Base64 is a group of binary-to-text encoding schemes that represent binary data in an ASCII string format. While it is one of the most common data formats encountered by developers, it is frequently misunderstood as a form of encryption. Base64 is not encryption; it is encoding.

1. Why Do We Need Base64?

Many legacy communication protocols (like SMTP for email) and structured data formats (like JSON or XML) are designed to handle only standard printable text characters. If you attempt to transmit raw binary data (like a JPEG image or a compiled executable) through these text-based protocols, special characters will be misinterpreted, corrupting the payload.

Base64 solves this by translating the raw binary 1s and 0s into a safe alphabet of 64 printable ASCII characters (A-Z, a-z, 0-9, +, and /).

2. How It Works Under the Hood

The algorithm takes 3 bytes of binary data (24 bits total) and divides them into 4 chunks of 6 bits. Each 6-bit chunk maps to a specific character in the Base64 alphabet. Because 3 bytes of raw data become 4 bytes of text data, Base64 encoding inherently increases file sizes by approximately 33%.

3. Common Web Use Cases

• Data URIs: Embedding small icons or placeholder images directly into HTML/CSS files to save HTTP requests (e.g., src="data:image/png;base64,iVBORw0KG...").
• JWT Tokens: JSON Web Tokens encode header and payload data in Base64URL format for safe transmission in HTTP headers.