C# ICMPv6校验和计算

Question

我需要计算ICMPv6校验和。我在RFC2460中找到了正确的手册，并在c#中编写了代码，这些代码粘贴在下面。在代码中，您可以看到，我将校验和添加到源IP、数据包的目标IP，而不是ICMPv6消息长度(邻居通告的长度为32字节)，然后添加ICMPv6的下一个报头ID ( 58 )。然后是FOR循环，它添加到校验和整个ICMPv6消息(以我相信的消息类型开始，例如88 00 ...用于邻居通告)。然后我做了计算和补码校验，但这是错误的。我正在尝试为实际嗅探的邻居通告计算此校验和，这也在下面，但我无法获得相同的校验和。我的代码中可能有什么错误？

static void Main(string[] args)
    {

        ICaptureDevice device = new OfflineCaptureDevice("icmp.pcap");
        device.Open();

        device.OnPacketArrival += new SharpPcap.PacketArrivalEventHandler(device_OnPacketArrival);
        device.Capture();


        Console.ReadKey();
    }

    private static void device_OnPacketArrival(object sender, SharpPcap.CaptureEventArgs e)
    {
        try
        {
            //packet conversions
            var packet = PacketDotNet.Packet.ParsePacket(e.Packet);
            var ethernetPacket = ((PacketDotNet.EthernetPacket)packet);
            int dlzka_packetu = e.Packet.Data.Length;
            string eth = BitConverter.ToString(ethernetPacket.Bytes);

            //now its in string field format - one string item is one byte, e.g. FF
            string[] eth_final2 = eth.Split('-');
            foreach (string bytes in eth_final2) { Console.Write(bytes + " "); }
            Console.WriteLine();

            //taking out source IP
            IPAddress src_ip = IPAddress.Parse(eth_final2[22]+eth_final2[23]+":"+eth_final2[24]+eth_final2[25]+":"+eth_final2[26]+eth_final2[27]+":"+eth_final2[28]+eth_final2[29]+":"+eth_final2[30]+eth_final2[31]+":"+eth_final2[32]+eth_final2[33]+":"+eth_final2[34]+eth_final2[35]+":"+eth_final2[36]+eth_final2[37]);

            //destination IP
            IPAddress dst_ip = IPAddress.Parse(eth_final2[38] + eth_final2[39] + ":" + eth_final2[40] + eth_final2[41] + ":" + eth_final2[42] + eth_final2[43] + ":" + eth_final2[44] + eth_final2[45] + ":" + eth_final2[46] + eth_final2[47] + ":" + eth_final2[48] + eth_final2[49] + ":" + eth_final2[50] + eth_final2[51] + ":" + eth_final2[52] + eth_final2[53]);

            Console.WriteLine(src_ip);
            Console.WriteLine(dst_ip);
            int icmpv6_length = 32;
            int next_header = 58;
            Console.WriteLine();

            string icmp_payload = "";

            //taking out ICMPv6 message
            for (int i = 54; i < 54 + 32; i++)
            {
                if (i == 56 || i == 57) { icmp_payload += "00"; }
                else icmp_payload += eth_final2[i];
            }

            Console.WriteLine(icmp_payload);
            byte[] icmp_bytes = GetStringToBytes(icmp_payload);


            //CALLING THE FUNCTION ICMPchecksum
            ushort sum = ICMPchecksum(src_ip.GetAddressBytes(), dst_ip.GetAddressBytes(), BitConverter.GetBytes(icmpv6_length), BitConverter.GetBytes(next_header), icmp_bytes);

            Console.WriteLine(sum.ToString("X"));


        }
        catch (Exception ex)
        {
            Console.WriteLine("ERROR");
        }


    }

    static byte[] GetStringToBytes(string value)
    {
        SoapHexBinary shb = SoapHexBinary.Parse(value);
        return shb.Value;
    }

    static ushort ICMPchecksum(byte[] src_ip, byte[] dst_ip, byte[] length, byte[] next, byte[] payload)
    {
        ushort checksum = 0;

        //length of byte fields
        Console.WriteLine("src_ip: "+src_ip.Length+" dst_ip: "+dst_ip.Length+" length: "+length.Length+" next_header: "+next.Length+" payload: "+payload.Length);

        //display all fields, which will be used for checksum calculation
        Console.WriteLine(BitConverter.ToString(src_ip));
        Console.WriteLine(BitConverter.ToString(dst_ip));
        Console.WriteLine(BitConverter.ToString(length));
        Console.WriteLine(BitConverter.ToString(next));
        Console.WriteLine(BitConverter.ToString(payload));


        //ADDS SOURCE IPv6 address
        checksum += BitConverter.ToUInt16(src_ip, 0);
        checksum += BitConverter.ToUInt16(src_ip, 2);
        checksum += BitConverter.ToUInt16(src_ip, 4);
        checksum += BitConverter.ToUInt16(src_ip, 6);
        checksum += BitConverter.ToUInt16(src_ip, 8);
        checksum += BitConverter.ToUInt16(src_ip, 10);
        checksum += BitConverter.ToUInt16(src_ip, 12);
        checksum += BitConverter.ToUInt16(src_ip, 14);

        //ADDS DEST IPv6 address
        checksum += BitConverter.ToUInt16(dst_ip, 0);
        checksum += BitConverter.ToUInt16(dst_ip, 2);
        checksum += BitConverter.ToUInt16(dst_ip, 4);
        checksum += BitConverter.ToUInt16(dst_ip, 6);
        checksum += BitConverter.ToUInt16(dst_ip, 8);
        checksum += BitConverter.ToUInt16(dst_ip, 10);
        checksum += BitConverter.ToUInt16(dst_ip, 12);
        checksum += BitConverter.ToUInt16(dst_ip, 14);

        //ADDS LENGTH OF ICMPv6 packet
        checksum += BitConverter.ToUInt16(length, 0);
        checksum += BitConverter.ToUInt16(length, 2);

        //ADDS NEXT HEADER ID = 58
        checksum += BitConverter.ToUInt16(next, 0);
        checksum += BitConverter.ToUInt16(next, 2);

        //ADDS WHOLE ICMPv6 message
        for (int i = 0; i < payload.Length; i = i + 2)
        {
            Console.WriteLine(i);
            checksum += BitConverter.ToUInt16(payload, i);
        }

        checksum += (ushort)(checksum >> 16);

        return (ushort)~checksum;
    }

这是数据包屏幕。

唯一链接：http://img831.imageshack.us/img831/7237/icmpv6.png

加上链接，你可以下载我用来测试的文件：

http://www.2shared.com/file/wIETWTWB/icmp.html

谢谢你的帮助。

Answer 1

在ICMPv6消息中使用

有效负载，因为它在我的问题中发布的图片中进行了签名

至少这是错误的。计算校验和时，应首先将表示校验和本身的字节替换为0。

更新

基于你的icmp.pcap，我已经创建了一个独立的程序来计算校验和。完整的源代码见下文。

最重要的错误是：

    ushort checksum = 0;

虽然校验和为16位，但此算法要求临时值至少为32位：

    uint checksum = 0;

校验和计算需要ones' complement arithmetic，其中加法进位回绕。为了提高性能，所有的包装都在最后完成；

checksum += (ushort)(checksum >> 16);

但这只有在校验和超过16位时才有可能。否则，这一行将是无用的。

但还有一些其他因素需要考虑。BitConverter.ToUInt16取决于处理器的endianness，可能是小端。这将使结果成为A5AB。这可能不是您所期望的，但是如果您交换字节，您将获得正确的版本。我在here中插入了一个函数来修复这个问题。这将使结果成为ABA5。另一方面，如果在计算之前没有将校验和设置为0，则如果校验和有效，则ICMPchecksum将始终为return 0。还要注意，您的函数不能处理奇数长度的有效负载。

class Program {
    static void Main (string [] args)
    {
        byte[] src_ip = new byte[]
                            {
                                0xfe, 0x80, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
                                0x02, 0x19, 0x55, 0xff, 0xfe, 0x27, 0x27, 0xd0
                            };

        byte[] dst_ip = new byte[]
                            {
                                0xfe, 0x80, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
                                0x02, 0x22, 0x75, 0xff, 0xfe, 0xd6, 0xfe, 0x50
                            };
        byte[] length = new byte[] {0, 0, 0, 32};
        byte [] next = new byte [] { 0, 0, 0, 58 };
        byte[] payload = new byte[]
                             {
                                 0x88, 0x00, 0xab, 0xa5, 0xe0, 0x00, 0x00, 0x00, 
                                 0xfe, 0x80, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 
                                 0x02, 0x19, 0x55, 0xff, 0xfe, 0x27, 0x27, 0xd0,
                                 0x02, 0x01, 0x00, 0x19, 0x55, 0x27, 0x27, 0xd0
                             };
#if true
        payload [2] = 0;
        payload [3] = 0;
#endif

        ushort checksum = ICMPchecksum(src_ip, dst_ip, length, next, payload);

        Console.WriteLine (checksum.ToString ("X"));
        Console.ReadKey ();
    }

    public static ushort BitConverterToUInt16 (byte [] value, int startIndex)
    {
#if false
            return System.BitConverter.ToUInt16 (value, startIndex);
#else
            return System.BitConverter.ToUInt16 (value.Reverse ().ToArray (), value.Length - sizeof (UInt16) - startIndex);
#endif
    }

    static ushort ICMPchecksum (byte [] src_ip, byte [] dst_ip, byte [] length, byte [] next, byte [] payload)
    {
        uint checksum = 0;

        //length of byte fields
        Console.WriteLine ("src_ip: " + src_ip.Length + " dst_ip: " + dst_ip.Length + " length: " + length.Length + " next_header: " + next.Length + " payload: " + payload.Length);

        //display all fields, which will be used for checksum calculation
        Console.WriteLine (BitConverter.ToString (src_ip));
        Console.WriteLine (BitConverter.ToString (dst_ip));
        Console.WriteLine (BitConverter.ToString (length));
        Console.WriteLine (BitConverter.ToString (next));
        Console.WriteLine (BitConverter.ToString (payload));


        //ADDS SOURCE IPv6 address
        checksum += BitConverterToUInt16 (src_ip, 0);
        checksum += BitConverterToUInt16 (src_ip, 2);
        checksum += BitConverterToUInt16 (src_ip, 4);
        checksum += BitConverterToUInt16 (src_ip, 6);
        checksum += BitConverterToUInt16 (src_ip, 8);
        checksum += BitConverterToUInt16 (src_ip, 10);
        checksum += BitConverterToUInt16 (src_ip, 12);
        checksum += BitConverterToUInt16 (src_ip, 14);

        //ADDS DEST IPv6 address
        checksum += BitConverterToUInt16 (dst_ip, 0);
        checksum += BitConverterToUInt16 (dst_ip, 2);
        checksum += BitConverterToUInt16 (dst_ip, 4);
        checksum += BitConverterToUInt16 (dst_ip, 6);
        checksum += BitConverterToUInt16 (dst_ip, 8);
        checksum += BitConverterToUInt16 (dst_ip, 10);
        checksum += BitConverterToUInt16 (dst_ip, 12);
        checksum += BitConverterToUInt16 (dst_ip, 14);

        //ADDS LENGTH OF ICMPv6 packet
        checksum += BitConverterToUInt16 (length, 0);
        checksum += BitConverterToUInt16 (length, 2);

        //ADDS NEXT HEADER ID = 58
        checksum += BitConverterToUInt16 (next, 0);
        checksum += BitConverterToUInt16 (next, 2);

        //ADDS WHOLE ICMPv6 message
        for (int i = 0; i < payload.Length; i = i + 2) {
            Console.WriteLine (i);
            checksum += BitConverterToUInt16 (payload, i);
        }

        checksum += (ushort)(checksum >> 16);

        return (ushort)~checksum;
    }
}