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.
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]
| Value | Char | Value | Char | Value | Char | Value | Char |
|---|---|---|---|---|---|---|---|
| 0 | A |
16 | Q |
32 | g |
48 | w |
| 1 | B |
17 | R |
33 | h |
49 | x |
| 2 | C |
18 | S |
34 | i |
50 | y |
| 3 | D |
19 | T |
35 | j |
51 | z |
| 4 | E |
20 | U |
36 | k |
52 | 0 |
| 5 | F |
21 | V |
37 | l |
53 | 1 |
| 6 | G |
22 | W |
38 | m |
54 | 2 |
| 7 | H |
23 | X |
39 | n |
55 | 3 |
| 8 | I |
24 | Y |
40 | o |
56 | 4 |
| 9 | J |
25 | Z |
41 | p |
57 | 5 |
| 10 | K |
26 | a |
42 | q |
58 | 6 |
| 11 | L |
27 | b |
43 | r |
59 | 7 |
| 12 | M |
28 | c |
44 | s |
60 | 8 |
| 13 | N |
29 | d |
45 | t |
61 | 9 |
| 14 | O |
30 | e |
46 | u |
62 | + |
| 15 | P |
31 | f |
47 | v |
63 | / |
This is a C library to encode ASCII string to base64 format and decode base64 string to ASCII.
-
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 ***********************************************/
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 formatdecode- Convert Base64 format into ASCII string
- Arguments
<source>- String or path/to/file to be converted<destination>- Path/to/converted/file