Hey there, HKD stands for Hierarchical Key Derivation, e.g. BIP32 [1] or ChainKD [2]. Alternatively known as "blinded keys" per Tor's draft [3].
All these schemes generate a scalar to be mixed with the parent public key P using an index or nonce i: h(i) := Hash(P || i || stuff) The first two schemes add a derivation factor (multiplied by the base point) to the parent pubkey, while the Tor's approach is to multiply the parent pubkey by the factor: Child(i) := P + h(i)*G // BIP32, ChainKD Child(i) := h(i)*P // Tor Last time I asked Pieter Wuille (BIP32's author) a couple years ago about their choice, his reply (if I recall correctly) was that scalar multiplication for a base point is more efficient than for an arbitrary point. I wonder if there's a difference in functionality if we add the factor (a-la BIP32) or multiply (a-la Tor). Maybe some weird ZK schemes benefit from blinding/derivation via multiplication instead of addition? [1] https://github.com/bitcoin/bips/blob/master/bip-0032.mediawiki [2] https://chain.com/docs/protocol/specifications/chainkd [3] https://gitweb.torproject.org/torspec.git/tree/proposals/224-rend-spec-ng.txt#n1979 _______________________________________________ Curves mailing list Curves@moderncrypto.org https://moderncrypto.org/mailman/listinfo/curves