Re: [bitcoin-dev] Multi-signature and multi-coin HD wallet in one BIP32 derivation path (new BIP)

From: Paul Brown <paul@345•systems>
To: Clark Moody <clark@clarkmoody•com>,
	Bitcoin Protocol Discussion
	<bitcoin-dev@lists•linuxfoundation.org>
Subject: Re: [bitcoin-dev] Multi-signature and multi-coin HD wallet in one BIP32 derivation path (new BIP)
Date: Wed, 25 Apr 2018 16:44:55 +0000	[thread overview]
Message-ID: <HE1PR09MB0266B019ECE16E62CD4E2DE9988F0@HE1PR09MB0266.eurprd09.prod.outlook.com> (raw)
In-Reply-To: <CAHGSxGt649Ok=jp0STnHkYvEhWSOTwMfh0oB+7jqY6MAmr4TKQ@mail.gmail.com>

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Hi Clark,

Thanks very much for the feedback, it is most appreciated.

The BIP does state that the address format would be bech32 serialized, using P2WPKH and P2WSH, however, I take your point as you would need to know it’s a BIP ‘46’ to know to use bech32 P2WPKH or P2WSH.  SLIP-0032 serialization format does solve it from the point of view of knowing which BIP the xpub is associated and therefore by association what address format to use.  Makes perfect sense and probably a good change to make to the proposed BIP.

Also, the nice thing about SLIP-0032 is that the serialization format additionally provides that extra check that the correct xpubs are distributed between parties where say, distributing a 3of5 xpub means you can check that the bytes at depth 3 and 4 represent the 3of5 path.

Ah yes, it was a little presumptuous of me to pick 46 for the BIP but in my defence I needed a ‘real’ number to generate the paths with 😊

Paul

From: clarkmoody@gmail•com <clarkmoody@gmail•com> On Behalf Of Clark Moody
Sent: 25 April 2018 15:36
To: Paul Brown <paul@345•systems>; Bitcoin Protocol Discussion <bitcoin-dev@lists•linuxfoundation.org>
Subject: Re: [bitcoin-dev] Multi-signature and multi-coin HD wallet in one BIP32 derivation path (new BIP)

Thanks for the proposal, Paul.

> - What address format is expected when discovering balances and creating transactions?

Your solution does not solve your first bullet point, since the xpub encoding looks no different than any other xpub (BIP 44, 45, 49, etc). At the least, you should propose new version bytes to change the "xpub" in the encoding to some other string.

Alternatively, I would suggest that you use the xpub serialization format described in SLIP-0032 (https://github.com/satoshilabs/slips/blob/master/slip-0032.md). It includes the derivation path within the xpub itself and uses Bech32 for encoding.

Given a normal xpub with no additional information, a wallet must scan the address space for the various formats. SLIP-0032 solves this bootstrapping problem and avoids the UX nightmare of users being required to know to which BIP number the xpub conforms.

Also, @luke-jr will give you a hard time to self-assigning a BIP number ;-)

Thanks

-Clark

On Wed, Apr 25, 2018 at 4:35 AM, Paul Brown via bitcoin-dev <bitcoin-dev@lists.linuxfoundation.org<mailto:bitcoin-dev@lists•linuxfoundation.org>> wrote:
Hi

I have written a new BIP describing a BIP32 derivation path that supports a single or multi-signature and multi-coin wallet from a single master seed.  It combines BIP44 and BIP45 and adds in a self-describing structure in the derivation path for multiple multi-sig combinations within the single wallet along with an extended public key export file format for public key distribution between parties.  I can particularly see this being useful for multiple Lightning Network 2of2 accounts for different payment channels.

The BIP can be found here: https://github.com/gluexchange/bip/blob/master/bip-0046.mediawiki

I appreciate that this might be re-hashing old ground as BIP44 in particular has been widely adopted, however, BIP44 does leave itself open to a lot of interpretation from a wallet portability perspective such as:

- What address format is expected when discovering balances and creating transactions?
- Does the master seed represent a single-sig or multi-sig wallet?
- If multi-sig, how many cosigners and what are their extended public keys (so that the wallet can generate the correctly formatted redeem script with public keys in the right order)?
- If multi-sig, how do you prevent collisions on the same address index (in a wallet that is occasionally connected)?

BIP45 solves the collision that occurs when the individual parties in a multi-sig group each give out a new address from a wallet, where the wallet hasn’t been able to sync to mark the address as ‘used’ (this could happen if they gave out addresses independently at the same time).  It uses a cosigner index in the derivation path so that each party has their own path to their addresses.  However, BIP45 drops the multi-coin support that BIP44 has.

This is a useful discussion on the problems of a collision and the merits of separating cosigners in the derivation path: https://www.mail-archive.com/bitcoin-development@lists.sourceforge.net/msg05188.html

For the purposes of the BIP text (and the example paths used to generate keys) I’ve temporarily assigned it the number 46.  It looks like that is available and seemed somewhat appropriate given that it builds on the good work of BIP44 and BIP45.

Paul Brown

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