re學習筆記（61）2020網鼎杯-青龍組-Re部分WP

新手一枚，如有錯誤（不足）請指正，謝謝！！

bang

找個軟件一鍵脫殼，jeb打開搜索就有flag，，

signal

虛擬機指令，看了一下貌似不能逆，，就直接用angr跑了

import angr
p = angr.Project('/home/cx330/Desktop/Debugging/signal.exe')
state = p.factory.entry_state()
sm = p.factory.simulation_manager(state)
def good(state):
    return b"good" in state.posix.dumps(1)

def bad(state):
    return b"what" in state.posix.dumps(1)
sm.explore(find = good, avoid = bad)
if sm.found:
    find_state = sm.found[0]
flag = find_state.posix.dumps(0)
print(flag)

輸出爲

b'757515121f3d478\x00\x89)\x02\xa2\x01\x8c\x00\x00\x01\x00\x01\x08\x02\x00\x8a\x08\x00*)\x00I\x00\x00\x1a\x00\x00\x00\x02\x0e\x00J\x1a\x0eJ\x00\x00J\x08\x02\x02\x00\x8a\x00\x19'

jocker

這題，挺操蛋

main函數無法F5，改一下棧指針。
然後是一個假的驗證，驗證下面是SMC自解密
附上IDC代碼（動調也可以

#include <idc.idc>

static main()
{
    auto addr = 0x401500;
    auto i = 0;
    for(i=0;i<187;i++)
    {
        PatchByte(addr+i,Byte(addr+i)^0x41);
    }
}

解密出來就一個異或運算，不過不全，，，少了5位。

腦洞就很難受

解題腳本

#include <stdio.h>
#include <string.h>
#include "defs.h"
unsigned int date[28] = {
    0x0000000E, 0x0000000D, 0x00000009, 0x00000006, 0x00000013, 0x00000005, 0x00000058, 0x00000056,
    0x0000003E, 0x00000006, 0x0000000C, 0x0000003C, 0x0000001F, 0x00000057, 0x00000014, 0x0000006B,
    0x00000057, 0x00000059, 0x0000000D, 0x00000000, 0x00000000, 0x00000000, 0x00000000, 0x00000000,
    0x00000000, 0x00000000, 0x00000000, 0x00000000
};
char str[] = "hahahaha_do_you_find_me?";
int main(void)
{
    int i = 0;
    char flag[25] = { 0 };
    for (i = 0; i < 19; i++)
        flag[i] = date[i] ^ str[i];
    flag[23] = '}';
    flag[22] = '}' ^ 58 ^ 38;
    flag[21] = '}' ^ 58 ^ 112;
    flag[20] = '}' ^ 58 ^ 116;
    flag[19] = '}' ^ 58 ^ 37;
    puts(flag);
}