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Base64 is also widely used for sending e-mail attachments, because SMTP – in its original form – was designed to transport 7-bit ASCII characters only. Encoding an attachment as Base64 before sending, and then decoding when received, assures older SMTP servers will not interfere with the attachment.
A binary-to-text encoding is encoding of data in plain text.More precisely, it is an encoding of binary data in a sequence of printable characters.These encodings are necessary for transmission of data when the communication channel does not allow binary data (such as email or NNTP) or is not 8-bit clean.
Quoted-Printable and Base64 are the two MIME content transfer encodings, if the trivial "7bit" and "8bit" encoding are not counted. If the text to be encoded does not contain many non-ASCII characters, then Quoted-Printable results in a fairly readable [ 1 ] and compact encoded result.
A number of schemes exist to pack 8-bit data into text-only representations which can pass through text mail systems, to be decoded at the destination. Examples of 6-bit character subsets used for packing binary data include Uuencode and Base64. These sets contain no control characters (only printable numbers, letters, some punctuation, and ...
A file signature is data used to identify or verify the content of a file. Such signatures are also known as magic numbers or magic bytes.. Many file formats are not intended to be read as text.
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:
The tag number is encoded in the following octets, where bit 8 of each is 1 if there are more octets, and bits 1–7 encode the tag number. The tag number bits combined, big-endian, encode the tag number. The least number of following octets should be encoded; that is, bits 1–7 should not all be 0 in the first following octet.
Decoding the Base64 string AA== also yields the null character. In documentation, the null character is sometimes represented as a single-em-width symbol containing the letters "NUL". In Unicode, there is a character for this: U+2400 ␀ SYMBOL FOR NULL.