What is Checksum?

Working of Checksum

The complete process of checking whether there is a loss of message or not occurs at both sender's and receiver's side. We will start from the sender's side.

Step 1 - Sender's Side

At the sender's side, the following steps take place:

1. Break the message into 'k' number of blocks and 'n' bit for each block.
2. Add all the 'k' data blocks.
3. Suppose, while adding, you encountered a carry, add it to the sum of the 'k' data blocks.
4. To get the checksum, do the 1's complement.

Step 2 - Data Transmission

1. The calculated checksum will be merged with the original data/message.
2. The process of sending the message to the receiver starts.

Step 3 - Receiver's Side

1. Break the bits of the message received from the sender into the 'k' number of blocks.
2. Now add all the blocks along with the checksum.
3. Perform the 1's complement to the result.
4. Now, there are two conditions:
   
   1. If the result is 0, the message has no loss/ error.
   2. If the result is not 0, the message has a loss/error.

Example of Checksum

Let's take an example to understand the process in a better way. Suppose we have 10011001 11100010 00100100 10000100.

Step 1: Let's break it into blocks of size 8-bit. 

Step 2: Now, we will add all the blocks together using the binary addition rule.

        1  0  0  1  1  0  0  1       (Block 1)

        1  1  1  0  0  0  1  0       (Block 2)

        0  0  1  0  0  1  0  0       (Block 3)

        1  0  0  0  0  1  0  0       (Block 4)

———————————————

1  0  0  0  1  0  0  0  1  1        

As you can see, we have a carry in the above step, so we have to wrap the carry in the resultant sum. Let go.

        0  0  1  0  0  0  1  1     

                                1  0     

   ——————————

        0  0  1  0  0  1  0  1

Step 3: Now, we will perform the 1's complement.

        0  0  1  0  0  1  0  1

         ————————————

        1  1  0  1  1  0  1  0        (Checksum)
 

Step 4: The sender will attach this checksum value to the original message but in a different block, as shown below.

Now, this message will be sent to the receiver along with the checksum. This is the receiver's responsibility to check if there are errors in the message. To do so, the receiver follows the below steps.

Step 5: At the receiver's end, the receiver will collect the message and perform the binary addition to all the bits present in the message along with the checksum.

        1  0  0  1  1  0  0  1       (Block 1)

        1  1  1  0  0  0  1  0       (Block 2)

        0  0  1  0  0  1  0  0       (Block 3)

        1  0  0  0  0  1  0  0       (Block 4)

        1  1  0  1  1  0  1  0       (Checksum)

   ——————————————

1  0  1  1  1  1  1  1  0  1  

Again, there is a carry, so we will again wrap the carry in the next step.

        1  1  1  1  1  1  0  1 

                                1  0  

   —————————————

        1  1  1  1  1  1  1  1

Step 6: The receiver will again do the 1's complement.

        1  1  1  1  1  1  1  1

   ————————————

        0  0  0  0  0  0  0  0         (1's complement)
 

Step 7: If the result is 0, the message has no loss/ error. Hence, there is no error in this message.

Advantages of Checksum

Let's discuss some of the advantages of using the checksum.

• The checksum detects all the errors involving an odd number of bits.
   
• It detects most of the errors involving an even number of bits.
   
• It also verifies the identity and file source by verifying the checksum values.

Disadvantages of Checksum

Now, we will discuss some of the disadvantages of using the checksum.

• Using checksum can be a difficult process.
   
• It takes some extra time to verify checksum values.
   
• The checksum process can be fooled by the parties who can manipulate the checksum values.

Frequently Asked Questions

What is the difference between the Checksum and the CRC?

The difference between them is checksum can detect a single-bit change in the data, while the CRC can detect double digits errors.

What are checksums used for?

Checksums are used to verify data integrity during storage or transmission. By generating a unique value based on the data, they help identify changes or corruption, ensuring that data remains accurate and unaltered.

What is the goal of checksum?

The goal of a checksum is to detect any errors or alterations in data by comparing the original checksum with the one recalculated after transmission or retrieval. This helps confirm that data has not been tampered with or corrupted.

Can checksum detect errors?

Yes, checksums can detect errors by revealing inconsistencies in the data. When data is altered, even slightly, the recalculated checksum differs from the original, signaling potential corruption or transmission errors.

Conclusion

In this article, we have discussed what Checksum is. Checksums play a vital role in ensuring data accuracy and reliability in digital communication and storage. By providing a straightforward way to detect errors or alterations, checksums act as a first line of defense against data corruption and tampering. From safeguarding file transfers to validating data in critical systems, checksums are indispensable in today’s technology landscape.

We hope this blog has helped you enhance your knowledge of the What is Checksum. If you want to learn more, then check out our articles.

• Complements
• Addition and Subtraction
• Decimal Arithmetic Unit and Operations