看我如何玩转PHP代码加密与解密

布满荆棘的人生 2021-10-20 00:30 553阅读 0赞

参考文献：

[https://xz.aliyun.com/t/2403][https_xz.aliyun.com_t_2403]

## 前言 ##

两次比赛，两个题目，两种方式，两个程序。

一切PHP的代码终究是要到**Zend Engine**上走一走的，因此一切PHP的源码加密都是可以被解密的。（不包括OpCode混淆-VMP）

## 代码混淆 ##

比较恶心人的一种处理方式，也不太算是加密。

单独拿出来是为了说明代码混淆和代码加密是两种方式。

本质是是对变量进行乱七八糟的修改，多用动态函数处理。处理应该没什么难度，就是比较复杂，浪费时间精力。

混淆方式是按照套路随机生成相关动态函数，替换明文函数，然后批量修改变量名。

该法常与代码加密联合使用。

## 代码加密解密 ##

用PHP代码进行PHP代码的加密，套了层壳。大多数代码加密都进行了一定的代码混淆，不同的加密工具也有不同的混淆。

*  壳混淆
 *  代码混淆
 *  壳和代码都分别混淆

**常见加密工具**

*  phpjiami

### 加密 ###

源码 -> 加密处理（压缩，替换，BASE64，转义）-> 安全处理（验证文件 MD5 值，限制 IP、限域名、限时间、防破解、防命令行调试）-> 加密程序成品，再简单的说：密文源码 + 自解密外壳 == 密文代码

[![aHR0cHM6Ly94emZpbGUuYWxpeXVuY3MuY29tL21lZGlhL3VwbG9hZC9waWN0dXJlLzIwMTgwNjIyMTQxNTQ3LWIzZjVmMjNlLTc1ZTMtMS5wbmc][]][aHR0cHM6Ly94emZpbGUuYWxpeXVuY3MuY29tL21lZGlhL3VwbG9hZC9waWN0dXJlLzIwMTgwNjIyMTQxNTQ3LWIzZjVmMjNlLTc1ZTMtMS5wbmc 1]

**加密方式**

1.  独立加密程序统一对明文代码进行加密处理

### 解密 ###

加密也好，混淆也罢，终归是要变成**Zend Engine**能处理的源码，该“加密”方法的的根本是通过**壳**把代码解密并通过`eval`等函数执行代码。

因此，只要用**HOOK EVAL**大法，将相关可执行代码的函数Hook住就能拿到其中需要执行的数据，也就是我们想要得到的源码。

调用`eval`等代码执行的函数，最终会调用**PHP内核**的`zend_compile_string`函数。

通过PHP本身提供的一个HOOK机制，写个插件轻松搞定。

// 声明一个临时的 compile_string 函数
    static zend_op_array *(*orig_compile_string)(zval *source_string, char *filename TSRMLS_DC);
    // 在 PHP_MINIT_FUNCTION 中替换
    orig_compile_string = zend_compile_string;
    zend_compile_string = phpjiami_decode_compile_string;
    // 在 PHP_MSHUTDOWN_FUNCTION 中恢复
    zend_compile_string = orig_compile_string;
    // 提取 compile_string 中的代码并保存
    static zend_op_array *phpjiami_decode_compile_string(zval *source_string, char *filename TSRMLS_DC)
    {
        int c, len, yes;
        char *content;
        FILE *fp = NULL;
        char fn[512];
        if (Z_TYPE_P(source_string) == IS_STRING) {
            len  = Z_STRLEN_P(source_string);
            content = estrndup(Z_STRVAL_P(source_string), len);
            if (len > strlen(content))
                for (c=0; c<len; c++)
                    if (content[c] == 0)
                        content[c] = '?';
            sprintf(fn, "/tmp/%s.php", zend_get_executed_filename(TSRMLS_C));
            fp = fopen(fn,"a+");
            if (fp!=NULL)
                fprintf(fp, "<?php\n%s\n?>\n\n", content);
            fclose(fp);
        }
        return orig_compile_string(source_string, filename TSRMLS_CC);
    }

### 案例 ###

**Challenge:** [PWNHUB 公开赛 / 傻 fufu 的工作日 Writeup][PWNHUB _ _ _ fufu _ Writeup]

[![aHR0cHM6Ly94emZpbGUuYWxpeXVuY3MuY29tL21lZGlhL3VwbG9hZC9waWN0dXJlLzIwMTgwNjIyMTQxNTQ3LWI0MTBiN2Q2LTc1ZTMtMS5wbmc][]][aHR0cHM6Ly94emZpbGUuYWxpeXVuY3MuY29tL21lZGlhL3VwbG9hZC9waWN0dXJlLzIwMTgwNjIyMTQxNTQ3LWI0MTBiN2Q2LTc1ZTMtMS5wbmc 1]

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## 扩展加密解密 ##

将文本源码进行加密存储，在使用的时候通过扩展实现解密。

**常见加密工具**

*  pm9screw
 *  pm9screw\_plus

### 加密 ###

源码 -> 加密处理（对称/非对称加密、自定义加密）-> 加密成品：密文代码

[![aHR0cHM6Ly94emZpbGUuYWxpeXVuY3MuY29tL21lZGlhL3VwbG9hZC9waWN0dXJlLzIwMTgwNjIyMTQxNTQ3LWI0NTdiMWFlLTc1ZTMtMS5wbmc][]][aHR0cHM6Ly94emZpbGUuYWxpeXVuY3MuY29tL21lZGlhL3VwbG9hZC9waWN0dXJlLzIwMTgwNjIyMTQxNTQ3LWI0NTdiMWFlLTc1ZTMtMS5wbmc 1]

**加密方式**

1.  独立加密程序统一对明文代码进行加密处理
2.  扩展存在加密解密功能，执行前判断源码是否经过加密处理，如果没有就进行加密

### 解密 ###

还是那句话，一切的源码都要到**Zend Engine**上执行，密文也得解密了再执行。那么在最终的执行之前，提取出来就可以了。

因此Hook住`zend_compile_file`函数就可以了。

但是其中有一个坑点，PHP的扩展是“栈”加载的，也就是先加载的先Hook，后执行。我们需要获取到解密之后的内容，所以需要让“加密”插件先执行，也就是我们的解密插件要先加载。

[![aHR0cHM6Ly94emZpbGUuYWxpeXVuY3MuY29tL21lZGlhL3VwbG9hZC9waWN0dXJlLzIwMTgwNjIyMTQxNTQ3LWI0NjQ1NzEwLTc1ZTMtMS5wbmc][]][aHR0cHM6Ly94emZpbGUuYWxpeXVuY3MuY29tL21lZGlhL3VwbG9hZC9waWN0dXJlLzIwMTgwNjIyMTQxNTQ3LWI0NjQ1NzEwLTc1ZTMtMS5wbmc 1]

要实现这个操作，只需要在INI配置文件中先写我们的插件。(不保证)

extension="decode.so"
    extension="encrypt.so"

这个方式需要能够加载执行**encrypt.so**，我觉得这个还是可以实现的。通过一定手段获取到**encrypt.so**和密文源码以及服务器，中间件相关信息（版本等）。

利用Docker运行一个基本相同的环境应该是可以做到的。

// 声明一个临时的 compile_file 函数
    static zend_op_array *(*orig_compile_file)(zend_file_handle *file_handle, int type TSRMLS_DC);
    // 在 PHP_MINIT_FUNCTION 中替换
    orig_compile_file = zend_compile_file;
    zend_compile_file = phpjiami_decode_compile_file;
    // 在 PHP_MSHUTDOWN_FUNCTION 中恢复
    zend_compile_file = orig_compile_file;
    // 提取 compile_file 中的代码并保存
    static zend_op_array *phpjiami_decode_compile_file(zend_file_handle *file_handle, int type TSRMLS_DC){
        char *buf;
        size_t size;
        if (zend_stream_fixup(file_handle, &buf, &size TSRMLS_CC) == SUCCESS) {
            FILE *ff = NULL;
            int i=0;
            php_printf("code size :\n%d\n\nsource code :\n%s\n\n", size, buf);
            ff = fopen("/tmp/decode.php","a+");
            if (ff!=NULL)
                for(i = 0; i <= size; i++)
                    fprintf(ff, "%c", buf[i]);
            fclose(ff);
        }
        return orig_compile_file(file_handle,type TSRMLS_DC);
    }

### 案例 ###

**Challenge:** [SCTF2018 BabySyc - Simple PHP Web Writeup - L3m0n][]

*  phpinfo

[![aHR0cHM6Ly94emZpbGUuYWxpeXVuY3MuY29tL21lZGlhL3VwbG9hZC9waWN0dXJlLzIwMTgwNjIyMTQxNTQ4LWI0NmY3ZjMyLTc1ZTMtMS5wbmc][]][aHR0cHM6Ly94emZpbGUuYWxpeXVuY3MuY29tL21lZGlhL3VwbG9hZC9waWN0dXJlLzIwMTgwNjIyMTQxNTQ4LWI0NmY3ZjMyLTc1ZTMtMS5wbmc 1]

[![aHR0cHM6Ly94emZpbGUuYWxpeXVuY3MuY29tL21lZGlhL3VwbG9hZC9waWN0dXJlLzIwMTgwNjIyMTQxNTQ4LWI0OTcyY2RhLTc1ZTMtMS5wbmc][]][aHR0cHM6Ly94emZpbGUuYWxpeXVuY3MuY29tL21lZGlhL3VwbG9hZC9waWN0dXJlLzIwMTgwNjIyMTQxNTQ4LWI0OTcyY2RhLTc1ZTMtMS5wbmc 1]

*  login.php

[![aHR0cHM6Ly94emZpbGUuYWxpeXVuY3MuY29tL21lZGlhL3VwbG9hZC9waWN0dXJlLzIwMTgwNjIyMTQxNTQ4LWI0YjM4NWUyLTc1ZTMtMS5wbmc][]][aHR0cHM6Ly94emZpbGUuYWxpeXVuY3MuY29tL21lZGlhL3VwbG9hZC9waWN0dXJlLzIwMTgwNjIyMTQxNTQ4LWI0YjM4NWUyLTc1ZTMtMS5wbmc 1]

[![aHR0cHM6Ly94emZpbGUuYWxpeXVuY3MuY29tL21lZGlhL3VwbG9hZC9waWN0dXJlLzIwMTgwNjIyMTQxNTQ4LWI0ZDY0MjRlLTc1ZTMtMS5wbmc][]][aHR0cHM6Ly94emZpbGUuYWxpeXVuY3MuY29tL21lZGlhL3VwbG9hZC9waWN0dXJlLzIwMTgwNjIyMTQxNTQ4LWI0ZDY0MjRlLTc1ZTMtMS5wbmc 1]

## OpCode混淆 ##

一种是比如**Swoole Compile**的方式，部分脱离了zend虚拟机，对opcode做了混淆，这就比较像是vmp的一种方式。

### 加密方式 ###

1.  独立加密程序统一对明文代码进行加密处理（猜测）

### 解密 ###

我不会啊！emmmmmmm

## 参考 ##

> 1.  [phpjiami 数种解密方法 - PHITHON][phpjiami _ - PHITHON]
> 2.  [Decrypt php VoiceStar encryption extension - 小鹿师傅][Decrypt php VoiceStar encryption extension -]
> 3.  [PHPDecode 在线解密工具 - Medici.Yan][PHPDecode _ - Medici.Yan]
> 4.  [Decoding a User Space Encoded PHP Script - Stefan Esser][]
> 5.  [PHP代码加密技术 郭新华 PHPCON2018 - swoole郭新华][PHP_ _ PHPCON2018 - swoole]

[https_xz.aliyun.com_t_2403]: https://xz.aliyun.com/t/2403
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[PWNHUB _ _ _ fufu _ Writeup]: https://www.virzz.com/2017/09/20/pwnhub_writeups_sha_fu_fu_workdays.html
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[SCTF2018 BabySyc - Simple PHP Web Writeup - L3m0n]: https://www.cnblogs.com/iamstudy/articles/sctf2018_simple_php_web_writeup.html
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[phpjiami _ - PHITHON]: https://www.leavesongs.com/PENETRATION/unobfuscated-phpjiami.html
[Decrypt php VoiceStar encryption extension -]: http://blog.th3s3v3n.xyz/2017/12/12/web/Decrypt_php_VoiceStar_encryption_extension/
[PHPDecode _ - Medici.Yan]: http://blog.evalbug.com/2017/09/21/phpdecode_01/
[Decoding a User Space Encoded PHP Script - Stefan Esser]: http://php-security.org/2010/05/13/article-decoding-a-user-space-encoded-php-script/index.html
[PHP_ _ PHPCON2018 - swoole]: https://myslide.cn/slides/9100?vertical=1