谁能定义Windows PE校验和算法？ [英] Can anyone define the Windows PE Checksum Algorithm?

问题描述

我想在C＃中实现这一点

I would like to implement this in C#

我在这里查看过：
http://www.codeproject.com/KB/cpp/PEChecksum.aspx

我知道ImageHlp.dll MapFileAndCheckSum函数。

And am aware of the ImageHlp.dll MapFileAndCheckSum function.

但是，由于各种原因，我想自己实现。

However, for various reasons, I would like to implement this myself.

我发现的最好的是：
http://forum.sysinternals.com/optional- header-checksum-calculation_topic24214.html

但是，我不明白该解释。有人可以澄清校验和的计算方式吗？

But, I don't understand the explanation. Can anyone clarify how the checksum is calculated?

谢谢！

更新

我来自代码示例，我不明白这是什么意思，以及如何将其转换为C＃

I from the code example, I do not understand what this means, and how to translate it into C#

sum -= sum < low 16 bits of CheckSum in file // 16-bit borrow 
sum -= low 16 bits of CheckSum in file 
sum -= sum < high 16 bits of CheckSum in file 
sum -= high 16 bits of CheckSum in file 

更新＃2

谢谢，偶然发现了一些类似的Python代码此处

Thanks, came across some Python code that does similar too here

    def generate_checksum(self):

    # This will make sure that the data representing the PE image
    # is updated with any changes that might have been made by
    # assigning values to header fields as those are not automatically
    # updated upon assignment.
    #
    self.__data__ = self.write()

    # Get the offset to the CheckSum field in the OptionalHeader
    #
    checksum_offset = self.OPTIONAL_HEADER.__file_offset__ + 0x40 # 64

    checksum = 0

    # Verify the data is dword-aligned. Add padding if needed
    #
    remainder = len(self.__data__) % 4
    data = self.__data__ + ( '\0' * ((4-remainder) * ( remainder != 0 )) )

    for i in range( len( data ) / 4 ):

        # Skip the checksum field
        #
        if i == checksum_offset / 4:
            continue

        dword = struct.unpack('I', data[ i*4 : i*4+4 ])[0]
        checksum = (checksum & 0xffffffff) + dword + (checksum>>32)
        if checksum > 2**32:
            checksum = (checksum & 0xffffffff) + (checksum >> 32)

    checksum = (checksum & 0xffff) + (checksum >> 16)
    checksum = (checksum) + (checksum >> 16)
    checksum = checksum & 0xffff

    # The length is the one of the original data, not the padded one
    #
    return checksum + len(self.__data__)

但是，它仍然对我不起作用-这是我对这段代码的转换：

However, it's still not working for me - here is my conversion of this code:

using System;
using System.IO;

namespace CheckSumTest
{
    class Program
    {
        static void Main(string[] args)
        {
            var data = File.ReadAllBytes(@"c:\Windows\notepad.exe");

            var PEStart = BitConverter.ToInt32(data, 0x3c);
            var PECoffStart = PEStart + 4;
            var PEOptionalStart = PECoffStart + 20;
            var PECheckSum = PEOptionalStart + 64;
            var checkSumInFile = BitConverter.ToInt32(data, PECheckSum);
            Console.WriteLine(string.Format("{0:x}", checkSumInFile));

            long checksum = 0;

            var remainder = data.Length % 4;
            if (remainder > 0)
            {
                Array.Resize(ref data, data.Length + (4 - remainder));
            }

            var top = Math.Pow(2, 32);

            for (int i = 0; i < data.Length / 4; i++)
            {
                if (i == PECheckSum / 4)
                {
                    continue;
                }
                var dword = BitConverter.ToInt32(data, i * 4);
                checksum = (checksum & 0xffffffff) + dword + (checksum >> 32);
                if (checksum > top)
                {
                    checksum = (checksum & 0xffffffff) + (checksum >> 32);
                }
            }

            checksum = (checksum & 0xffff) + (checksum >> 16);
            checksum = (checksum) + (checksum >> 16);
            checksum = checksum & 0xffff;

            checksum += (uint)data.Length; 
            Console.WriteLine(string.Format("{0:x}", checksum));

            Console.ReadKey();
        }
    }
}

有人可以告诉我我在哪里

Can anyone tell me where I'm being stupid?

推荐答案

好，终于可以正常工作了……我的问题是我使用的是整数而不是整数!!!
因此，此代码有效（假设数据是4字节对齐的，否则您必须将其填充一点）-PECheckSum是PE中CheckSum值的位置（在以下情况下显然不使用该值）计算校验和！！！！）

Ok, finally got it working ok... my problem was that I was using ints not uints!!! So, this code works (assuming data is 4-byte aligned, otherwise you'll have to pad it out a little) - and PECheckSum is the position of the CheckSum value within the PE (which is clearly not used when calculating the checksum!!!!)

static uint CalcCheckSum(byte[] data, int PECheckSum)
{
    long checksum = 0;
    var top = Math.Pow(2, 32);

    for (var i = 0; i < data.Length / 4; i++)
    {
        if (i == PECheckSum / 4)
        {
            continue;
        }
        var dword = BitConverter.ToUInt32(data, i * 4);
        checksum = (checksum & 0xffffffff) + dword + (checksum >> 32);
        if (checksum > top)
        {
            checksum = (checksum & 0xffffffff) + (checksum >> 32);
        }
    }

    checksum = (checksum & 0xffff) + (checksum >> 16);
    checksum = (checksum) + (checksum >> 16);
    checksum = checksum & 0xffff;

    checksum += (uint)data.Length;
    return (uint)checksum;

}

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