code: MAC newReadMAC() throws NoSuchAlgorithmException, InvalidKeyException {
          MacAlg macAlg = cipherSuite.macAlg;
          MAC mac;
          if (isClient) {
              mac = macAlg.newMac(protocolVersion, svrMacSecret);
              svrMacSecret = null;
          } else {
              mac = macAlg.newMac(protocolVersion, clntMacSecret);
              clntMacSecret = null;
          }
          return mac;
      }
docs: Create a new read MAC and return it to caller.