Digital signature

Digital signature is a sequence of bits that are calculated mathematically while signing a given document. Since it is easy to copy, alter or move a file on computers without leaving any trail, one needs to be very careful in designing a signature scheme. In keeping with the properties of a handwritten signature, a digital signature should depend on some secret known only to the signer and on the content of the message should be able to distinguish between a forgery and a valid signature without requiring the signer to reveal any secret information. A general digital scheme consists of three algorithms:
1. A key generation algorithm
2. A signing algorithm
3. A verification algorithm
Cryptography: The process or skill of communicating in or deciphering secret writings or ciphers.
Working of digital signature:
Public key cryptography gives reliable method for digital signing and signature verification system based on public/private key pairs. A person can sign a given digital message with private key. The two steps involved are:
1. Calculate the hash value
In the first step of the process, a hash value of the message is calculated by applying some cryptographic hashing algorithm. The calculated hash value is a sequence of bits, usually with affixed length, extracted in some manner from the message. All reliable algorithms for message digest calculation apply such mathematical that when just a single bit from the input message is changed, a completely different digest is obtained.
2. Calculate the digital signature
In the second step of digitally signing a message, the information obtained in the first step hash-value of the message is encrypted with the private key of the person who signs the message and thus an encrypted hash-value, also called digital signature is obtained.
Verifying signed data
A digital signature is associated with a X.509 certificate which contains the sender’s public key. This key is used to decrypt the digital signature into the original hash value on the recipient’s computer. To verify the digital signature, the same hashing algorithm is used to generate a hash value based on the original data. The decrypted hash value is compared to the generated hash value. If the values match, the digital signature is valid.
1. Calculate the current hash value
2. Calculate the original hash value
3. Compare the current and the original hash-value
Benefits of digital signature:
Authenticity
Although digital signatures alone cannot prevent the content from being manipulated during delivery, using digital signatures provides a mechanism to detect tampering of it occurs. If the data is altered in any way after being digitally signed, the recipient can tell via properties of the signature that the data sent does not match the data received.

Acknowledgement
Data can be signed by the recipient as well as the sender. When a recipient signs the data and returns it to the sender, this signature is an acknowledgement. Digital signatures used in this way also provide no repudiation; the ability to prove that the data was sent by the signer.

WEB PAGE SET UP

Creation of a personal web page
A personal homepage is your means of putting your own information on the world wide web (www). A web page is nothing more than a text file written with special tags that format the contents, point to other pages, andinsert images and sounds. The tags arecalled hypertext markup language, or html.
There are a variety of ways to generate a web page:
• We may create our text file in many different ways using a text editor such as notepad (windows), simpletext(mac) or pico(unix).
• There are many software packages, such as dream weaver, that you can use to generate the html code for you. Additionally most word processing packages such as ms word, will usually save to the HTML format as well.
• We may choose to use a template (an existing frame of a document) and just fill in the details.
We will now discuss some of the basic HTML tags used:
HEAD TAG
tag has no attributes. Several tags are included inside it.
1.BASEFONT Tag
It defines the font size to be used in html document.




2.BASE Tag
It is useful for setting some global parameters of an html document.





3.META Tag
This tag is used to include additional information about the document and can be used to pass additional information to a browser. There is no ending tag for and a document can have multiple tags. The attribute the meta tag are NAME, CONTENT, and HTTP-EQUIV.

CONTENT=”woodworking, cabinetmaking, handmade furniture”>


HTML and colors
There are two ways of defining colors in HTML documents. One involves simple color names , such as blue, cranberry, green, orange etc. However, since different browsers have different lists and since the definitions of individual colors may vary from browser to browser, we recommend using the color numbering scheme. For eg:
000000 means 00or no red, 00 of green, and 00of blue. So, 000000 represents black.# sign is to denote that they represent a color.

BODY TAG
The text and HTML code that goes between the body beginning and ending tags is rendered and displayed in the document area of the browser’s window.

1.TEXT color

The text attribute is used to change the default text color for an entire document.


2. BACKGROUND color

The BGCOLOR attribute is used to set the background of an HTML document to a single color.


3.HYPERLINK colors
Three attributes are used for changing the color of a hyperlink, where the color depends on the current state of the hyperlink. The three possible states are: unvisited, visited , and currently thinking of visiting.
LINK unvisited hyperlink
VLINK visited hyperlink
ALINK a hyperlink the user is thinking of visiting. The A stands for active hyperlink.
LINK=”#FF0000”
VLINK=”#808080”
ALINK=”#FFFF00”>

HTML FONT COLORS
It allows us to change the color of any portion of text.

I am going swimming today

ATM & ADSL

A Virtual Channel (VC) denotes the transport of ATM cells which have the same unique identifier, called the Virtual Channel Identifier (VCI). This identifier is encoded in the cell header. A virtual channel represents the basic means of communication between two end-points, and is analogous to an X.25 virtual circuit.
A Virtual Path (VP) denotes the transport of ATM cells belonging to virtual channels which share a common identifier, called the Virtual Path Identifier (VPI), which is also encoded in the cell header. A virtual path, in other words, is a grouping of virtual channels which connect the same end-points. This two layer approach results in improved network performance. Once a virtual path is set up, the addition/removal of virtual channels is straightforward.
ATM has proved very successful in the WAN scenario and numerous telecommunication providers have implemented ATM in their wide-area network cores. Also many ADSL implementations use ATM. However, ATM has failed to gain wide use as a LAN technology, and its complexity has held back its full deployment as the single integrating network technology in the way that its inventors originally intended.
Many people, particularly in the Internet protocol-design community, considered this vision to be mistaken. Their argument went something like this: We know that there will always be both brand-new and obsolescent link-layer technologies, particularly in the LAN area, and it is fair to assume that not all of them will fit neatly into the synchronous optical networking model for which ATM was designed. Therefore, some sort of protocol is needed to provide a unifying layer over both ATM and non-ATM link layers, and ATM itself cannot fill that role. Conveniently, we have this protocol called "IP" which already does that. Ergo, there is no point in implementing ATM at the network layer.
In addition, the need for cells to reduce jitter has reduced as transport speeds increased (see below), and improvements in Voice over IP (VoIP) have made the integration of speech and data possible at the IP layer, again removing the incentive for ubiquitous deployment of ATM. Most

Assymetrical Digital Subscriber Line (ADSL) is a form of DSL, a data communications technology that enables faster data transmission over copper telephone lines than a conventional voiceband modem can provide. It does this by utilizing frequencies that are not used by a voice telephone call. A splitter or micro filters allow a single telephone connection to be used for both ADSL service and voice calls at the same time. Because phone lines vary in quality and were not originally engineered with ADSL in mind, it can generally only be used over short distances, typically less than 3mi (5 km). At the telephone exchange the line generally terminates at a DSLAM where another frequency splitter separates the voice band signal for the conventional phone network. Data carried by the ADSL is typically routed over the telephone company's data network and eventually reaches a conventional internet network.
The distinguishing characteristic of ADSL over other forms of DSL is that the volume of data flow is greater in one direction than the other, i.e. it is asymmetric. Providers usually market ADSL as a service for consumers to connect to the Internet in a relatively passive mode: able to use the higher speed direction for the "download" from the Internet but not needing to run servers that would require high speed in the other direction.

Internet & World Wide Web

The Internet is a worldwide, publicly accessible series of interconnected computer networks that transmit data by packet switching using the standard Internet Protocol (IP). It is a "network of networks" that consists of millions of smaller domestic, academic, business, and government networks, which together carry various information and services, such as electronic mail, online chat, file transfer, and the interlinked Web pages and other documents of the World Wide Web.

WWW's historical logo designed by Robert CailliauThe World Wide Web (commonly shortened to the Web) is a system of interlinked, hypertext documents accessed via the Internet. With a web browser, a user views web pages that may contain text, images, videos, and other multimedia and navigates between them using hyperlinks. The World Wide Web was created in 1989 by Sir Tim Berners-Lee from the United Kingdom, and Robert Cailliau from Belgium, working at CERN in Geneva, Switzerland. Since then, Berners-Lee has played an active role in guiding the development of web standards (such as the markup languages in which web pages are composed), and in recent years has advocated his vision of a Semantic Web.

The Internet and the World Wide Web are not synonymous. The Internet is a collection of interconnected computer networks, linked by copper wires, fiber-optic cables, wireless connections, etc. In contrast, the Web is a collection of interconnected documents and other resources, linked by hyperlinks and URLs. The World Wide Web is one of the services accessible via the Internet, along with many others including e-mail, file sharing and others described below. The Internet protocol suite is a collection of standards and protocols organized into layers so that each layer provides the foundation and the services required by the layer above. In this scheme, the Internet consists of the computers and networks that handle Internet Protocol (IP) data packets. Transmission Control Protocol (TCP) depends on IP and solves problems like data packets arriving out of order or not at all. Next comes Hypertext Transfer Protocol (HTTP), which is an application layer protocol. It runs on top of TCP/IP and provides user agents, such as web browsers, with access to the files, documents and other resources of the World Wide Web.

Local Area Network (LAN)

A local area network (LAN) is usually privately owned and links the devices in a single office, building, or campus (see Figure 1.4). Depending on the needs of an organisation and the type of technology used, a LAN can be as simple as two PCs and a printer in someone's home office, or it can extend throughout a company and include voice, sound, and video peripherals. Currently, LAN size is limited to a few kilometers.
LANs are designed to allow resources to be shared between personal computers or workstations. The resources to be shared can include hardware (e.g., a printer), software (e.g., an application program), or data. A common example of a LAN, found in many business environments, links a work group of task related computers, for example, engineering workstations or accounting PCs. One of the computers may be given a large-capacity disk drive and become a server to the other clients. Software can be stored on this central server and used as needed by the whole group. In this example, the size of the LAN may be determined by licensing restrictions on the number of users per copy of software, or by restrictions on the number of users licensed to access the operating system.
In addition to size, LANs are distinguished from other types of networks by their transmission media and topology. In general, a given LAN will use only one type of transmission medium. The most common LAN topologies are bus, ring, and star. Traditionally, LANs have data rates in the 4 to 16 Mbps range. Today, however speeds are increasing and can reach 100 Mbps with gigabit systems in development.

PLUG INS

A SOFTWARE application designed to extend the functionality of a web browser. Plug-ins are launched from within the browser and are capable of playing audio, showing movies, and running animations, among other things.
All plug in models require two entities the plug-in host and the plug-in itself. The host could be an application, operating system, or even other plug-in. plug-ins are written and compiled entirely from the host, typically by another developer. When the host code is executed , it uses whatever mechanism is provided by the plug-in architecture to locate compatible plug-ins and load them, thus adding capabilities to the host that were not previously available.

When the host application is launched , it searches for all plug-ins with the appropriate identifier. For each plug-in found , the host uses the plug-in architecture to obtain the processing description string and a pointer to the processing function..

Adbhai Indian social classifieds

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