code: public static SecretKey generateKey(String algorithm, KeySpec keySpec) {
  		final SecretKeyFactory keyFactory = getSecretKeyFactory(algorithm);
  		try {
  			return keyFactory.generateSecret(keySpec);
  		} catch (InvalidKeySpecException e) {
  			throw new CryptoException(e);
  		}
  	}
docs: 生成 {@link SecretKey}，仅用于对称加密和摘要算法
  
  @param algorithm 算法
  @param keySpec {@link KeySpec}
  @return {@link SecretKey}