How Can We Calculate the CRC Checksum?

Introduction

Maintaining data integrity is crucial when it comes to digital data transmission and storage. A single bit error in a data stream can have serious consequences, such as corrupt files or broken communication lines. Several error-detecting methods have been developed to overcome this issue; the Cyclic Redundancy Check (CRC) checksum is one of the most used. 

What is CRC (Cyclic Redundancy Check)?

To identify unintentional modifications to raw data, digital networks and storage devices use the CRC error-detecting code approach. CRC offers a quick and easy approach to identify problems rather than attempting to fix them like error-correcting codes do. It is especially helpful in situations where error correction could be too costly or difficult, like data storage or telecommunications.

How does CRC work?

Fundamentally, CRC is the process of creating a fixed-size checksum from the data that is being verified. The data is transferred or stored with this checksum applied to it. The recipient recalculates the CRC checksum using the received data upon retrieval or reception and compares it to the sent checksum. It is quite likely that the data is secure if the two checksums match; if not, an error is assumed.

Example

using System;
using System.Text;

public class CRC_CheckSum
{
    public static void Main(string[] args)
    {
        string dataString = "123490705110026304";
        byte[] bytes = Encoding.ASCII.GetBytes(dataString);
        ushort crc = 0xFFFF; // Initialize CRC value
        foreach (byte b in bytes)
        {
            crc ^= (ushort)(b << 8);
            for (int i = 0; i < 8; i++)
            {
                if ((crc & 0x8000) != 0)
                {
                    crc = (ushort)((crc << 1) ^ 0x1021);
                }
                else
                {
                    crc <<= 1;
                }
            }
        }

        Console.WriteLine($"CRC Value: {crc:X4}");
    }
}
//output
//CRC Value: 817E

• Generator Polynomial- The mathematical methods utilized in the CRC computation are defined by this polynomial. The polynomial in the example given is 0x1021.
• Initial Value- The CRC register's or the checksum calculation's initial value. It has the value 0xFFFF in the example.
• Final XOR Value- The checksum that results from the CRC computation can be XORed with a constant value. Although not specifically mentioned in the example, this step can be added if necessary.

Conclusion

To ensure the reliability and confidentiality of digital information, it is important that everyone involved in data communication understands CRC and its uses. CRC algorithms provide dependable error detection capabilities in a variety of applications, such as storage devices and telecommunications, by utilizing polynomial division and carefully selected generator polynomials.