Re: [bitcoin-dev] BIP32/43-based standard for Schnorr signatures & decentralized identity

[Dr Maxim Orlovsky <orlovsky@protonmail.com>]

Hi Dmitry,

Thank you very much for readying and analyzing my proposal!

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

You are right, agree

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

Not sure whether the purpose is the correct place to indicate testnet: in this case it we will have to support one testnet per each blockchain type (which is not the case). So probably we should reserve a single dedicated value for any testnet withing ``blockchain` field using hardened path as you suggested - for instance, 0xFFFFFFFF may do the job.

Kind regards,
Maxim