【CTF解题】BUUCTF Reverse篇

APK 简单注册器

APK程序逆向，这道题目比较简单判断flag成立就解密flag并输出。

char[] x = "dd2940c04462b4dd7c450528835cca15".toCharArray();
x[2] = (char) ((x[2] + x[3]) - 50);
x[4] = (char) ((x[2] + x[5]) - 48);
x[30] = (char) ((x[31] + x[9]) - 48);
x[14] = (char) ((x[27] + x[28]) - 97);
for (int i = 0; i < 16; i++) {
    char a = x[31 - i];
    x[31 - i] = x[i];
    x[i] = a;
}
String bbb = String.valueOf(x);
textview.setText("flag{" + bbb + "}");

我们只需要按它的算法流程仿写，再运行一遍就能出flag。

x = list("dd2940c04462b4dd7c450528835cca15")
x[2] = chr(ord(x[2]) + ord(x[3]) - 50)
x[4] = chr(ord(x[2]) + ord(x[5]) - 48)
x[30] = chr(ord(x[31]) + ord(x[9]) - 48)
x[14] = chr(ord(x[27]) + ord(x[28]) - 97)
for i in range(16):
    a = x[31 - i]
    x[31 - i] = x[i]
    x[i] = a
bbb = ''.join(x)
print("flag{" + bbb + "}")

flag{59acc538825054c7de4b26440c0999dd}