Is HKDF FIPS compliant? Yes, in more ways than one. It's approved for key-agreement as SP 800-56C Rev. 2 and for general-purpose use per SP 800-133 Rev. 2 (Section 6.3 Option #3) and SP 800-108. I didn't really believe it, so I went and tested x/crypto/hkdf against SP 800-108 ACVP vectors.

The FIPS Compliance of HKDF

The FIPS compliance of HKDF is a somewhat confusing and controversial topic, partially because the normative reference is split over at least four separate documents, but in practice it’s approved for...

Great stuff Filippo.

This took the better part of two days to chase down. I have made some life choices. (And yes, those are Blahaj, what's your question?)