Description:
Base64 is a group of similar binary-to-text encoding schemes that represent binary data in 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. Thus, three 8-bit bytes (i.e. total 24 bits) can be represented by four 6-bit base64 digits.
A certain set of 64 characters chosen to represent the 64 place-values for the base varies between implementations. The overall strategy is to choose
64 characters, which are members of a subset common to most encodings, as well as printable. This combination leaves the data unlikely to be modified
when transmitting through information systems such as e-mail, which have not traditionally been 8-bit clean. For example, the Base64 MIME implementation uses A - Z, A-z, and 0-9
for the first 62 values. Other variants share this property, but differ in the characters selected for the last two values; an example is UTF-7.
The earliest instances of this type of encoding were created for dial-up communication between systems running the same OS — for example, UUENCODE for UNIX,
BinHex for the TRS-80 (later adapted for the Macintosh) — and could therefore make more assumptions about what characters were safe to use.
For example, uuencode uses uppercase letters, numbers, and many punctuation marks, but not lowercase.
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