func HMAC1(sum *[blake2s.Size]byte, key, in0 []byte) {
	mac := hmac.New(func() hash.Hash {
		h, _ := blake2s.New256(nil)
		return h
	}, key)
	mac.Write(in0)
	mac.Sum(sum[:0])
}
/* KDF related functions.
HMAC-based Key Derivation Function (HKDF)
https://tools.ietf.org/html/rfc5869
package device
import (
	"crypto/hmac"
	"crypto/rand"
	"crypto/subtle"
	"golang.org/x/crypto/blake2s"
	"golang.org/x/crypto/curve25519"
	"hash"
)