Base64

Base64 is a group of similar binary-to-text encoding schemes that represent binary data in an ASCII string format by translating it into a radix-64 representation. The term Base64 originates from a specific MIME content transfer encoding. Each base64 digit represents exactly 6 bits of data.

The particular set of 64 characters chosen to represent the 64 place-values for the base varies between implementations. The general strategy is to choose 64 characters that are both members of a subset common to most encodings, and also printable. This combination leaves the data unlikely to be modified in transit through information systems, such as email, that were traditionally not 8-bit clean.[1] For example, MIME's Base64 implementation uses A–Z, a–z, and 0–9 for the first 62 values.

Example

A quote from Thomas Hobbes' Leviathan:

Man is distinguished, not only by his reason, but by this singular passion from other animals, which is a lust of the mind, that by a perseverance of delight in the continued and indefatigable generation of knowledge, exceeds the short vehemence of any carnal pleasure.

is represented as a byte sequence of 8-bit-padded ASCII characters encoded in MIME's Base64 scheme as follows:

TWFuIGlzIGRpc3Rpbmd1aXNoZWQsIG5vdCBvbmx5IGJ5IGhpcyByZWFzb24sIGJ1dCBieSB0aGlzIHNpbmd1bGFyIHBhc3Npb24gZnJvbSBvdGhlciBhbmltYWxzLCB3aGljaCBpcyBhIGx1c3Qgb2YgdGhlIG1pbmQsIHRoYXQgYnkgYSBwZXJzZXZlcmFuY2Ugb2YgZGVsaWdodCBpbiB0aGUgY29udGludWVkIGFuZCBpbmRlZmF0aWdhYmxlIGdlbmVyYXRpb24gb2Yga25vd2xlZGdlLCBleGNlZWRzIHRoZSBzaG9ydCB2ZWhlbWVuY2Ugb2YgYW55IGNhcm5hbCBwbGVhc3VyZS4K

In the above quote, the encoded value of Man is TWFu. Encoded in ASCII, the characters M, a, and n are stored as the bytes 77, 97, and 110, which are the 8-bit binary values 01001101, 01100001, and 01101110. These three values are joined together into a 24-bit string, producing 010011010110000101101110. Groups of 6 bits (6 bits have a maximum of 26 = 64 different binary values) are converted into individual numbers from left to right (in this case, there are four numbers in a 24-bit string), which are then converted into their corresponding Base64 character values.

The Base64 index table: [2]

Base64 Library

This is a C library to encode ASCII string to base64 format and decode base64 string to ASCII.

Functions

• base64_encode

  char* base64_encode(char* plain);
  /***********************************************
  Encodes ASCCI string into base64 format string
  @param plain: ASCII string to be encoded
  @return encoded base64 format string
  ***********************************************/
  

• base64_decode

  char* base64_decode(char* cipher);
  /***********************************************
  decodes base64 format string into ASCCI string
  @param plain encoded base64 format string
  @return ASCII string to be encoded
  ***********************************************/
  

Base64 App Example

An Example program to demonstrate the Base64 library by giving the inputs through command line arguments and getting the output on the screen or written in a file.

• Usage base64 (encode | decode) <source> [<destination>]
• Options
  • encode - Convert ASCII string into Base64 format
  • decode - Convert Base64 format into ASCII string
• Arguments
  • <source> - String or path/to/file to be converted
  • <destination> - Path/to/converted/file