Dear Hugo Krawcyck:Thank you for the detailed answers. I still have a question about HMAC as compared to other MACs. Feel free to point me to existing documents if they answer my question. Suppose I were to instantiate HKDF with the keyed PRF being a cipher based MAC such as Poly1305 instead of HMAC. Which of the arguments for HKDF's security would still apply?
Regards, Zooko