Base64
Base64 is a group of similar binary-to-text encoding schemes that represent binary data in an ASCII string format by transforming it into a radix-64 representation. The term Base64 originates from a specific MIME content transfer encoding.
When the term “Base64” is used on its own to refer to a specific algorithm, it typically refers to the version of Base64 outlined in RFC 4648, section 4, which uses the following alphabet to represent the radix-64 digits, alongside = as a padding character:
ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/A common variant is “Base64 URL safe”, which omits the padding and replaces +/ with -_ to avoid characters that might cause problems in URL path segments or query parameters.
Base64 encoding schemes are commonly used to encode binary data for storage or transfer over media that can only deal with ASCII text.
Encoded size increase
Each Base64 digit represents 6 bits of data. So, three 8-bit bytes of the input string/binary file (3×8 bits = 24 bits) can be represented by four 6-bit Base64 digits (4×6 = 24 bits).
This means that the Base64 version of a string or file is typically roughly a third larger than its source.
JavaScript support
- Window.btoa() (also available in workers): creates a Base64-encoded ASCII string from a string of binary data (“btoa” should be read as “binary to ASCII”).
- Window.atob() (also available in workers): decodes a Base64-encoded string (“atob” should be read as “ASCII to binary”).