-
[newstarctf2023] --RE wp
AndroGenshin:
rc4加密表，base64换表：
脚本梭就行
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 = 0 out = [] for i in range(256): j = (j + S[i] + key[i % len(key)]) % 256 S[i], S[j] = S[j], S[i] i = j = 0 for t in data: i = (i + 1) % 256 j = (j + S[i]) % 256 S[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：
先来看主函数部分：
c
int __cdecl main(int argc, const char **argv, const char **envp) { DWORD *v3; // eax v3 = (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!"); else puts("Lose!"); return system("pause"); }主函数比较简洁明了，就是sub_403040这个函数不知道，是由sub_401042这个函数解密而成的，看一下加密函数
c
char sub_401042() { int i; // ecx char result; // al for ( i = 0; i < 38; ++i ) { result = byte_403068[i & 3]; sub_403040[i] ^= result; } return result; }接着动调把解密后的函数搞出来就行
可以直接set ip直接跳到目标函数处，patch掉反调试代码
解密函数如下：
就是异或再加5，直接梭脚本就行
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)^0x11 print(chr(char),end="")Petals:
看主函数：
c
__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; }逻辑依旧比较清晰，看一下sub_160C函数
c
int __fastcall sub_160C(const void *a1, const void *a2, unsigned int a3) { if ( !memcmp(a1, a2, a3) ) return puts("I love you."); else return puts("I hate you!"); }数据的判断语句，要判断的数据是
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]
再来看一下上一个函数log_1209:
发现爆红。初步判断应该是加了花指令
果然，经典花指令，在call那里按u，然后将剩下的代码按c转化为代码即可
去花函数为
c
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] BYREF unsigned __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); }其实加密过程很直接，第一个for循环生成密码表，然后再根据字符作为下标就行加密
就是在密码表中找对应的，然后下标就是加密前的数据。脚本如下：
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]*256 for i in range(256): v5[i]=~(i^25)&0xff print(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#编写的程序，dnspy打开即可
找到加密函数部分
c
// 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; } } }其实加密过程不复杂，就是加密过程很乱，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) + 10 v10[j + 21] -= j ^ 2 v10[j + 14] -= 2 * j v10[j + 7] -= ord(a2[j]) % 5 v10[j] -= j ^ -(ord(a2[j]) % 4) for i in range(v6): v10[i] -= i v10[i] += 32 print(chr(v10[i]%256), end='')R4ndom：
主函数逻辑：
c
int __cdecl main(int argc, const char **argv, const char **envp) { char v3; // bl int v4; // eax int 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!!"); else puts("Maybe your flag is Wrong o.O?"); return 0; }直接看最关键的代码逻辑
c
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!!"); else puts("Maybe your flag is Wrong o.O?"); return 0; }这里data和s2进行判断，s2的数据上面已经给出了，for循环这里还有一个rand(),我们来看一下函数列表有没有srand函数，发现是有的，我们交叉引用到调用处
发现是这个b函数进行了调用，再来交叉引用一下发现是在init_array处进行调用，也就是在main函数前就已经设置好了随机数种子
回到主函数这里，可以直接爆破求值就行，注意这是elf文件，需要在linux下编译运行
c
#include
#include #include 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：
看主函数逻辑
c
__int64 sub_140016070() { char *v0; // rdi __int64 i; // rcx char v3[32]; // [rsp+0h] [rbp-20h] BYREF char v4; // [rsp+20h] [rbp+0h] BYREF __int64 v5[9]; // [rsp+28h] [rbp+8h] char data[132]; // [rsp+70h] [rbp+50h] BYREF int j; // [rsp+F4h] [rbp+D4h] char Buf1[5]; // [rsp+120h] [rbp+100h] BYREF char v9[127]; // [rsp+125h] [rbp+105h] BYREF int 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, "其实这里的加密是比较清晰的，只是数据比较那里那里有点小问题，这里buf1是包括v9的，所以比较的字符串长度为29
接着看一下四个加密函数即可
c
__int64 __fastcall sub_140015B80(__int64 a1) { __int64 result; // rax int 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; }c
__int64 __fastcall sub_140015CE0(__int64 a1) { char *v1; // rdi __int64 i; // rcx char v4[32]; // [rsp+0h] [rbp-20h] BYREF char v5; // [rsp+20h] [rbp+0h] BYREF char Str[44]; // [rsp+28h] [rbp+8h] BYREF int 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); }c
__int64 __fastcall sub_140012B40(__int64 a1) { __int64 result; // rax int 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; }c
__int64 __fastcall sub_140011830(__int64 a1) { __int64 result; // rax int 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
c
#include
#include // 第一个加密函数 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; } -
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- 原文地址：https://blog.csdn.net/question55/article/details/136244095
