Why does encoded message have a = or ==

Base64 Basics

• Converts binary data to text using 64 characters (A-Z, a-z, 0-9, +, /)

• Used for sending binary data through text-only systems (e.g., email)

How It Works

• Takes 3 bytes (24 bits) of binary data at a time

• Splits these 24 bits into four 6-bit groups

• Each 6-bit group is represented by one base64 character

The '=' Padding

• Added when the input length is not divisible by 3

• Ensures the output length is always a multiple of 4 characters

Why Padding is Needed

• Tells the decoder how many meaningful bytes are in the last group

• Prevents decoding errors

Padding Rules

• No '=' : Input length is divisible by 3

• One '=': Two bytes in the final group (4 real bits in last character)

• Two '==': One byte in the final group (2 real bits in last character)

Example

• "Man" → "TWFu" (3 bytes, no padding)

• "Ma" → "TWE=" (2 bytes, one '=' padding)

• "M" → "TQ==" (1 byte, two '==' padding)

Key Point

• The '=' is not part of the encoded data; it's just a marker for the decoder