code: def DeriveReportKey(cls, root_key, report_id, sent_timestamp):
          
  
          signed_data = struct.pack("<LLL", AuthProvider.ReportKeyMagic, report_id, sent_timestamp)
  
          hmac_calc = hmac.new(root_key, signed_data, hashlib.sha256)
          return bytearray(hmac_calc.digest())
docs: Derive a standard one time use report signing key.
  
          The standard method is HMAC-SHA256(root_key, MAGIC_NUMBER || report_id || sent_timestamp)
          where MAGIC_NUMBER is 0x00000002 and all integers are in little endian.