Thanks for starting the discussion on finding a better structure.

For me, the most important thing is either we're 100% interoperable or
0%. There should not be anything inbetween, as users will delete seeds
without knowing there is still money in them on another implementation.
I heard from multiple sources that using this standard some wallets will
only see a subset of the addresses/keys of some other wallets.
Implementation differences can always happen (and should addresses as
bugs), but I think its unacceptable that this source of issues is by design.

I suggest we agree on an even simpler least common denominator and
wallets that want to implement some feature on top of that can do but
are encouraged to pick a totally different "cointype". I guess that
would mean removing reserved and account.

I'm still thinking it might be a good idea to have a separate chain for
"refunds". Refunds will be rarely used and thus need a much slower
moving window than receiving addresses or change.

On 03/26/2014 09:49 PM, Mike Hearn wrote:
> Myself, Thomas V (Electrum) and Marek (Trezor) got together to make sure
> our BIP32 wallet structures would be compatible - and I discovered that
> only I was planning to use the default structure.
> Because I'm hopeful that we can get a lot of interoperability between
> wallets with regards to importing 12-words paper wallets, we
> brainstormed to find a structure acceptable to everyone and ended up with:
>   /m/cointype/reserved'/account'/change/n
> The extra levels require some explanation:
>   * cointype:  This is zero for Bitcoin. This is here to support two
>     things, one is supporting alt coins based off the same root seed.
>     Right now nobody seemed very bothered about alt coins but sometimes
>     feature requests do come in for this. Arguably there is no need and
>     alt coins could just use the same keys as Bitcoin, but it may help
>     avoid confusion if they don't.
>     More usefully, cointype can distinguish between keys intended for
>     things like multisig outputs, e.g. for watchdog services. This means
>     if your wallet does not know about the extra protocol layers
>     involved in this, it can still import the "raw" money and it will
>     just ignore/not see the keys used in more complex transactions.
>   * reserved is for "other stuff". I actually don't recall why we ended
>     up with this. It may have been intended to split out multisig
>     outputs etc from cointype. Marek, Thomas?
>   * account is for keeping essentially wallets-within-a-wallet to avoid
>     mixing of coins. If you want that.
>   * change is 0 for receiving addresses, 1 for change addresses.
>   * n is the actual key index
> For bitcoinj we're targeting a deliberately limited feature set for hdw
> v1 so I would just set the first three values all to zero and that is a
> perfectly fine way to be compatible.
> The goal here is that the same seed can be written down once, and meet
> all the users needs, whilst still allowing some drift between what
> wallets support.
> Pieter made the I think valid point that you can't really encode how
> keys are meant to be used into just an HDW hierarchy and normally you'd
> need some metadata as well. However, I feel interop between wallets is
> more important than arriving at the most perfect possible arrangement,
> which feels a little like bikeshedding, so I'm happy to just go with the
> flow on this one.
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