2025 湾区杯 REVERSE 复现

xuanbin 210 次阅读 发布于 2025-09-13

hardtest

patch过猜数字游戏，分析发现两处加密

第一处加密对输入进行了8位下的循环左移

第二处加密8位下循环左移，sub_5916B1F85313经分析是用快速幂算法求逆元，随后循环右移两位查表

因为每一位输入独立运算，所以可以逐位爆破

#include<iostream>
using namespace std;
int rol2(unsigned char a1,int a2)
{
    return (a1 << a2) | (unsigned int)((int)a1 >> (8 - a2));
}
__int64 __fastcall sub_5E9DB60E8313(unsigned __int8 a1)
{
    for(int i=0;i<257;i++)
    {
        if((a1*i)%257==1)
        {
            return i;
        }
    }
    return 0;
}
unsigned char rol1(unsigned __int8 a1, char a2)
{
    return ((int)a1 >> a2) | (a1 << (8 - a2));
}
int main()
{
    unsigned char target[] =
{
  0x97, 0xD5, 0x60, 0x43, 0xB4, 0x10, 0x43, 0x73, 0x0F, 0xDA, 
  0x43, 0xCD, 0xD3, 0xE8, 0x73, 0x4A, 0x94, 0xC3, 0xCD, 0x71, 
  0xBD, 0xDC, 0x97, 0x1A
};
    unsigned char ida_chars[] =
{
  0x63, 0x7C, 0x77, 0x7B, 0xF2, 0x6B, 0x6F, 0xC5, 0x30, 0x01, 
  0x67, 0x2B, 0xFE, 0xD7, 0xAB, 0x76, 0xCA, 0x82, 0xC9, 0x7D, 
  0xFA, 0x59, 0x47, 0xF0, 0xAD, 0xD4, 0xA2, 0xAF, 0x9C, 0xA4, 
  0x72, 0xC0, 0xB7, 0xFD, 0x93, 0x26, 0x36, 0x3F, 0xF7, 0xCC, 
  0x34, 0xA5, 0xE5, 0xF1, 0x71, 0xD8, 0x31, 0x15, 0x04, 0xC7, 
  0x23, 0xC3, 0x18, 0x96, 0x05, 0x9A, 0x07, 0x12, 0x80, 0xE2, 
  0xEB, 0x27, 0xB2, 0x75, 0x09, 0x83, 0x2C, 0x1A, 0x1B, 0x6E, 
  0x5A, 0xA0, 0x52, 0x3B, 0xD6, 0xB3, 0x29, 0xE3, 0x2F, 0x84, 
  0x53, 0xD1, 0x00, 0xED, 0x20, 0xFC, 0xB1, 0x5B, 0x6A, 0xCB, 
  0xBE, 0x39, 0x4A, 0x4C, 0x58, 0xCF, 0xD0, 0xEF, 0xAA, 0xFB, 
  0x43, 0x4D, 0x33, 0x85, 0x45, 0xF9, 0x02, 0x7F, 0x50, 0x3C, 
  0x9F, 0xA8, 0x51, 0xA3, 0x40, 0x8F, 0x92, 0x9D, 0x38, 0xF5, 
  0xBC, 0xB6, 0xDA, 0x21, 0x10, 0xFF, 0xF3, 0xD2, 0xCD, 0x0C, 
  0x13, 0xEC, 0x5F, 0x97, 0x44, 0x17, 0xC4, 0xA7, 0x7E, 0x3D, 
  0x64, 0x5D, 0x19, 0x73, 0x60, 0x81, 0x4F, 0xDC, 0x22, 0x2A, 
  0x90, 0x88, 0x46, 0xEE, 0xB8, 0x14, 0xDE, 0x5E, 0x0B, 0xDB, 
  0xE0, 0x32, 0x3A, 0x0A, 0x49, 0x06, 0x24, 0x5C, 0xC2, 0xD3, 
  0xAC, 0x62, 0x91, 0x95, 0xE4, 0x79, 0xE7, 0xC8, 0x37, 0x6D, 
  0x8D, 0xD5, 0x4E, 0xA9, 0x6C, 0x56, 0xF4, 0xEA, 0x65, 0x7A, 
  0xAE, 0x08, 0xBA, 0x78, 0x25, 0x2E, 0x1C, 0xA6, 0xB4, 0xC6, 
  0xE8, 0xDD, 0x74, 0x1F, 0x4B, 0xBD, 0x8B, 0x8A, 0x70, 0x3E, 
  0xB5, 0x66, 0x48, 0x03, 0xF6, 0x0E, 0x61, 0x35, 0x57, 0xB9, 
  0x86, 0xC1, 0x1D, 0x9E, 0xE1, 0xF8, 0x98, 0x11, 0x69, 0xD9, 
  0x8E, 0x94, 0x9B, 0x1E, 0x87, 0xE9, 0xCE, 0x55, 0x28, 0xDF, 
  0x8C, 0xA1, 0x89, 0x0D, 0xBF, 0xE6, 0x42, 0x68, 0x41, 0x99, 
  0x2D, 0x0F, 0xB0, 0x54, 0xBB, 0x16
};
    unsigned char flag[24];
    for(int i=0;i<24;i++)
    {
        unsigned char temp;
        for(int j=0x0;j<127;j++)
        {
            temp=j;
            temp=rol1(temp,i%7+1);
            temp=rol1(temp^0x5A,3);
            temp=(unsigned __int8)((16 * ((3 * (temp >> 4)) & 0xF)) | (5 * (temp & 0xF)) & 0xF);
            temp = sub_5E9DB60E8313(temp);
            temp=ida_chars[rol2(temp,2)];
            if(temp==target[i])
            {
                flag[i]=j;
                break;
            }
        }
        cout<<flag[i];
    }
}