SYSREVEAL

Okey, I have been criticized by Niucool & Bananas as there is none post in this blog from me.
Feeling shamed~~~
So I decided to post something to let your guys know that I am alive.

Do you interesting antivirus engine? Do you wanna know what is it?
Hmmm, I think that I can not give u the answer. It’s a kidding

Many people think that eset nod32 is a good antivirus, and … so do I.
Hereby, I intend to play with it and give you a short info about it.

In the nod32 AppData folder(Or other folder? I forgot it!), you may find out some data files. They called “em???_32.dat”.

What’s meaning for this name?
I guess: “e” – Eset, “m” – Module, ??? – it’s just a id number, 32 – means 32 bit(I am not sure).
Before I analyzed it, I think that these files are the virus database file.
But in fact, I am wrong. They are the extend engine module!

Basically, the file format contains 6 major parts. They are:
1. File header:

size = variant (from 0 to the first 0x0A0D0A0D), the signature and checksum included in this section,
we are not interesting in this;

2. File info:

size = 0×100, all info are text string, you can view it directly;

3. Module record header:

size = 0x1C:
offset        comment
0×00        signature = 0x45FA785E
0×04        signature = 0×05
0x0C        decrypt key
0×18        checksum for this section

4. Module control header:

size = 0×108, the function as PE header,
some useful values in this section:

offset    comment
0xD4    entrypoint
0xD8    size of seg with access ER-
0xDC    size of seg with access -R-
0xE0    size of seg with access -RW

(E – Executabe, R – Readabe, W – writable)

5. Module section array:
This is a section array, just like section table in PE structure.
The last one is “NULL” section.

section struct:
size = 0×24
00    section name(“CODE” | “DATA” | “UNPC” | “UNPR” | “RELO” | “NULL”)
04    raw offset for segment (calculate from “File Info” part);
08    checksum of segment data
0C    raw size of segment
10    virtual size of segment
1C    compress flag ??? (1 – compressed, other – no compressed???)
20    checksum of this section

6. Module segment array:
Like segment in PE;

The data in part 4,5 and 6 are crypted. If compressed flags is set, the data is also compressed.
To decompress, we could use zlib inflate() function.
To decrypt (note: only tested on nod32 v3.x and v4.x version, this could be changed!!!):

static unsigned char g_decrypt_table[0x288] = {
	0x27, 0x45, 0xFB, 0x82, 0x66, 0x0F, 0xDC, 0x69, 0x31, 0xA7, 0xDA, 0x00, 0xAC, 0x24, 0x57, 0x8F,
	0x6B, 0xA3, 0xC2, 0xAB, 0xD6, 0x54, 0xEF, 0x37, 0x49, 0x00, 0x00, 0x00, 0xF7, 0x32, 0x94, 0x0F,
	0x0B, 0xB0, 0x1A, 0x92, 0x26, 0x55, 0x2C, 0x4B, 0xEE, 0x8A, 0xE3, 0x23, 0x85, 0x00, 0x00, 0x00,
	0x54, 0x7A, 0x67, 0x68, 0xC1, 0x50, 0x14, 0xCC, 0xFA, 0x17, 0xDF, 0x8C, 0xB8, 0xF5, 0x7E, 0x72,
	0xA7, 0x02, 0xF3, 0x34, 0x04, 0x52, 0xF1, 0x00, 0x08, 0x13, 0x10, 0xD1, 0x05, 0xEB, 0x6A, 0x8F,
	0xCE, 0x66, 0xC5, 0x59, 0x82, 0xB0, 0x99, 0x61, 0x41, 0xB3, 0x1A, 0x0D, 0x82, 0x47, 0xAD, 0x56,
	0x8C, 0x26, 0xB5, 0xA4, 0xC8, 0x00, 0x00, 0x00, 0x41, 0xEC, 0x9B, 0x52, 0x1F, 0x57, 0x81, 0xE1,
	0xAE, 0xB3, 0x36, 0x23, 0x6F, 0x50, 0xBB, 0x74, 0x0F, 0xC0, 0x3A, 0xE2, 0xC7, 0xEA, 0x46, 0xBE,
	0xE3, 0x71, 0x45, 0xBF, 0x9E, 0xDE, 0x07, 0x00, 0x00, 0x00, 0x21, 0x10, 0x42, 0x20, 0x63, 0x30,
	0x84, 0x40, 0xA5, 0x50, 0xC6, 0x60, 0xE7, 0x70, 0x08, 0x81, 0x29, 0x91, 0x4A, 0xA1, 0x6B, 0xB1,
	0x8C, 0xC1, 0xAD, 0xD1, 0xCE, 0xE1, 0xEF, 0xF1, 0x31, 0x12, 0x10, 0x02, 0x73, 0x32, 0x52, 0x22,
	0xB5, 0x52, 0x94, 0x42, 0xF7, 0x72, 0xD6, 0x62, 0x39, 0x93, 0x18, 0x83, 0x7B, 0xB3, 0x5A, 0xA3,
	0xBD, 0xD3, 0x9C, 0xC3, 0xFF, 0xF3, 0xDE, 0xE3, 0x62, 0x24, 0x43, 0x34, 0x20, 0x04, 0x01, 0x14,
	0xE6, 0x64, 0xC7, 0x74, 0xA4, 0x44, 0x85, 0x54, 0x6A, 0xA5, 0x4B, 0xB5, 0x28, 0x85, 0x09, 0x95,
	0xEE, 0xE5, 0xCF, 0xF5, 0xAC, 0xC5, 0x8D, 0xD5, 0x53, 0x36, 0x72, 0x26, 0x11, 0x16, 0x30, 0x06,
	0xD7, 0x76, 0xF6, 0x66, 0x95, 0x56, 0xB4, 0x46, 0x5B, 0xB7, 0x7A, 0xA7, 0x19, 0x97, 0x38, 0x87,
	0xDF, 0xF7, 0xFE, 0xE7, 0x9D, 0xD7, 0xBC, 0xC7, 0xC4, 0x48, 0xE5, 0x58, 0x86, 0x68, 0xA7, 0x78,
	0x40, 0x08, 0x61, 0x18, 0x02, 0x28, 0x23, 0x38, 0xCC, 0xC9, 0xED, 0xD9, 0x8E, 0xE9, 0xAF, 0xF9,
	0x48, 0x89, 0x69, 0x99, 0x0A, 0xA9, 0x2B, 0xB9, 0xF5, 0x5A, 0xD4, 0x4A, 0xB7, 0x7A, 0x96, 0x6A,
	0x71, 0x1A, 0x50, 0x0A, 0x33, 0x3A, 0x12, 0x2A, 0xFD, 0xDB, 0xDC, 0xCB, 0xBF, 0xFB, 0x9E, 0xEB,
	0x79, 0x9B, 0x58, 0x8B, 0x3B, 0xBB, 0x1A, 0xAB, 0xA6, 0x6C, 0x87, 0x7C, 0xE4, 0x4C, 0xC5, 0x5C,
	0x22, 0x2C, 0x03, 0x3C, 0x60, 0x0C, 0x41, 0x1C, 0xAE, 0xED, 0x8F, 0xFD, 0xEC, 0xCD, 0xCD, 0xDD,
	0x2A, 0xAD, 0x0B, 0xBD, 0x68, 0x8D, 0x49, 0x9D, 0x97, 0x7E, 0xB6, 0x6E, 0xD5, 0x5E, 0xF4, 0x4E,
	0x13, 0x3E, 0x32, 0x2E, 0x51, 0x1E, 0x70, 0x0E, 0x9F, 0xFF, 0xBE, 0xEF, 0xDD, 0xDF, 0xFC, 0xCF,
	0x1B, 0xBF, 0x3A, 0xAF, 0x59, 0x9F, 0x78, 0x8F, 0x88, 0x91, 0xA9, 0x81, 0xCA, 0xB1, 0xEB, 0xA1,
	0x0C, 0xD1, 0x2D, 0xC1, 0x4E, 0xF1, 0x6F, 0xE1, 0x80, 0x10, 0xA1, 0x00, 0xC2, 0x30, 0xE3, 0x20,
	0x04, 0x50, 0x25, 0x40, 0x46, 0x70, 0x67, 0x60, 0xB9, 0x83, 0x98, 0x93, 0xFB, 0xA3, 0xDA, 0xB3,
	0x3D, 0xC3, 0x1C, 0xD3, 0x7F, 0xE3, 0x5E, 0xF3, 0xB1, 0x02, 0x90, 0x12, 0xF3, 0x22, 0xD2, 0x32,
	0x35, 0x42, 0x14, 0x52, 0x77, 0x62, 0x56, 0x72, 0xEA, 0xB5, 0xCB, 0xA5, 0xA8, 0x95, 0x89, 0x85,
	0x6E, 0xF5, 0x4F, 0xE5, 0x2C, 0xD5, 0x0D, 0xC5, 0xE2, 0x34, 0xC3, 0x24, 0xA0, 0x14, 0x81, 0x04,
	0x66, 0x74, 0x47, 0x64, 0x24, 0x54, 0x05, 0x44, 0xDB, 0xA7, 0xFA, 0xB7, 0x99, 0x87, 0xB8, 0x97,
	0x5F, 0xE7, 0x7E, 0xF7, 0x1D, 0xC7, 0x3C, 0xD7, 0xD3, 0x26, 0xF2, 0x36, 0x91, 0x06, 0xB0, 0x16,
	0x57, 0x66, 0x76, 0x76, 0x15, 0x46, 0x34, 0x56, 0x4C, 0xD9, 0x6D, 0xC9, 0x0E, 0xF9, 0x2F, 0xE9,
	0xC8, 0x99, 0xE9, 0x89, 0x8A, 0xB9, 0xAB, 0xA9, 0x44, 0x58, 0x65, 0x48, 0x06, 0x78, 0x27, 0x68,
	0xC0, 0x18, 0xE1, 0x08, 0x82, 0x38, 0xA3, 0x28, 0x7D, 0xCB, 0x5C, 0xDB, 0x3F, 0xEB, 0x1E, 0xFB,
	0xF9, 0x8B, 0xD8, 0x9B, 0xBB, 0xAB, 0x9A, 0xBB, 0x75, 0x4A, 0x54, 0x5A, 0x37, 0x6A, 0x16, 0x7A,
	0xF1, 0x0A, 0xD0, 0x1A, 0xB3, 0x2A, 0x92, 0x3A, 0x2E, 0xFD, 0x0F, 0xED, 0x6C, 0xDD, 0x4D, 0xCD,
	0xAA, 0xBD, 0x8B, 0xAD, 0xE8, 0x9D, 0xC9, 0x8D, 0x26, 0x7C, 0x07, 0x6C, 0x64, 0x5C, 0x45, 0x4C,
	0xA2, 0x3C, 0x83, 0x2C, 0xE0, 0x1C, 0xC1, 0x0C, 0x1F, 0xEF, 0x3E, 0xFF, 0x5D, 0xCF, 0x7C, 0xDF,
	0x9B, 0xAF, 0xBA, 0xBF, 0xD9, 0x8F, 0xF8, 0x9F, 0x17, 0x6E, 0x36, 0x7E, 0x55, 0x4E, 0x74, 0x5E,
	0x93, 0x2E, 0xB2, 0x3E, 0xD1, 0x0E, 0xF0, 0x1E
};

static unsigned char * g_decrypt_table1 = &g_decrypt_table[0x0];
static unsigned char * g_decrypt_table2 = &g_decrypt_table[0xC];
static unsigned char * g_decrypt_table3 = &g_decrypt_table[0x1C];
static unsigned char * g_decrypt_table4 = &g_decrypt_table[0x30];
static unsigned char * g_decrypt_table5 = &g_decrypt_table[0x48];
static unsigned char * g_decrypt_table6 = &g_decrypt_table[0x68];

unsigned int get_mul_high_uint(unsigned int x, unsigned int y)
{
	unsigned int z;

	__asm
	{
		pusha
		mov eax, x
		mov ecx, y
		mul ecx
		mov z, edx
		popa
	}

	return z;
}

void decrypt (unsigned char * buffer, int length, unsigned int xkey)
{
	unsigned int m, n;
	int x, i;
	char c1, c2, c3, c4, c5, c6, c, cc;

	// 4079BA
	n = get_mul_high_uint(xkey, 0xBA2E8BA3);
	n >>= 3;
	c = (char)n * 0x0B;
	c1 = (char)xkey - c;

	// 4079CE
	n = get_mul_high_uint(xkey, 0x4EC4EC4F);
	n >>= 2;
	c = (char)n * 0x0D;
	c2 = (char)xkey - c;

	// 4079E6
	n = get_mul_high_uint(xkey, 0xF0F0F0F1);
	n >>= 4;
	c = (char)n * 0x11;
	c3 = (char)xkey - c;

	// 4079FE
	n = get_mul_high_uint(xkey, 0xB21642C9);
	n >>= 4;
	c = (char)n * 0x17;
	c4 = (char)xkey - c;

	// 407A16
	n = get_mul_high_uint(xkey, 0x8D3DCB09);
	n >>= 4;
	c = (char)n * 0x1D;
	c5 = (char)xkey - c;

	// 407A2E
	m = get_mul_high_uint(xkey, 0x8421085);
	n = xkey - m;
	n >>= 1;
	n += m;
	n >>= 4;
	c = (char)n * 0x1F;
	c6 = (char)xkey - c;

	// 407A46
	if (length<=0)
		return;

	for (i=0; i<length; i++) {
		// 407A51
		c = g_decrypt_table6[c6]
			^ g_decrypt_table5[c5]
			^ g_decrypt_table4[c4]
			^ g_decrypt_table3[c3];

		// 407A84
		x = c2;

		// 407A90
		cc = c ^ g_decrypt_table2[c2] ^ g_decrypt_table1[c1];

		// 407AA4
		c1 ++;

		buffer[i] ^= cc;
		if (c1 >= 0x0B)
			c1 += 0xF5;	// c1 = 0;

		// 407AB6
		c2 ++;

		if (c2>=0x0D)
			c2 += 0xF3;	// c2 = 0

		// 407AC6
		c3 ++;
		if (c3>=0x11)
			c3 += 0xEF;	// c3 = 0

		// 407AD9
		c4 ++;
		if (c4>=0x17)
			c4 += 0xE9;	// c4 = 0

		// 407AEC
		c5 ++;
		if (c5>=0x1D)
			c5 += 0xE3;	// c5 = 0

		// 407AFF
		c6 ++;
		if (c6>=0x1F)
			c6 += 0xE1;	// c6 = 0
	}
}