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Intro to Info Security

by: Alayna Veum

Intro to Info Security CS 4235

Alayna Veum

GPA 3.81

Christopher Peikert

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Christopher Peikert
Class Notes
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This 0 page Class Notes was uploaded by Alayna Veum on Monday November 2, 2015. The Class Notes belongs to CS 4235 at Georgia Institute of Technology - Main Campus taught by Christopher Peikert in Fall. Since its upload, it has received 12 views. For similar materials see /class/234028/cs-4235-georgia-institute-of-technology-main-campus in ComputerScienence at Georgia Institute of Technology - Main Campus.

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Date Created: 11/02/15
Notes 1112010 Monday November 01 2010 1017 AM Today Some insecure Internet protocols and attacks Firewall has policy about whattraffic is allowed through Possibly policies 0 N0 connections originatingoutsideare letthrough 0 Allow incomingon port 80 25 to machines 32 66 Drawbacks 0 Must control entire perimeter 0 Policy is often quotdumbquot firewall has little 39 I Can39t lookinside data it may be encrypted Hostbased firewalls Idea put decisions closerto services Strengths 0 Perimeter is more easily controlled 0 It39s easiertodo packet ANDsession inspection for individual applications Drawbacks 0 May be easiertotamperwith since it39s software 0 Apps Firewall Network maliciuu whether Remember Internet was developed in the 1960s Many protocols inthe 70s and 80s TCP sets up a handshake starts a session between two hosts A and B ClientA sends SYN TCP packet t0ServerB It says quotHey let39s synchronize Server B says quotAl right I39ll put A39s IP address in a queuequot Server B sends SYN and ACK sequence number to Client A CIientAsendsACKsequence numberl ServerD quot 1 A pushesquotquot quotquot quotta quot There39s a problem thoughwhat ifthe client never returnsthe ACK 0 SYNACK protocol says Bshould hold the connection fora few minutes timeout Another problem isa quotSYN floodquot attack client sends many SYNs no ACKs 0 Server is left holding many halfopen connections 0 In most implementations the server39s queuewas 8entries 0 Ifthe queue is ful I the serverdoesn39t accept any new attempts D Complete DoSon TCP stack Ideasto mitigate What ifthe serveronly holds 8 per IP address Doesn39t quite work since you can spoofIP addresses The main problem isthatthe server is allocatinglongterm resources atthe request ofa client The solution SYN quotcookiesquot Puttingthe burden ofstoring resources onthe client quotClientA l ServerB l Choose symmetric key Kfora MAC i Connect l SYNgt r l S MACKsrcaddrp0rt dst addrport current minute ltSYNACK ACKs 39 l Forget aboutA l ACKs1gt PostMidterm Pag e 1 Notes 10252010 Monday ctober 25 2010 1006 AIVI Today Network Security AnetworkisZcomputersthat can communicate What39suniqueaboutnetworks o ComputerswerefirstdesignedforstandaloneuseTrustassumptions often fail catastrophically Software thatl run is benign Inputstothecomputeraretrustworthy Datastored on computeris inaccessible tothe outside El Confidentialntegrity Similarlyfallaciousassumptionsfromlocalnetworkstowider areanetworks o ComputershavevaluableresourcesonthemNetworkthemselvesare valuable resources I Thenetworlethecomputer o Networksusuallyprovide I Anonymity Actions on a networkare not linkedto the actors in the realworld I Automation Nodesdowhatthey39retold I Locality Connectmachinesaroundtheworld I Dispersion Actionson networkcrossadminownership boundaries Difficulttogetcollectiveaction Howdonetworkswork o OSImodelzkeyabstraction o ExamplezfetchingawebpageH39l39l39P Layer l 7 7 l App Browser GET frontpagehtml 6 Presentation 5 Session I 4 Transport TCP Port 80 Seq 3 l Network IP Src address Dst address 2 l Link EthWiFi MACaddress 1 l Physical Signals Each chunk ofdata is quotopaquequot to the layer below 0 Thisabstractionmodularityhasbene ts I Layersthemselvesworkfaster I Easiertotroubleshootthichlayerismisbehaving I Layers can be agnosticto lowerlevelhigherlevel implementations Mixand matchwiredwifiopticalcarrierpigeon NewapplicationsSkypeVoPweb What39s good and bad about layered model PostMidterm Pag e 1


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