How to Calculate MD5 Hash From a String in C#

1. Using the MD5 Algorithm in C#
2. Use the System.Security.Cryptography Library to Calculate MD5 Hash From a C# String

The Hashing algorithms are mathematical algorithms used in mapping arbitrary input data to a fixed size hash. They are used for multiple purposes like storing data in data structures like hash maps, password verification, message digestion, and cryptocurrency security.

The MD5 belongs to the message digesting class of hashing algorithms. Rivest developed MD5 and other algorithms like MD2, MD4, etc.

The algorithm was originally designed to authenticate digital signatures. But later, many vulnerabilities were discovered that led to its deprecation.

Nevertheless, it is still used for data integrity verification and forms a foundation for understanding advanced algorithms. MD5 algorithm, like all message digestion algorithms, takes as input a message of unknown length and converts it into a fixed-size hash.

A minor change into the input string will result in a completely different hash. This article will learn how to calculate the MD5 hash using C#.

Using the MD5 Algorithm in C#

The MD5 algorithm consists of the following four main steps:

First, append padding bits.

In this step, we add padding bits so that the number of total bits becomes 64 less than the closest multiple of 512. It is done so that the algorithm can process data in the size of 512 bits and step 2, the length of string expressed in 64 bits is added to get an even multiple of 512.

Second, append length bits.

Calculate the length of the string in 64 bits. Append them to the output formed in step 1.

Third, initialize MD buffer.

We initialize 4 message digesting buffers of 32 bits named A, B, C, and D. They are as follows:

A = 01 23 45 67
B = 89 ab cd ef
C = fe dc ba 98
D = 76 54 32 10

Fourth is the Processing of individual 512-bit blocks.

The whole bits are broken into blocks of size 512. Each block formed is divided into 16 sub-blocks of 32 bits. All the 16 blocks formed are passed through a series of 4 operations with the buffers A, B, C, and D to give the final hash.

Use the System.Security.Cryptography Library to Calculate MD5 Hash From a C# String

using System;
using System.Security.Cryptography;
using System.Text;

public class Test {
  public static string ComputeMd5Hash(string message) {
    using (MD5 md5 = MD5.Create()) {
      byte[] input = Encoding.ASCII.GetBytes(message);
      byte[] hash = md5.ComputeHash(input);

      StringBuilder sb = new StringBuilder();
      for (int i = 0; i < hash.Length; i++) {
        sb.Append(hash[i].ToString("X2"));
      }
      return sb.ToString();
    }
  }
  public static void Main() {
    string message = "Welcome to DelfStack";
    Console.WriteLine(ComputeMd5Hash(message));
  }
}

Output:

53C62733BB54F2B720A32490E6C447FF

In the above program, we create an object of the MD5 class present in C# that provides a readymade implementation of the md5 algorithm through the method ComputeHash().

We convert our message string into a byte stream to match the function signature of the ComputeHash() method, which then returns the result in the form of a byte stream. We then use the string builder class to convert the byte stream into a valid C# string.