(I am reading the bip32 for an altcoin development.)
In the bip32 specification, it is written that listing all incoming and outgoing payments of a hierarchical deterministic wallet would required the extended public keys.
In case an auditor needs full access to the list of incoming and outgoing payments, one can share all account public extended keys. This will allow the auditor to see all transactions from and to the wallet, in all accounts, but not a single secret key.
Wouldn't the (non-extended) elliptic curve encryption's public keys work too ?
Furthermore, if I understand the spec properly, sharing an extended public key isn't really safe since knowing a descending non-hardened private key would then expose all the keys descending from this first extended public key...and sharing a non-extended public key would avoid the problem.