!感谢这位作者

对于逆向研究而言frida是一款非常好用的工具,同时Frida是一款跨平台工具.话不多说 今天来hook下oc的函数 以及常用的加密的破解

1.首先需要一台越狱机 Frida的安装这里就不赘述了 新建一个工程!DesDemo

2.跟踪函数实例
分析下CCCrypt这个函数的加密 一般我们加密都会用得到这个函数

CCCryptorStatus CCCrypt( 
  CCOperation op, //kCCEncrypt为加密，kCCDecrypt为解密 
  CCAlgorithm alg, //加密方式 kCCAlgorithmAES128为AES加密
  CCOptions options, //增充方式
  const void *key,   //密钥
  size_t keyLength,  //密钥长度
  const void *iv,    // IV
  const void *dataIn, //待加密的原文
  size_t dataInLength, //原文长度
  void *dataOut,       //加密后输出的数据
  size_t dataOutAvailable,  
  size_t *dataOutMoved)

frida-trace -U -i CCCrypt DesDemo

WeChate762d2399f277eb969cd627c3310556c.png

找到如图所示的js文件 修改里面的代码

/*
 * Auto-generated by Frida. Please modify to match the signature of CCCrypt.
 * This stub is currently auto-generated from manpages when available.
 *
 * For full API reference, see: http://www.frida.re/docs/javascript-api/
 */

{
  /**
   * Called synchronously when about to call CCCrypt.
   *
   * @this {object} - Object allowing you to store state for use in onLeave.
   * @param {function} log - Call this function with a string to be presented to the user.
   * @param {array} args - Function arguments represented as an array of NativePointer objects.
   * For example use args[0].readUtf8String() if the first argument is a pointer to a C string encoded as UTF-8.
   * It is also possible to modify arguments by assigning a NativePointer object to an element of this array.
   * @param {object} state - Object allowing you to keep state across function calls.
   * Only one JavaScript function will execute at a time, so do not worry about race-conditions.
   * However, do not use this to store function arguments across onEnter/onLeave, but instead
   * use "this" which is an object for keeping state local to an invocation.
   */
  onEnter: function (log, args, state) {
    log('CCCrypt(' +
      'op=' + args[0] +
      ', alg=' + args[1] +
      ', options=' + args[2] +
      ', key=' + args[3] +
      ', keyLength=' + args[4] +
      ', iv=' + args[5] +
      ', dataIn=' + args[6] +
      ', dataInLength=' + args[7] +
      ', dataOut=' + args[8] +
      ', dataOutAvailable=' + args[9] +
      ', dataOutMoved=' + args[10] +
    ')');
    //保存参数
    this.operation   = args[0]
    this.CCAlgorithm = args[1]
    this.CCOptions   = args[2]
    this.keyBytes    = args[3]
    this.keyLength   = args[4]
    this.ivBuffer    = args[5]
    this.inBuffer    = args[6]
    this.inLength    = args[7]
    this.outBuffer   = args[8]
    this.outLength   = args[9]
    this.outCountPtr = args[10]
    //this.operation == 0 代表是加密
    if (this.operation == 0) {
      //打印加密前的原文
        console.log("In buffer:")
        console.log(hexdump(ptr(this.inBuffer), {
            length: this.inLength.toInt32(),
            header: true,
            ansi: true
        }))
        //打印密钥
        console.log("Key: ")
        console.log(hexdump(ptr(this.keyBytes), {
            length: this.keyLength.toInt32(),
            header: true,
            ansi: true
        }))
        //打印 IV
        console.log("IV: ")
        console.log(hexdump(ptr(this.ivBuffer), {
            length: this.keyLength.toInt32(),
            header: true,
            ansi: true
        }))
    }
  },

  /**
   * Called synchronously when about to return from CCCrypt.
   *
   * See onEnter for details.
   *
   * @this {object} - Object allowing you to access state stored in onEnter.
   * @param {function} log - Call this function with a string to be presented to the user.
   * @param {NativePointer} retval - Return value represented as a NativePointer object.
   * @param {object} state - Object allowing you to keep state across function calls.
   */
  onLeave: function (log, retval, state) {
  }
}

control + c 终止frida 重新运行frida

为了保险起见 我字符串还进行加密了

#pragma mark 字符加密
+(NSString*)getStr {

    //采用这样的方式,这些字符不会进入字符常量区.编译器直接换算成异或结果
    unsigned char key[]={
        (STRING_ENCRYPT_KEY ^ 'r'),
        (STRING_ENCRYPT_KEY ^ '2'),
        (STRING_ENCRYPT_KEY ^ '4'),
        (STRING_ENCRYPT_KEY ^ '3'),
        (STRING_ENCRYPT_KEY ^ '4'),
        (STRING_ENCRYPT_KEY ^ '3'),
        (STRING_ENCRYPT_KEY ^ '4'),
        (STRING_ENCRYPT_KEY ^ '3'),
        (STRING_ENCRYPT_KEY ^ '4'),
        (STRING_ENCRYPT_KEY ^ '3'),
        (STRING_ENCRYPT_KEY ^ '\0')
    };
    unsigned char * p = key;
    while (((*p) ^= STRING_ENCRYPT_KEY) != '\0') p++;
    return [NSString stringWithUTF8String:(const char *)key];
}
-(void)btnClick{

       
       NSString *encryptionString=[LCdes lcEncryUseDES:[ViewController getStr]];
       NSLog(@"加密后的的字符串:%@",encryptionString);
       
//       NSString *decryptionString=[LCdes lcDecryUseDES:encryptionString];
//       NSLog(@"解密后的字符串:%@",decryptionString);
}

触发函数加密

WeChat3f4e3340b5ff8478df01356e7f800106.png

能清晰的看到函数加密前的字符