Binary-to-text encoding: Difference between revisions

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A '''binary to text encoding''' is an [[encoding]] of data in [[plain text]]. More precisely, it is an encoding of [[binary and text files|binary data]] in a sequence of [[ASCII]] printable characters. These encodings are necessary for transmission of data when the channel or the protocol only allows ASCII printable characters, such as [[e-mail]] or [[usenet]].

==Description==

Binary to text encoding is common in [[email]] and [[USENET]] communication. The most used forms of binary to text encodings are:

The [[ASCII]] text-encoding standard uses 128 unique values (0–127) to represent the alphabetic, numeric, and punctuation characters commonly used in the [[English language]], plus a selection of 'control codes' which do not represent printable characters. For example, the capital letter ''A'' is ASCII character 65, the numeral ''2'' is ASCII 50, the character ''}'' is ASCII 125, and the metacharacter ''carriage return'' is ASCII 13. Systems based on ASCII use seven bits to represent these values digitally.

By contrast, most computers store data in memory organised in eight-bit [[byte]]s, and, in the case of machine-executable code and non-textual data formats where maximum storage density is desirable, use the full range of 256 possible values in each eight-bit byte. Many computer programs came to rely on this distinction between seven-bit ''text'' and eight-bit ''binary'' data, and would not function properly if non-ASCII characters appeared in data that was expected to include only ASCII text. For example, the value of the eighth bit might not be preserved, or the program might interpret a byte value above 127 as a flag telling it to perform some function.

It is often desirable, however, to be able to send non-textual data through text-based systems, such as when one might attach an image file to an e-mail message. To accomplish this, the data are encoded in some way, such that eight-bit data are encoded into seven-bit ASCII characters (generally using only alphanumeric and punctuation characters). Upon safe arrival at its destination, it is then decoded back to its eight-bit form. This process is referred to as ASCII Armoring.

One older method of accomplishing this is the [[uuencode]] standard. Today, the [[Base64]] encoding is among the most commonly used methods. Other special-purpose encoding standards include [[Ascii85]], [[xxcode]], [[BinHex]], [[Quoted-printable]] and [[yEnc]]. Some older and today uncommon formats include BOO, BTOA, and USR encoding. Many programs perform ASCII armoring to allow for data-transport, such as [[PGP]] and [[GNU Privacy Guard]] ([[GPG]]). PGP uses Radix-64 conversion in which 3 characters or bytes(24 bits) are converted in to 4 parts having 6 bits each.

==Encoding standards==

Binary to text encoding is common in [[email]] and [[USENET]] communication. The most used forms of binary to text encodings are:

* [[base64]]