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Date: Fri, 5 Feb 2021 23:00:29 +0100
From: Dmitry Petukhov <dp@simplexum.com>
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Subject: Re: [bitcoin-dev] BIP32/43-based standard for Schnorr signatures &
 decentralized identity
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=D0=92 Fri, 05 Feb 2021 17:51:27 +0000
Dr Maxim Orlovsky via bitcoin-dev
<bitcoin-dev@lists.linuxfoundation.org> wrote:

> Testnet path is unhardened from this point & till the end of the
> derivation path: no need to prevent private key leak there,
> simplifies test software (hardened paths require private key access
> for derivation).

I believe this will reduce robustness and will add complexity to the
test software instead. If the derivation path is hardened in 'production
code' and is unhardened in 'test code', then: code paths that depend on
hardened derivation may not be tested; there will be unnecessary
code that will need to deal with 'un-hardening' the paths for test code.

It is much more robust to just change the 'purpose' part of the path,
and leave the rest unchanged.

It is OK to require privkey access to hardened paths in test
software, because the same behaviour is expected in 'production'.