counter++ if counter == 0 { panic("hkdf: counter overflow") } if counter > 1 { expander.Reset() } expander.Write(buf) expander.Write([]byte(info)) expander.Write([]byte{counter}) buf = expander.Sum(buf[:0]) remain := keyLen - len(out) remain = min(remain, len(buf)) out = append(out, buf[:remain]...) } return out } func Key[H fips140.Hash](h func() H, secret, salt []byte, info string, keyLen int) []byte { prk := Extract(h, secret, salt) return Expand(h, prk, info, keyLen) } golang.org/fips140@v1.0...