APK逆向分析教学：以某音频转文字工具为例<\/h1>

1. 前期准备<\/h2>

1.1 工具准备<\/h3>

PKID<\/strong>：用于查壳分析<\/li>
MT管理器<\/strong>：多功能逆向工具，可用于查看APK结构、修改smali代码等<\/li>
Jadx<\/strong>：Java反编译工具，用于查看源代码<\/li>
Frida<\/strong>：动态分析工具，用于hook应用函数<\/li>

Android Studio<\/strong>：用于查看logcat日志<\/li> <\/ul>
1.2 目标APK基本信息<\/h3>

未加固但进行了代码混淆<\/li>
主要功能：音频转文字（疑似调用百度API）<\/li>
会员验证机制较为严格<\/li> <\/ul>
2. 初步分析<\/h2>
2.1 查壳分析<\/h3>
使用PKID或MT管理器检查APK是否加固：<\/p>

确认该APK没有加固<\/strong>，但进行了代码混淆<\/li>
混淆后的代码增加了分析难度，但主要逻辑仍可辨识<\/li> <\/ul>
2.2 代码结构分析<\/h3>

使用Jadx打开APK查看源码<\/li>
发现代码被混淆，但关键Activity名称仍可识别<\/li>
主要Activity：

XsrdSplashActivity<\/code>：启动页<\/li>
XsrdVipChargeActivity<\/code>：会员开通页<\/li>
XsrdTabPageActivity<\/code>：主界面<\/li> <\/ul> <\/li> <\/ol> 3. 动态分析<\/h2> 3.1 Activity跳转分析<\/h3> 使用MT管理器的Activity记录器观察应用跳转流程：<\/p> XsrdSplashActivity → XsrdVipChargeActivity（非会员） XsrdSplashActivity → XsrdTabPageActivity（会员） <\/code><\/pre> 3.2 关键跳转逻辑<\/h3> 在XsrdSplashActivity<\/code>中发现会员验证逻辑：<\/p> public<\/span> final<\/span> void<\/span> zr<\/span>()<\/span> {<\/span> <\/span><\/span> XsrdTabPageActivity.<\/span>w<\/span>.<\/span>z<\/span>(<\/span>XsrdTabPageActivity.<\/span>f24770wW<\/span>,<\/span> this<\/span>,<\/span> null<\/span>,<\/span> null<\/span>,<\/span> 6<\/span>,<\/span> null<\/span>);<\/span> <\/span><\/span> if<\/span> (!<\/span>w.<\/span>f1188w<\/span>.<\/span>u<\/span>())<\/span> {<\/span> <\/span><\/span> \/\/ 非会员跳转逻辑 <\/span><\/span><\/span><\/span> if<\/span> (<\/span>aI.<\/span>w<\/span>.<\/span>f1098w<\/span>.<\/span>l<\/span>())<\/span> {<\/span> <\/span><\/span> int<\/span> y2 =<\/span> com.<\/span>xinshang<\/span>.<\/span>recording<\/span>.<\/span>config<\/span>.<\/span>z<\/span>.<\/span>f24764w<\/span>.<\/span>y<\/span>();<\/span> <\/span><\/span> if<\/span> (<\/span>y2 ==<\/span> 1<\/span> ||<\/span> y2 ==<\/span> 2<\/span>)<\/span> {<\/span> <\/span><\/span> XsrdVipChargeActivity.<\/span>w<\/span>.<\/span>z<\/span>(<\/span>XsrdVipChargeActivity.<\/span>f26193wG<\/span>,<\/span> this<\/span>,<\/span> "start_up_2"<\/span>,<\/span> 0<\/span>,<\/span> 4<\/span>,<\/span> null<\/span>);<\/span> <\/span><\/span> }<\/span> <\/span><\/span> }<\/span> else<\/span> {<\/span> <\/span><\/span> int<\/span> k2 =<\/span> com.<\/span>xinshang<\/span>.<\/span>recording<\/span>.<\/span>config<\/span>.<\/span>z<\/span>.<\/span>f24764w<\/span>.<\/span>k<\/span>();<\/span> <\/span><\/span> if<\/span> (<\/span>k2 ==<\/span> 1<\/span> ||<\/span> k2 ==<\/span> 2<\/span>)<\/span> {<\/span> <\/span><\/span> XsrdVipChargeActivity.<\/span>w<\/span>.<\/span>z<\/span>(<\/span>XsrdVipChargeActivity.<\/span>f26193wG<\/span>,<\/span> this<\/span>,<\/span> "start_up_1"<\/span>,<\/span> 0<\/span>,<\/span> 4<\/span>,<\/span> null<\/span>);<\/span> <\/span><\/span> }<\/span> <\/span><\/span> }<\/span> <\/span><\/span> }<\/span> <\/span><\/span> pJ.<\/span>z<\/span>.<\/span>q<\/span>(<\/span>this<\/span>);<\/span> <\/span><\/span> overridePendingTransition(<\/span>R.<\/span>anim<\/span>.<\/span>xs_anim_transition_fade_in<\/span>,<\/span> R.<\/span>anim<\/span>.<\/span>xs_anim_transition_fade_out<\/span>);<\/span> <\/span><\/span>}<\/span> <\/span><\/span><\/code><\/pre>4. 逆向修改方案<\/h2> 4.1 方案一：修改启动Activity<\/h3> 直接修改AndroidManifest.xml文件<\/li> 将启动Activity从XsrdSplashActivity<\/code>改为XsrdTabPageActivity<\/code><\/li> 优点：简单直接，完全跳过会员验证<\/li> 缺点：仍会显示短暂启动页<\/li> <\/ol> 4.2 方案二：修改会员验证逻辑<\/h3> 分析关键函数w.f1188w.u()<\/code>：<\/p> 该函数会检查VIP信息<\/li> 若VIP信息为空返回false<\/li> 不为空则调用XsRecordUserVIPInfo.a()<\/code><\/li> <\/ol> 修改步骤：<\/p> 反编译APK获取smali代码<\/li> 找到u()<\/code>方法实现<\/li> 修改返回值逻辑：注释掉VIP信息是否为空的判断<\/li> 强制返回true或修改相关变量为1<\/li> <\/ul> <\/li> <\/ol> 关键修改点：<\/p> # 原始代码 .method public u()Z .locals 1 # 各种验证逻辑... return v0 .end method # 修改后 .method public u()Z .locals 1 const\/4 v0, 0x1 # 强制返回true return v0 .end method <\/code><\/pre> 4.3 绕过Frida检测<\/h3> 当使用Frida进行hook时遇到检测，尝试以下方案：<\/p> TracerPid检测绕过：<\/li> <\/ol> var<\/span> fgetsPtr<\/span> =<\/span> Module<\/span>.findExportByName<\/span>("libc.so"<\/span>, "fgets"<\/span>); <\/span><\/span>var<\/span> fgets<\/span> =<\/span> new<\/span> NativeFunction<\/span>(fgetsPtr<\/span>, 'pointer'<\/span>, ['pointer'<\/span>, 'int'<\/span>, 'pointer'<\/span>]); <\/span><\/span>Interceptor<\/span>.replace<\/span>(fgetsPtr<\/span>, new<\/span> NativeCallback<\/span>(function<\/span>(buffer<\/span>, size<\/span>, fp<\/span>) { <\/span><\/span> var<\/span> retval<\/span> =<\/span> fgets<\/span>(buffer<\/span>, size<\/span>, fp<\/span>); <\/span><\/span> var<\/span> bufstr<\/span> =<\/span> Memory<\/span>.readUtf8String<\/span>(buffer<\/span>); <\/span><\/span> if<\/span> (bufstr<\/span>.indexOf<\/span>("TracerPid:"<\/span>) ><\/span> -<\/span>1<\/span>) { <\/span><\/span> Memory<\/span>.writeUtf8String<\/span>(buffer<\/span>, "TracerPid:\t0"<\/span>); <\/span><\/span> console<\/span>.log<\/span>("tracerpid replaced: "<\/span> +<\/span> Memory<\/span>.readUtf8String<\/span>(buffer<\/span>)); <\/span><\/span> } <\/span><\/span> return<\/span> retval<\/span>; <\/span><\/span>}, 'pointer'<\/span>, ['pointer'<\/span>, 'int'<\/span>, 'pointer'<\/span>])); <\/span><\/span><\/code><\/pre> 若仍有检测，可能需要分析libart.so中的pthread_create<\/code>调用<\/li> <\/ol> 5. VIP功能破解<\/h2> 5.1 关键验证函数<\/h3> a()<\/code>：判断VIP是否有效包含VIP状态和剩余时间验证<\/li> <\/ul> <\/li> h()<\/code>：判断当前VIP状态<\/li> x()<\/code>：判断会员时间是否到期<\/li> <\/ol> 5.2 修改方案<\/h3> 修改a()<\/code>函数强制返回true<\/li> 或修改h()<\/code>和x()<\/code>的返回值<\/li> 效果：虽然界面不显示VIP标识，但所有VIP功能可用<\/li> <\/ol> 6. 功能实现分析<\/h2> 音频转文字功能疑似直接调用百度API<\/li> 会员验证仅为前端限制，修改后可直接使用所有功能<\/li> <\/ul> 7. 完整逆向流程总结<\/h2> 分析阶段<\/strong>：<\/p> 查壳确认无加固<\/li> 使用Jadx分析混淆代码<\/li> 动态跟踪Activity跳转<\/li> <\/ul> <\/li> 定位关键点<\/strong>：<\/p> 启动流程：Splash → 会员验证 → 主界面<\/li> VIP验证函数调用链<\/li> <\/ul> <\/li> 修改方案<\/strong>：<\/p> 直接修改启动Activity（简单）<\/li> 深入修改会员验证逻辑（彻底）<\/li> <\/ul> <\/li> 绕过保护<\/strong>：<\/p> 处理Frida检测<\/li> 必要时分析so文件<\/li> <\/ul> <\/li> 验证效果<\/strong>：<\/p> 跳过会员验证界面<\/li> 解锁VIP功能<\/li> <\/ul> <\/li> <\/ol> 8. 注意事项<\/h2> 本教程仅用于学习Android安全技术<\/li> 实际应用中可能存在更复杂的保护措施<\/li> 修改他人APK可能涉及法律问题，请遵守相关法律法规<\/li> 商业应用通常会有更完善的保护机制，包括：服务端验证<\/li> 签名校验<\/li> 代码混淆+加固组合<\/li> <\/ul> <\/li> <\/ol> 9. 扩展学习<\/h2> 深入学习smali语法<\/li> 掌握更多动态分析工具如Xposed<\/li> 了解常见加固方案的逆向方法<\/li> 学习服务端验证的绕过技术<\/li> <\/ol> 通过本案例可以掌握基本的APK逆向分析流程，包括静态分析、动态调试、代码修改等技术要点。<\/p>