Misplaced Pages

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98-529: As with all binary-to-text encoding schemes, Base64 is designed to carry data stored in binary formats across channels that only reliably support text content. Base64 is particularly prevalent on the World Wide Web where one of its uses is the ability to embed image files or other binary assets inside textual assets such as HTML and CSS files. Base64 is also widely used for sending e-mail attachments, because SMTP  – in its original form –

196-406: A & ( ∼ a + 1 ) {\displaystyle a\And (\sim a+1)} , where & {\displaystyle \And } means bitwise operation AND and ∼ {\displaystyle \sim } means bitwise operation NOT on a {\displaystyle a} . For MSb 1 numbering, the value of an unsigned binary integer

294-583: A > . Such a collection of useful, related resources, interconnected via hypertext links is dubbed a web of information. Publication on the Internet created what Tim Berners-Lee first called the WorldWideWeb (in its original CamelCase , which was subsequently discarded) in November 1990. The hyperlink structure of the web is described by the webgraph : the nodes of the web graph correspond to

392-442: A binary number . In computing , the least significant bit ( LSb ) is the bit position in a binary integer representing the binary 1s place of the integer. Similarly, the most significant bit ( MSb ) represents the highest-order place of the binary integer. The LSb is sometimes referred to as the low-order bit or right-most bit , due to the convention in positional notation of writing less significant digits further to

490-520: A home page containing a directory of the site web content . Some websites require user registration or subscription to access content. Examples of subscription websites include many business sites, news websites, academic journal websites, gaming websites, file-sharing websites, message boards , web-based email , social networking websites, websites providing real-time price quotations for different types of markets, as well as sites providing various other services. End users can access websites on

588-494: A web application . Consequently, a static web page displays the same information for all users, from all contexts, subject to modern capabilities of a web server to negotiate content-type or language of the document where such versions are available and the server is configured to do so. A server-side dynamic web page is a web page whose construction is controlled by an application server processing server-side scripts. In server-side scripting, parameters determine how

686-588: A web page on the World Wide Web normally begins either by typing the URL of the page into a web browser or by following a hyperlink to that page or resource. The web browser then initiates a series of background communication messages to fetch and display the requested page. In the 1990s, using a browser to view web pages—and to move from one web page to another through hyperlinks—came to be known as 'browsing,' 'web surfing' (after channel surfing ), or 'navigating

784-404: A 24-bit string), which are then converted into their corresponding Base64 character values. As this example illustrates, Base64 encoding converts three octets into four encoded characters. = padding characters might be added to make the last encoded block contain four Base64 characters. Hexadecimal to octal transformation is useful to convert between binary and Base64. Such conversion

882-410: A 64-character alphabet consisting of upper- and lower-case Roman letters ( A – Z , a – z ), the numerals ( 0 – 9 ), and the + and / symbols. The = symbol is also used as a padding suffix. The original specification, RFC   989 , additionally used the * symbol to delimit encoded but unencrypted data within the output stream. To convert data to PEM printable encoding,

980-546: A browser called WorldWideWeb (which became the name of the project and of the network) and an HTTP server running at CERN. As part of that development he defined the first version of the HTTP protocol, the basic URL syntax, and implicitly made HTML the primary document format. The technology was released outside CERN to other research institutions starting in January 1991, and then to the whole Internet on 23 August 1991. The Web

1078-420: A compliant decoder, although most implementations use a CR/LF newline pair to delimit encoded lines. Thus, the actual length of MIME-compliant Base64-encoded binary data is usually about 137% of the original data length ( 4 ⁄ 3 × 78 ⁄ 76 ), though for very short messages the overhead can be much higher due to the overhead of the headers. Very roughly, the final size of Base64-encoded binary data

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1176-625: A frenzy for the Web and started the dot-com bubble . Microsoft responded by developing its own browser, Internet Explorer , starting the browser wars . By bundling it with Windows, it became the dominant browser for 14 years. Berners-Lee founded the World Wide Web Consortium (W3C) which created XML in 1996 and recommended replacing HTML with stricter XHTML . In the meantime, developers began exploiting an IE feature called XMLHttpRequest to make Ajax applications and launched

1274-490: A network, a web browser can retrieve a web page from a remote web server . The web server may restrict access to a private network such as a corporate intranet. The web browser uses the Hypertext Transfer Protocol (HTTP) to make such requests to the web server . A static web page is delivered exactly as stored, as web content in the web server's file system . In contrast, a dynamic web page

1372-627: A particular topic or purpose, ranging from entertainment and social networking to providing news and education. All publicly accessible websites collectively constitute the World Wide Web, while private websites, such as a company's website for its employees, are typically a part of an intranet . Web pages, which are the building blocks of websites, are documents , typically composed in plain text interspersed with formatting instructions of Hypertext Markup Language ( HTML , XHTML ). They may incorporate elements from other websites with suitable markup anchors . Web pages are accessed and transported with

1470-472: A public Internet Protocol (IP) network, such as the Internet , or a private local area network (LAN), by referencing a uniform resource locator (URL) that identifies the site. Websites can have many functions and can be used in various fashions; a website can be a personal website , a corporate website for a company, a government website, an organization website, etc. Websites are typically dedicated to

1568-422: A range of devices, including desktop and laptop computers , tablet computers , smartphones and smart TVs . A web browser (commonly referred to as a browser ) is a software user agent for accessing information on the World Wide Web. To connect to a website's server and display its pages, a user needs to have a web browser program. This is the program that the user runs to download, format, and display

1666-439: A translation that reflects the design concept and proliferation of the World Wide Web. Use of the www prefix has been declining, especially when web applications sought to brand their domain names and make them easily pronounceable. As the mobile Web grew in popularity, services like Gmail .com, Outlook.com , Myspace .com, Facebook .com and Twitter .com are most often mentioned without adding "www." (or, indeed, ".com") to

1764-641: A way that is convenient for inclusion in URLs, including in hidden web form fields, and Base64 is a convenient encoding to render them in a compact way. Using standard Base64 in URL requires encoding of ' + ', ' / ' and ' = ' characters into special percent-encoded hexadecimal sequences (' + ' becomes ' %2B ', ' / ' becomes ' %2F ' and ' = ' becomes ' %3D '), which makes the string unnecessarily longer. For this reason, modified Base64 for URL variants exist (such as base64url in RFC   4648 ), where

1862-429: A web browser in its address bar input field, some web browsers automatically try adding the prefix "www" to the beginning of it and possibly ".com", ".org" and ".net" at the end, depending on what might be missing. For example, entering "microsoft" may be transformed to http://www.microsoft.com/ and "openoffice" to http://www.openoffice.org . This feature started appearing in early versions of Firefox , when it still had

1960-429: A web page on the user's computer. In addition to allowing users to find, display, and move between web pages, a web browser will usually have features like keeping bookmarks, recording history, managing cookies (see below), and home pages and may have facilities for recording passwords for logging into web sites. The most popular browsers are Chrome , Firefox , Safari , Internet Explorer , and Edge . A Web server

2058-507: A year. Mosaic was a graphical browser that could display inline images and submit forms that were processed by the HTTPd server . Marc Andreessen and Jim Clark founded Netscape the following year and released the Navigator browser , which introduced Java and JavaScript to the Web. It quickly became the dominant browser. Netscape became a public company in 1995 which triggered

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2156-399: Is server software , or hardware dedicated to running said software, that can satisfy World Wide Web client requests. A web server can, in general, contain one or more websites. A web server processes incoming network requests over HTTP and several other related protocols. Least significant bit In computing , bit numbering is the convention used to identify the bit positions in

2254-437: Is a property of the numeric value in binary itself. This is often utilized in programming via bit shifting : A value of 1 << n corresponds to the n bit of a binary integer (with a value of 2 ). In digital steganography , sensitive messages may be concealed by manipulating and storing information in the least significant bits of an image or a sound file. The user may later recover this information by extracting

2352-588: Is a variant of the Base64 encoding used in MIME. The "Modified Base64" alphabet consists of the MIME Base64 alphabet, but does not use the " = " padding character. UTF-7 is intended for use in mail headers (defined in RFC   2047 ), and the " = " character is reserved in that context as the escape character for "quoted-printable" encoding. Modified Base64 simply omits the padding and ends immediately after

2450-494: Is available for both advanced calculators and programming languages. For example, the hexadecimal representation of the 24 bits above is 4D616E. The octal representation is 23260556. Those 8 octal digits can be split into pairs ( 23 26 05 56 ), and each pair is converted to decimal to yield 19 22 05 46 . Using those four decimal numbers as indices for the Base64 alphabet, the corresponding ASCII characters are TWFu . If there are only two significant input octets (e.g., 'Ma'), or when

2548-441: Is delivered with the page that can make additional HTTP requests to the server, either in response to user actions such as mouse movements or clicks, or based on elapsed time. The server's responses are used to modify the current page rather than creating a new page with each response, so the server needs only to provide limited, incremental information. Multiple Ajax requests can be handled at the same time, and users can interact with

2646-412: Is equal to 1.37 times the original data size + 814 bytes (for headers). The size of the decoded data can be approximated with this formula: UTF-7 , described first in RFC   1642 , which was later superseded by RFC   2152 , introduced a system called modified Base64 . This data encoding scheme is used to encode UTF-16 as ASCII characters for use in 7-bit transports such as SMTP . It

2744-403: Is generated by a web application , usually driven by server-side software . Dynamic web pages are used when each user may require completely different information, for example, bank websites, web email etc. A static web page (sometimes called a flat page/stationary page ) is a web page that is delivered to the user exactly as stored, in contrast to dynamic web pages which are generated by

2842-439: Is not possible, because a single Base64 character only contains 6 bits, and 8 bits are required to create a byte, so a minimum of two Base64 characters are required: The first character contributes 6 bits, and the second character contributes its first 2 bits. For example: Decoding without padding is not performed consistently among decoders. In addition, allowing padless decoding by definition allows multiple strings to decode into

2940-450: Is not required by any technical or policy standard and many websites do not use it; the first web server was nxoc01.cern.ch . According to Paolo Palazzi, who worked at CERN along with Tim Berners-Lee, the popular use of www as subdomain was accidental; the World Wide Web project page was intended to be published at www.cern.ch while info.cern.ch was intended to be the CERN home page; however

3038-464: Is officially spelled as three separate words, each capitalised, with no intervening hyphens. Nonetheless, it is often called simply the Web , and also often the web ; see Capitalization of Internet for details. In Mandarin Chinese, World Wide Web is commonly translated via a phono-semantic matching to wàn wéi wǎng ( 万维网 ), which satisfies www and literally means "10,000-dimensional net",

Base64 - Misplaced Pages Continue

3136-529: Is the Base64 alphabet defined in RFC 4648 §4 . See also § Variants summary table . The example below uses ASCII text for simplicity, but this is not a typical use case, as it can already be safely transferred across all systems that can handle Base64. The more typical use is to encode binary data (such as an image); the resulting Base64 data will only contain 64 different ASCII characters, all of which can reliably be transferred across systems that may corrupt

3234-533: Is the best known of such efforts. Many hostnames used for the World Wide Web begin with www because of the long-standing practice of naming Internet hosts according to the services they provide. The hostname of a web server is often www , in the same way that it may be ftp for an FTP server , and news or nntp for a Usenet news server . These hostnames appear as Domain Name System (DNS) or subdomain names, as in www.example.com . The use of www

3332-407: Is the common practice of following such hyperlinks across multiple websites. Web applications are web pages that function as application software . The information in the Web is transferred across the Internet using HTTP. Multiple web resources with a common theme and usually a common domain name make up a website . A single web server may provide multiple websites, while some websites, especially

3430-435: Is the standard markup language for creating web pages and web applications . With Cascading Style Sheets (CSS) and JavaScript , it forms a triad of cornerstone technologies for the World Wide Web. Web browsers receive HTML documents from a web server or from local storage and render the documents into multimedia web pages. HTML describes the structure of a web page semantically and originally included cues for

3528-405: Is then encoded with the same Base64 algorithm and, prefixed by the " = " symbol as the separator, appended to the encoded output data. RFC   3548 , entitled The Base16, Base32, and Base64 Data Encodings , is an informational (non-normative) memo that attempts to unify the RFC   1421 and RFC   2045 specifications of Base64 encodings, alternative-alphabet encodings, and

3626-431: The Hypertext Transfer Protocol (HTTP), which may optionally employ encryption ( HTTP Secure , HTTPS) to provide security and privacy for the user. The user's application, often a web browser , renders the page content according to its HTML markup instructions onto a display terminal . Hyperlinking between web pages conveys to the reader the site structure and guides the navigation of the site, which often starts with

3724-764: The Web 2.0 revolution. Mozilla , Opera , and Apple rejected XHTML and created the WHATWG which developed HTML5 . In 2009, the W3C conceded and abandoned XHTML. In 2019, it ceded control of the HTML specification to the WHATWG. The World Wide Web has been central to the development of the Information Age and is the primary tool billions of people use to interact on the Internet . Tim Berners-Lee states that World Wide Web

3822-400: The two's complement method. The MSb most significant bit has a negative weight in signed integers, in this case -2 = -128. The other bits have positive weights. The lsb ( least significant bit ) has weight 2 =1. The signed value is in this case -128+2 = -126. The expressions most significant bit first and least significant bit at last are indications on the ordering of the sequence of

3920-581: The web browsing history forward of the displayed page. Using Ajax technologies the end user gets one dynamic page managed as a single page in the web browser while the actual web content rendered on that page can vary. The Ajax engine sits only on the browser requesting parts of its DOM, the DOM, for its client, from an application server. Dynamic HTML, or DHTML, is the umbrella term for technologies and methods used to create web pages that are not static web pages , though it has fallen out of common use since

4018-423: The ' + ' and ' / ' characters of standard Base64 are respectively replaced by ' - ' and ' _ ', so that using URL encoders/decoders is no longer necessary and has no effect on the length of the encoded value, leaving the same encoded form intact for use in relational databases, web forms, and object identifiers in general. A popular site to make use of such is YouTube . Some variants allow or require omitting

Base64 - Misplaced Pages Continue

4116-425: The 64-digit values for the base varies between implementations. The general strategy is to choose 64 characters that are common to most encodings and that are also printable. This combination leaves the data unlikely to be modified in transit through information systems, such as email, that were traditionally not 8-bit clean . For example, MIME 's Base64 implementation uses A – Z , a – z , and 0 – 9 for

4214-466: The Base32 (which is seldom used) and Base16 encodings. Unless implementations are written to a specification that refers to RFC   3548 and specifically requires otherwise, RFC 3548 forbids implementations from generating messages containing characters outside the encoding alphabet or without padding, and it also declares that decoder implementations must reject data that contain characters outside

4312-473: The DNS records were never switched, and the practice of prepending www to an institution's website domain name was subsequently copied. Many established websites still use the prefix, or they employ other subdomain names such as www2 , secure or en for special purposes. Many such web servers are set up so that both the main domain name (e.g., example.com) and the www subdomain (e.g., www.example.com) refer to

4410-455: The HTML and the CSS standards, has encouraged the use of CSS over explicit presentational HTML since 1997. Most web pages contain hyperlinks to other related pages and perhaps to downloadable files, source documents, definitions and other web resources. In the underlying HTML, a hyperlink looks like this: < a href = "http://example.org/home.html" > Example.org Homepage </

4508-423: The HTTP service so that the receiving host can distinguish an HTTP request from other network protocols it may be servicing. HTTP normally uses port number 80 and for HTTPS it normally uses port number 443 . The content of the HTTP request can be as simple as two lines of text: The computer receiving the HTTP request delivers it to web server software listening for requests on port 80. If the web server can fulfil

4606-449: The Internet according to specific rules of the Hypertext Transfer Protocol (HTTP). The Web was invented by English computer scientist Tim Berners-Lee while at CERN in 1989 and opened to the public in 1991. It was conceived as a "universal linked information system". Documents and other media content are made available to the network through web servers and can be accessed by programs such as web browsers . Servers and resources on

4704-411: The Internet. The Web was invented by English computer scientist Tim Berners-Lee while working at CERN . He was motivated by the problem of storing, updating, and finding documents and data files in that large and constantly changing organization, as well as distributing them to collaborators outside CERN. In his design, Berners-Lee dismissed the common tree structure approach, used for instance in

4802-461: The URLs of other resources such as images, other embedded media, scripts that affect page behaviour, and Cascading Style Sheets that affect page layout. The browser makes additional HTTP requests to the web server for these other Internet media types . As it receives their content from the web server, the browser progressively renders the page onto the screen as specified by its HTML and these additional resources. Hypertext Markup Language (HTML)

4900-451: The Web'. Early studies of this new behaviour investigated user patterns in using web browsers. One study, for example, found five user patterns: exploratory surfing, window surfing, evolved surfing, bounded navigation and targeted navigation. The following example demonstrates the functioning of a web browser when accessing a page at the URL http://example.org/home.html . The browser resolves

4998-675: The World Wide Web and web browsers . A web browser displays a web page on a monitor or mobile device . The term web page usually refers to what is visible, but may also refer to the contents of the computer file itself, which is usually a text file containing hypertext written in HTML or a comparable markup language . Typical web pages provide hypertext for browsing to other web pages via hyperlinks , often referred to as links . Web browsers will frequently have to access multiple web resource elements, such as reading style sheets , scripts , and images, while presenting each web page. On

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5096-623: The World Wide Web are identified and located through character strings called uniform resource locators (URLs). The original and still very common document type is a web page formatted in Hypertext Markup Language (HTML). This markup language supports plain text , images , embedded video and audio contents, and scripts (short programs) that implement complex user interaction. The HTML language also supports hyperlinks (embedded URLs) which provide immediate access to other web resources. Web navigation , or web surfing,

5194-581: The above quote, the encoded value of Man is TWFu . Encoded in ASCII, the characters M , a , and n are stored as the byte values 77 , 97 , and 110 , which are the 8-bit binary values 01001101 , 01100001 , and 01101110 . These three values are joined together into a 24-bit string, producing 010011010110000101101110 . Groups of 6 bits (6 bits have a maximum of 2 = 64 different binary values) are converted into individual numbers from start to end (in this case, there are four numbers in

5292-543: The appearance of the document. HTML elements are the building blocks of HTML pages. With HTML constructs, images and other objects such as interactive forms may be embedded into the rendered page. HTML provides a means to create structured documents by denoting structural semantics for text such as headings, paragraphs, lists, links , quotes and other items. HTML elements are delineated by tags , written using angle brackets . Tags such as < img /> and < input /> directly introduce content into

5390-452: The assembly of every new web page proceeds, including the setting up of more client-side processing. A client-side dynamic web page processes the web page using JavaScript running in the browser. JavaScript programs can interact with the document via Document Object Model , or DOM, to query page state and alter it. The same client-side techniques can then dynamically update or change the DOM in

5488-516: The bit number and a base of 2. The value of an unsigned binary integer is therefore where b i denotes the value of the bit with number i , and N denotes the number of bits in total. When the bit numbering starts at zero for the most significant bit (MSb) the numbering scheme is called MSb 0 . The value of an unsigned binary integer is therefore LSb of a number can be calculated with time complexity of O ( n ) {\displaystyle O(n)} with formula

5586-433: The bits in the bytes sent over a wire in a serial transmission protocol or in a stream (e.g. an audio stream). Most significant bit first means that the most significant bit will arrive first: hence e.g. the hexadecimal number 0x12 , 00010010 in binary representation, will arrive as the sequence 0 0 0 1 0 0 1 0 . Least significant bit first means that the least significant bit will arrive first: hence e.g.

5684-669: The domain. In English, www is usually read as double-u double-u double-u . Some users pronounce it dub-dub-dub , particularly in New Zealand. Stephen Fry , in his "Podgrams" series of podcasts, pronounces it wuh wuh wuh . The English writer Douglas Adams once quipped in The Independent on Sunday (1999): "The World Wide Web is the only thing I know of whose shortened form takes three times longer to say than what it's short for". The terms Internet and World Wide Web are often used without much distinction. However,

5782-503: The encoding alphabet. RFC   4648 obsoletes RFC   3548 and focuses on Base64/32/16: Base64 encoding can be helpful when fairly lengthy identifying information is used in an HTTP environment. For example, a database persistence framework for Java objects might use Base64 encoding to encode a relatively large unique id (generally 128-bit UUIDs ) into a string for use as an HTTP parameter in HTTP forms or HTTP GET URLs . Also, many applications need to encode binary data in

5880-564: The existing CERNDOC documentation system and in the Unix filesystem , as well as approaches that relied in tagging files with keywords , as in the VAX/NOTES system. Instead he adopted concepts he had put into practice with his private ENQUIRE system (1980) built at CERN. When he became aware of Ted Nelson 's hypertext model (1965), in which documents can be linked in unconstrained ways through hyperlinks associated with "hot spots" embedded in

5978-551: The first = and another 2 trailing bits for the other = . In this instance, we would get 6 bits from the d , and another 6 bits from the w for a bit string of length 12, but since we remove 2 bits for each = (for a total of 4 bits), the dw== ends up producing 8 bits (1 byte) when decoded. Without padding, after normal decoding of four characters to three bytes over and over again, fewer than four encoded characters may remain. In this situation, only two or three characters can remain. A single remaining encoded character

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6076-674: The first 62 values. Other variations share this property but differ in the symbols chosen 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 and BinHex for the TRS-80 (later adapted for the Macintosh ) – and could therefore make more assumptions about what characters were safe to use. For instance, uuencode uses uppercase letters, digits, and many punctuation characters, but no lowercase. This

6174-445: The first byte is placed in the most significant eight bits of a 24-bit buffer , the next in the middle eight, and the third in the least significant eight bits. If there are fewer than three bytes left to encode (or in total), the remaining buffer bits will be zero. The buffer is then used, six bits at a time, most significant first, as indices into the string: " ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/ ", and

6272-506: The first two Base64 digits (12 bits); the four least significant bits of the last content-bearing 6-bit block will turn out to be zero, and discarded on decoding (along with the succeeding two = padding characters): Because Base64 is a six-bit encoding, and because the decoded values are divided into 8-bit octets, every four characters of Base64-encoded text (4 sextets = 4 × 6 = 24 bits) represents three octets of unencoded text or data (3 octets = 3 × 8 = 24 bits). This means that when

6370-516: The four characters will decode to only two bytes, while == indicates that the four characters will decode to only a single byte. For example: Another way to interpret the padding character is to consider it as an instruction to discard 2 trailing bits from the bit string each time a = is encountered. For example, when ` bGlnaHQg dw== ` is decoded, we convert each character (except the trailing occurrences of = ) into their corresponding 6-bit representation, and then discard 2 trailing bits for

6468-450: The indicated character is output. The process is repeated on the remaining data until fewer than four octets remain. If three octets remain, they are processed normally. If fewer than three octets (24 bits) are remaining to encode, the input data is right-padded with zero bits to form an integral multiple of six bits. After encoding the non-padded data, if two octets of the 24-bit buffer are padded-zeros, two = characters are appended to

6566-568: The input of the atob() method. Base64 can be used in a variety of contexts: Some applications use a Base64 alphabet that is significantly different from the alphabets used in the most common Base64 variants (see Variants summary table above). World Wide Web The World Wide Web ( WWW or simply the Web ) is an information system that enables content sharing over the Internet through user-friendly ways meant to appeal to users beyond IT specialists and hobbyists. It allows documents and other web resources to be accessed over

6664-402: The last Base64 digit containing useful bits leaving up to three unused bits in the last Base64 digit. OpenPGP , described in RFC   4880 , describes Radix-64 encoding, also known as " ASCII armor ". Radix-64 is identical to the "Base64" encoding described by MIME, with the addition of an optional 24-bit CRC . The checksum is calculated on the input data before encoding; the checksum

6762-442: The last input group contains only two octets, all 16 bits will be captured in the first three Base64 digits (18 bits); the two least significant bits of the last content-bearing 6-bit block will turn out to be zero, and discarded on decoding (along with the succeeding = padding character): If there is only one significant input octet (e.g., 'M'), or when the last input group contains only one octet, all 8 bits will be captured in

6860-415: The last line, which may contain fewer printable characters. Lines are delimited by whitespace characters according to local (platform-specific) conventions. The MIME (Multipurpose Internet Mail Extensions) specification lists Base64 as one of two binary-to-text encoding schemes (the other being quoted-printable ). MIME's Base64 encoding is based on that of the RFC   1421 version of PEM: it uses

6958-450: The last two bits illustrates the least significant bits changed in the binary representation. This table illustrates an example of decimal value of 149 and the location of LSb. In this particular example, the position of unit value (decimal 1 or 0) is located in bit position 0 (n = 0). MSb stands for most significant bit , while LSb stands for least significant bit . This table illustrates an example of an 8 bit signed decimal value using

7056-443: The least significant bits of the manipulated pixels to recover the original message. This allows the storage or transfer of digital information to remain concealed. [REDACTED] A diagram showing how manipulating the least significant bits of a color can have a very subtle and generally unnoticeable affect on the color. In this diagram, green is represented by its RGB value, both in decimal and in binary. The red box surrounding

7154-418: The length of the unencoded input is not a multiple of three, the encoded output must have padding added so that its length is a multiple of four. The padding character is = , which indicates that no further bits are needed to fully encode the input. (This is different from A , which means that the remaining bits are all zeros.) The example below illustrates how truncating the input of the above quote changes

7252-433: The most popular ones, may be provided by multiple servers. Website content is provided by a myriad of companies, organizations, government agencies, and individual users ; and comprises an enormous amount of educational, entertainment, commercial, and government information. The Web has become the world's dominant information systems platform . It is the primary tool that billions of people worldwide use to interact with

7350-510: The new system to documents organized in other ways (such as traditional computer file systems or the Usenet ). Finally, he insisted that the system should be decentralized, without any central control or coordination over the creation of links. Berners-Lee submitted a proposal to CERN in May 1989, without giving the system a name. He got a working system implemented by the end of 1990, including

7448-546: The output padding: The padding character is not essential for decoding, since the number of missing bytes can be inferred from the length of the encoded text. In some implementations, the padding character is mandatory, while for others it is not used. An exception in which padding characters are required is when multiple Base64 encoded files have been concatenated. When decoding Base64 text, four characters are typically converted back to three bytes. The only exceptions are when padding characters exist. A single = indicates that

7546-402: The output; if one octet of the 24-bit buffer is filled with padded-zeros, one = character is appended. This signals the decoder that the zero bits added due to padding should be excluded from the reconstructed data. This also guarantees that the encoded output length is a multiple of 4 bytes. PEM requires that all encoded lines consist of exactly 64 printable characters, with the exception of

7644-570: The padding ' = ' signs to avoid them being confused with field separators, or require that any such padding be percent-encoded. Some libraries will encode ' = ' to ' . ', potentially exposing applications to relative path attacks when a folder name is encoded from user data. The atob() and btoa() JavaScript methods, defined in the HTML5 draft specification, provide Base64 encoding and decoding functionality to web pages. The btoa() method outputs padding characters, but these are optional in

7742-427: The page while data is retrieved. Web pages may also regularly poll the server to check whether new information is available. A website is a collection of related web resources including web pages , multimedia content, typically identified with a common domain name , and published on at least one web server . Notable examples are wikipedia .org, google .com, and amazon.com . A website may be accessible via

7840-485: The page. Other tags such as < p > surround and provide information about document text and may include other tags as sub-elements. Browsers do not display the HTML tags, but use them to interpret the content of the page. HTML can embed programs written in a scripting language such as JavaScript , which affects the behaviour and content of web pages. Inclusion of CSS defines the look and layout of content. The World Wide Web Consortium (W3C), maintainer of both

7938-542: The popularization of AJAX , a term which is now itself rarely used. Client-side-scripting, server-side scripting, or a combination of these make for the dynamic web experience in a browser. JavaScript is a scripting language that was initially developed in 1995 by Brendan Eich , then of Netscape , for use within web pages. The standardised version is ECMAScript . To make web pages more interactive, some web applications also use JavaScript techniques such as Ajax ( asynchronous JavaScript and XML ). Client-side script

8036-484: The raw source bytes. Here is a well-known idiom from distributed computing : Many hands make light work. When the quote (without trailing whitespace) is encoded into Base64, it is represented as a byte sequence of 8-bit-padded ASCII characters encoded in MIME 's Base64 scheme as follows (newlines and white spaces may be present anywhere but are to be ignored on decoding): TWFueSBoYW5kcyBtYWtlIGxpZ2h0IHdvcmsu In

8134-458: The request and response. The HTTP protocol is fundamental to the operation of the World Wide Web, and the added encryption layer in HTTPS is essential when browsers send or retrieve confidential data, such as passwords or banking information. Web browsers usually automatically prepend http:// to user-entered URIs, if omitted. A web page (also written as webpage ) is a document that is suitable for

8232-431: The request it sends an HTTP response back to the browser indicating success: followed by the content of the requested page. Hypertext Markup Language ( HTML ) for a basic web page might look like this: The web browser parses the HTML and interprets the markup ( < title > , < p > for paragraph, and such) that surrounds the words to format the text on the screen. Many web pages use HTML to reference

8330-477: The right. The MSb is similarly referred to as the high-order bit or left-most bit . In both cases, the LSb and MSb correlate directly to the least significant digit and most significant digit of a decimal integer. Bit indexing correlates to the positional notation of the value in base 2. For this reason, bit index is not affected by how the value is stored on the device, such as the value's byte order . Rather, it

8428-431: The same 64-character alphabet and encoding mechanism as PEM and uses the = symbol for output padding in the same way, as described at RFC   2045 . MIME does not specify a fixed length for Base64-encoded lines, but it does specify a maximum line length of 76 characters. Additionally, it specifies that any character outside the standard set of 64 encoding characters (For example CRLF sequences), must be ignored by

8526-414: The same hexadecimal number 0x12 , again 00010010 in binary representation, will arrive as the (reversed) sequence 0 1 0 0 1 0 0 0 . When the bit numbering starts at zero for the least significant bit (LSb) the numbering scheme is called LSb 0 . This bit numbering method has the advantage that for any unsigned number the value of the number can be calculated by using exponentiation with

8624-414: The same set of bytes, which can be a security risk. Implementations may have some constraints on the alphabet used for representing some bit patterns. This notably concerns the last two characters used in the alphabet at positions 62 and 63, and the character used for padding (which may be mandatory in some protocols or removed in others). The table below summarizes these known variants and provides links to

8722-421: The same site; others require one form or the other, or they may map to different web sites. The use of a subdomain name is useful for load balancing incoming web traffic by creating a CNAME record that points to a cluster of web servers. Since, currently , only a subdomain can be used in a CNAME, the same result cannot be achieved by using the bare domain root. When a user submits an incomplete domain name to

8820-420: The same way. A dynamic web page is then reloaded by the user or by a computer program to change some variable content. The updating information could come from the server, or from changes made to that page's DOM. This may or may not truncate the browsing history or create a saved version to go back to, but a dynamic web page update using Ajax technologies will neither create a page to go back to nor truncate

8918-415: The server name of the URL ( example.org ) into an Internet Protocol address using the globally distributed Domain Name System (DNS). This lookup returns an IP address such as 203.0.113.4 or 2001:db8:2e::7334 . The browser then requests the resource by sending an HTTP request across the Internet to the computer at that address. It requests service from a specific TCP port number that is well known for

9016-589: The subsections below. The first known standardized use of the encoding now called MIME Base64 was in the Privacy-enhanced Electronic Mail (PEM) protocol, proposed by RFC   989 in 1987. PEM defines a "printable encoding" scheme that uses Base64 encoding to transform an arbitrary sequence of octets to a format that can be expressed in short lines of 6-bit characters, as required by transfer protocols such as SMTP . The current version of PEM (specified in RFC   1421 ) uses

9114-625: The text, it helped to confirm the validity of his concept. The model was later popularized by Apple 's HyperCard system. Unlike Hypercard, Berners-Lee's new system from the outset was meant to support links between multiple databases on independent computers, and to allow simultaneous access by many users from any computer on the Internet. He also specified that the system should eventually handle other media besides text, such as graphics, speech, and video. Links could refer to mutable data files, or even fire up programs on their server computer. He also conceived "gateways" that would allow access through

9212-441: The two terms do not mean the same thing. The Internet is a global system of computer networks interconnected through telecommunications and optical networking . In contrast, the World Wide Web is a global collection of documents and other resources , linked by hyperlinks and URIs . Web resources are accessed using HTTP or HTTPS , which are application-level Internet protocols that use the Internet transport protocols. Viewing

9310-465: The web pages (or URLs) the directed edges between them to the hyperlinks. Over time, many web resources pointed to by hyperlinks disappear, relocate, or are replaced with different content. This makes hyperlinks obsolete, a phenomenon referred to in some circles as link rot, and the hyperlinks affected by it are often called "dead" links . The ephemeral nature of the Web has prompted many efforts to archive websites. The Internet Archive , active since 1996,

9408-417: The working title 'Firebird' in early 2003, from an earlier practice in browsers such as Lynx . It is reported that Microsoft was granted a US patent for the same idea in 2008, but only for mobile devices. The scheme specifiers http:// and https:// at the start of a web URI refer to Hypertext Transfer Protocol or HTTP Secure , respectively. They specify the communication protocol to use for

9506-507: Was a success at CERN, and began to spread to other scientific and academic institutions. Within the next two years, there were 50 websites created . CERN made the Web protocol and code available royalty free in 1993, enabling its widespread use. After the NCSA released the Mosaic web browser later that year, the Web's popularity grew rapidly as thousands of websites sprang up in less than

9604-433: 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. Base64 encoding causes an overhead of 33–37% relative to the size of the original binary data (33% by the encoding itself; up to 4% more by the inserted line breaks). The particular set of 64 characters chosen to represent

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