I want to do generate individual AES keys for a number of smart cards, based on a random master key (key diversification) and the serial number of the card.
According to the answers to this question HKDF is the/one way to go.
HKDF has three inputs,
info. Feeding in the serial number as part of
ikm seems to be incorrect usage (and maybe dangerous because it makes the IKM less random?). That leaves
info, which one should I use?