Download Exploring Decimal, Binary, and Email in Arithmetic & Internet and more Quizzes Information Technology in PDF only on Docsity!
base 10
number
2183 is a base 10 number, 3 is a 3X10^0 = 3 8 is a 8X10^ = 80 1is a 1X10^2 = 100 2 is a 2X10^3 = 200 b10, base10, bin (2^), baseHex TERM 2
binary number
DEFINITION 2 10^0,1,2,3,4,5,6,7,8,9 and 2^0,1 11010111 = 2^0, 2^1.2^7 starting right to left 1 = 1 10 = 2 11 =3 100 = 4 101 = 5 110 = 4+2 = 6 111 = 7 1000 = 8 1001 = 9 1010 = 10 -these match base10 numbers TERM 3
hexadecimal
DEFINITION 3 In mathematics and computer science, hexadecimal (also base , or hex) is a positional numeral system with a radix, or base, of 16. It uses sixteen distinct symbols, most often the symbols 0-9 to represent values zero to nine, and A, B, C, D, E, F (or alternatively a to f) to represent values ten to fifteen. has 16 digits, goes from 0-f, hex^0,1,2,3,4,5,6,7,8,9,a so 0 = 0 = 0, 1 = 1 = 1, 2 = 10 = 2. 10 = 1010 = a 10^ 9, 10, 11, 12, 14, 14, 15 2^1001, 1010, 1011, 1100, 1101, 1110, 1111 hex^9, a, b, c, d, e, f 9b to base10 is 16^0, 16^3 right to left b4 10110100 = 8 bits da 11011010 = 8 bits TERM 4
Arithmetic in multiple
bases
DEFINITION 4 decimal arithmetic: what we do in everyday life, ten digits of 0-9, columns represent increasing powers of 10 increasing right to left TERM 5
Disclaimer
DEFINITION 5 note: in principle, decimal arithmetic is not special in any way. Base 10 is mathematically no better than any other base. Worse than many from practical POV sociologically we all grew up learning base 10 and decimal arithmetic is built into the English language, still we have to speak English, spoken ten means base 10
Binary Arithmetic
what almost all computers do, two digits of 0 and 1, columns represent increasing powers of 2 increasing right to left TERM 7
Conventions
DEFINITION 7 decimal should have the dec subscript when theres a serious chance of confusion, binary should have the bin subscript, unless there are exactly 8 bits often leading with 0 - hexadecimal should have the hex subscript TERM 8
Top level domain names
DEFINITION 8 rightmost element describes hosts organization. Original seven aka gTLD: .mil > military, .edu > educational, .org > organization, .com > commercial, .int > international, .gov > government, .net > network, -Country specific ccTLE: .us > United States, .de > Germany, .uk > United Kindom -new gTLD names: .aero, .coop, .jobs, .tv TERM 9
Nslookup (net server look
up)
DEFINITION 9 -Nslookup asks DNS server for IP of host name, reverse lookup asks for host name of IP address TERM 10
Who govern internet?
DEFINITION 10 no one, internet has no head or chairman, individual networks have their authorities, at commercial access providers e.g. aol.com, its the usual corporate structure
Internationally
-no body outside US is happy with US domination of ICANN but they cant figure out how to wrest control away from US government, theyre generally pleased with how things are working -in the US some people see internet as international but are afraid to put control of the house of cards into the hands of UN bureaucrats TERM 17
Where do IP addresses come from?
DEFINITION 17 -technical limitations: finite number of IP addresses: 2^23 = 4.3 billion, cant all be used though because of tie to routing, IPv6 intended in part to allow for more addresses -IANA manages the process TERM 18
New website:
DEFINITION 18 -request is made to ISP provider -begin to build website - render fee to ISP -ISP assigns IP to site -ISP assigns IP to site - ISP informs local domain server of new IP -payment made from bottom through all hands TERM 19
The application layer: clients and servers (the
first application) Application layer
DEFINITION 19 -the internet exists because of the usefulness of the applications that use it -its wild success has been based on its versatility-new applications can use the lower layers without modifying them- (domain, TCP, IP, link) TERM 20
Clients and servers
DEFINITION 20 -a TCP connection is symmetric either side can transmit and the other receives -IP is connectionless -On the other hand, the functionality of the computers is generally NOT symmetric or not at equal levels -one side requests that the other perform assorted functions -clients request services from servers terms are imbedded in net jargon/slang
Clients and servers
examples
-clients: assorted software, outlook, browser, assorted workstations, IP telephones -Servers: printer in closet, Oak, web server, file servers, call manager TERM 22
Always on?
DEFINITION 22 -comer says servers must be always on and always connected -not necessarily only if the service they provide is to be available 24/ TERM 23
New applications
DEFINITION 23 -created every day, not really daily but the potential is there every day -can be private, limited use, TCP/IP is standard. Anyone can write/acquire software to create TCP connection, after that you can send anything you want over the connection. No one else knows, cares TERM 24
Some real, new applications
DEFINITION 24 -world wide web WWW does not = internet -first there was hypertext, text with links -initial implementation was for entire document to reside on single computer -in 1990, Tim Berners Lee, physicist at CERN created a hypertext variant in which the links could point to pages on other computers anywhere on the already existing internet -internet: a set of group or set of networks utilized for transferring information between host devices -www: the hypermedia transfer system used for text, images, video, etc. TERM 25
VoIP
DEFINITION 25 -VoIP is voice over internet protocol -if the internet is fast enough, if your computer can digitize audio fast enough, if someone elses computer can interpret digital audio into actual sounds, you can talk to them -to replace a phone: addressing issues, connection to legacy public switched telephone network, reliability (including 911), audio quality
Addressing
-individually assigned mailboxes, messages can be added, exclusive access by owner network manager -mailbox assigned unique address -2 parts > 2nd part IDs computer (domain name), 1st part IDs mailbox -different servers can use same mailbox name -2 part division permits exchange of email -most mailboxes use mnemonic names > tony_mele@, tigerlily@, not_really_here@, 281650@ TERM 32
Client server paradigm
DEFINITION 32 -email modeled after office memo > one to one or one to many TERM 33
Format
DEFINITION 33 -header > defined by keywords with colons like To: From: Cc: subject: and body -Bcc: blind carbon copy, persons receiving cc do not know who others receiving cc are -body > the message TERM 34
Some mail protocols
DEFINITION 34 -SMTP, POP, IMAP, MIMES > different email applications TERM 35
In the beginning
DEFINITION 35 -mainframe hosts with users at terminals -solutions: SMTP or simple mail transfer protocol
SMTP > simple mail transport protocol
-text based > non text material must be encoded into text format, IETF has protocols for this -no security > users can do their own encryption, PGP or pretty good privacy -uses DNS to get IP address of HugeCorp mail server -uses TCP transport, sender establishes TCP connection with recipient using PORT25 -everything of course uses IP and LAN/Link, message exchange through TCP connection TERM 37
Not part of the protocol
DEFINITION 37 -SMTP doesnt specify everything about how email might work just how the hosts communicate -not specified for instance: internal structure of software or data storage, behavior if distant machine is unavailable, some systems wait and try again -spam blocking/ virus checking, server might delete messages automatically -user interface, this is typical of internet standards TERM 38
What about PCs?
DEFINITION 38 -PCs get online in a variety of ways: LANs, broadband modem access e.g. cable modems, Dial up, WiFi -there is no expectation that: PC is online 24/7, PC has a permanent reliable IP address, PC has a DNS domain name, and anyone knows their MAC address -can use SMTP to send mail, they do, cant use SMTP to receive mail TERM 39
Retrieving your email POP
DEFINITION 39 -post office protocol, version 3 aka POP3, currently in use, used for downloading email from server to PC client -expectation: server storage is temporary: client will download all messages and save on PC -passe now: security is after thought, although okay, not so good for shared mailboxes, transaction oriented, must download entire message before seeing any of it -IMAP or internet message access protocol, expected operation: server storage is common -improvement in many ways: connection oriented operation, including connect to multiple accounts, shared mailboxes, download part of message: to/from/subj,, built in support for encrypted login and transport -MIME or multipurpose internet mail extensions, standard email limited to ASCII text code, MIME allows: binary or graphics converted to another code (hexadecimal), no single coding standard, new codes come as upgrades, code info. in header (MIME: 1.0) TERM 40
POP limitations
DEFINITION 40 -must download whole mailbox: on the road, on a trip, hotel, etc. cant organize mail on server, cant have different folders on server, cant partially check email contents before downloading (header)
Data communication
-TCP port20, designed to maximize throughput, must define: file type, data structure, transmission code TERM 47
Not part of the protocol
DEFINITION 47 -FTP doesnt specify everything about how clients might work, just how the servers and clients communicate, not specified for instance: internal structure of software, user interface, this is typical of internet standards TERM 48
security is like performance
DEFINITION 48 -security is an attribute of the whole system including all of it components, it isnt local to a single place, it must be every where -you can buy products to enhance security but there is no magic bullet -security is very hard to assess unlike performance -absence of evidence of insecurity is not evidence of security TERM 49
Appropriate security
DEFINITION 49 -specific security measures are effective against specific threats, great network security wont help if a trusted employee is dishonest -real world security means anticipating threats and blocking them - the cost of security measures must be judged against the value of whats being secured, it is worth million s to keep the world from knowing your gpa grades? -enhanced security often means reduced ease of use -users will evade onerous security measures TERM 50
Security at the mall
DEFINITION 50 -we have: outer perimeter doors, inner doors, chains through sleeves, camera, strolling security guards
Vulnerability
-a specific weakness in a system that can be used to damage the system or data stored on it -for instance: unchecked buffer, outlook naively executing scripts to forward them - due to poor design, lax programming practices and or bug, philosophically not the same TERM 52
Sample vulnerabilities 1-fancy email
DEFINITION 52 -java scripts in email, part of html code in email used to make attractive dynamic email msgs., email packages at one time executed html/java in msg by default TERM 53
Sample vulnerabilities 2-unchecked buffer
DEFINITION 53 -buffers are storage area within programs, fixed size, contents of one buffer often copied to another, what happens when you copy contents of 1500 byte buffer in 500 byte buffer? -should: quit copy at 500 bytes or give error message, sometimes: copy all 1500 bytes overwriting innocent memory containing other data or programs, when program then executes TERM 54
Exploit
DEFINITION 54 -software to take advantage of a vulnerability -for instance a program to actually write malicious code into an unchecked buffer is an exploit -use of exploits requires much less expertise than writing them script kiddies are low end hackers who use exploits they didnt write and dont understand TERM 55
Patch
DEFINITION 55 -small piece of software designed to repair larger previously installed programs, commonly designed to repair or eliminate vulnerabilities -announcement of patch isnt the end of the game, patches must be distributed and then run on vulnerable machines
Hardware firewall
-its a device, its a router with specialized software that analyzes traffic and attempts to pass only good traffic, located at vulnerable point(s) between corporate and internet TERM 62
Remember TCP:
DEFINITION 62 -is connection oriented full duplex stream service with flow control and error control, uses port numbers where many are standard, has complicated startup and shutdown: eleven states with prescribed transitions implied memory on part of each end TERM 63
Firewall strategies I- packet
filtering
DEFINITION 63 -look at header of each packet independently, pass/dont pass based on: direction, i.e. inbound or outbound, IP source and/or destination address, TCP source and/or destination port # -list of rules, checked one at a time until one firs, packets from outside to inside port 80 or to inside ports > 1023 are dropped by firewall, aka stateless or memory-less firewalls TERM 64
Firewall strategies
II
DEFINITION 64 -examine packet contents: track TCP connections, allow only packets based on appropriate applications to pass -proxy server aka application gateway, proxy in between examining packets at application level -make FTP transfers in incoming only; log all information transfers for analysis TERM 65
Software firewall
DEFINITION 65 -modify the protocol stack software, typically packet filtering with added application limits: unwilling to provide services to unexpected applications, unwilling to deal with external connection attempts, blocks outside IP address query, recommendation: turn on windows firewall
Malware-malicious software
-malware: software thats up to no good, payload: code that actually does damage -payloads range from: annoying to destructive, mindless to subtle, destructive to subversive - but the payload must be delivered, malware classified by propagation type TERM 67
Virus
DEFINITION 67 -code attaches itself to another file, doesnt exist as standalone file, anti-virus software inspects files for signs of infection, OU has deal with McAfee, recommendation: install it! Use it! Keep it updated! TERM 68
Worms
DEFINITION 68 -standalone Malware programs that propagate themselves, commonly as email attachment sent by infected computer, lucky recipient must execute the worm: helpful office productivity tools sometimes do it for you -worms often called viruses in media, casual conversation TERM 69
What to do about worms
DEFINITION 69 -keep them away from your computer, email scanning on your server before they ever enter IMAP box -IMAP give yourself a chance to delete it this TERM 70
Lines of defense against worms
DEFINITION 70 -keep your supplications up to date, outlook service pack 2 cured many key vulnerabilities, scanning software must have up to date data, keep your paranoia level high when in doubt click delete or call sender, recommendation: use Microsoft update! -switch to Linux? Fans say its more secure, everyone agrees: Microsoft is the common target because of large number of windows systems in use
