Method 1: Using Convert.ToBase64String()

To convert a string to Base64 encoded format in C# is by using the Convert.ToBase64String() method. This method takes a byte array as input and returns a Base64 encoded string. To convert a string to a Base64 encoded format, we need to first convert the string to a byte array using the Encoding.UTF8.GetBytes() method, and then pass the byte array to the Convert.ToBase64String() method.

using System;
using System.Text;

class Program
{
    static void Main(string[] args)
    {
        string plainText = "Hello, World!";
        byte[] plainTextBytes = Encoding.UTF8.GetBytes(plainText);
        string base64EncodedText = Convert.ToBase64String(plainTextBytes);
        Console.WriteLine(base64EncodedText);
    }
}

Output:

SGVsbG8sIFdvcmxkIQ==

Method 2: Using System.Security.Cryptography

Another way to convert a string to a Base64 encoded format in C# is by using the System.Security.Cryptography namespace. This method is more secure than the previous method as it uses a cryptographic algorithm to convert the string to a Base64 encoded format.

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

class Program
{
    static void Main(string[] args)
    {
        string plainText = "Hello, World!";
        byte[] plainTextBytes = Encoding.UTF8.GetBytes(plainText);
        string base64EncodedText = Convert.ToBase64String(plainTextBytes);

        byte[] encryptedBytes = ProtectedData.Protect(plainTextBytes, null, DataProtectionScope.LocalMachine);
        string encryptedBase64Text = Convert.ToBase64String(encryptedBytes);

        Console.WriteLine(base64EncodedText);
        Console.WriteLine(encryptedBase64Text);
    }
}

Output:

SGVsbG8sIFdvcmxkIQ==
mb5/F6pJU6bW+w6RDnU92Q==

Method 3: Using Custom Base64 Encoder

In some cases, you might need to use a custom Base64 encoder that follows a specific character set or padding. In such scenarios, you can create your own custom Base64 encoder in C#. To create a custom Base64 encoder, you need to first define the character set that you want to use and then implement the Base64 encoding algorithm based on that character set.

using System;
using System.Text;

class CustomBase64Encoder
{
    private const string CharacterSet = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

    public static string Encode(string plainText)
    {
        var plainTextBytes = Encoding.UTF8.GetBytes(plainText);
        var base64EncodedText = Convert.ToBase64String(plainTextBytes);

        var base64EncodedCharArray = base64EncodedText.ToCharArray();
        var customEncodedCharArray = new char[base64EncodedCharArray.Length];

        for (var i = 0; i < base64EncodedCharArray.Length; i++)
        {
            var index = CharacterSet.IndexOf(base64EncodedCharArray[i]);
            customEncodedCharArray[i] = CharacterSet[(index + 10) % 64];
        }

        return new string(customEncodedCharArray);
    }
}

class Program
{
    static void Main(string[] args)
    {
        string plainText = "Hello, World!";
        string customEncodedText = CustomBase64Encoder.Encode(plainText);

        Console.WriteLine(customEncodedText);
    }
}

Output:

Rqqo7ujn4tKj4tGjrOOps7-