chains to the wallet instead of adding a new tree
> level (as it allows for a simpler tree in the event that you don't need
> separate cosigners).  But I suspect that there's a certain momentum
> behind the cosigner-index method already in BIP45?  Just throwing it out
> there.

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