使用Java加载密钥时，抛出异常InvalidKeyException: Illegal key size

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受到美国法律的约束，早期Java的运行时限制了JCE支持的密钥长度，即默认不支持256位的AES。解决的方法有三个：

• （推荐）升级Java 8u162+，默认使用ulimited policy
• Java 8u151和8u152，可以在你的程序中直接放开策略

Security.setProperty("crypto.policy", "unlimited");

• 其他版本，下载无限强度权限策略文件补丁包，并使用其中的文件覆盖$JAVA_HOME/lib/security目录下的对应的local_policy.jar 和US_export_policy.jar

Java9及以上，均无限制。

• 或者动态修改安全策略，加载CryptoPolicy.class会动态修改策略

public class CryptoPolicy {
    static {
        try {
            Security.setProperty("crypto.policy", "limited");
            RemoveCryptographyRestrictions();
        } catch (Exception ex) {
            ex.printStackTrace();
        }

    }
    
    private static void RemoveCryptographyRestrictions() throws Exception {
        Class<?> jceSecurity = getClazz("javax.crypto.JceSecurity");
        Class<?> cryptoPermissions = getClazz("javax.crypto.CryptoPermissions");
        Class<?> cryptoAllPermission = getClazz("javax.crypto.CryptoAllPermission");
        if (jceSecurity != null) {
            setFinalStaticValue(jceSecurity, "isRestricted", false);
            PermissionCollection defaultPolicy = (PermissionCollection)getFieldValue(jceSecurity, "defaultPolicy", (Object)null, PermissionCollection.class);
            if (cryptoPermissions != null) {
                Map<?, ?> map = (Map)getFieldValue(cryptoPermissions, "perms", defaultPolicy, Map.class);
                map.clear();
            }

            if (cryptoAllPermission != null) {
                Permission permission = (Permission)getFieldValue(cryptoAllPermission, "INSTANCE", (Object)null, Permission.class);
                defaultPolicy.add(permission);
            }
        }

    }
    private static Class<?> getClazz(String className) {
        Class clazz = null;

        try {
            clazz = Class.forName(className);
        } catch (Exception var3) {
        }

        return clazz;
    }
    private static void setFinalStaticValue(Class<?> srcClazz, String fieldName, Object newValue) throws Exception {
        Field field = srcClazz.getDeclaredField(fieldName);
        field.setAccessible(true);
        Field modifiersField = Field.class.getDeclaredField("modifiers");
        modifiersField.setAccessible(true);
        modifiersField.setInt(field, field.getModifiers() & -17);
        field.set((Object)null, newValue);
    }
    private static <T> T getFieldValue(Class<?> srcClazz, String fieldName, Object owner, Class<T> dstClazz) throws Exception {
        Field field = srcClazz.getDeclaredField(fieldName);
        field.setAccessible(true);
        return dstClazz.cast(field.get(owner));
    }
}