def expand(self, info=b"<STR_LIT>", length=<NUM_LIT:32>):
return hkdf_expand(self._prk, info, length, self._hash)<EOL>
Generate output key material based on an `info` value

Arguments:
- info - context to generate the OKM
- length - length in bytes of the key to generate

See the HKDF draft RFC for guidance.