MIME content transfer encoding.

Content-Transfer-Encoding[edit] In June 1992, MIME (RFC 1341, since made obsolete by RFC 2045) defined a set of methods for representing binary data in formats other than ASCII text format. The content-transfer-encoding: MIME header has 2-sided significance: It indicates whether or not a binary-to-text encoding scheme has been used on top of the original encoding as specified within the Content-Type header: If such a binary-to-text encoding method has been used, it states which one. If not, it provides a descriptive label for the format of content, with respect to the presence of 8-bit or binary content. The RFC and the IANA's list of transfer encodings define the values shown below, which are not case sensitive. Note that '7bit', '8bit', and 'binary' mean that no binary-to-text encoding on top of the original encoding was used. In these cases, the header is actually redundant for the email client to decode the message body, but it may still be useful as an indicator of what type of object is being sent. Values 'quoted-printable' and 'base64' tell the email client that a binary-to-text encoding scheme was used and that appropriate initial decoding is necessary before the message can be read with its original encoding (e.g. UTF-8). Suitable for use with normal SMTP: 7bit – up to 998 octets per line of the code range 1..127 with CR and LF (codes 13 and 10 respectively) only allowed to appear as part of a CRLF line ending. This is the default value. quoted-printable – used to encode arbitrary octet sequences into a form that satisfies the rules of 7bit. Designed to be efficient and mostly human readable when used for text data consisting primarily of US-ASCII characters but also containing a small proportion of bytes with values outside that range. base64 – used to encode arbitrary octet sequences into a form that satisfies the rules of 7bit. Designed to be efficient for non-text 8 bit and binary data. Sometimes used for text data that frequently uses non-US-ASCII characters. Suitable for use with SMTP servers that support the 8BITMIME SMTP extension (RFC 6152): 8bit – up to 998 octets per line with CR and LF (codes 13 and 10 respectively) only allowed to appear as part of a CRLF line ending. Suitable for use with SMTP servers that support the BINARYMIME SMTP extension (RFC 3030): binary – any sequence of octets. There is no encoding defined which is explicitly designed for sending arbitrary binary data through SMTP transports with the 8BITMIME extension. Thus, if BINARYMIME isn't supported, base64 or quoted-printable (with their associated inefficiency) are sometimes still useful. This restriction does not apply to other uses of MIME such as Web Services with MIME attachments or MTOM.

Radix

In mathematical numeral systems, the radix or base is the number of unique digits, including zero, used to represent numbers in a positional numeral system. For example, for the decimal system (the most common system in use today) the radix is ten, because it uses the ten digits from 0 through 9. In any positional numeral system (except unary, where the radix is 1), the number x and its base y are conventionally written as (x)_y, although for base ten the subscript is usually assumed and not written, as it is the most common way to express value. For example, (100)_{10} (in the decimal system) represents the number one hundred, whilst (100)_2 (in the binary system with base 2) represents the number four.[1] we will update it soon...

ASCII

ASCII (Listeni/ˈæski/ ass-kee), abbreviated from American Standard Code for Information Interchange,[1] is a character-encoding scheme (the IANA prefers the name US-ASCII[2]). ASCII codes represent text in computers, communications equipment, and other devices that use text. Most modern character-encoding schemes are based on ASCII, though they support many additional characters. ASCII was the most common character encoding on the World Wide Web until December 2007, when it was surpassed by UTF-8, which includes ASCII as a subset.[3][4][5] ASCII developed from telegraphic codes. Its first commercial use was as a seven-bit teleprinter code promoted by Bell data services. Work on the ASCII standard began on October 6, 1960, with the first meeting of the American Standards Association's (ASA) X3.2 subcommittee. The first edition of the standard was published during 1963,[6][7] a major revision during 1967,[8][9] and the most recent update during 1986.[10] Compared to earlier telegraph codes, the proposed Bell code and ASCII were both ordered for more convenient sorting (i.e., alphabetization) of lists, and added features for devices other than teleprinters. Originally based on the English alphabet, ASCII encodes 128 specified characters into seven-bit binary integers as shown by the ASCII chart on the right.[11] The characters encoded are numbers 0 to 9, lowercase letters a to z, uppercase letters A to Z, basic punctuation symbols, control codes that originated with Teletype machines, and a space. For example, lowercase j would become binary 1101010 and decimal 106. ASCII includes definitions for 128 characters: 33 are non-printing control characters (many now obsolete)[12] that affect how text and space are processed[13] and 95 printable characters, including the space (which is considered an invisible graphic[14][15]:223). we will update it soon....

Binary data

Binary data is data whose unit can take on only two possible states, traditionally termed 0 and +1 in accordance with the binary numeral system and Boolean algebra. Forms and interpretations of binary data come in different technical and scientific fields. Such two-valued unit can be termed: "bit" (binary digit) in computer science, "truth value" in mathematical logic and related domains, "binary variable" in statistics. we will update it soon...

Binary-to-text encoding

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 characters. These encodings are necessary for transmission of data when the channel does not allow binary data (such as email or NNTP) or is not 8-bit clean. PGP documentation (RFC 4880) uses the term ASCII armor for binary-to-text encoding when referring to Radix-64.

What is the Base64?

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. Base64 encoding schemes are commonly used when there is a need to encode binary data that needs to be stored and transferred over media that is designed to deal with textual data. This is to ensure that the data remains intact without modification during transport. Base64 is commonly used in a number of applications, including email via MIME, and storing complex data in XML. we will update it soon...