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In computer programming, Base64 (also known as tetrasexagesimal) is a group of binary-to-text encoding schemes that transforms binary data into a sequence of printable characters, limited to a set of 64 unique characters. More specifically, the source binary data is taken 6 bits at a time, then this group of 6 bits is mapped to one of 64 unique ...
With this it is possible to encode 128 (i.e. 2 7) unique values (0–127) to represent the alphabetic, numeric, and punctuation characters commonly used in English, plus a selection of Control characters which do not represent printable characters. For example, the capital letter A is represented in 7 bits as 100 0001 2, 0x41 (101 8) , the ...
The resulting string is encoded using a variant of Base64 (+/ and with padding). The authorization method and a space character (e.g. "Basic ") is then prepended to the encoded string. For example, if the browser uses Aladdin as the username and open sesame as the password, then the field's value is the Base64 encoding of Aladdin:open sesame ...
If the data is Base64-encoded, then the data part may contain only valid Base64 characters. [7] Note that Base64-encoded data: URIs use the standard Base64 character set (with '+' and '/' as characters 62 and 63) rather than the so-called "URL-safe Base64" character set. Examples of data URIs showing most of the features are:
In caret notation the null character is ^@. On some keyboards, one can enter a null character by holding down Ctrl and pressing @ (on US layouts just Ctrl+2 will often work, there being no need for ⇧ Shift to get the @ sign). The hexadecimal notation for null is 00. Decoding the Base64 string AA== also yields the null character.
Quoted-Printable, or QP encoding, is a binary-to-text encoding system using printable ASCII characters (alphanumeric and the equals sign =) to transmit 8-bit data over a 7-bit data path or, generally, over a medium which is not 8-bit clean.
More common today is the Base64 format, which is based on the same concept of alphanumeric-only as opposed to ASCII 32–95. All three formats use 6 bits (64 different characters) to represent their input data. Base64 can also be generated by the uuencode program and is similar in format, except for the actual character translation:
encoded text is the Q-encoded or base64-encoded text. An encoded-word may not be more than 75 characters long, including charset, encoding, encoded text, and delimiters. If it is desirable to encode more text than will fit in an encoded-word of 75 characters, multiple encoded-words (separated by CRLF SPACE) may be used.