March 2005 1R. Smith - University of St Thomas - Minnesota

CISC 210 - Class TodayCISC 210 - Class Today

• Going over the Exam AnswersGoing over the Exam Answers• Intro NetworkingIntro Networking

Question 1Question 1

• Assets: A, NAssets: A, N• Risks: D, E, K, MRisks: D, E, K, M• Policy: G, LPolicy: G, L

– Optional: B, H, IOptional: B, H, I

• Defenses (optional): O, B, H, JDefenses (optional): O, B, H, J• Monitor: C, F, PMonitor: C, F, P

– Optional: O, JOptional: O, J

• Recover (optional): IRecover (optional): I

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Questions 2-6Questions 2-6

• Desktop: 1 – KNOWDesktop: 1 – KNOW

• Desktop + Fingerprint Reader: 2 – KNOW, AREDesktop + Fingerprint Reader: 2 – KNOW, ARE

• ATM: 2 – HAVE, KNOWATM: 2 – HAVE, KNOW

• Web site: 1 – KNOWWeb site: 1 – KNOW

• Charlie’s Angels: 1 – ARECharlie’s Angels: 1 – ARE

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Access PermissionsAccess Permissions

• Question 7 – YESQuestion 7 – YES

• Question 8:Question 8:– Owner – Bob or TinaOwner – Bob or Tina– Group – any nameGroup – any name– Members – Bob and TinaMembers – Bob and Tina– Owner Access – RWOwner Access – RW– Group Access – RWGroup Access – RW– World Access – --World Access – --

March 2005 4R. Smith - University of St Thomas - Minnesota

Web Browser Secret KeysWeb Browser Secret Keys

• 128-bit key with 88 bits published128-bit key with 88 bits published• Question 9: 40 bits, 10Question 9: 40 bits, 101212

• Question 10Question 10– Doubles 8 times over 12 yearsDoubles 8 times over 12 years– Doubling = 1 bit, so size increases by 8 bitsDoubling = 1 bit, so size increases by 8 bits– = 48 bits= 48 bits

• Question 11Question 11– 40 bits in the browser secret + 16 bits = 56 bits in DES40 bits in the browser secret + 16 bits = 56 bits in DES

• NOT 144 bits (128 + 16)NOT 144 bits (128 + 16)– If we double 8 times over 12 years, then 16 times over 24 yearsIf we double 8 times over 12 years, then 16 times over 24 years– 1995 + 24 = 20191995 + 24 = 2019

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Question 12Question 12

• 1 bit broken in first ciphertext block1 bit broken in first ciphertext block– Xored with encrypted IV = 1 bit broken in 1Xored with encrypted IV = 1 bit broken in 1stst plaintext block plaintext block

• First ciphertext block is block encryptedFirst ciphertext block is block encrypted– Encrypted result is ALL GARBAGEEncrypted result is ALL GARBAGE– Result XORed with second ciphertext blockResult XORed with second ciphertext block– Second plaintext block = ALL GARBAGESecond plaintext block = ALL GARBAGE

• Second ciphertext block is block encryptedSecond ciphertext block is block encrypted– Ciphertext is clean -> plaintext is undamagedCiphertext is clean -> plaintext is undamaged

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Questions 13 and 14Questions 13 and 14

• Question 13Question 13– 32000 / (2 * .25) = 64,00032000 / (2 * .25) = 64,000

• Question 14Question 14– Provide inputs from the ciphertext fileProvide inputs from the ciphertext file

• Ciphertext AND NonceCiphertext AND Nonce• Create the key with the one-way hashCreate the key with the one-way hash

– MistakesMistakes• Not showing the right source for the nonceNot showing the right source for the nonce• Not showing all the functionsNot showing all the functions• Not giving all inputs to the functionsNot giving all inputs to the functions

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Networking Intro for SecurityNetworking Intro for Security

• Types of network connectionsTypes of network connections

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Types of network connectionsTypes of network connections

– Point-to-point – a raw set of wiresPoint-to-point – a raw set of wires• Connects point A to point B, and that’s allConnects point A to point B, and that’s all• Classic phone system = sets of point to point wiresClassic phone system = sets of point to point wires

– Wired broadcast – like digital cable TV signalsWired broadcast – like digital cable TV signals• Everyone on the wire hears the signalEveryone on the wire hears the signal• Classic Ethernet was like thisClassic Ethernet was like this• 10- 100- 1000-baseT uses ‘star’ hubs, switches to do this10- 100- 1000-baseT uses ‘star’ hubs, switches to do this

– Wireless broadcast – everyone hears itWireless broadcast – everyone hears it• Alohanet – the grandad of EthernetAlohanet – the grandad of Ethernet• Modern satellite TV is a digital broadcastModern satellite TV is a digital broadcast

– Directed wireless “line of sight” transmissionDirected wireless “line of sight” transmission• Classic microwave towersClassic microwave towers• Satellite – to some extentSatellite – to some extent

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Network TopologiesNetwork Topologies

• Goal is “everyone talks to everyone”Goal is “everyone talks to everyone”• Here are the ‘real’ topologiesHere are the ‘real’ topologies

– Bus or “Star Hub”Bus or “Star Hub”• Everyone links on and hears everythingEveryone links on and hears everything

– Switched StarSwitched Star• Everyone connects to everyone, linked through a switchEveryone connects to everyone, linked through a switch• Can’t eavesdrop as easilyCan’t eavesdrop as easily

– Daisy Chain or RingDaisy Chain or Ring• Like a game of ‘hot potato’ = pass messages alongLike a game of ‘hot potato’ = pass messages along• Appears in some metropolitan optical networksAppears in some metropolitan optical networks

– Distributed LinksDistributed Links• Phone system, Internet = lots of ‘hops’ as data travelsPhone system, Internet = lots of ‘hops’ as data travels

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Connection implicationsConnection implications

• Can attacker Can attacker hearhear the messages? the messages?– ““Passive” attackPassive” attack

• Can attacker Can attacker produce produce messages?messages?– ““Active” attackActive” attack

• If so, what must the attacker do to ‘hook up’?If so, what must the attacker do to ‘hook up’?– Consider each type of network connectionConsider each type of network connection

• Defense questionsDefense questions– Can we shield our messages from eavesdropping?Can we shield our messages from eavesdropping?– Can we block outsiders from joining our network?Can we block outsiders from joining our network?– Can we detect/discard traffic from outsiders?Can we detect/discard traffic from outsiders?

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Other technical nitsOther technical nits

• Digital versus analog transmissionDigital versus analog transmission– Computers don’t ‘do’ analog by themselvesComputers don’t ‘do’ analog by themselves

• Need D/A and A/D converters handle analog signalsNeed D/A and A/D converters handle analog signals– Modems – for systematic transmission over analog linesModems – for systematic transmission over analog lines

• Converts digital to analog for transmission, then back againConverts digital to analog for transmission, then back again

• Synchronous vs AsynchronousSynchronous vs Asynchronous– ““Synchronous” digital data is supposedly more efficientSynchronous” digital data is supposedly more efficient

• A bit or byte of data is sent EVERY time periodA bit or byte of data is sent EVERY time period• Whether data is available or notWhether data is available or not

– A tradition from the days of IBM mainframe ‘terminals’A tradition from the days of IBM mainframe ‘terminals’– Asynchronous is more flexibleAsynchronous is more flexible

• Start or stop according to data availabilityStart or stop according to data availability

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Local Nets and the InternetLocal Nets and the Internet

• Local nets (LANs) connect machines with a Local nets (LANs) connect machines with a single technology, and one set of reachable single technology, and one set of reachable addressesaddresses– Usually you can easily broadcast on your local netUsually you can easily broadcast on your local net– It’s a ‘wiring’ question to join your LANIt’s a ‘wiring’ question to join your LAN

• The Internet allows us to ‘hop across’ LANs to The Internet allows us to ‘hop across’ LANs to get from one computer to anotherget from one computer to another– Internet provides globally recognized addresses for computersInternet provides globally recognized addresses for computers– Internet routers send packets between LANsInternet routers send packets between LANs

• Directs them to the right LAN to get closer to the Directs them to the right LAN to get closer to the destinationdestination

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Networking and “Layers”Networking and “Layers”

• Modern networking is built in layersModern networking is built in layers– Network software is called the “protocol stack”Network software is called the “protocol stack”– Different software layers for different levels of protocolDifferent software layers for different levels of protocol

• The layersThe layers– Application layer – programs and services like Web or e-mailApplication layer – programs and services like Web or e-mail– Socket interface – between application and TCP/IPSocket interface – between application and TCP/IP– TCP/UDP – provides reliability or process addressingTCP/UDP – provides reliability or process addressing

• TCP = reliable, orderly data delivery to a specific processTCP = reliable, orderly data delivery to a specific process• UDP = unverified data delivery to a specific processUDP = unverified data delivery to a specific process

– IP – provides addressing ACROSS local networksIP – provides addressing ACROSS local networks– Link – provides addressing on a LANLink – provides addressing on a LAN

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Addressing and ConnectingAddressing and Connecting

• Modern computers connect at 4 levelsModern computers connect at 4 levels

• Physical – wireless or a wirePhysical – wireless or a wire• Node-node – connecting on a LANNode-node – connecting on a LAN• Host-host – Internet addressingHost-host – Internet addressing• Socket-socket – applications and processesSocket-socket – applications and processes

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