题目流程比较简洁，初步判断该exe定义了一个大的结构体进行操作，简单根据偏移量进行了结构体判断。
重新对main进行解析，比较友好了。
存在较多的反调试。
流程较为清晰：
1、keys = MD5(Enj0y_1t_4_fuuuN)
2、AES(keys , 16bytes , plain , cipher , 32bytes) == byte_40B200[0:20]
直接进行解密计算发现是乱码，判断算法进行了改变。
直接使用MD5(Enj0y_1t_4_fuuuN)结果。并未具体分析过程，因为是固定值。
整个AES算法结构比较标准，在正常的128bit密钥流程中增加了对16字节输入输出的转置操作。
需要找一份类似的代码实现。
密钥扩展函数正常。
字节替换函数中，查表方式没变，但是查看交叉引用时，发现sub_402330函数对其进行了修改。
原S盒中的：SBox[0x71] = 0xa3、SBox[0xa3]=0x0a，
这里修改为了：SBox[0x71] = 0x0a、SBox[0xa3]=0xa3
因此解密inv_sub_bytes的时候，RBox也应该进行相应的修改：
原本RBox[0xA3] = 0x71、RBox[0x0A] = 0xA3
修改为：RBox[0xA3] = 0xA3、RBox[0x0A] = 0x71
反编译时提示401bef无法转换，直接nop掉反调试的指令。
该题目对行变换函数进行了修改。直接分析16字节输入，魔改的变换如下：
0 1 2 3 -> 0 1 2 3
4 5 6 7 -> 7 4 5 6
8 9 10 11 -> 10 11 8 9
12 13 14 15 -> 13 14 15 12
在进行inv_shift_rows直接对如上变换方式进行逆变换即可。
列混淆函数中，计算时取的是state矩阵的转置，在编写Inv_MixColumn时也在取计算结果时，取state矩阵的转置。
加轮密钥中，也对要异或的16字节密钥进行了转置操作ExtendKey[i][j] = u32Extendkey[j] >> (8 * (3 - i))。解密时直接调用该函数即可。
根据对AES加密函数相应的修改，编写对应的解密函数。直接对byte_40B200开始的32字节进行解密，发现不对，直接获取内存值发现有修改，查看交叉引用，发现sub_4023D0对校验值进行修改。求解得到flag。
struct context{
int iterator1; //0
int unknow1; //1
unsigned int md5[5]; //2-6
int unknow7; //7
int unknow8; //8
byte keys[16]; //9-12
int unknow13; //13
int unknow14; //14
int unknow15; //15
int iterator2; //16
int unknow17; //17
unsigned int cipher[10]; //18-27
int unknow28; //28
int unknow29; //29
char sn[4000];
int a3;
int a4;
};
struct context{
int iterator1; //0
int unknow1; //1
unsigned int md5[5]; //2-6
int unknow7; //7
int unknow8; //8
byte keys[16]; //9-12
int unknow13; //13
int unknow14; //14
int unknow15; //15
int iterator2; //16
int unknow17; //17
unsigned int cipher[10]; //18-27
int unknow28; //28
int unknow29; //29
char sn[4000];
int a3;
int a4;
};
int __cdecl main_0(int argc, const char **argv, const char **envp)
{
void *v3; // esp
int result; // eax
char v7; // [esp-10h] [ebp-1048h]
context ctx; // [esp+0h] [ebp-1038h] BYREF
CPPEH_RECORD ms_exc; // [esp+1020h] [ebp-18h]
v3 = alloca(4128);
memset(&ctx, 0xCCu, sizeof(ctx));
ms_exc.registration.ScopeTable = (ms_exc.registration.ScopeTable ^ __security_cookie);
memset(ctx.sn, 0, sizeof(ctx.sn));
ctx.cipher[0] = 0;
ctx.cipher[1] = 0;
ctx.cipher[2] = 0;
ctx.cipher[3] = 0;
ctx.cipher[4] = 0;
ctx.cipher[5] = 0;
ctx.cipher[6] = 0;
ctx.cipher[7] = 0;
ctx.cipher[8] = 0;
ctx.cipher[9] = 0;
gets_s(ctx.sn, 4000u);
if ( strlen(ctx.sn) == 32 )
{
for ( ctx.iterator2 = 0; ctx.iterator2 < 512; ++ctx.iterator2 )
{
ctx.unknow15 = 0;
MEMORY[0] = ctx.iterator2;
ms_exc.registration.TryLevel = 0xFFFFFFFE;
}
strcpy(ctx.keys, "Enj0y_1t_4_fuuuN"); // 16bytes
_DX = 0x5F00;
*(&ctx.unknow13 + 1) = 0;
HIBYTE(ctx.unknow13) = 0;
ctx.md5[0] = 0;
ctx.md5[1] = 0;
ctx.md5[2] = 0;
ctx.md5[3] = 0;
ctx.md5[4] = 0;
for ( ctx.iterator1 = 0; ctx.iterator1 < 512; ++ctx.iterator1 )
{
__asm { insb }
ms_exc.registration.TryLevel = -2;
_DX = LOWORD(ctx.iterator1) + 1;
}
j_MD5_402DB0(ctx.keys, 0x10u, ctx.md5);
j_aes_402070(ctx.md5, 0x10u, ctx.sn, ctx.cipher, 32);
if ( !memcmp(ctx.cipher, byte_40B200, 0x20u) )
printf_401037("OK\n", v7);
else
printf_401037("NO\n", v7);
result = 0;
}
else
{
printf_401037("NO\n", v7);
result = 0;
}
return result;
}
int __cdecl main_0(int argc, const char **argv, const char **envp)
{
void *v3; // esp
int result; // eax
char v7; // [esp-10h] [ebp-1048h]
context ctx; // [esp+0h] [ebp-1038h] BYREF
CPPEH_RECORD ms_exc; // [esp+1020h] [ebp-18h]
v3 = alloca(4128);
memset(&ctx, 0xCCu, sizeof(ctx));
ms_exc.registration.ScopeTable = (ms_exc.registration.ScopeTable ^ __security_cookie);
memset(ctx.sn, 0, sizeof(ctx.sn));
ctx.cipher[0] = 0;
ctx.cipher[1] = 0;
ctx.cipher[2] = 0;
ctx.cipher[3] = 0;
ctx.cipher[4] = 0;
ctx.cipher[5] = 0;
ctx.cipher[6] = 0;
ctx.cipher[7] = 0;
ctx.cipher[8] = 0;
ctx.cipher[9] = 0;
gets_s(ctx.sn, 4000u);
if ( strlen(ctx.sn) == 32 )
{
for ( ctx.iterator2 = 0; ctx.iterator2 < 512; ++ctx.iterator2 )
{
ctx.unknow15 = 0;
MEMORY[0] = ctx.iterator2;
ms_exc.registration.TryLevel = 0xFFFFFFFE;
}
strcpy(ctx.keys, "Enj0y_1t_4_fuuuN"); // 16bytes
_DX = 0x5F00;
*(&ctx.unknow13 + 1) = 0;
HIBYTE(ctx.unknow13) = 0;
ctx.md5[0] = 0;
ctx.md5[1] = 0;
ctx.md5[2] = 0;
ctx.md5[3] = 0;
ctx.md5[4] = 0;
for ( ctx.iterator1 = 0; ctx.iterator1 < 512; ++ctx.iterator1 )
{
__asm { insb }
ms_exc.registration.TryLevel = -2;
_DX = LOWORD(ctx.iterator1) + 1;
}
j_MD5_402DB0(ctx.keys, 0x10u, ctx.md5);
j_aes_402070(ctx.md5, 0x10u, ctx.sn, ctx.cipher, 32);
if ( !memcmp(ctx.cipher, byte_40B200, 0x20u) )
printf_401037("OK\n", v7);
else
printf_401037("NO\n", v7);
result = 0;
}
else
{
printf_401037("NO\n", v7);
result = 0;
}
return result;
}
int __cdecl aes_402070(void *Src, size_t KeySize, unsigned __int8 input[], unsigned __int8 uccipher[], int iLen)
{
int j; // [esp+4h] [ebp-1C8h]
unsigned int i; // [esp+8h] [ebp-1C4h]
int state[6]; // [esp+10h] [ebp-1BCh] BYREF
int key[11]; // [esp+28h] [ebp-1A4h] BYREF
unsigned int *iKeyOffset; // [esp+54h] [ebp-178h]
unsigned __int8 *__attribute__((__org_arrdim(0,0))) output; // [esp+58h] [ebp-174h]
unsigned int KeyExtend[90]; // [esp+60h] [ebp-16Ch] BYREF
output = uccipher;
iKeyOffset = KeyExtend;
key[6] = 0;
key[7] = 0;
key[8] = 0;
key[9] = 0;
key[0] = 0;
key[1] = 0;
key[2] = 0;
key[3] = 0;
state[0] = 0;
state[1] = 0;
state[2] = 0;
state[3] = 0;
if ( !Src || !input || !uccipher )
return -1;
if ( KeySize > 0x10 )
return -1;
if ( iLen % 0x10u )
return -1;
memcpy(key, Src, KeySize);
KeyExtend_4010BE(key, 16, KeyExtend);
for ( i = 0; i < iLen; i += 16 )
{
input_transpose_401145(state, input);
AddRoundKey_401186(state, iKeyOffset);
for ( j = 1; j < 10; ++j )
{
iKeyOffset += 4;
ByteSub_401172(state);
ShiftRow_40122B(state);
MixColumn_40100F(state);
AddRoundKey_401186(state, iKeyOffset);
}
ByteSub_401172(state);
ShiftRow_40122B(state);
AddRoundKey_401186(state, iKeyOffset + 4);
output_transpose_40125D(state, output);
output += 16;
input += 16;
iKeyOffset = KeyExtend;
}
return 0;
}
int __cdecl aes_402070(void *Src, size_t KeySize, unsigned __int8 input[], unsigned __int8 uccipher[], int iLen)
{
int j; // [esp+4h] [ebp-1C8h]
unsigned int i; // [esp+8h] [ebp-1C4h]
int state[6]; // [esp+10h] [ebp-1BCh] BYREF
int key[11]; // [esp+28h] [ebp-1A4h] BYREF
unsigned int *iKeyOffset; // [esp+54h] [ebp-178h]
unsigned __int8 *__attribute__((__org_arrdim(0,0))) output; // [esp+58h] [ebp-174h]
unsigned int KeyExtend[90]; // [esp+60h] [ebp-16Ch] BYREF
output = uccipher;
iKeyOffset = KeyExtend;
key[6] = 0;
key[7] = 0;
key[8] = 0;
key[9] = 0;
key[0] = 0;
key[1] = 0;
key[2] = 0;
key[3] = 0;
state[0] = 0;
state[1] = 0;
state[2] = 0;
state[3] = 0;
if ( !Src || !input || !uccipher )
return -1;
if ( KeySize > 0x10 )
return -1;
if ( iLen % 0x10u )
return -1;
memcpy(key, Src, KeySize);
KeyExtend_4010BE(key, 16, KeyExtend);
for ( i = 0; i < iLen; i += 16 )
{
input_transpose_401145(state, input);
AddRoundKey_401186(state, iKeyOffset);
for ( j = 1; j < 10; ++j )
{
iKeyOffset += 4;
ByteSub_401172(state);
ShiftRow_40122B(state);
MixColumn_40100F(state);
AddRoundKey_401186(state, iKeyOffset);
}
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最后于 2022-5-16 20:49
被kanxue编辑
，原因：
