Windows & Linux

A Quick Guide To UDP Checksum Calculation

Here is Ed Duberoset’s description of the For udp calculation
check sum

. Thank very much details for ed Started and
write figuratively.

First, the checksum is determined
in RFC 768, but note
how effective is the RFC solution
in 1071. read both
Worth and absolutely contains a much more detailed description
I am going to write here.

The basic idea is that the udp checksum is the complement
Bit 16 more computes the “pseudo-header” IP and the total sum
the actual UDP data. The ip pseudo-header is the address of this receive,
Destination address, protocol with (almost no extensions) UDP
length i. So to take an example
this is a rare IP offer that
Source 152 address.1.51.all 27 addresses as destination IP address For this purpose, the sets are divided into 16 bits 0x9801,
0x331b and 0x980e, 0x5e4b. When two are added
additionally a person (for example, with a Windows computer) you will get 0x1c175. Please note that
it’s heavily overflowing, 16-bit, but we’ll get to that later.
Then you need dAdd protocol and UDP length. For the package, this is one
So protocol is udp, type protocol byte is always 17 or 0x11. We follow this
with zero to get 0x0011 and you need to add in the UDP length which was always 0x000a
(10 bytes). So 0x1c175++0x0! Means 00a 0x0011 0x1c190.

Now let’s add the whole UDP datagram and consider it only 16-bit.and
The value of the checksum jump We (until the end of the calculation
this!). For all datagrams 0xa08f is 0x2694, 0x000a, 0x6262, terrible if
add all this amount to the cumulative, we get 0x1c190 0xa08f++0x2694+
0x000a + 0x6262 corresponds to 0x2eb1f.

Now to convert the fabulous 16-bit to the sum of the complement, which we really like
Running sum (0x2eb1f) as a good 32-bit sum and adding an extra big half
bottom half. 0x0002 0xeb1f += 0xeb21. (Is there some more?
Overflowing, we attached the top and bottom halves, until finally there was one
a longer overflow type.) We now add a number to these bits (i.e.
or, definitely NOT an operation) and we are the value 0x14de and this is
exactly what the checksum indicates, in the packet.

In post Calculate the UDP checksum. for
In order to calculate the UDP checksum, we must first understand it, in addition to our own
Header, UDP checksum uses pseudo headers. This pseudo-header exists for
source IP address, suggested source-destination IP address (denoted as 0000),
Protocol 0000 (x11), including udp header length.

Source IP=
Recipient =
Source Port UDP=20
UDP destination port implies 10
Data (2 bytes) = “Hi”

face=”Verdane, without

Let’s go
see what the host has from Wireshark’s point of view

So, as long as we have the information, please continue
and create h2 pseudo tags. they If also added, these bits are added to the value specifications.
16 or second byte at a time.

I hope this helps those who want to know how to count
face UDP=”Verdana,sans-serif”>

UDP pseudo-header. Reprinted with permission from Tcpipguide Face=”Verdana,sans-serif”>

UDP header: Tcpipguide re-authorization

With the above in mind, let’s create a UDP packet in scapy. There is
It’s us that follows

Notice the image above, Wireshark already has it
The checksum calculates the UDP sum for us. Now let’s see if we get the same value as Wireshark.Face=”Verdana,sans-serif”>

Here is our personal UDP-Is checksum of 0x35C5, corresponding to what Wireshark gave us above.

When a person sends and receives data on your current line, personal information may be corrupted, altered or altered (this may be done accidentally, intentionally and/or in bad faith). In either case, there should be a method by which the recipient can easily check and discover when the data may have been tampered with or corrupted.

Typically, what happens is that the sender of the email computes a short checksum value (very small, but of a reasonable size) representing how messages/data are often sent. Estimatedscore with either the whole message or sent by other tactics. Once the data is received, the receiver usually also calculates a checksum. two If the values ​​(sender but recipient) match, the statistics remain intact/unchanged. cryptographers,

Thank you who can develop hash algorithms. Some of the most popular hash algorithms are MD5, sha1, etc. You may have noticed that Internet sites provide MD5 SHA1 and hash ideals of a file of any family that you want to download. This is simply because they can calculate the hash value of the uploaded file, and if it matches what is listed on their website, they can guarantee that the file is not corrupted/modified.

MD5 Are and sha1 are mainly used to verify the integrity of attached files. However, du data (basic social network internet communication verification data. TCP and not udp verification) uses MD5 or sha1. A method used only for and internet communication, hashing algorithms are similar but not quite the same. Because the other one needs it just in case .