Base64 Encoding: How and Why It Works

2025-09-25

Introduction

Ever noticed strange strings like aGVsbG8gd29ybGQ= in JSON APIs or JWT tokens? That’s Base64 encoding, a scheme for safely representing binary data in text form.

👉 Experiment online: Free Online Utils – Base64 Encoder/Decoder

Why Do We Need Base64?

Many protocols (HTTP headers, SMTP email) were designed for ASCII text, not binary. Base64 encodes binary data into ASCII characters [A-Z][a-z][0-9]+/ plus = for padding.

The Algorithm

  1. Take 3 bytes (24 bits).
  2. Split into 4 groups of 6 bits.
  3. Map each 6-bit group to a Base64 character.
  4. If input isn’t multiple of 3, add = padding.

Example: "hello"

  • Binary → groups → "aGVsbG8="

Code Examples

Python

import base64
print(base64.b64encode(b"hello world").decode())
# aGVsbG8gd29ybGQ=

Javascript

btoa("hello world"); // "aGVsbG8gd29ybGQ="

Variants

  • Base64 URL-safe: replaces + → -, / → _.
  • Base32: limited alphabet, used in DNS.
  • Base58: removes lookalike chars, used in Bitcoin addresses.

Applications

  • Email attachments (MIME).
  • JSON Web Tokens (JWT).
  • Data URLs in HTML/CSS.
  • Storing small blobs in databases.

Limitations

  • Size overhead (~33% larger).
  • Not encryption (just encoding).

References