java aes 256 java.security.InvalidKeyException:安装策略后非法密钥大小

我用AES 256密钥加密字节有问题.我已经安装了这个政策.这就是我所做的:

下载文件:http://www.oracle.com/technetwork/java/javase/downloads/jce-7-download-432124.html

我将文件local_policy和US_export_policy移动到目录/Library/Java/JavaVirtualMachines/jdk1.7.0_40.jdk/Contents/Home/jre/lib/security

我重启mac

但我仍然收到以下代码的错误消息:

KeyGenerator keyGenerator = KeyGenerator.getInstance("AES");
keyGenerator.init(256);
SecretKey secretKey = keyGenerator.generateKey();
Cipher decryption = Cipher.getInstance("AES/CBC/PKCS5PADDING");
decryption.init(Cipher.DECRYPT_MODE, secretKey, 
new IvParameterSpec(secretKey.getEncoded())); // <-- Illegal key size

我的Java版本:

java version "1.7.0_40"
Java(TM) SE Runtime Environment (build 1.7.0_40-b43)
Java HotSpot(TM) 64-Bit Server VM (build 24.0-b56, mixed mode)

我需要做什么,使用256 AES加密？