Internet usage and Security
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Commands while using FTP:
To control FTP session: ASCII, binary, cr, hash, prompt, status, user, verbose
for moving around among directories on remote machine: pwd, cd, cdup, dir, mdir, ls, mls, lcd
to move files back and forth: get, recv, put, send mget, mput
Archie-
Database for files and directories
Submit queries by archie client program or e-mail
Queries sorted by hostname then path
Provides file permission, size, date and name
Usenet
Developed ate UNIX community and circulated by UUCP initially and then NNTP
Tools for reading news:
Access to Internet host
FQDN
Newsreader
Types of Newsreader:
Line mode reader- Eg:Readnews
Full-screen reader- Eg:Vnews, tin
Left to right specification of subject increases in a newsgroup name Contd…
Categories Of newsgroup:
comp-computer related topics
misc-topics that cut across categories
news-Net news related distribution and s/w topics
rec- topics on recreational activities, art etc.
sci- topics science related
soc- social issues topics
talk- open-ended debates for groups
To introduce new Newsgroup:
Submitting a proposal
Discussion followed by voting
E-mail: the message and medium
Store-and-forward service
Mailer- program used while sending or receiving messages via Internet access provider.
Addressing non-local user:login_name@domain_name
Accessing Internet Service through E-mail:
Mailing lists and how to find them
Mail-based Bulletin boards: The Almanac Service
The Archie E-mail interface
FTP via E-mail: Ftpmail
Telnet
Network application to log in to one computer on the Internet from another
Use Internet and exchange data between the two connected computers much faster
Session requires a user ID valid on remote computer
Telnet on Internet access provider’s computer via conventional dialup.
Telnet client on home computer via protocol dialup.
Working on Telnet you need:
IP address to identify the computer to which you want to connect
Valid login name and password on computer you reached.
Other than input mode command mode is also there
Advantage of using Telnet:
When Internet access providers offer only protocol dialup
Using the Internet’s client-server applications when there’s no client program on your local computer
To get in touch with the Internet’s stand-alone applications
Web browsers support the Telnet protocol indirectly
Install a Telnet client program and configure your Web browser to start that client to work with Telnet resources from Web browsers
Internet security
Being on the Internet: the risks
Unauthorized access to the information system from the outside
“Trojan horses” and viruses sneaking in through transferring data
Using false identities
Risk- extent of the damage to be expected if an event occurs and predicted probability of its occuring
Risk analysis:
Phase 1: Defining the scope
Phase 2: Finding the risks
Phase 3: Risk assessment
Computer crime: Who does it?
Hackers from college:
Do no harm
Just want to successfully break-in and share experience
Staff:
can range from simple methods to data thefts
Intend to destroy or sabotage out of frustration
Hackers from computer underground:
Just intend to get in and out of top security sites safely
Old-fashioned criminals:
Target is finance and purchasing system since Internet crime is easy
Cybercrime: Professional Hackers
Attack points and weaknesses
Internet: faulty software design
Architecture of TCP/IP and UDP protocols
Lack of safeguards
poorly configured & administered systems
Poor service programs
Computer Organization as a risk
No focus on training for systems manager
Care on formulating security measures
Hit list of hacking methods
Sniffer attacks- These use “invisible” miniature programs smuggled in on Internet hosts to monitor data flows and retrieve passwords and system IDs
IP spoofing- attacker gives his own data packets addresses which are in the address range of the target network to overcome packet filters and proxy firewalls
Sendmail attacks- use faults in the mail server application “sendmail”
Attacks via NIS and NFS
Authentication

Core of all authentication systems is how they check a user’s identity and what rights they are cleared for
Ways of capturing password apart from guessing:
Analyzing the protocol and filtering the password
Monitoring login/passwords using TSR programs
Social hacking
Protecting “passwd” file:
Avoid “true” passwd file get into file ranges of anonymous Internet servers
Services like NIS should be deactivated
Password shadowing
Analyzing protocols and finding passwords-
Sniffer programs allow NIC to accept any data packet. Using filter and trigger functions Internet addresses and passwords can be filtered.
Password monitoring using TSR programs
Run in the background mode, constantly spying on all keyboard inputs and saving character sequences
Fishing passwords with “Trojan horses”
It boots as the user’s OS and retrieves the user ID and password
One-Time Passwords
Each time you login it is with a different password
Encryption
Encoding plain text to cipher text
Two ways of encoding:
Substitution- Caesar Cipher, Mono-alphabetic Cipher, Homophonic, Polygram & Polyalphabetic Substitution Cipher
Transposition- Rail Fence Technique, Simple Columnar Transposition Technique, Vernam Cipher, Book Cipher
Two aspects of encryption: algorithm and key
A key is an input cipher text used for one- time pad method for encryption.
Two cryptography methods based on keys:
Symmetric- same key used for encryption & decryption
Asymmetric- different keys used for encryption & decryption
Firewalls
Network components connecting an internal, private corporate network to an external, public network
Benefits of using firewall:
Concentrates risk on a single area
Monitoring and control systems installed in firewall only
Connections monitored and controlled as via firewall
Different access control systems:
Packet filters- filters data packets with specified attributes
Circuit relays-let use applications without letting things at protocol level
Application relays- let you use applications without comms links break through the firewall system at protocol level
Architecture of firewall systems:
Border routers
Border router with secure subnet
Dual home bastion hosts
Dual home bastion host with demilitarized zone (DMZ)
Cascaded dual home bastion hosts
Monitoring systems: display connection by user & service
Display when security functions are activated
Display repeated attempts to get through the firewall system
Limits of firewalls
Can’t keep out data carried inside applications and prevent the network being penetrated by viruses
Don’t offer any security against unauthorized physical attacks on an internal computer system
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