Post
Topic
Board Development & Technical Discussion
Merits 5 from 3 users
Re: Do invalid keys in BIP44 path matter?
by
Coding Enthusiast
on 14/07/2020, 02:57:59 UTC
⭐ Merited by o_e_l_e_o (2) ,ETFbitcoin (2) ,NeuroticFish (1)
It could potentially cause problems if we ignore validity (being in range) of the parent derived keys because even though BIP-32 may look like any other Key Derivation Function but it is more than a simple KDF. For instance each non-hardened child key is derived using the parent's public key which means that parent key must have been in range to be used in EC multiplication.

BIP-44 is not relevant here but since you mentioned it, lets take the path used in this BIP:
m / 44' / 0' / 0' / 0 / 0
The bold one is the child keys used in creating addresses.
You won't notice the problem in first 3 depths since they are all hardened but the last one is not. If the parent key at m/44'/0'/0'/0 returned a key that is outside of curve range you can't derive the child key at  m / 44'/0'/0'/0/0 anymore.
So the standard has to enforce this validity check on each step.