code: public SymmetricCrypto init(String algorithm, SecretKey key) {
  		this.secretKey = key;
  		if (algorithm.startsWith("PBE")) {
  			// 对于PBE算法使用随机数加盐
  			this.params = new PBEParameterSpec(RandomUtil.randomBytes(8), 100);
  		}
  		this.cipher = SecureUtil.createCipher(algorithm);
  		return this;
  	}
docs: 初始化
  
  @param algorithm 算法
  @param key 密钥，如果为<code>null</code>自动生成一个key
  @return {@link SymmetricCrypto}