We support a change to the version bits of the HD serialization that will
inform the receiving utility of the exact derivation method used for the
pubkeys. Third-parties handling xpubs must not require additional
information from the user about the derivation path or serialization format
of the addresses under that xpub. When you have to ask, "Is this a SegWit
xpub?" then you've already lost.

Avoiding a total UX nightmare is in everyone's interests.

I think Luke and Thomas may be talking past one another. When exporting a
root master HD seed, encoding the {x,y,z}{pub,prv} distinctions makes no
sense, as the root seed should derive all paths for all coins. Wallets may
need additional code to discover which paths have been used when importing
a root seed. But when exporting / importing an account-level seed for
watch-only and receive address generation, changing the serialization
version bytes is appropriate and (in our view) essential to avoid loss of
funds.

The Electrum approach is nice but may not go far enough, as xpub and zpub
both list "P2PKH or P2SH." Why not expand the number of version prefixes to
eliminate the ambiguity?


On Tue, Sep 5, 2017 at 1:09 PM, Thomas Voegtlin via bitcoin-dev <
bitcoin-dev@lists.linuxfoundation.org> wrote:

>
>
> On 05.09.2017 19:03, Luke Dashjr wrote:
>
> > It seems desirable to use the same seed for all different script
> formats...
>
> That does not seem desirable to everybody.
>
> If you want to guarantee that users will be able to recover all their
> funds from their mnemonic seed (and that is what they expect), then
> wallets must implement all script formats, even the ones that are
> deprecated. In addition, the list of script formats that must be
> supported is not defined in advance, but it keeps growing. This makes
> wallet implementation increasingly difficult. In the long run, seed
> portability is guaranteed to fail in such a system.
>
> > As you note, xpub\xprv are already being used for both P2PKH and P2SH. It
> > really doesn't make sense to differentiate segwit specifically.
>
> That's not a reason. The fact that xpub/xprv can be used for both P2PKH
> and P2SH has already resulted in users receiving coins on addresses they
> do not control.
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>



-- 
-Kabuto

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