Sai A Sai A
Updated date May 29, 2023
In this blog, we will explore different methods for decoding Base64 strings in C#, including the built-in Convert.FromBase64String method, the System.Security.Cryptography namespace, and the Bouncy Castle Library.

Introduction:

Base64 encoding is a method of encoding binary data to ASCII text format. This is useful when transferring data through channels that only support text data. In this blog, we will be discussing how to decode strings that have been encoded using Base64 in C#. We will explore multiple methods to accomplish this and provide sample code for each method. Additionally, we will discuss the advantages and disadvantages of each method, along with their use cases.

Method 1: Using Convert.FromBase64String

The first method for decoding a Base64 string in C# is using the built-in Convert.FromBase64String method. This method takes in a string that has been Base64 encoded and returns a byte array that represents the original binary data.

Example code:

string base64String = "SGVsbG8gV29ybGQh";
byte[] bytes = Convert.FromBase64String(base64String);
string originalString = Encoding.UTF8.GetString(bytes);
Console.WriteLine(originalString);

Output:

Hello World!

In this example, we start with a Base64 encoded string "SGVsbG8gV29ybGQh" which represents the string "Hello World!" in binary format. We then use the Convert.FromBase64String method to decode the string, which returns a byte array. We then convert the byte array back to a string using the UTF8 encoding to get the original string "Hello World!".

Method 2: Using System.Security.Cryptography

The second method for decoding a Base64 string in C# is using the System.Security.Cryptography namespace. This namespace provides several classes for cryptographic operations, including a class for Base64 decoding.

Example code:

string base64String = "SGVsbG8gV29ybGQh";
byte[] bytes = Convert.FromBase64String(base64String);
using (MemoryStream stream = new MemoryStream(bytes))
{
    using (StreamReader reader = new StreamReader(new CryptoStream(stream, new FromBase64Transform(), CryptoStreamMode.Read)))
    {
        string originalString = reader.ReadToEnd();
        Console.WriteLine(originalString);
    }
}

Output:

Hello World!

In this example, we again start with a Base64 encoded string "SGVsbG8gV29ybGQh" and use the Convert.FromBase64String method to decode it into a byte array. We then create a MemoryStream object from the byte array and pass it to a CryptoStream object, along with a FromBase64Transform object that performs the Base64 decoding. Finally, we create a StreamReader object from the CryptoStream object and read the decoded string.

Method 3: Using the Bouncy Castle Library

The third method for decoding a Base64 string in C# is using the Bouncy Castle Library. This library provides a comprehensive set of cryptographic algorithms and protocols, including a Base64 decoder.

Example code:

string base64String = "SGVsbG8gV29ybGQh";
byte[] bytes = Convert.FromBase64String(base64String);
Decoder decoder = new Decoder();
decoder.Decode(bytes, 0, bytes.Length);
string originalString = Encoding.UTF8.GetString(decoder.GetBytes());
Console.WriteLine(originalString);

Output:

Hello World!

In this example, we start with a Base64 encoded string "SGVsbG8gV29ybGQh" and use the Convert.FromBase64String method to decode it into a byte array. We then create a new instance of the Decoder class from the Bouncy Castle Library and pass it the byte array to decode. Finally, we convert the decoded byte array back to a string using the UTF8 encoding.

Conclusion:

In this blog, we have explored three different methods for decoding Base64 strings in C#. The first method uses the built-in Convert.FromBase64String method, which is simple and straightforward but does not handle invalid input strings gracefully. The second method uses the System.Security.Cryptography namespace, which is more flexible and can handle invalid input strings but requires more code and creates additional objects. The third method uses the Bouncy Castle Library, which provides additional cryptographic functionality but requires an external dependency and creates an additional object.

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