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Welcome Back StudentsApplications of Computers

Lecture-3

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Revision

Before the break, we covered databases and their applications

Binary Search Tree Network DBMS Relational DBMS E-commerce Customer concerns

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Overview

Today we look at data encryption for secret message transmission over public network

We also look at computer’s use in jobs involving multimedia components

We discuss images, video and audio data formats, compression and transmission

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Encryption and Data Security

For successful e-commerce, we must ensure that the sensitive data has been encrypted and secured

Encryption transforms the data using a “key” into a value that is meaningless in its normal form

This encrypted value can only be decrypted by authorized agency or person

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Encryption Basics

For encryption, XOR logical operation is widely used The data to be encrypted is XORed with the key XOR has the property that it can transform a binary

value into another totally different value. This encrypted value is sent instead of the original value

The recipient performs XOR of the received encrypted value with the key, restoring original value

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Class Exercise

The data to be sent is: 0111 1011 The 4-bit key is 1010 SENDER: Encrypt the data and send it to

the recipient RECIPIENT: Decrypt the data

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Encryption Keys

There are two types of encryption schemes in use

In symmetric or secret key ciphers, the encryption and decryption keys are symmetric and identical

As an example, consider this diagram then encrypt following message with your own encryption scheme

“Please transfer six million dollars into my checking account”

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Symmetric Cipher

Adapted for academic use from “Exploring The Digital Domain” by Abernethy Allen, ITP 1999

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Public Key Encryption

In symmetric secret key cipher, the key must be sent to recipient, otherwise the message cannot be decrypted

Sending the key on public network is like putting your house key in locksmith’s shop and allowing everyone to duplicate it

Alternatives are to restrict access to secret key to a few individuals

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DES

DES (Data Encryption Standard) is one example of symmetric key encryption

DES uses a 56-bit key which can be doubled in length to 112 bits

Breaking messages encrypted with DES would require a considerable amount of computing time and effort

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Asymmetric or Public Keys

Asymmetric keys give a more robust performance

The RSA algorithm works as follows:– Sender gets the public key of recipient

(available to everyone)and uses it to encrypt the message

– Receiver uses private key (only known to receiver) to decrypt the message

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Digital Signatures

Authentication is a core issue in e-commerce Authentication is to verify the source of a

document Authentication of paper documents is done with

watermarks, stamps, signatures and seals How to authenticate the electronic documents?

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Authentication

With little effort, the public-private keys can be applied in reverse to perform verification of e-documents

For example, consider this e-conversation between two persons on the internet

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Authentication

Bob--> Chuck Hi, Bob here Chuck-->Bob Prove you are Bob Bob-->Chuck Send me a random

message, I will return a digital signature (message digest encrypted using my private key)

Chuck-->Bob Random message Bob-->Chuck digital signature Chuck decrypts the message using Bob’s public key

and matches it to message digest

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Multimedia Applications

Computers have become multimedia devices with an increasing number of applications with audio, video and graphics images

We look at basics of digitizing images and other multimedia stuff

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Images

Computer Screen consists of thousands of pixels. Each pixel is intersection of a row and a column

Images can be digitized using bit-mapping Bit-mapped images contain pixel color and

intensity information for all the pixels on screen

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Images

Let us assume we want to store a bit-mapped black-and-white image to memory

Each pixel can be represented by one bit that can be zero (black) or one (white)

Determine the number of bytes needed to store the image if the screen resolution is 1024 X 768

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Images

Normally, the images stored in the computer contain much more information

TRUE-COLOR images contains 24-bit information for each pixel.

This translates into 8 bits for each of the RGB colors that are emitted in the CRT

Each color’s effect can be enhanced by increasing its 8-bit value

How many colors are possible?

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How Many Colors?

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Animation

Animation is a visual effect that can show things moving by rapidly changing displayed frames on screen

Animated GIF’s are easy to construct and shareware GIFConstruction Set can be used to build a series of frames that are displayed in rapid succession

Morphing is a visual technique that transforms one image into another.

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Audio

In order to digitize analog signals such as sound, we need an ADC (analog to digital converter)

Normal conversation can be recorded in 8-bit values but for hi-fi sound, we will need 16-bit samples

Audio CD’s are recorded at the rate of 44.1KHz, the higher the sampling rate, the better is the reproduction

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Sampling Sound

Adapted for academic use from “Exploring The Digital Domain” by Abernethy Allen, ITP 1999

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Editing Sound

Once sound is digitized, we can edit it using digital signal processing techniques

Adding an echo effect involves inserting amplitudes equal to a percentage of some selected values at a slightly later time

Changing amplitudes involves clipping, or re-adjusting values outside the range to the max value

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Digital Video

The analog video already consists of frames that are in a time sequence

The digitization involves capturing each frame and sampling its pixels

Raw digital video has a lot of digital still images

Digital video can be edited, it is randomly accessible and scalable

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Compressing the Video

In its raw form, digital video delivery will push the computer to its limits

With 640X480 Frame, 24-bits color info per pixel, and 30 frames per second, we are talking about 216,000 Kbits per second

Mix with it audio rate of 1378 Kbits per second (stereo 16 bits per channel 44,100 samples per second) and we get total 26.5 MB per second

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Compressing the Video

Therefore, it is necessary to compress the video at source and decompress it on displaying

This will also be good for our networks as we mostly have 10Mbps LAN connections

MPEG is the compression standard for video and it is based partly on JPEG

MPEG-1 has 150KB/s and MPEG-2 has 1.2 MB/s data rate

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Class Work Wednesday Nov29

For the class on Nov29th, please follow the link number 5 (“Ethics in Computing”) under useful links on the course homepage (http://www.cs.fredonia.edu/~zubairi/f2k/cs120.html).

Select one of the topics and go to “References” Read the references and then solve the

worksheet alone or in a group of 2 to 3 students