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KCTF2022 Q1 第三题 石像病毒
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发表于: 2022-5-13 17:23
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考点：异常处理
引入结构体
分析主要逻辑
逻辑比较简单
下面主要分析j_aesEncrypt
找到相似项目：lmshao/AES: Advanced Encryption Standard
手动导入结构体及符号
两处魔改
patch try部分，看到KeyExpansion
交换Sbox[113]与sbox[163]
前段偶数次循环，不改变sbox
后段奇数次循环，交换sbox
相同办法分析shiftRows
程序将ROF修改为ROR
代码如下
修改逆函数及逆s盒
这里要注意到对比结果在sub_6523D0被修改
简单赋值
实际上执行点位于GMul，通过相同的try catch处理方式
执行解密
flag：flag{db5c6a8dfec4d0ec5569899640}
struct INP{ BYTE unknown1[8];
BYTE key[28];
BYTE hash[28];
BYTE unknown2[8];
BYTE output[48];
BYTE input[4008];
};struct INP{ BYTE unknown1[8];
BYTE key[28];
BYTE hash[28];
BYTE unknown2[8];
BYTE output[48];
BYTE input[4008];
};int sub_652330()
{ sbox[113] ^= sbox[163];
sbox[163] ^= sbox[113];
sbox[113] ^= sbox[163];
return 1;
}int sub_652330()
{ sbox[113] ^= sbox[163];
sbox[163] ^= sbox[113];
sbox[113] ^= sbox[163];
return 1;
}int shiftRows(uint8_t (*state)[4]) {
uint32_t block[4] = {0};
/* i: row */
for (int i = 0; i < 4; ++i) {
LOAD32H(block[i], state[i]);
block[i] = ROR32(block[i], 8*i);
STORE32H(block[i], state[i]);
}
return 0;
}int shiftRows(uint8_t (*state)[4]) {
uint32_t block[4] = {0};
/* i: row */
for (int i = 0; i < 4; ++i) {
LOAD32H(block[i], state[i]);
block[i] = ROR32(block[i], 8*i);
STORE32H(block[i], state[i]);
}
return 0;
}unsigned char inv_S[256] = {
0x52, 0x09, 0x6a, 0xd5, 0x30, 0x36, 0xa5, 0x38, 0xbf, 0x40, 0x71, 0x9e, 0x81, 0xf3, 0xd7, 0xfb,
0x7c, 0xe3, 0x39, 0x82, 0x9b, 0x2f, 0xff, 0x87, 0x34, 0x8e, 0x43, 0x44, 0xc4, 0xde, 0xe9, 0xcb,
0x54, 0x7b, 0x94, 0x32, 0xa6, 0xc2, 0x23, 0x3d, 0xee, 0x4c, 0x95, 0x0b, 0x42, 0xfa, 0xc3, 0x4e,
0x08, 0x2e, 0xa1, 0x66, 0x28, 0xd9, 0x24, 0xb2, 0x76, 0x5b, 0xa2, 0x49, 0x6d, 0x8b, 0xd1, 0x25,
0x72, 0xf8, 0xf6, 0x64, 0x86, 0x68, 0x98, 0x16, 0xd4, 0xa4, 0x5c, 0xcc, 0x5d, 0x65, 0xb6, 0x92,
0x6c, 0x70, 0x48, 0x50, 0xfd, 0xed, 0xb9, 0xda, 0x5e, 0x15, 0x46, 0x57, 0xa7, 0x8d, 0x9d, 0x84,
0x90, 0xd8, 0xab, 0x00, 0x8c, 0xbc, 0xd3, 0x0a, 0xf7, 0xe4, 0x58, 0x05, 0xb8, 0xb3, 0x45, 0x06,
0xd0, 0x2c, 0x1e, 0x8f, 0xca, 0x3f, 0x0f, 0x02, 0xc1, 0xaf, 0xbd, 0x03, 0x01, 0x13, 0x8a, 0x6b,
0x3a, 0x91, 0x11, 0x41, 0x4f, 0x67, 0xdc, 0xea, 0x97, 0xf2, 0xcf, 0xce, 0xf0, 0xb4, 0xe6, 0x73,
0x96, 0xac, 0x74, 0x22, 0xe7, 0xad, 0x35, 0x85, 0xe2, 0xf9, 0x37, 0xe8, 0x1c, 0x75, 0xdf, 0x6e,
0x47, 0xf1, 0x1a, 0xa3, 0x1d, 0x29, 0xc5, 0x89, 0x6f, 0xb7, 0x62, 0x0e, 0xaa, 0x18, 0xbe, 0x1b,
0xfc, 0x56, 0x3e, 0x4b, 0xc6, 0xd2, 0x79, 0x20, 0x9a, 0xdb, 0xc0, 0xfe, 0x78, 0xcd, 0x5a, 0xf4,
0x1f, 0xdd, 0xa8, 0x33, 0x88, 0x07, 0xc7, 0x31, 0xb1, 0x12, 0x10, 0x59, 0x27, 0x80, 0xec, 0x5f,
0x60, 0x51, 0x7f, 0xa9, 0x19, 0xb5, 0x4a, 0x0d, 0x2d, 0xe5, 0x7a, 0x9f, 0x93, 0xc9, 0x9c, 0xef,
0xa0, 0xe0, 0x3b, 0x4d, 0xae, 0x2a, 0xf5, 0xb0, 0xc8, 0xeb, 0xbb, 0x3c, 0x83, 0x53, 0x99, 0x61,
0x17, 0x2b, 0x04, 0x7e, 0xba, 0x77, 0xd6, 0x26, 0xe1, 0x69, 0x14, 0x63, 0x55, 0x21, 0x0c, 0x7d};
// ···
int invShiftRows(uint8_t (*state)[4]) {
uint32_t block[4] = {0};
/* i: row */
for (int i = 0; i < 4; ++i) {
LOAD32H(block[i], state[i]);
block[i] = ROF32(block[i], 8*i);
STORE32H(block[i], state[i]);
}
return 0;
}unsigned char inv_S[256] = {
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最后于 2022-5-13 17:39
被sunfishi编辑
，原因：
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