code: def postprocess_key_for_export(self, key, client_random, server_random,
                                     con_end, read_or_write, req_len):
          
          s = con_end + read_or_write
          s = (s == "clientwrite" or s == "serverread")
  
          if self.tls_version < 0x0300:
              return None
          elif self.tls_version == 0x0300:
              if s:
                  tbh = key + client_random + server_random
              else:
                  tbh = key + server_random + client_random
              export_key = _tls_hash_algs["MD5"]().digest(tbh)[:req_len]
          else:
              if s:
                  tag = b"client write key"
              else:
                  tag = b"server write key"
              export_key = self.prf(key,
                                    tag,
                                    client_random + server_random,
                                    req_len)
          return export_key
docs: Postprocess cipher key for EXPORT ciphersuite, i.e. weakens it.
          An export key generation example is given in section 6.3.1 of RFC 2246.
          See also page 86 of EKR's book.