By: Akhil KaushikAssistant professor, CSE Deptt

Email stands for Electronic Mail

Email is very quicker than snail mail

It is basically an informal mail formats most popular over the internet

Ex: Yahoo, Gmail, Rediff, Hotmail, etc

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As Email is an informal method of communication, a lot of abbreviations & slangs are used

Ex: LOL = Lots Of Laughter IMHO = In My Humble Opinion BRB = Be Right Back BTW = By The Way

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Smiley Meaning Smiley Meaning:- ) I’m happy =):- ) Uncle Sam:- ( I’m sad ;- ) I’m winking: - ( o ) I’m yelling : + ) Big nose:- )) Double chin :- {) Mustache8 - ) Wears Glass C : -) Large brain

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Sending a message to many people was inconvenient

Message had no internal structure

Sender never knew if a mail was delivered

Forwarding emails was not easy

Hard to create & send mails containing a mixture of text, drawings, facsimile & voice

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Mailboxes: to store & manage incoming email Mailing List : a list of email addresses Carbon copies: cc Blind carbon copies: bcc High-priority emails Encrypted emails Alternative recipient if original sender is not

available Ability to read boss’s email if he is away

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Email normally consists of:1. User Agent: which allow people to read and

send email- Local programs, interface b/w user & email

system

2. Message Transfer Agent: which move the message from source to destination - Daemons, runs at the background

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Composition: process of creating emails

Transfer: moving emails from sender to receiver, also establish connection

Reporting: tell the sender what hap to email

Displaying: incoming emails so users can read it

Disposit ion: what user does after receiving email

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1. Internet Message Access Protocol (IMAP):It is a standard protocol for accessing email from local server. (Port no-143)

It is a client/server based protocol in which email is received and held for us by the mail server

We don’t need to transfer files on local pc from mail server every time

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2. Post Office Protocol (POP):POP provides a simple, standardized

way for users to access mailboxes and download messages to their computers (Port no-110)

In POP, all the messages will be downloaded to the local pc from the mail server

Thus after messages have been downloaded, internet connection can be terminated

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3. Simple Mail Transfer Protocol (SMTP):SMTP is used by Mail Transfer

Agent(MTA) to deliver our email to recipient’s mail server.

(Port no-25)

SMTP is used only for sending emails, not for receiving them

SMTP also works on the client server basis

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WWW is an architectural framework for accessing documents which are spread out over a no. of machines over internet

It a web of pages of information which is spread around the world

People have become aware of power of internet thru’ WWW

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It began in 1989 at CERN, the European center for nuclear research

It was designed to get collaboration of scientists from across the globe

It provides info to user on every subject It is basically a client server architecture The web pages are written in HTML or Java It also supports hypermedia i.e. hypertext pages

with audio, video or animation

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WWW is a collection of standard protocols or instructions, sent back & forth over internet to gain access to information

Internet is a network of networks – a more physical entity

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Client looks at web as vast world wide collection of documents called pages

Links: Each page may contain links or pointers to related pages anywhere in world

Hypertext: Pages which point to other pages

Browser: Interface used for viewing pages. It fetches requested page and displays them

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Every website has a server process

It is listening to port 80 on which incoming clients (browsers) are connected

Once connection is established, client sends a request and server replies for that

The protocol used for defining legal request and replies in HTTP

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URL has 3 parts:1. Name of protocol (ex: html)2. Name of machine where page is located3. Name of file containing page

Ex: http://wwww4.org/www/project.html http-name of protocol

wwww4.org – name of machine www/project.html – name of file

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Browser determine the URL Browser asks DNS for IP address of URL Browser establishes a TCP connection to port 80

on m/c with the resolved IP address Browser then sends a command for file The specified m/c sends the requested file TCP connection is released Browser displays all text in the file Browser establishes a new TCP connection to

port 80 to fetch and display every images

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Multimedia means combination of 2 or more continuous media

Media components maybe:1. Text2. Images or Graphics3. Animation4. Sound5. Video

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Multimedia applications are classified into two types:

1. Based on timing considerations (Delay Sensitive)

2. Based on data loss tolerance (Loss Tolerant)

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Multimedia applications are categorized into three classes:

1. Streaming stored audio/ video: Ex- Stored audio songs, famous lectures, etc

2. Streaming l ive audio/ video: Ex- Internet radio, Cricket match broadcast

3. Interactive audio/ video: Ex- Internet teleconferencing and internet telephony

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Expectations of multimedia from internet are:-

1. Real time characteristics2. High bandwidth3. Multicasting support4. Error characteristics of medium5. Security6. Mobility7. Session individually

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“Searching the internet requires part ski l ls, part luck & l i t t le bit of art ”

Search engine is a software program that searches for sites based on words that you designate as search terms

Search engines look thru’ their own database of info to find what you are looking for

Search engines don’t search the entire web page, thus they make overlook the info

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Search engines automatically create web site listings by using spiders that crawl “web pages”, index their info and optimally follows that site’s links to other pages

Spiders return to already crawled websites looking for updates or changes

Ex: Google, Altavista, Yahoo, AOL, MSN, etc

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It is a search tool that sends user requests to several other search engines and/or databases and aggregates the result into a single list or displays them according to their source

It enable users to enter search criteria once & access several search engines simultaneously

It has a virtual database to compile the result

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E-com stands for electronic commerce

E-com refers to all commerce transactions conducted over the internet

E-com includes online banking, investing, bill paying, buying & selling online

Ex: e-bay, paying phone bill by credit card

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E-com grew b/w 1993 & 2000 and influenced the mainstream business

To a customer, most popular use of e-com is showing online catalogue, selecting items online & paying it electronically i.e. retail purchase

E-com become feasible when browsers included a security feature for transactions

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Credit cards are convenient for making large purchases, but they incur overhead as user have to enter credit card details

Many groups have proposed an alternative known as digital money or digital cash, which is electronically equivalent of cash that people carry with them to make small purchases & have less overhead

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An easy way to understand digital cash is in form of debit card

A person begins with electronic visit to bank to authorize a withdrawal from their bank account and place the money in digital wallet

Bank returns the wallet, which users store on their pc and specify them to make electronic payment

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Whenever user sends data online, there are 2 possibilities:

1. Automated security: It requires encryption i.e. browser automatically encrypts the message before sending it

2. Warning: If the browser doesn’t have specified secure transfer, it issues a warning. Then, it depends on user to send data or not

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The most widely used technology is Secure Socket Layer

When the browser encrypts info, process is entirely hidden from the user

A user must look at security icon displayed by browser (picture of padlock either locked or unlocked) to check if encryption is used

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Here, 2 different keys are used for encryption & decryption

Before encryption, browser must obtain app. Encryption key of server and must verify authenticity of both server & key

All steps are automatically done by the browser w/o bothering the user

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It is a mechanism for authentication

It allows a receiver to know who sent a given electronic document in the same way as conventional signature

It is created by encrypting info about document using the sender’s private key

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Digital signature is different from digit ized signature, which is merely a scanned version of conventional signature

Another difference b/w digital signature & digitized signature is that digital signature can’t be duplicated

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It refers to the structured transmission of data b/w organizations by electronic means

It is used to transfer electronic documents from one pc to another, i.e. from one trading partner to another trading partner

It is more than emails and is normally not used for monetary transactions

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EDI implies a sequence of strictly formatted messages between two parties

In EDI, the usual processing of received messages is by computer only

Human intervention in the processing of a received message is typically intended only for error conditions, for quality review, and for special situations

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As electronic data & financial data can be crucial for a company, security is a major aspect for network

Organizations face a lot of threat to security of their info on the n/w, like:

1. Data may be stolen, misused or altered2. Attack on hardware 3. Crash the systems, etc

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Confidential i ty : Data is kept private

Authenticity: Verifying the identity of communicating party

Authority: Data only for authorized users

Integrity: Data is not altered

Availabil i ty: Data is available when required

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a) Physical Security Threatb) Software Security Threatc) Inconsistent Usage Threat (Passwords)d) Denial of service attacke) Virus, worms & Trojan horsesf) Data diddling & data destructiong) Unauthorized Access

- Hacking- Shoulder surfing- Spoofing

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Cryptography word is derived from the Greek word kruptos, meaning hidden

The art and science of keeping messages secure by altering or transforming them

It provides privacy, authorization & authentication

It avoids eavesdropping & data diddling

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Plaintext - Text that is in readable form Cipher text - Results from plaintext by applying

the encryption key Encryption - Process of converting plain text into

cipher text. Decryption - Process of converting cipher text

back to plain text. Key - Rules used to convert a plain text into

cipher text.

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Also known as “Private Key Encryption”

In this cryptography, the same key is used for encryption & decryption

Ex: 1. DES (Data Encryption Standard), 2. AES (Advanced Encryption Standard)

The prevalent issue here is the distribution of the secret key to the receiver

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Also known as “Public Key Encryption”.

In this cryptography, different keys are used for encryption & decryption at both ends

Example: 1. RSA (Rivest Shamir Adleman) 2. Diffie-Hellman Algorithm

The primary concern here is the complexity of the encryption & decryption process

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Firewall is a software/ hardware which enforces an access control policy b/w an internal n/w in an organization & internet

It can also be used b/w 2 parts of same internal n/w

A firewall blocks some traffic & permits some, based on policy specified

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It can’t protect against attacks that don’t go thru’ firewall

It can’t protect against traitors or idiots inside the n/w

It can’t protect against bad things being allowed thru’ them. Ex: Trojan horse use IRC protocol

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Application/ Proxy Gateways: First firewall

Considered most secure

Slowest of all

They run a special s/w called “proxy server”, that runs on Application layer of OSI model

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Packet Filtering: Here, routers have ACLs turned on Every data packet must pass thru’ firewall and

access lists

Circuits Gateways: Least used & least secured firewall as it do not

check data in the packet It used to make LAN invisible behind it

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Stateful packet Inspection: It checks contents of packet to know type of

communication More rigorous in packet inspections

Internet Connection Firewall: ICF is used by Windows XP It means ports on firewall are checked It prevents hackers to from scanning the pc

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