Encoding Data Formats Developer Fundamentals

Base64 Encoding & Decoding: How Binary Data Travels Through Text Systems

By MDToolsOne •
Base64 encoding binary data into text How binary data is safely encoded for transport through text systems

Modern systems constantly move binary data through environments that were originally designed for plain text — email, HTTP headers, JSON, XML, and logs.

Base64 encoding exists to solve this exact problem: safely representing binary data using printable ASCII characters.

This article explains how Base64 works internally, when to use it, when not to use it, and why misunderstanding it causes performance and security issues.

What Is Base64?

Base64 is a binary-to-text encoding scheme. It converts arbitrary binary data into a limited set of safe characters: 

A–Z a–z 0–9 + /

Padding is added using the = character.

Base64 is not encryption, not compression, and not security.

Why Base64 Exists

Many legacy and modern systems cannot safely transport raw binary:

  • Email protocols (SMTP, MIME)
  • HTTP headers
  • JSON and XML payloads
  • Log files and configuration files

Base64 ensures data remains intact when passing through systems that expect readable characters.

How Base64 Works Internally

Base64 works by:

  1. Taking binary input (bytes)
  2. Grouping bits into 24-bit blocks
  3. Splitting into 6-bit chunks
  4. Mapping each chunk to a printable character
Binary:   01001000 01101001
ASCII:    H          i
Base64:   SGk=

Each Base64 character represents exactly 6 bits of data.

Why Base64 Increases Size

Base64 encoding increases data size by approximately 33%.

Original Size Base64 Size
3 bytes 4 characters
30 KB ~40 KB

This is why Base64 should be avoided for large files unless absolutely necessary.

Common Use Cases

  • Email attachments (MIME)
  • JWT tokens
  • Embedding images in HTML or CSS
  • API payloads carrying binary data
  • Cryptographic keys and signatures

Common Mistakes

  • Assuming Base64 provides security
  • Using Base64 instead of file uploads
  • Double-encoding data
  • Ignoring size overhead
  • Logging Base64 secrets

Base64 in Email and HTTP

Email systems rely heavily on Base64 because SMTP was originally limited to 7-bit ASCII.

HTTP uses Base64 for:

  • Basic Authentication headers
  • Embedded resources
  • Token transport

Final Thoughts

Base64 is a foundational encoding technique — simple, powerful, and often misunderstood.

Understanding its internal mechanics helps developers make better architectural, performance, and security decisions.

MD Tools