blob: f6d23f0e1088223d31d657131ddd2ff3a7e9e7e5 (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
|
#include "pe_checksum.h"
#include "pe_structures.h"
#include "pe_base.h"
namespace pe_bliss
{
using namespace pe_win;
//Calculate checksum of image
uint32_t calculate_checksum(std::istream& file)
{
//Save istream state
std::ios_base::iostate state = file.exceptions();
std::streamoff old_offset = file.tellg();
//Checksum value
unsigned long long checksum = 0;
try
{
image_dos_header header;
file.exceptions(std::ios::goodbit);
//Read DOS header
pe_base::read_dos_header(file, header);
//Calculate PE checksum
file.seekg(0);
unsigned long long top = 0xFFFFFFFF;
top++;
//"CheckSum" field position in optional PE headers - it's always 64 for PE and PE+
static const unsigned long checksum_pos_in_optional_headers = 64;
//Calculate real PE headers "CheckSum" field position
//Sum is safe here
unsigned long pe_checksum_pos = header.e_lfanew + sizeof(image_file_header) + sizeof(uint32_t) + checksum_pos_in_optional_headers;
//Calculate checksum for each byte of file
std::streamoff filesize = pe_utils::get_file_size(file);
for(long long i = 0; i < filesize; i += 4)
{
unsigned long dw = 0;
//Read DWORD from file
file.read(reinterpret_cast<char*>(&dw), sizeof(unsigned long));
//Skip "CheckSum" DWORD
if(i == pe_checksum_pos)
continue;
//Calculate checksum
checksum = (checksum & 0xffffffff) + dw + (checksum >> 32);
if(checksum > top)
checksum = (checksum & 0xffffffff) + (checksum >> 32);
}
//Finish checksum
checksum = (checksum & 0xffff) + (checksum >> 16);
checksum = (checksum) + (checksum >> 16);
checksum = checksum & 0xffff;
checksum += static_cast<unsigned long>(filesize);
}
catch(const std::exception&)
{
//If something went wrong, restore istream state
file.exceptions(state);
file.seekg(old_offset);
file.clear();
//Rethrow
throw;
}
//Restore istream state
file.exceptions(state);
file.seekg(old_offset);
file.clear();
//Return checksum
return static_cast<uint32_t>(checksum);
}
}
|