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[原创]看雪_众安 2021 KCTF 秋季赛-签到题 身在何处
2021-11-15 23:19 715

[原创]看雪_众安 2021 KCTF 秋季赛-签到题 身在何处

2021-11-15 23:19
715

程序逻辑主要如下

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int __cdecl check(HWND hDlg){
    int v1; // ebx
    unsigned int user_CRC32; // ebx
    unsigned int serial_strtol; // eax
    int result; // eax
    signed int v5; // [esp+Ch] [ebp-260h]
    char v6[200]; // [esp+10h] [ebp-25Ch] BYREF
    CHAR username[200]; // [esp+D8h] [ebp-194h] BYREF
    CHAR serial[200]; // [esp+1A0h] [ebp-CCh] BYREF
    memset(username, 0, sizeof(username));
    memset(v6, 0, sizeof(v6));
    memset(serial, 0, sizeof(serial));
    v1 = GetDlgItemTextA(hDlg, 1000, username, 201);
    if(v1
        && (v5 = GetDlgItemTextA(hDlg, 1001, serial, 201),
            user_CRC32 = crc32(username, v1),
            strspn(serial, "0123456789") == strlen(serial))// 判断序列号是否为9
        && v5 <= 10
        && (serial_strtol = strtol(serial)) != 0
        && (itoa(user_CRC32 ^ serial_strtol, v6, 0x10), crc32(v6, 8) == 0x13B88C77)){
        SetDlgItemTextA(hDlg, 1001, "Success!");
        result = 1;
    }
    else{
        SetDlgItemTextA(hDlg, 1001, "Wrong Serial!");
        result = 0;
    }
    return result;
}

最后这个crc32(v6, 8)中的 v6 肯定要等于 0x52A1ED5A,这样才能得出 0x13B88C77

 

再加上 user_CRC32 也可以被调试出来数值

 

那么我们只要直接异或一下得出 serial_strtol 就好了

 

我的脚本是学习了一下如何使用题目的 CRC 32 表

 

其实这个题只要做一下异或就好了

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from ctypes import *
 
CRC_32_Tbl = [
0x00000000, 0x77073096, 0xee0e612c, 0x990951ba, 0x76dc419, 0x706af48f, 0xe963a535,
0x9e6495a3, 0x0edb8832, 0x79dcb8a4, 0xe0d5e91e, 0x97d2d988, 0x9b64c2b, 0x7eb17cbd,
0xe7b82d07, 0x90bf1d91, 0x1db71064, 0x6ab020f2, 0xf3b97148, 0x84be41de, 0x1adad47d,
0x6ddde4eb, 0xf4d4b551, 0x83d385c7, 0x136c9856, 0x646ba8c0, 0xfd62f97a, 0x8a65c9ec,
0x14015c4f, 0x63066cd9, 0xfa0f3d63, 0x8d080df5, 0x3b6e20c8, 0x4c69105e, 0xd56041e4,
0xa2677172, 0x3c03e4d1, 0x4b04d447, 0xd20d85fd, 0xa50ab56b, 0x35b5a8fa, 0x42b2986c,
0xdbbbc9d6, 0xacbcf940, 0x32d86ce3, 0x45df5c75, 0xdcd60dcf, 0xabd13d59, 0x26d930ac,
0x51de003a, 0xc8d75180, 0xbfd06116, 0x21b4f4b5, 0x56b3c423, 0xcfba9599, 0xb8bda50f,
0x2802b89e, 0x5f058808, 0xc60cd9b2, 0xb10be924, 0x2f6f7c87, 0x58684c11, 0xc1611dab,
0xb6662d3d, 0x76dc4190, 0x1db7106, 0x98d220bc, 0xefd5102a, 0x71b18589, 0x6b6b51f,
0x9fbfe4a5, 0xe8b8d433, 0x7807c9a2, 0xf00f934, 0x9609a88e, 0xe10e9818, 0x7f6a0dbb,
0x86d3d2d, 0x91646c97, 0xe6635c01, 0x6b6b51f4, 0x1c6c6162, 0x856530d8, 0xf262004e,
0x6c0695ed, 0x1b01a57b, 0x8208f4c1, 0xf50fc457, 0x65b0d9c6, 0x12b7e950, 0x8bbeb8ea,
0xfcb9887c, 0x62dd1ddf, 0x15da2d49, 0x8cd37cf3, 0xfbd44c65, 0x4db26158, 0x3ab551ce,
0xa3bc0074, 0xd4bb30e2, 0x4adfa541, 0x3dd895d7, 0xa4d1c46d, 0xd3d6f4fb, 0x4369e96a,
0x346ed9fc, 0xad678846, 0xda60b8d0, 0x44042d73, 0x33031de5, 0xaa0a4c5f, 0xdd0d7cc9,
0x5005713c, 0x270241aa, 0xbe0b1010, 0xc90c2086, 0x5768b525, 0x206f85b3, 0xb966d409,
0xce61e49f, 0x5edef90e, 0x29d9c998, 0xb0d09822, 0xc7d7a8b4, 0x59b33d17, 0x2eb40d81,
0xb7bd5c3b, 0xc0ba6cad, 0xedb88320, 0x9abfb3b6, 0x3b6e20c, 0x74b1d29a, 0xead54739,
0x9dd277af, 0x4db2615, 0x73dc1683, 0xe3630b12, 0x94643b84, 0xd6d6a3e, 0x7a6a5aa8,
0xe40ecf0b, 0x9309ff9d, 0xa00ae27, 0x7d079eb1, 0xf00f9344, 0x8708a3d2, 0x1e01f268,
0x6906c2fe, 0xf762575d, 0x806567cb, 0x196c3671, 0x6e6b06e7, 0xfed41b76, 0x89d32be0,
0x10da7a5a, 0x67dd4acc, 0xf9b9df6f, 0x8ebeeff9, 0x17b7be43, 0x60b08ed5, 0xd6d6a3e8,
0xa1d1937e, 0x38d8c2c4, 0x4fdff252, 0xd1bb67f1, 0xa6bc5767, 0x3fb506dd, 0x48b2364b,
0xd80d2bda, 0xaf0a1b4c, 0x36034af6, 0x41047a60, 0xdf60efc3, 0xa867df55, 0x316e8eef,
0x4669be79, 0xcb61b38c, 0xbc66831a, 0x256fd2a0, 0x5268e236, 0xcc0c7795, 0xbb0b4703,
0x220216b9, 0x5505262f, 0xc5ba3bbe, 0xb2bd0b28, 0x2bb45a92, 0x5cb36a04, 0xc2d7ffa7,
0xb5d0cf31, 0x2cd99e8b, 0x5bdeae1d, 0x9b64c2b0, 0xec63f226, 0x756aa39c, 0x26d930a,
0x9c0906a9, 0xeb0e363f, 0x72076785, 0x5005713, 0x95bf4a82, 0xe2b87a14, 0x7bb12bae,
0xcb61b38, 0x92d28e9b, 0xe5d5be0d, 0x7cdcefb7, 0xbdbdf21, 0x86d3d2d4, 0xf1d4e242,
0x68ddb3f8, 0x1fda836e, 0x81be16cd, 0xf6b9265b, 0x6fb077e1, 0x18b74777, 0x88085ae6,
0xff0f6a70, 0x66063bca, 0x11010b5c, 0x8f659eff, 0xf862ae69, 0x616bffd3, 0x166ccf45,
0xa00ae278, 0xd70dd2ee, 0x4e048354, 0x3903b3c2, 0xa7672661, 0xd06016f7, 0x4969474d,
0x3e6e77db, 0xaed16a4a, 0xd9d65adc, 0x40df0b66, 0x37d83bf0, 0xa9bcae53, 0xdebb9ec5,
0x47b2cf7f, 0x30b5ffe9, 0xbdbdf21c, 0xcabac28a, 0x53b39330, 0x24b4a3a6, 0xbad03605,
0xcdd70693, 0x54de5729, 0x23d967bf, 0xb3667a2e, 0xc4614ab8, 0x5d681b02, 0x2a6f2b94,
0xb40bbe37, 0xc30c8ea1, 0x5a05df1b, 0x2d02ef8d]
# ~0xA11AB0B3 == 0x5EE54F4C
username = "KCTF"
CRC32 = c_uint(-1)
for i in range(0, 4):
    CRC32 = c_uint(CRC_32_Tbl[(CRC32.value ^ ord(username[i])) & 0xff] ^ (CRC32.value >> 8))
username_CRC32 = int(c_uint(~CRC32.value).value)
print(hex(username_CRC32))
key_CRC32 = 0x52A1ED5A
print(username_CRC32 ^ key_CRC32)

【看雪培训】《Adroid高级研修班》2022年夏季班招生中!

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雪    币: 20
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binLep 活跃值 2021-11-15 23:22
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az,交题解应该不会被公布被大家看到吧,第一次交emmm
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