[转帖]JCE无限制权限策略文件

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## Summary of the content: This text explains how to overcome limitations on Java 8 Update 144 and earlier versions regarding AES encryption. **Problem:** * By default, Java 8 Update 144 and earlier versions don't allow 256-bit keys for AES encryption, requiring policy file modifications. **Solution:** * Download and install the `unlimited-strength-jce-policy.jar` file from Oracle's website. * Replace the existing `policy.jar` file with this downloaded jar file. * Note: Back up the original `policy.jar` files (`US_export_policy.jar` and `local_policy.jar`) before replacing. * For versions 8.151 and higher, enable the `unlimited-strength-jce-policy` by modifying `crypto.policy` in the `$JAVA_HOME/jre/lib/security` file. **Benefits:** * Allows 256-bit keys for AES encryption. **Additional Notes:** * This solution assumes you have the necessary permissions to modify the `policy.jar` file. * The provided link leads to the download for various Java versions, including specific versions of Java 8 Update 144 and higher.

正文

https://www.cnblogs.com/rinack/p/13648157.html

因为某些国家的进口管制限制，Java发布的运行环境包中的加解密有一定的限制。比如默认不允许256位密钥的AES加解密，解决方法就是修改策略文件。

对于Java 8 Update 144和更早版本，需要安装Java密码学扩展（JCE）无限强度管辖权策略文件：

从此处下载无限强度的JCE策略文件
解压缩下载的文件
用$JAVA_HOME/jre/lib/security提取的无限强度策略JAR文件替换现有的策略JAR文件

注意：如果您以后决定恢复到原始的受限策略版本，请首先在中备份原始JCE策略文件（US_export_policy.jar和local_policy.jar）$JAVA_HOME/jre/lib/security。

Java 8 Update 151及更高版本

包括了“无限强度管辖策略”，但默认情况下不使用。要启用它，您需要java.security在$JAVA_HOME/jre/lib/security（对于JDK）或$JAVA_HOME/lib/security（对于JRE）中编辑文件。取消注释（或包括）该行：

crypto.policy=unlimited

官方网站提供了JCE无限制权限策略文件的下载：

JDK6的下载地址：
http://www.oracle.com/technetwork/java/javase/downloads/jce-6-download-429243.html

JDK7的下载地址：
http://www.oracle.com/technetwork/java/javase/downloads/jce-7-download-432124.html

JDK8的下载地址：
http://www.oracle.com/technetwork/java/javase/downloads/jce8-download-2133166.html

使用反射修改JDK关键代码

//这里是通过反射移除了isRestricted 的变量修饰符：final
//然后将isRestricted 赋值为false即可
static {
   //break JCE crypto policy limit
   try {
       Class<?> clazz = Class.forName("javax.crypto.JceSecurity");
       Field nameField = clazz.getDeclaredField("isRestricted");

       Field modifiersField = Field.class.getDeclaredField("modifiers");
       modifiersField.setAccessible(true);
       modifiersField.setInt(nameField, nameField.getModifiers() & ~Modifier.FINAL);

       nameField.setAccessible(true);
       nameField.set(null, java.lang.Boolean.FALSE);
    } catch (Exception ex) {
       ex.printStackTrace();
    }
}