CPS120 Introduction to Computer Science

Lecture 2

Types of Programming Languages

• Machine language

• Procedure-oriented languages

• Object-oriented languages

• Event-driven languages

What Can a Program Do?

• A program can only instruct a computer to:– Read Input– Sequence– Calculate– Store data– Compare and branch– Iterate or Loop– Write Output

Fundamental Programming Concepts

• Assignment of values to a variable

• Iteration (Looping)– Over a set of set of statements– With respect to a logical expressions

(conditions)

• Delegation of sub-tasks to functions / procedures

The Structure Theorem

The Structure Theorem states that any algorithm can be built from three basic control structures.

• One-after-another (Sequence)• Decision-making (Selection)

– Making choices between 2 or more alternatives

• Repetition (Iteration)– Concerned with repetitive tasks (and the termination

conditions of loops)

Electronic CommunicationsCPS120 Introduction to Computer Science

E-Mail• Addresses

– Location of an individual mailbox on the Internet

– User name, @ sign, domain – no spaces

Web-based E-mail• Don’t need email client

• Popular Web-based E-mail Services– www.hotmail.com– www.email.com– mail.yahoo.com

Organization• By type:

• .com

• .edu

• .gov

• .mil

• .net

• .org

• By country• Australia - .au

• Canada - .ca

• Ireland - .ie

• Italy - .it

• Japan - .jp

• United Kingdom - .uk

Other new codes have been defined

Newest Additions to the Web

New domain names:

• .info

• .biz

• .name

• .pro

• .museum

• .coop

• .aero

E-mail Features• Address books

• Signatures

• Attachment of files– Try to keep under 50Kb– Sometimes certain types of files are screened

E-Mail Issues• Emoticons• :-)• Abbreviations

– LOL – TTFN

• Netiquette– Shouting– Flame

Viruses• An e-mail virus is a program that can disrupt the

normal operation of a computer– Display of unusual messages– Destroying files on the hard drive– Sending mail to people in your address book

• Triggered by opening files; sometimes only in preview

• Anti-Virus programs available commercially– Must be kept up-to-date

Newsgroups and Chat

Mail Groups• A mailing list is a discussion group that

uses e-mail to communicate– A list of mailing lists is at www.liszt.com

• Moderated vs. un-moderated lists• Must subscribe to participate• Two addresses

– Mailing list addresses– Administrative addresses

Newsgroups• A discussion group that allows people with

common interests to communicate with each other• USENET (User’s Network)

– All the computes that distribute newsgroup information

• Messages– Individual posts

• Threads– Messages and all replies

Addressing• First word describes the main topic

• Each additional word is separated by a dot and serves to narrow the topic

Networking Aspects• Newsreader – program that lets you read

and post online– Microsoft Outlook has a built-in reader– Gravity– Free Agent

• News server– A computer that stores newsgroup messages

Newsgroup Categoriesalt

biz

comp

misc

rec

sci

Soc

talk

• General Interest

• Business

• Computers

• Miscellaneous

• Recreation & Hobbies

• Science

• Social (culture/politics)

• Debate

• alt.fans.actors

• biz.entrepreneurs

• comp.security.misc

• misc.books.technical

• rec.food.recipes

• sci.physics

• soc.history

• talk.politics.misc

Newsgroup Etiquette• Lurk first

• Read FAQ

• Reply

• Send a private reply

Chatting• One of the most popular features on the Internet

(but no one admits to doing it)• Text-based• Multi-media

– Internet Relay Chat (IRC) channels• Need a program to participate (www.mirc.com)

• Instant messaging allows you to communicate privately with others– MSN or AOL

Networks

CPS120 Introduction to Computer Science

What Is a Network

• A network is a group of connected computers that allow people to share information and equipment

Types of Networks

• LAN (Local Area Network) connects computers within a small geographic area like a building

• WAN (Wide Area Network) connects computers across a large geographic area like a city or country (often via satellite)

• Internet: World-wide network of networks

Advantages to Networking

• Road warriors

• Eliminate “sneakernet”

• Share information

• Share equipment

Who Runs It?

• A network administrator manages the network and makes sure it runs smoothly– Often called a systems administrator or an IS

manager

Network Applications

• Electronic mail

• Groupware– Calendaring– Scheduling

• Video-conferencing– Requires sound card, speakers, mike & camera

Physical Networking

• Hubs– A hub is a device that provides a central location where

all the cables on a network come together

• NICs (Network Interface Card)– An expansion card that physically connects each

computer to the network

• Cables– Coaxial, Unshielded Twisted Pair (UTP), Shielded

Twisted Pair, Fiber-optic– Wireless

How Information Is Stored

• Client-Server:– Used for large networks

– Files are stored on a central computer and everyone who can access the network can be given access them

• Easy to create scheme to backup and protect files

– Client: a computer that can access information stored on the server

– Server: Central computer that stores files

– NetWare, UNIX, Windows NT/2000

How Information Is Stored

• Peer-to-Peer:– Used for a small number of computes (e.g. 10)– Files stored on own computers; access given to

them to others on the network– LANtastic, Windows-98, Windows-ME

How Information Is Exchanged

• Ethernet:– Most popular and least expensive solution– Each computer waits for a pause before sending

information• Like polite conversation

– Collisions between information often occur• Computers wait a moment, then resend

– Ethernet – 10 Mbps, Fast Ethernet – 100 Mbps, Gigabit Ethernet 1000 Mbps

How Information Is Exchanged

• Token-ring is a type of network where a token that collects and delivers information is passed from compute to computer– Speeds of 4 or 16 Mbps

• Asynchronous Transfer Mode (ATM) is a type of network that works by sending information in equal-sized pieces called cells– 25, 155, 622 or 2488 Mbps

– Often networks networks

Network Security

• Operating System Security– Other system software

• Firewall – specialized hardware or software package designed to protect a private computer network from unauthorized access– Think “Moat”

• User name and password– Used for authentication– Good passwords

Intranet

• Small version of the Internet in a company

• Uses familiar web-browsers and email packages

• Allows hyper-linking

• VPNs (Virtual Private Network)– End-to-end encryption– More cost efficient than private lines

Internet and WWW

Chapter 10

Internet Fundamentals

• Dates from DARPA in the 1960s• Consists of thousands of connected networks

around the world– Each organization on the Internet is responsible for

maintaining its own equipment• These organizations allow you to pass-through their nets

• Designed to provide multiple routing to bypass disabled computers

• Called cyber-space or the information superhighway

Internet Offerings

• Electronic mail (Most popular application)

• Information

• Entertainment

• Discussion Groups

• Chat

• Programs (Shareware)

• Online shopping

Connecting

• Computer

• Software

• Modem or high-speed connection

• ISP (Internet Service Provider)– Access for a fee

World Wide Web

• Part of the Internet consisting of a huge collection of documents stored on computers around the world– Web server: computer that stores and delivers

web pages– Web site: collection of web pages

• URL (Uniform Resource Locator) – unique address– HTTP, Computer, Directory, Name of Page

– Hyperlinks jump to different web pages

Browsers

• A program that lets you view and navigate information on the World Wide Web– Home Page: Web page that appears each time you start

your web browser

– Browser:• Internet Explorer

• Netscape Navigator

– Features• Bookmark

• History lists

Multimedia

• MP3 – compressed files containing music or video– WinAmp

• Streaming video – requires player– RealPlayer, QuickTime

• Enhancements– Java

– JavaScript

– ActiveX

Web Portal

• Central starting point for browsing personalized by the individual– Yahoo, Excite, Go, Lycos– Info– Free services like email, shopping, chat, games,

stock quotes and sports scores

Create & Publish Web Pages

• HyperText Mark-up Language is a computer code used to create Web pages

• There are many programs available, called visual editors which can help you create Web pages without having to learn HTML

• Publishing your pages – loaded to an addressable server

Security

CPS120

Introduction to Computer Science

Aspects of Computer Security

• A. Hardware

• B. Files

• C. Connectivity

Key Areas Addressed by Security

• Physical security – how do I keep my hardware and key files safe

• Password security – what is a good password and how do you set one

• Computer viruses – what they are and how to protect your computer

• Network security -- how to protect yourself

• Firewalls - what the can and can’t do and why they are important for always-on connections

• Backup strategies - why and how to backup your work

Physical Security

All Computers• Temperature

– If too high, components malfunction

– Components generate heat which must be removed

• Humidity – If too high: condensation and corrosion of metal parts

– If too low: static electricity (very high voltage!)

• Electric power – Irregularities: power spikes, dips, and brown-outs

– Special care during thunderstorms!

– Power failure: un-interruptible power supply (UPS)

Physical Access

• Access to the computer room– Logs of who goes in and out– Console security

• Screen passwords, etc.

• Access to the physical network• Locking laptops, protecting components on

desktops, servers, etc.• Policies• Contingency planning

Password Security

Security Principles

• Access is restricted to safeguard the computer. Use is allowed only with user code and password: – User ID:

• Like hotel room number• Gives private access to data files

– Password: • Like hotel room key

• All users must enter valid user code and password before doing anything– Combines who you are and what you know

Password Cracking• There are many software programs available now that can

guess your password if you are using words that are in the English or foreign dictionary

• When guessing passwords involves simple transformations such as:– Converting all the letters in a word to lowercase– Applying user specific information about a person to a password– Using numeric suffixes

• The number 1 is far and away the most common suffix. More than all other digits combined

– Using numeric prefixes– The number 1 is the most common prefix. The number 2 is a

distant second– 0 and 6 are rarely used as prefixes

Creating Good Passwords• In order to be useful in authentication and

authorization, a password should meet the following criteria:– Passwords must be at least six characters

– Passwords must include three of four types of characters:

– Uppercase letters

– Lowercase letters

– Numbers

– Non-alphabetic characters such as punctuation marks

• Passwords shouldn't contain personal information

Pass-phrases

• If you are serious about good password security, get in the habit of using ‘pass-phrases’. For example, it is easy enough to remember a phrase like ‘…born on the 4th of July’, but creating a password from it like bot4thoJ would create a password that meets the criteria discussed above.

Computer Viruses

Virus Definition• A computer virus is a computer program that

can infect other computer programs by modifying them in such a way as to include a copy of itself. A virus, by definition, can't exist by itself. It must infect an executable program.

– A simple virus that can make a copy of itself over and over again is relatively easy to produce. Even such a simple virus is dangerous because it will quickly use all available memory and bring the system to a halt.

Other Types of Viruses

• An e-mail virus is not any different from a regular virus; it just has a different mode of transportation ILOVEYOU"– Melissa

• Script viruses are destructive code that does its damage by executing a program on a client machine

• A macro virus is a type of computer virus that is encoded as a macro embedded in a document

Virus Software• Use of a virus checker regularly is the

best way to combat viruses– Freeware, shareware, and commercial

anti-virus programs are widely available

Combating Script Viruses• The most important thing to do is to check every

email you receive, file you download or are sent for a double file type (ie: .txt.vbs, or .html.jse, or whatever).

• Never save executable attachments from email messages to your computer and run them – (files that end with .EXE, .COM, .VBS, and .BAT are

executable on Windows computers). – Change the default on your machine to open those file

types in an editor rather than run them• "Hardening your PC"

• If you want to make your PC more secure in regard to script viruses, you may want to remove the Windows Scripting host from your machine.

Anti-Virus Software

• Anti-viral software can be set up to run automatically each time you boot up the machine or run an executable. You can also execute anti-viral software manually if you suspect you have had a problem or you have received a suspicious attachment or some sort of un-trusted media.

• There are two parts to most pieces of anti-viral software; the engine and the definitions. – The definitions change all the time. This is the part of anti-viral software

that needs to be updated constantly, because the population of viruses changes rapidly, with newly developed viruses springing up along with minor modifications of existing viruses (mutations) appearing constantly.

– The engine, on the other hand, is static and changes only at major release points. The engine is the driving force behind a virus program that checks for virus signatures on you machine and in your software.

Stay Current

• The program you use isn't as important as how often you use it and that you keep it updated with the most recent virus definitions– To be effective, antiviral software must be

current -- even two-month-old software can be dangerously outdated

Other Types of 'Malware'

• A worm is a special type of virus that can replicate itself and use memory, but cannot attach itself to other programs– 'Code Red'– Nimda

• A Trojan horse is a program that pretends to do something useful, but instead does something nefarious. – Trojans aren't infectious– Often they place executables on the drive

Combating 'Malware'

• Promptly apply all security patches to all Internet-exposed systems and replace with more secure products those that continually have vulnerabilities exposed.

Network Security

Hardening Your System

• The term "hardening" refers to the process of configuring software so as to minimize potential security risks

• Hardening security-specific applications like firewalls, intrusion detection systems, and antiviral tools involves turning on features and setting restrictive access rules

Your Security Profile

• A port is an interface on a computer to which you can connect a device– A port is an endpoint to a logical connection

– The port number identifies what type of port it is

• Personal computers have various types of ports. In this context

• A key to determining your computer’s security profile is to determine port usage

Firewalls

What is a Firewall

• A system designed to prevent unauthorized access to or from a private network

• Firewalls can be both hardware and software, or a combination of both

• Firewalls are used to prevent unauthorized Internet users from accessing private networks connected to the Internet

How Does It Work

• A firewall is analogous to a moat around a medieval castle. In essence, the moat and drawbridge represent a "choke" point for all traffic in and out

• A single point is much easier to monitor and can be closed if needed– All messages entering or leaving the intranet pass

through the firewall, which examines each message and blocks those that do not meet the specified security criteria

How Does it Work Technically?

• Firewalls act as proxy servers, by masking the address of internal machines

• Or packet filters using a "wall of code" that inspects each individual "packet" of data as it arrives at either side of the firewall

Backups

Making Backups

• Copy original files onto another medium. This is called "making a backup"– Program files:

• Copy or install the original disks to a hard disk

• Use the copy and store the originals in a safe place

– Data files:• Copy the originals to another disk or tape

• Put the backup disk or tape in a safe place

Backups for This Class

• Diskettes, Zip Disks, CD-R's:For every floppy you own, have a backup copy

• Hard disk: backup on diskettes, tapes, removable hard disk, CD-RW or networked drive

Different Types of Backups

• Different types– Full– Incremental– Differential

Full Backups

• Includes all files on your drive(s)– Advantages

• Files are easily found when needed– All of the most current information can be found on

the last backup tape

– Disadvantages• Full backups are redundant backups

• Full backups take longer to perform and can be very time consuming

Incremental Backups

• Includes files that were created or changed since the last backup

• Advantages– Incremental backups provide better use of media

– Much less data storage space required

– Less time is also required

• Disadvantages– Multiple disks or tapes are needed for restore

– You may have to search several volumes to find the file you wish to restore

Differential Backups• Includes all files that were created or

modified since last Full backup– Advantages

• Differential backups take less time• Provides more efficient restores• Maximum of two media sets to perform a full

restore– The last Full backup and the last Differential backup tape

– Disadvantages• As time goes on a longer and longer time needed for

a differential backup• The amount of data gets larger and larger each day

Backup Plans

• Backups are performed according to a schedule. For example:– Weekly: back up all files ("complete" backup);

Often done on the Friday evening– Daily: back up only files that have been

changed ("incremental" backup)• Incremental

• Differential

Contingency Plans

• A "system backup plan" is like an insurance policy: a contract with company having a computer system similar to ours or a 'hot' site– In case of computer disaster, we can use theirs