Encoding

Why Encode Data?

Encoding prevents invalid values during transmission (communication can have various issues with cookies, etc.)

Example: Base64 in Android

result = Base64.encodeToString(bytes, Base64.NO_WRAP);

Why Use Base64?

Use Cases

  1. Converting binary data to text
    • When you need to handle binary data as text
  2. Storing binary in databases
    • Databases often cannot store raw binary values directly
    • Convert binary to text format
  3. Embedding images in HTML
    • Include images directly without external links (inline images)

When to Use Base64

  1. Not needed when:
    • Both sides have same encoding/decoding rules
    • Data is already binary (like images)
    • Start and end of binary data is clear
  2. Required for:
    • Data managed by humans (DBMS, Excel, etc.)
    • Binary data must be represented as ASCII
  3. For different character sets:
    • Use BASE64/HEX as intermediate format to transfer binary data between systems with different character sets

How Base64 Works

Base64 encoding converts binary data into a string of 64 printable ASCII characters. The encoding process works as follows:

  1. Take the input binary data
  2. Split it into groups of 6 bits (since 2^6 = 64)
  3. Map each 6-bit group to one of 64 characters: A-Z, a-z, 0-9, +, /
  4. If the input length is not a multiple of 3 bytes, pad with = characters

Encoding Example

The string "Hi" in binary:

H = 01001000
i = 01101001

Split into 6-bit groups:

010010 | 000110 | 1001xx

Pad the last group with zeros:

010010 | 000110 | 100100

Map to Base64 characters:

S      | G      | k=

Result: "SGk="

Code Examples

Python

import base64

# Encode
encoded = base64.b64encode(b"Hello World")
print(encoded)  # b'SGVsbG8gV29ybGQ='

# Decode
decoded = base64.b64decode(encoded)
print(decoded)  # b'Hello World'

JavaScript

// Encode
const encoded = btoa("Hello World");
console.log(encoded);  // "SGVsbG8gV29ybGQ="

// Decode
const decoded = atob(encoded);
console.log(decoded);  // "Hello World"

Java

import java.util.Base64;

// Encode
String encoded = Base64.getEncoder().encodeToString("Hello World".getBytes());

// Decode
byte[] decoded = Base64.getDecoder().decode(encoded);
String original = new String(decoded);

Base64 Variants

Variant Characters Used Padding Common Use
Standard (RFC 4648) A-Z, a-z, 0-9, +, / = General purpose
URL-safe A-Z, a-z, 0-9, -, _ Optional URLs, filenames
MIME Standard + line breaks every 76 chars = Email attachments

The URL-safe variant replaces + with - and / with _ because + and / have special meanings in URLs.

Base64 Size Overhead

Base64 encoding increases data size by approximately 33%. Every 3 bytes of input becomes 4 bytes of output. This means:

Original Size Base64 Size Overhead
1 KB ~1.37 KB +37%
1 MB ~1.37 MB +37%
10 MB ~13.7 MB +37%

This overhead is the trade-off for the ability to safely transmit binary data through text-only channels. For large files, direct binary transfer is preferred when possible.

Common Pitfalls

  1. Base64 is NOT encryption: Base64 is an encoding scheme, not a security measure. Anyone can decode Base64 data. Never use it to “hide” sensitive information.

  2. Line length limits: Some systems (like email) require Base64 output to be broken into lines of 76 characters. Use the MIME variant for these cases.

  3. Padding issues: Some implementations strip padding characters (=). Ensure both encoder and decoder agree on whether padding is used.

  4. Performance: Encoding and decoding large files with Base64 consumes CPU and memory. For large binary transfers, use binary protocols instead of Base64-encoded text.

Reference