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Ques2

A digital signature or digital signature scheme is a mathematical schemefor demonstrating the authenticity of a digital message or document. A validdigital signature gives a recipient reason to believe that the message wascreated by a known sender, and that it was not altered in transit. Digitalsignatures are commonly used for software distribution, financialtransactions, and in other cases where it is important to detect forgery ortampering.

Digital signatures are often used to implement electronic signatures, abroader term that refers to any electronic data that carries the intent of asignature, but not all electronic signatures use digital signatures. In somecountries, including the United States, India, and members of the EuropeanUnion, electronic signatures have legal significance. However, lawsconcerning electronic signatures do not always make clear whether they aredigital cryptographic signatures in the sense used here, leaving the legaldefinition, and so their importance, somewhat confused.

Digital signatures employ a type of asymmetric cryptography. For messagessent through a non-secure channel, a properly implemented digital signaturegives the receiver reason to believe the message was sent by the claimedsender. Digital signatures are equivalent to traditional handwritten signaturesin many respects; properly implemented digital signatures are more difficultto forge than the handwritten type. Digital signature schemes in the senseused here are cryptographically based, and must be implemented properly tobe effective. Digital signatures can also provide non-repudiation, meaningthat the signer cannot successfully claim they did not sign a message, whilealso claiming their private key remains secret; further, some non-repudiationschemes offer a time stamp for the digital signature, so that even if theprivate key is exposed, the signature is valid nonetheless. Digitally signedmessages may be anything representable as a bit-string: examples includeelectronic mail, contracts, or a message sent via some other cryptographicprotocol.

A digital signature (not to be confused with a digital certificate) is anelectronic signature that can be used to authenticate the identity of the

sender of a message or the signer of a document, and possibly to ensure thatthe original content of the message or document that has been sent isunchanged. Digital signatures are easily transportable, cannot be imitated bysomeone else, and can be automatically time-stamped. The ability to ensurethat the original signed message arrived means that the sender cannot easilyrepudiate it later.

A digital signature can be used with any kind of message, whether it isencrypted or not, simply so that the receiver can be sure of the sender'sidentity and that the message arrived intact. A digital certificate contains thedigital signature of the certificate-issuing authority so that anyone can verifythat the certificate is real.

How It Works

Assume you were going to send the draft of a contract to your lawyer inanother town. You want to give your lawyer the assurance that it wasunchanged from what you sent and that it is really from you.

1. You copy-and-paste the contract (it's a short one) into an e-mail note.

2. Using special software, you obtain a message hash (mathematicalsummary) of the contract.

3. You then use a private key that you have previously obtained from a public-private key authority to encrypt the hash.

4. The encrypted hash becomes your digital signature of the message. (Notethat it will be different each time you send a message.)

At the other end, your lawyer receives the message.

1. To make sure it's intact and from you, your lawyer makes a hash of thereceived message.

2. Your lawyer then uses your public key to decrypt the message hash orsummary.

3. If the hashes match, the received message is valid.

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Ques3

The Domain Name System (DNS) is a hierarchical naming system built on adistributed database for computers, services, or any resource connected tothe Internet or a private network. Most importantly, it translates domainnames meaningful to humans into the numerical identifiers associated withnetworking equipment for the purpose of locating and addressing thesedevices worldwide.

An often-used analogy to explain the Domain Name System is that it servesas the phone book for the Internet by translating human-friendly computerhost names into IP addresses. For example, the domain namewww.example.com translates to the addresses 192.0.32.10 (IPv4) and2620:0:2d0:200::10 (IPv6).

The Domain Name System makes it possible to assign domain names togroups of Internet resources and users in a meaningful way, independent ofeach entity's physical location. Because of this, World Wide Web (WWW)hyperlinks and Internet contact information can remain consistent andconstant even if the current Internet routing arrangements change or theparticipant uses a mobile device. Internet domain names are easier toremember than IP addresses such as 208.77.188.166 (IPv4) or2001:db8:1f70::999:de8:7648:6e8 (IPv6). Users take advantage of this whenthey recite meaningful Uniform Resource Locators (URLs) and e-mailaddresses without having to know how the computer actually locates them.

The Domain Name System distributes the responsibility of assigning domainnames and mapping those names to IP addresses by designatingauthoritative name servers for each domain. Authoritative name servers areassigned to be responsible for their particular domains, and in turn can assignother authoritative name servers for their sub-domains. This mechanism hasmade the DNS distributed and fault tolerant and has helped avoid the needfor a single central register to be continually consulted and updated.Ingeneral, the Domain Name System also stores other types of information,such as the list of mail servers that accept email for a given Internet domain.By providing a worldwide, distributed keyword-based redirection service, theDomain Name System is an essential component of the functionality of theInternet.

A DNS sever is where the computer goes to translate a web address that youtype in into a series of numbers and goes to that address.So basically youtype www.geekstogo.com into Internet Explorer (or any other web browser, itworks in exactly the same way). The browser goes to a DNS server eitheryou've specified or it has been given. It converts geekstogo.com into a seriesof numbers, in this case 72.232.135.12 and goes there.When you specify DNSservers in the fashion you have, this is the order they're referred to whenlooking up IP addresses. Basically you go to a web site, the computer asks (inyour case) the server at 208.67.222.222 for the proper number. If this serverdoesn't give a number (for example because its overloaded with requests oroffline or generally not working) then the computer will ask the server at208.67.220.220 for the site's IP. Then it just claims there is no page tofind.You can add as many DNS servers as you like, the computer will just workits way down the list trying to find a requested site's proper address beforetiming out. A common scenario when connected to a provider is that theprovider is so busy with its user-base the DNS servers get overloaded. So youcan connect but you can't go anywhere.

Name System, or DNS, makes browsing the Web simpler and more intuitive. Itallows the tens of millions of computers connected to the Internet to find oneanother and communicate efficiently. DNS also allows individual nations toidentify and optimize their websites for local populations, according to theInternet Corporation for Assigned Names and Numbers.

Hierarchies : Domain names are grouped into a series of top-level domains orTLDs such as .com, .net, .org and .gov. In addition, every country has its ownTLD: for example, the TLD for the United States is ".us"; ".fr" representsFrance, ".in" denotes India, and so on. The TLD appears at the end of the fulldomain name.

The second-level domain contains the name of the website. For example, in"ehow.com", the second-level domain name is "ehow".The third-level domain,which appears at the beginning of some domain names, was used in the earlydays of the World Wide Web to signify that the domain was either a website(represented by ".www") or a file transfer site (".ftp"). The third-level domainis now used to signify any sub-domain, which is often just a sub-section of aparticular website.

Convenience : Without DNS, people wishing to access a particular onlineresource would have to know the IP address or would be required to look itup. The IP address is a cumbersome series of three-digit numbers separatedby dots or decimal points. The DNS system automatically converts these longnumbers into convenient domain names that humans can easily use andremember.

Optimized Service : The top-level domain often indicates the nation of originthrough a two-character abbreviation. The ability to recognized websites bycountry allows national registry operators to apply the best mix of linguisticand cultural policies for those domains, thereby optimizing websites forconvenient access by users in each nation

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Ques4

A proxy server is computer that functions as an intermediary between a webbrowser (such as Internet Explorer) and the Internet. Proxy servers helpimprove web performance by storing a copy of frequently used webpages.When a browser requests a webpage stored in the proxy server's collection(its cache), it is provided by the proxy server, which is faster than going tothe web. Proxy servers also help improve security by filtering out some webcontent and malicious software. Proxy servers are used mostly by networks inorganizations and companies. Typically, people connecting to the Internetfrom home will not use a proxy server.

The primary purpose of a proxy server is to provide a local cache, thusreducing network traffic on the WAN while providing short response times tolocal network clients. For example, an organization might serve 100 internalclients (web browsers, for example) with one http proxy server. Rarelychanging web content such as the facebook page background or theanswers.com logo can then be served from the proxy server's local storage,thus saving network burden and usage fees on the WAN connection whileproviding a fast response to the user.

Proxy servers implement one or more of the following functions:

Caching

A caching proxy server stores frequently-accessed resources (pictures,videos, or whole websites), which speeds up loading times and savesbandwidth.

Content Filtering

A content filtering proxy, used in schools, businesses, and even countries,restricts access to certain web pages and sites by using a database ofblacklisted sites or flagging websites containing certain keywords.

Circumvention

Circumventing proxies attempt to override the instructions of a content-filtering proxy in order to gain access to a blocked website.

Anonymity

Web surfing can often be tracked by inspecting visitors' IP addresses andsearch histories. Some proxy servers enable the user to hide his IP addressbehind the proxy in order to browse the web anonymously.

Eavesdropping

Just as anonymous web proxies allow for browsing anonymity, "hostile"proxies can eavesdrop on a user's web browsing.

Security

Reverse proxy servers send Internet requests through a proxy before hitting awebsite. As the traffic passes through, the proxy can encrypt the information,such as a password, before passing it onto the website.

Access control: Some proxy servers implement a logon requirement. In largeorganizations, authorized users must log on to gain access to the web. The

organization can thereby track usage to individuals.

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