[newstarctf2023] --RE wp

AndroGenshin:

rc4加密表，base64換表：

腳本梭就行

python

username = b"genshinimpact"
base64_table = [125, 239, 101, 151, 77, 163, 163, 110, 58, 230, 186, 206, 84, 84, 189, 193, 30, 63, 104, 178, 130, 211,164, 94, 75, 16, 32, 33, 193, 160, 120, 47, 30, 127, 157, 66, 163, 181, 177, 47, 0, 236, 106, 107, 144,231, 250, 16, 36, 34, 91, 9, 188, 81, 5, 241, 235,3, 54, 150, 40, 119, 202, 150]
def rc4(key, data):S = list(range(256))j = 0out = []for i in range(256):j = (j + S[i] + key[i % len(key)]) % 256S[i], S[j] = S[j], S[i]i = j = 0for t in data:i = (i + 1) % 256j = (j + S[i]) % 256S[i], S[j] = S[j], S[i]out.append(t^ S[(S[i] + S[j]) % 256])return out
import base64
def base64_custom_decode(data, custom_table):original_table = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"decode_table = str.maketrans(custom_table, original_table)decoded_data = base64.b64decode(data.translate(decode_table))return decoded_data
retval = rc4(username, base64_table)
new_table = "".join([chr(t) for t in retval])
enc_data = "YnwgY2txbE8TRyQecyE1bE8DZWMkMiRgJW1="
print(base64_custom_decode(enc_data, new_table))

SMC：

先來看主函數部分：

int __cdecl main(int argc, const char **argv, const char **envp)
{DWORD *v3; // eaxv3 = (DWORD *)malloc(0x26u);VirtualProtect(&sub_403040, 0x26u, 0x40u, v3);puts("Please enter your flag:");sub_401025("%s", data);if ( NtCurrentPeb()->BeingDebugged ){MessageBoxA(0, "Debug Detected!", "Warning!", 0);Sleep(0x1388u);exit(0);}sub_401042();if ( ((int (__cdecl *)(char *, void *))sub_403040)(data, &byte_403020) )puts("Win!");elseputs("Lose!");return system("pause");
}

主函數比較簡潔明了，就是sub_403040這個函數不知道，是由sub_401042這個函數解密而成的，看一下加密函數

char sub_401042()
{int i; // ecxchar result; // alfor ( i = 0; i < 38; ++i ){result = byte_403068[i & 3];sub_403040[i] ^= result;}return result;
}

接著動調把解密后的函數搞出來就行

可以直接set ip直接跳到目標函數處，patch掉反調試代碼

解密函數如下：

就是異或再加5，直接梭腳本就行

python

data=[0x7C, 0x82, 0x75, 0x7B, 0x6F, 0x47, 0x61, 0x57, 0x53, 0x25, 
0x47, 0x53, 0x25, 0x84, 0x6A, 0x27, 0x68, 0x27, 0x67, 0x6A, 
0x7D, 0x84, 0x7B, 0x35, 0x35, 0x48, 0x25, 0x7B, 0x7E, 0x6A, 
0x33, 0x71]for i in data:char=(i-5)^0x11print(chr(char),end="")

Petals:

看主函數：

__int64 __fastcall main(int a1, char **a2, char **a3)
{unsigned int v4; // [rsp+Ch] [rbp-4h]puts("Here is a pack of flowers, to my best love --- you.");puts("But I must check your identity, please input the right passwd");__isoc99_scanf("%s", byte_4080);v4 = strlen(byte_4080);if ( strlen(byte_4080) != 25 ){puts("Please check your input's format!");exit(-1);}((void (__fastcall *)(char *, _QWORD))loc_1209)(byte_4080, v4);sub_160C(byte_4080, &unk_4020, v4);printf("If you are succeed, the flag is flag{md5(your input)}");return 0LL;
}

邏輯依舊比較清晰，看一下sub_160C函數

int __fastcall sub_160C(const void *a1, const void *a2, unsigned int a3)
{if ( !memcmp(a1, a2, a3) )return puts("I love you.");elsereturn puts("I hate you!");
}

數據的判斷語句，要判斷的數據是

data=[ ?0xD0, 0xD0, 0x85, 0x85, 0x80, 0x80, 0xC5, 0x8A, 0x93, 0x89,

? 0x92, 0x8F, 0x87, 0x88, 0x9F, 0x8F, 0xC5, 0x84, 0xD6, 0xD1,

? 0xD2, 0x82, 0xD3, 0xDE, 0x87]

再來看一下上一個函數log_1209:

發現爆紅。初步判斷應該是加了花指令

果然，經典花指令，在call那里按u，然后將剩下的代碼按c轉化為代碼即可

去花函數為

unsigned __int64 __fastcall sub_1209(__int64 a1, unsigned int a2)
{int i; // [rsp+18h] [rbp-118h]unsigned int j; // [rsp+1Ch] [rbp-114h]__int64 v5[33]; // [rsp+20h] [rbp-110h] BYREFunsigned __int64 v6; // [rsp+128h] [rbp-8h]v6 = __readfsqword(0x28u);memset(v5, 0, 256);for ( i = 0; i <= 255; ++i )*((_BYTE *)v5 + i) = ~(i ^ a2);for ( j = 0; a2 > j; ++j )*(_BYTE *)((int)j + a1) = *((_BYTE *)v5 + *(unsigned __int8 *)((int)j + a1));return v6 - __readfsqword(0x28u);
}

其實加密過程很直接，第一個for循環生成密碼表，然后再根據字符作為下標就行加密

就是在密碼表中找對應的，然后下標就是加密前的數據。腳本如下：

python

data=[  0xD0, 0xD0, 0x85, 0x85, 0x80, 0x80, 0xC5, 0x8A, 0x93, 0x89, 0x92, 0x8F, 0x87, 0x88, 0x9F, 0x8F, 0xC5, 0x84, 0xD6, 0xD1, 0xD2, 0x82, 0xD3, 0xDE, 0x87]v5=[0]*256for i in range(256):v5[i]=~(i^25)&0xffprint(v5)    
flag=""
for i in range(25):flag+=v5.index(data[i])
print("\n")
import hashlib
md5=hashlib.md5()
md5.update(flag.encode())
result=md5.hexdigest()
print(result)

C？C++？：

c#編寫的程序，dnspy打開即可

找到加密函數部分

// ConsoleApp1.Program
// Token: 0x06000001 RID: 1 RVA: 0x00002050 File Offset: 0x00000250
private static void Main(string[] args)
{int num = 35;int[] array = new int[]{68, 75, 66, 72, 99, 19, 19, 78, 83, 74,91, 86, 35, 39, 77, 85, 44, 89, 47, 92,49, 88, 48, 91, 88, 102, 105, 51, 76, 115,-124, 125, 79, 122, -103};char[] array2 = new char[35];int[] array3 = new int[35];Console.Write("Input your flag: ");string text = Console.ReadLine();for (int i = 0; i < text.Length; i++){array2[i] = text[i];}string text2 = "NEWSTAR";for (int j = 0; j < num; j++){char[] array4 = array2;int num2 = j;array4[num2] += (char)j;char[] array5 = array2;int num3 = j;array5[num3] -= ' ';}for (int k = 0; k < 7; k++){char[] array6 = array2;int num4 = k;array6[num4] += (char)(k ^ (int)(-(int)(text2[k] % '\u0004')));char[] array7 = array2;int num5 = k + 7;array7[num5] += text2[k] % '\u0005';char[] array8 = array2;int num6 = k + 14;array8[num6] += (char)(2 * k);char[] array9 = array2;int num7 = k + 21;array9[num7] += (char)(k ^ 2);char[] array10 = array2;int num8 = k + 28;array10[num8] += text2[k] / '\u0005' + '\n';}for (int l = 0; l < num; l++){int num9 = (int)array2[l];array3[l] = num9;}for (int m = 0; m < 35; m++){bool flag = m == 34 && array3[m] == array[m];if (flag){Console.WriteLine("Right!");}bool flag2 = array3[m] == array[m];if (!flag2){Console.WriteLine("Wrong!");break;}}
}

其實加密過程不復雜，就是加密過程很亂，慢慢分析一下即可

python

v6 = 35
j = 0
v10 = [68,75,66,72,99,19,19,78,83,74,91,86,35,39,77,85,44,89,47,92,49,88,48,91,88,102,105,51,76,115,-124,125,79,122,-103]
a2 = "NEWSTAR"for j in range(7):v10[j + 28] -= (ord(a2[j])//5) + 10v10[j + 21] -= j ^ 2v10[j + 14] -= 2 * jv10[j + 7] -= ord(a2[j]) % 5v10[j] -= j ^ -(ord(a2[j]) % 4)for i in range(v6):v10[i] -= iv10[i] += 32print(chr(v10[i]%256), end='')

R4ndom：

主函數邏輯：

int __cdecl main(int argc, const char **argv, const char **envp)
{char v3; // blint v4; // eaxint i; // [rsp+Ch] [rbp-94h]__int64 s2[6]; // [rsp+10h] [rbp-90h] BYREF__int16 v8; // [rsp+40h] [rbp-60h]char data[8]; // [rsp+50h] [rbp-50h] BYREF__int64 v10; // [rsp+58h] [rbp-48h]__int64 v11; // [rsp+60h] [rbp-40h]__int64 v12; // [rsp+68h] [rbp-38h]__int64 v13; // [rsp+70h] [rbp-30h]__int64 v14; // [rsp+78h] [rbp-28h]__int16 v15; // [rsp+80h] [rbp-20h]unsigned __int64 v16; // [rsp+88h] [rbp-18h]v16 = __readfsqword(0x28u);s2[0] = 0x3513AB8AB2D7E6EELL;s2[1] = 0x2EEDBA9CB9C97B02LL;s2[2] = 0x16E4F8C8EEFA4FBDLL;s2[3] = 0x383014F4983B6382LL;s2[4] = 0xEA32360C3D843607LL;s2[5] = 42581LL;v8 = 0;puts("Can You Find the Secret?");puts("Give me your flag");*(_QWORD *)data = 0LL;v10 = 0LL;v11 = 0LL;v12 = 0LL;v13 = 0LL;v14 = 0LL;v15 = 0;__isoc99_scanf("%s", data);if ( strlen(data) != 42 )exit(0);for ( i = 0; i < strlen(data); ++i ){v3 = data[i];v4 = rand();data[i] = Table[(16 * ((unsigned __int8)(v3 + v4 % 255) >> 4) + 15) & (unsigned __int8)(v3 + v4 % 255)];}if ( !memcmp(data, s2, 0x2AuLL) )puts("You get the Right Flag!!");elseputs("Maybe your flag is Wrong o.O?");return 0;
}

直接看最關鍵的代碼邏輯

for ( i = 0; i < strlen(data); ++i ){v3 = data[i];v4 = rand();data[i] = Table[(16 * ((unsigned __int8)(v3 + v4 % 255) >> 4) + 15) & (unsigned __int8)(v3 + v4 % 255)];}if ( !memcmp(data, s2, 0x2AuLL) )puts("You get the Right Flag!!");elseputs("Maybe your flag is Wrong o.O?");return 0;
}

這里data和s2進行判斷，s2的數據上面已經給出了，for循環這里還有一個rand(),我們來看一下函數列表有沒有srand函數，發現是有的，我們交叉引用到調用處

發現是這個b函數進行了調用，再來交叉引用一下發現是在init_array處進行調用，也就是在main函數前就已經設置好了隨機數種子

回到主函數這里，可以直接爆破求值就行，注意這是elf文件，需要在linux下編譯運行

#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>int main() {uint64_t s2[6];s2[0] = 0x3513AB8AB2D7E6EELL;s2[1] = 0x2EEDBA9CB9C97B02LL;s2[2] = 0x16E4F8C8EEFA4FBDLL;s2[3] = 0x383014F4983B6382LL;s2[4] = 0xEA32360C3D843607LL;s2[5] = 42581LL;unsigned char* flag = (unsigned char*)s2;unsigned char table[] ={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 int flags[42];srand(1400333646);for(int i = 0; i < 42; i++) {int flag_char = flag[i];int random = rand();for(int num = 33; num < 127; num++) {int found = 0;for(int j = 0; j < 256; j++) {if (flag_char == table[(16 * ((unsigned char)(num + random % 255) >> 4) + 15) & (unsigned char)(num + random % 255)]) {flags[i] = num;found = 1;break;}}if (found) {break;}}}puts("\nDecrypted flag:");for(int i = 0; i < 42; i++) {printf("%c", flags[i]);}return 0;
}

easy_enc：

看主函數邏輯

__int64 sub_140016070()
{char *v0; // rdi__int64 i; // rcxchar v3[32]; // [rsp+0h] [rbp-20h] BYREFchar v4; // [rsp+20h] [rbp+0h] BYREF__int64 v5[9]; // [rsp+28h] [rbp+8h]char data[132]; // [rsp+70h] [rbp+50h] BYREFint j; // [rsp+F4h] [rbp+D4h]char Buf1[5]; // [rsp+120h] [rbp+100h] BYREFchar v9[127]; // [rsp+125h] [rbp+105h] BYREFint v10; // [rsp+1A4h] [rbp+184h]v0 = &v4;for ( i = 106i64; i; --i ){*(_DWORD *)v0 = -858993460;v0 += 4;}sub_14001135C(&unk_140021018);v5[0] = (__int64)sub_1400113C5;v5[1] = (__int64)sub_1400113CA;v5[2] = (__int64)sub_1400113F2;v5[3] = (__int64)sub_1400113ED;memset(data, 0, 0x64ui64);sub_14001118B("Input Your flag(format:A-Z a-z): ");sub_1400113FC((__int64)&unk_140019C18, (__int64)data);length = j_strlen(data);for ( j = 0; j < 4; ++j )((void (__fastcall *)(char *))v5[j])(data);Buf1[0] = -24;Buf1[1] = 0x80;Buf1[2] = -124;Buf1[3] = 8;Buf1[4] = 24;strcpy(v9, "<xh");v9[4] = 112;v9[5] = 124;v9[6] = -108;v9[7] = -56;v9[8] = -32;v9[9] = 16;v9[10] = -20;v9[11] = -76;v9[12] = -84;v9[13] = 104;v9[14] = -88;v9[15] = 12;v9[16] = 28;v9[17] = -112;v9[18] = -52;v9[19] = 84;v9[20] = 60;v9[21] = 20;v9[22] = -36;v9[23] = 48;memset(&v9[24], 0, 0x47ui64);v10 = 1;if ( !j_memcmp(Buf1, data, length) )sub_14001118B("Right!! flag is flag{your input}\n");elsesub_14001118B("Wrong!!\n");sub_1400112F3(v3, &unk_14001AA10);return 0i64;
}

其實這里的加密是比較清晰的，只是數據比較那里那里有點小問題，這里buf1是包括v9的，所以比較的字符串長度為29

接著看一下四個加密函數即可

__int64 __fastcall sub_140015B80(__int64 a1)
{__int64 result; // raxint i; // [rsp+24h] [rbp+4h]sub_14001135C(&unk_140021018);for ( i = 0; ; ++i ){result = (unsigned int)length;if ( i >= length )break;if ( *(unsigned __int8 *)(a1 + i) < (unsigned int)'A' || *(unsigned __int8 *)(a1 + i) > (unsigned int)'Z' ){if ( *(unsigned __int8 *)(a1 + i) < (unsigned int)'0' || *(unsigned __int8 *)(a1 + i) > (unsigned int)'9' ){if ( *(unsigned __int8 *)(a1 + i) >= (unsigned int)'a' && *(unsigned __int8 *)(a1 + i) <= (unsigned int)'z' )*(_BYTE *)(a1 + i) = (*(unsigned __int8 *)(a1 + i) - 89) % 26 + 97;}else{*(_BYTE *)(a1 + i) = (*(unsigned __int8 *)(a1 + i) - 45) % 10 + 48;}}else{*(_BYTE *)(a1 + i) = (*(unsigned __int8 *)(a1 + i) - 52) % 26 + 65;}}return result;
}

__int64 __fastcall sub_140015CE0(__int64 a1)
{char *v1; // rdi__int64 i; // rcxchar v4[32]; // [rsp+0h] [rbp-20h] BYREFchar v5; // [rsp+20h] [rbp+0h] BYREFchar Str[44]; // [rsp+28h] [rbp+8h] BYREFint j; // [rsp+54h] [rbp+34h]__int64 v8; // [rsp+128h] [rbp+108h]__int64 v9; // [rsp+130h] [rbp+110h]size_t v10; // [rsp+138h] [rbp+118h]v1 = &v5;for ( i = 28i64; i; --i ){*(_DWORD *)v1 = -858993460;v1 += 4;}sub_14001135C(&unk_140021018);strcpy(Str, "NewStarCTF");memset(&Str[11], 0, 9ui64);for ( j = 0; j < length; ++j ){v8 = j;v9 = j;v10 = j_strlen(Str);*(_BYTE *)(a1 + j) += Str[j % v10];}return sub_1400112F3(v4, &unk_14001A920);
}

__int64 __fastcall sub_140012B40(__int64 a1)
{__int64 result; // raxint i; // [rsp+24h] [rbp+4h]sub_14001135C(&unk_140021018);for ( i = 0; ; ++i ){result = (unsigned int)length;if ( i >= length )break;*(_BYTE *)(a1 + i) = ~*(_BYTE *)(a1 + i);}return result;
}

__int64 __fastcall sub_140011830(__int64 a1)
{__int64 result; // raxint i; // [rsp+24h] [rbp+4h]sub_14001135C(&unk_140021018);for ( i = 0; ; ++i ){result = (unsigned int)length;if ( i >= length )break;*(_BYTE *)(a1 + i) *= 52;}return result;
}

逆是不可能逆了，直接爆破

#include <stdio.h>
#include <string.h>// 第一個加密函數
unsigned char encrypt_first(unsigned char data, int i) {if ( data < (unsigned int)'A' || data > (unsigned int)'Z' ){if ( data < (unsigned int)'0' || data > (unsigned int)'9' ){if ( data >= (unsigned int)'a' && data <= (unsigned int)'z' )data = (data - 89) % 26 + 97;}else{data = (data - 45) % 10 + 48;}}else{data = (data - 52) % 26 + 65;}