Namaste Friends,

Today, I m going to share with you actual method to calculate the checksum of TCP header packet at the binary level.

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Are you working on a networking project where you created TCP/UDP packets from scratch but don't know how to find checksum of from pseudo TCP packets? well, friend, you come to the right place. here, I am going to share with you the actual binary concept to calculate the checksum of pseudo TCP packets. Before starting this tutorial, I want to highlight that for this tutorial you need basic information of binary number operations.

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I am assuming that you already aware of TCP pseudo concept. basically, to calculate the checksum of TCP packet we need to create a TCP pseudo packet to calculate the actual checksum of TCP packet. if you don't know about pseudo concept then, I think you need to take a look here.

Now, let's focus on theory again. first, we have to divide and slice binary data into 16 bits pieces. After slicing in 16-bit pieces, we have to do find out the binary addition of all sliced pieces. After getting the binary sum of 16-bit pieces, there is one more small trick before one's complement of the binary sum. actually, we just need to take a 4-bit number from starting point of binary number and then add it again with the main binary sum. At last, calculate one's complement of the binary sum. done! I hope now you got the basic concept of TCP Packet CheckSum.

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Let assume that We have 4 bytes of pseudo header data (32-bits).

Divide binary Number Into 16-bit pieces.

Calculate the sum of all sliced pieces of binary numbers.

Add 4-bits of binary number into the calculated binary number. here, these 4 bits are nothing other than starting 4 digits of the same calculated binary number.

Find One's Complement. (Just Change All 0's Into 1's).

Done! That One's Complemented binary number is our checksum. hence, with this method, you can easily find the correct checksum of any TCP/UDP packets.

I hope you enjoyed this tutorial.

if you have any suggestion or query.

comment below

have a nice day.

Today, I m going to share with you actual method to calculate the checksum of TCP header packet at the binary level.

####

Introduction

Are you working on a networking project where you created TCP/UDP packets from scratch but don't know how to find checksum of from pseudo TCP packets? well, friend, you come to the right place. here, I am going to share with you the actual binary concept to calculate the checksum of pseudo TCP packets. Before starting this tutorial, I want to highlight that for this tutorial you need basic information of binary number operations.####

How it works?

I am assuming that you already aware of TCP pseudo concept. basically, to calculate the checksum of TCP packet we need to create a TCP pseudo packet to calculate the actual checksum of TCP packet. if you don't know about pseudo concept then, I think you need to take a look here.

Now, let's focus on theory again. first, we have to divide and slice binary data into 16 bits pieces. After slicing in 16-bit pieces, we have to do find out the binary addition of all sliced pieces. After getting the binary sum of 16-bit pieces, there is one more small trick before one's complement of the binary sum. actually, we just need to take a 4-bit number from starting point of binary number and then add it again with the main binary sum. At last, calculate one's complement of the binary sum. done! I hope now you got the basic concept of TCP Packet CheckSum.

####

Example To Understand Theory.

**Step 1.**Let assume that We have 4 bytes of pseudo header data (32-bits).

Binary Representation = 10000000111111100101011111001010

**Step 2.**Divide binary Number Into 16-bit pieces.

0 16-bit 32-bit --------------------------------------- 1000000011111110 0101011111001010 ---------------------------------------

**Step 3.**Calculate the sum of all sliced pieces of binary numbers.

0-bit 16-bit 1000000011111110 + 0101011111001010 ---------------------- 01101100011001000 -----------------------

**Step 4.**Add 4-bits of binary number into the calculated binary number. here, these 4 bits are nothing other than starting 4 digits of the same calculated binary number.

Calculated Binary Numbers = 01101100011001000 4-bit to add into same binary number = { 0110 } 1100011001000 Addtion: 0-bit 16-bit 01101100011001000 + 0110 ---------------------- 01101100011001110 -----------------------

**Step 5.**Find One's Complement. (Just Change All 0's Into 1's).

Binary Number = 01101100011001110 One's Complement = 00010011100110001

**Step 6.**Done! That One's Complemented binary number is our checksum. hence, with this method, you can easily find the correct checksum of any TCP/UDP packets.

CheckSum = One's Complement = 00010011100110001

I hope you enjoyed this tutorial.

if you have any suggestion or query.

comment below

have a nice day.

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