code: public static void eraseKey(byte[] keyToErase) {
          if (keyToErase != null) {
              SecureRandom random;
              try {
                  random = SecureRandom.getInstance("SHA1PRNG");
                  random.nextBytes(keyToErase);
              } catch (NoSuchAlgorithmException e) {
                  // never reached
              }
          }
      }
docs: Overwrites the supplied byte array with RNG generated data which destroys
  the original contents.
  
  @param keyToErase
  The content key to erase.