iOS逆向入门与技巧分享 - 以ByteCTF的极限逃脱为例<\/h1>

一、iOS逆向基础流程<\/h2>

标准逆向流程<\/strong>：<\/p>

脱壳 -> class-dump -> 抓包 -> 逆向分析<\/li>
分析软件核心算法<\/li> <\/ul> <\/li>

iOS应用特点<\/strong>：<\/p>

苹果市场会对应用进行加壳<\/li>
可使用frida进行dump脱壳<\/li>
iOS函数参考可在Apple Development上查找<\/li> <\/ul> <\/li> <\/ol>
二、常用工具推荐<\/h2>
硬件选择<\/h3>

Android设备<\/strong>：<\/p>

推荐Pixel\/Nexus系列<\/li>
系统版本6~13<\/li>
通过Magisk进行root<\/li> <\/ul> <\/li>

iOS设备<\/strong>：<\/p>

推荐iPhone 6、iPhone 8\/X\/SE等<\/li>
系统版本13或14<\/li>
注意是否有ID锁和刷机可能性<\/li> <\/ul> <\/li> <\/ul>
iOS越狱后必备插件<\/h3>

Apple File Conduit"2"：激活助手类工具的访问权限<\/li>
AppSync Unified：绕过应用签名验证<\/li>
Filza File Manager：文件管理器<\/li>
SSL Kill Switch 2：iOS版的justtrustme<\/li>
OpenSSH：用于电脑连接<\/li> <\/ol>
电脑端工具<\/h3>

IDA：经典逆向分析工具<\/li>
ifunbox：iPhone文件管理<\/li>
frida：动态分析框架<\/li>
frida-ios-dump：一键脱壳工具<\/li>
class-dump：提取头文件<\/li>
iproxy：端口转发工具<\/li> <\/ol>
三、ByteCTF极限逃脱题目分析<\/h2>
1. 题目特点<\/h3>

直接提供ipa文件<\/li>
解压ipa后可直接用IDA分析<\/li> <\/ul>
2. 逆向分析逻辑<\/h3>
第一部分：随机数验证<\/h4>
void<\/span> __cdecl<\/span> -<\/span>[ViewController firsButtonClicked:](ViewController *<\/span>self, SEL a2, id a3) { <\/span><\/span> uint32_t<\/span> v4 =<\/span> arc4random_uniform(0x1F4u<\/span>); \/\/ 生成随机数 <\/span><\/span><\/span><\/span> \/\/ ...省略部分代码... <\/span><\/span><\/span><\/span> if<\/span> ( v12 ==<\/span> (void<\/span> *<\/span>)v4 ) { \/\/ 输入值与随机数比较 <\/span><\/span><\/span><\/span> \/\/ 验证成功逻辑 <\/span><\/span><\/span><\/span> \/\/ 显示提示信息"恭喜你拿到入场券" <\/span><\/span><\/span><\/span> \/\/ 解锁后续功能 <\/span><\/span><\/span><\/span> } else<\/span> { <\/span><\/span> \/\/ 验证失败逻辑 <\/span><\/span><\/span><\/span> \/\/ 显示"咒语错误" <\/span><\/span><\/span><\/span> } <\/span><\/span>} <\/span><\/span><\/code><\/pre>关键点<\/strong>：<\/p> 使用arc4random_uniform<\/code>生成随机数<\/li> 需要绕过随机数验证才能进入第二部分<\/li> <\/ul> 第二部分：Flag验证<\/h4> 输入处理流程<\/strong>：<\/p> 检查输入格式：<\/p> CFSTR("^ByteCTF<\/span>\\<\/span>{([0-9a-z]){8}-([0-9a-z]){4}-([0-9a-z]){4}-([0-9a-z]){4}-([0-9a-z]){12}"<\/span>) <\/span><\/span><\/code><\/pre> 标准格式：ByteCTF{xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx}<\/code><\/li> <\/ul> <\/li> 去除格式标记：<\/p> 去掉"ByteCTF"前缀<\/li> 去掉花括号"{"和"}"<\/li> 按"-"分隔字符串<\/li> <\/ul> <\/li> <\/ol> 字符串重构<\/strong>：<\/p> 获取五个固定字符串：<\/p> id __cdecl<\/span> -<\/span>[ViewController first](ViewController *<\/span>self, SEL a2) { return<\/span> CFSTR("ffb53588"<\/span>); } <\/span><\/span>id __cdecl<\/span> -<\/span>[ViewController second](ViewController *<\/span>self, SEL a2) { return<\/span> CFSTR("b092"<\/span>); } <\/span><\/span>id __cdecl<\/span> -<\/span>[ViewController third](ViewController *<\/span>self, SEL a2) { return<\/span> CFSTR("bd3e"<\/span>); } <\/span><\/span>id __cdecl<\/span> -<\/span>[ViewController fourth](ViewController *<\/span>self, SEL a2) { return<\/span> CFSTR("e777"<\/span>); } <\/span><\/span>id __cdecl<\/span> -<\/span>[ViewController fifth](ViewController *<\/span>self, SEL a2) { return<\/span> CFSTR("a67be199da4b"<\/span>); } <\/span><\/span><\/code><\/pre><\/li> 按5-2-3-4-5格式重构字符串：<\/p> 最终格式：a67be199da4b-b092-bd3e-e777-a67be199da4b<\/code><\/li> <\/ul> <\/li> <\/ol> 加密处理<\/strong>：<\/p> 对重构字符串进行SHA256加密：<\/p> CC_SHA256(v47, v48, (unsigned<\/span> __int8<\/span> *<\/span>)md); <\/span><\/span><\/code><\/pre> 得到哈希值：6c9838a3c6810bdb2633ed5910b8547c09a7a4c08bf69ae3a95c5c37f9e8f57e<\/code><\/li> <\/ul> <\/li> 字符串处理：<\/p> 取前32位：6c9838a3c6810bdb2633ed5910b8547c<\/code><\/li> <\/ul> <\/li> <\/ol> 最终Flag构造<\/strong>：<\/p> flag =<\/span> "6c9838a3c6810bdb2633ed5910b8547c"<\/span> <\/span><\/span>print("ByteCTF{"<\/span>,end=<\/span>""<\/span>) <\/span><\/span>print(flag[1<\/span>:9<\/span>],end=<\/span>"-"<\/span>) # 第1-9字符，长度8<\/span> <\/span><\/span>print(flag[9<\/span>:9<\/span>+<\/span>4<\/span>],end=<\/span>"-"<\/span>) # 第9-13字符，长度4<\/span> <\/span><\/span>print(flag[5<\/span>:5<\/span>+<\/span>4<\/span>],end=<\/span>"-"<\/span>) # 第5-9字符，长度4<\/span> <\/span><\/span>print(flag[5<\/span>:5<\/span>+<\/span>4<\/span>],end=<\/span>"-"<\/span>) # 第5-9字符，长度4<\/span> <\/span><\/span>print(flag[5<\/span>:5<\/span>+<\/span>12<\/span>],end=<\/span>"}"<\/span>) # 第5-17字符，长度12<\/span> <\/span><\/span><\/code><\/pre>最终Flag<\/strong>： ByteCTF{c9838b3c-6810-8a3d-8a3c-8a3c6810bdb2}<\/code><\/p> 四、总结<\/h2> iOS逆向与Android逆向流程相似，主要区别在于：<\/p> 文件格式不同<\/li> 使用的库函数不同<\/li> <\/ul> <\/li> 关键技巧：<\/p> 熟悉Objective-C方法调用模式<\/li> 掌握iOS特有的加密和字符串处理方式<\/li> 理解iOS应用的沙盒机制和权限系统<\/li> <\/ul> <\/li> 对于熟悉Android逆向的开发者，过渡到iOS逆向并不困难，主要需要适应不同的工具链和API。<\/p> <\/li> <\/ol>