Base64 encoding is used when embedding binary in text based formats such as JSON, XML, YML etc. in such cases if we need to add a binary type, such as images or files etc. and we must pass then via a text format, then we need to Base64 encode this type of data first.

Use cases

Within web applications this is often used to pass binary within a JSON request/response object, but can be also seen when embedding images directly into HTML, for example

<img src="data:image/png;base64,your-binary-encoded-data..." />

It’s also used for Email attachments (MIME) as well as Authentication tokens – JWT tokens often use Base64URL (a variant of Base64).

Other use cases include clipboard copy/pasting of blobs (images/files etc.) into a text based clipboard format as well as being used from transporting over text only channels.

Where and why not to use Base64 encoding?

Base64 should NOT be used for streaming raw binary (application/octet-stream), large files or in binary safe protocols such as gRPC, websockets and HTTP when using the aforementioned large binary data etc.

First off, these protocols already support raw binary data so the affects of encoding are only on the negative side – if we encode to Base64 we will see, potentially, significant increases in the data size…

To Base54 encode using Javascript in the browser we can use

// encode 
const text = "Hello, world!";
const encoded = btoa(text);

// decode
const decoded = atob(encoded); 

In C# we can use

// encode
byte[] bytes = Encoding.UTF8.GetBytes("Hello, world!");
string base64 = Convert.ToBase64String(bytes);

// decode
byte[] decodedBytes = Convert.FromBase64String(base64);
string decoded = Encoding.UTF8.GetString(decodedBytes);

Calculating the Base64 encoding affects

Base64 encoding encodes every 3 bytes of binary data in 4 ASCII characters, so we essentially expand a binary data payload when using Base64 encoding

var base64Size = (binarySize/3) * 4

Or we can approximate with

var base64Size = 1.33 * binarySize;

Plus up to 2 padding characters “=” if the binary size is not divisible by 3.

This means that for every 1MB (1048576 bytes) the Base64 size is about 1.4MB (1398104 chars) giving us a 33% overhead.

This ofcourse is significant in streaming of data as it adds to the bandwidth and memory overhead along with increases in CPU usage for the encoding/decoding.