Class Note for CMPSCI 591 at UMass(2)
Class Note for CMPSCI 591 at UMass(2)
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Date Created: 02/06/15
Chapter 8 Network Security Chapter goals El understand principles of network security 0 cryptography and its manyuses beyond quotconfidentialityquot O authentication 0 message integrity 0 key distribution El security in practice 0 firewalls 0 security in application transport network link layers 8 Network Security 84 Chapter 8 roadmap 81 What is network security 82 Principles of cryptography 83 Authentication 84 Integrity 85 Key Distribution and certification 86 Access control firewalls 87 Attacks and counter measures 88 Security in many layers 8 Network Security 872 What is ne rwor39k secur39i ry Confiden riali ry only sender in rended receiver should unders rand message con ren rs o sender encryp rs message 0 receiver decryp rs message Au rhen rica rion sender receiver wan r To confirm iden ri ry of each o rher Message InTegri ry sender receiver wan r To ensure message no r alTered in Transi r or af rerwards wi rhou r deTecTion Access and Availabili ry services musT be accessible and available To users a Nemmk Secumv 373 Friends and enemies Alice Bob Trudy El well known in ne rwork securiTy world El Bob Alice lovers wan r To communicaTe quotsecurelyquot El Trudy inTruder may in rercep r dele re add messages Alice Bob ch annel dafacon139rol messages secure sender secure receiver da ra d T a Nemmk Secumv m Who might Bob Alice be El well rea 39fe Bobs and Alices El Web browserserver for electronic transactions eg online purchases El online banking clientserver El DNS servers El routers exchanging routing table updates El other examples 8 Network Security 875 There are bad guys and girls out there 9 What can a bad guyquot do a lot 0 eavesdrap intercept messages 0 actively insem messages into connection 0 I39mpequotsana an can fake spoof source address in packet or any field in packet O hoboMg take overquot ongoing connection by removing sender or receiver inserting himself in place 0 dem39a afsequotvca prevent service from being used by others eg by overloading resources more an f1s a7 equot 8 Network Security 876 Chap ier39 8 r39oadmap 81 What is network security 82 Principles of cryp i39ogr aphy 83 Au i39hen rica i39ion 84 In i39egr i i39y 85 Key Dis i39r39ibu rion and ceri ifica i ion 86 Access control firewalls 87 A H39acks and counter measures 88 Security in many layers a Nemmk Sammy 377 The lanquaqe of cr39yp ioqr39aphy EAlice39s 3 Bob39s KA encryption K decryption ke Y i key Pluimexf encrypTIarI cipheri exi decrypTIon plaimext algorithm algorithm a 4 symmeTric key crypTo sender receiver keys I39denrb a public key crypTo encrypTion key pubIr decrypTion key secrer priva re a Nemmk Sammy H Symme r ric key crypfog raphy substitution cipher substituting one thing for another 0 monoaiphabetie cipher substitute one letter for another plaintext abcdefghij klmnopqrstuvwxyz ciphertext mnbvcxzasdfghj klpo iuytrewq Plaintext bob ciphertext nkn i love you alice s gktc wky mgst 9 How hard To break This simple cipher i brufe force how hard i o i her x Newark Secumv x v Symme r ric key crypfog raphy plaintext decryption message m algorithm symmefric ke crypfa Bob and Alice share know same symmefric key AVE El eg key is knowing subsfifufion pa ern in mono alphabefic subsfifufion cipher El 9 how do Bob and Alice agree on key value x Newark Secumv x tn Symmetric key crypto DES DES Data Encryption Standard El US encryption standard NIST 1993 El 56bit symmetric key 64bit plaintext input El How secure is DES O DES Challenge 56bitkeyencrypted phrase Strong cryptography makes the world a safer placequot decrypted brute force in 4 months 0 no known backdoor decryption approach El making DES more secure 0 use three keys sequentially 3DES on each datum 0 use cipherblock chaining a Nemm Secuv v 541 M by input l bbwkcy pevule i Symmetric key crypto DES DES operation u s 1 I 7 A bil l MANN A initial permutation ASMKQ 16 Identical rounds of function application each using different 48 bits of key i fInal permutation i Q AEbiiKl H7 g Permu e Abilou39piv a Nemm seem m AES Advanced EncrypTion STandard El new Nov 2001 symme rrickey NIST s randard replacing DES El processes da ra in 128 bi r blocks El 128 192 or 256 bi r keys El bru re force decryp rion rry each key Taking 1 sec on DES rakes 149 Trillion years for AES 8 Network Security 843 Public Key CrypToqraphy symmefn39c key cryp ro publo key cryp roqraphy Pl CI requires sender El radically different receiver know shared approach Diffie secre r key Hellman76 RSA78 CI Q how To agree on key CI sender receiver do in firs r place mn share secre r key particularly if never fquot CI publo encryp rion key me known To a CI pn39vafe decryp rion key known only To receiver 8 Network Security 844 Public key crxp rogr39aghx K Bob39spublic B key K Bob39s privafe B key l Si ciherTexT decryption Elainfexf Km algorithm message B m KgKm pluinTexT message m E Nemmk Secumy 845 Public key encr yp rion alqor i rhms Requirements need and K39B such The KBKBm m given public key Kg i r should be impossible Tocompu re priva l e key KB RSA Rivesf Shamir Adelson algorithm 8 Nemmk Secumy 845 RSA Choosinq keys 1 Choose Two large prime numbers p q eg 1024 bi rs each 2 Compu re n pq 2quot 074 3 Choose 5 wi rh eltn rha r has no common fac rors wi rh z e zare rela rively primequot 4 Choose dsuch rha r ed J is exac rly divisible by z in o rher words 50 mod 2 J 5 PubI39c key is 075 Prvafe key is nd Hi We KB KB 8 Network Security 847 RSA Encryption decryp rion 0 Given ne and no as compu red above 1 To encryp r bi r pa r rern m compu re c m5 mod n ie remainder when me is divided by n 2 To decryp r received bi r pa r rern c compu re m cdmod n ie remainder when c is divided by n Magic e 039 happens m m mod n mod n C 8 Network Security 848 RSA example Bob chooses p5 qZ Then n35 224 55 so 5 zrelaTively prime 29 so ed J exachy divisible by 2 f m m me C memod n encryp 39 I 12 1524832 17 decrypT 9 Ed m cdmod n leTTer 17 481968572106750915091411825223071697 12 8 Network Security 849 Why is ThaT m memod ndmod n Useful number Theory resulT If pq prime and n Then pq Xymod n XymOd 0 Hal 1 mod n memod I7dmod n megmod n med mod pJqJ mod n using number Theory resulT above m mod n since we chose ea To be divisible by pJqJ wiTh remainder 1 39 I71 8 NelworkSecurily 8720 10 RSA anofher imporfanf properfy The following proper ry will be very useful la rer K39BKm m KK39Bm 2 2 use public key use priva re key firs r followed firs r followed by priva re key by public key Resuf is ve same 8 Network Security 8721 Chap rer 8 roadmap 81 Wha r is ne rwork securi ry 82 Principles of cryp rography 83 Au rhen rica rion 84 In regri ry 85 Key Dis rribu rion and cer rifica rion 86 Access con rrol firewalls 87 A r racks and coun rer measures 88 Securi ry in many layers 8 Network Security 8722 11 Au rhen rica rion Goal Bob wan rs Alice 1390 quotprovequot her iden ri ry To him ProTocol agl0 Alice says I am Alicequot 1 I am Alicequot gt Failure scenario a Nemmk Secumy 8723 Au rhen rica rion Goal Bob wan rs Alice 1390 quotprovequot her iden ri ry To him ProTocol agl0 Alice says I am Alicequot 39 in a ne rwork a 94 Bob can no r see Alice so Trudy simply V39 I am Nice declares herself To be Alice a Nemmk Secumy arm 12 Au rhen rica rion ano rher Try ProTocol aEZO Alice says I am Alicequot in an IP packe r con raining her source IP address Alice39s IP address r FaIlure scenarIo I am Alicequot a Nemmk Secumy 8725 Au rhen rica rion ano rher Tr ProTocol aEZO Alice says I am Alicequot in an IP packe r con raining her source IP address Trudy can crea re a packe r V AI u I quot I spoofngquot IP al rsess I 0quotquot Allce AlIce39s address a Nemmk Secumy 8726 13 Au rhen rica rion ano rher er ProTocol ap30 Alice says I am Alicequot and sends her secre r password To quotprovequot i r Alice39s Alice39s IPuddr password ImAl39 4 Alice39s IP uddr OK Failure scenario a Nemmk Secumy 8727 Au rhen rica rion ano rher Tr ProTocol ap30 Alice says I am Alicequot and sends her secre r password To quotprovequot i r Alice39s Alice39s T IPaddr password m Alicequot I playback affack Trudy Alice39s 3i records Alice39s pocket I addquot 0 and later la 5 it back To Bab P y Alice39s Alice39s i IPuddr password ImAl39ce a Nemmk Secumy 8728 14 Au rhen rica rion ye r ano rher rr39v ProTocol ap31 Alice says I am Alicequot and sends her encrypfedsecre r password To quotprovequot i r Alice39s encrypted IPuddr password ImAl39 Alice39s Failure scenario IP addr a Nemmk Secumy 8729 Au rhen rica rion ano rher Tr ProTocol ap31 Alice says I am Alicequot and sends her encrypfedsecre r password To quotprovequot i r Alice39s encryptedu IPaddr password quotAl39 record and Alice39s OK I 4 playback IPuddr sTill works Alice39s encrypted IPuddr password ImAl39ce a Nemmk Secumy Eran Au rhenficafion ye r anofher TEX Goal avoid playback affack Nance number R used only once naI39ferme 2240 To prove Alice live Bob sends Alice nonce R Alice must refurn R encryp139ed wifh shared secre139 key I am Alicequot R Alice is live and KLamp only Alice knows key to encrypt nonce so it must Failures drawbacks be Allcrz x mm Secumv x n Au rhenficafion a950 ap40 requires shared symmefric key D can we aufheni39icafe using public key Techniques ap50 use nonce public key crypfography I am Alicequot 4 RgtC Eobcom pines 39 KAKAR R Wgt and knows only Alice nmdm W ubm could have the private y P z key that encrypted l2 suci that K K 01 i2 x mm Secumv x 32 16 ap50 securi ry hole Man woman in The middle aTTack Trudy poses as Alice To Bob and as Bob To Alice I am Alice M K R W T KA Trudy 92139s KTL m K K m 90quot sendslrlfgglli m K39K no encrypfed with A A Alice39s public key a NeMukaecumy 3733 ap50 securi ry hole Man woman in The middle aTTack Trudy poses as Alice To Bob and as Bob To Alice 4 I y 4 V W Difficul r To deTecT El Bob receives every rhing Tha r Alice sends and vice versa eg so Bob Alice can meeT one week laTer and recall conversaTion El problem is Tha r Trudy receives all messages as well a Nemmk Secumy 8730 17 Chapter 8 roadmap 81 What is network security 82 Principles of cryptography 83 Authentication 84 Message integrity 85 Key Distribution and certification 86 Access control firewalls 87 Attacks and counter measures 88 Security in many layers 8 Network Security 8735 Digital Signatures Cryptographic technique analogous to hand written signatures EI sender Bob digitally signs document establishing he is document ownercreator CI verifiable nonforgeable recipient Alice can prove to someone that Bob and no one else including Alice must have signed document 8 Network Security 8736 18 DigiTal SignaTures Simple digiTal signaTure for message m CI Bob signs in by encrypTing wiTh his privaTe key Kg creaTing quotsignedquot message Krm Bob39s message m a Kl Eob39s PrivaTe K m 3 Dear Alice Bob s message Oh howl have missed youthink ofyou all the PUbllc m Signed time bah blah blah enCF39YPTIOH SnCWpteCl With Bob algoriThm his private key 8 Network Security 8737 DiqiTal SiqnaTures more CI Suppose Alice receives msg m digiTal signaTure K m CI Alice verifies m signed by Bob by applying Bob39s public key K To Kgm Then checks KK m in CI If KK m m whoever signed in musT have used Bob39s privaTe key Alice Thus verifies ThaT J Bob signed in J No one else signed in J Bob signed in and noT m39 NonrepudiaTion Alice can Take m and signaTure K m To courT and prove ThaT Bob signed in 8 Network Security 8738 19 Message Digesfs quotquot9quotquot H Hash mesjage Function Compu ra rionally expensive ro publickeyencr yp r long messages 50 5 fixedleng rh 05Y39 Hash func rion pr oper fies focompu re digi ral D mam404 fmger Pr m r g produces fixedsize msg 3 apply hash func rlon H digeer fingerprin r ro m ge r fixed size d f message digest Hm El given message Iges x compu ra rlonally infeasible To find m such rha r x Hm 8 Network Security 8739 Infer nef check3um poor39 cr ypfo hash funcfion Inferne r checksum has some pr oper fies of hash func rion produces fixed leng rh diges r 16bi r sum of message is manyfoone Bu r given message wi rh given hash value if is easy To find ano rher message wi rh same hash value message ASCII forma r message ASCII forma r IOUl 494F5531 IOUg 494F55 009 30302E39 001 30302E 9BOB 3942D242 9BOB 3942D242 B2 c1 D2 AC differem messages 32 c1 D2 AC buf iden rical checksums 8 Network Security 840 20 Diqifal siqnafure siqned messaqe diqesT Alice verifies signa rure and Bob sends digifally signed infegrify of digifally signed message message large H H h messa e 1 as T d m g funcTIon 1 riggrzlg K Hm Bob39s a d39939ml large l private gt Slgnamre messa e I key K39 encryp r m g Eff a dIgITal B Puklc quotLquot Signa rur e v eY K d encrypted H Hash B BCWPT msg digest funcTIon K39Hm l B i 8 Network Securlty 81H Hash FuncTion Alqor39iThms CI MD5 hash func rion widely used RFC 1321 O compu res 128bi r message diges r in 4s rep process 0 arbi rrary128bi r s rring x appears difficul r ro cons rruc r msg m whose MD5 hash is equal m x CI SHAl is also used 0 US s randard NIST FIPS PUB 1801 0 160bi r message diges r 8 Network Securlty 842 21 Chapter 8 roadmap 81 What is network security 82 Principles of cryptography 83 Authentication 84 Integrity 85 Key distribution and certification 86 Access control firewalls 87 Attacks and counter measures 88 Security in many layers 8 Network Security 843 Trusted Intermediaries Svmmetric key problem Public key problem CI How do two entities CI When Alice obtains establish shared secret Bob39s public key from key over network web site email solu on diskette how does she know it is Bob39s public CI trusted key distribution key of Trudys center KDC acting as intermediary between 5 lU l39l0n1 entities CI trusted certification authority CA 8 Network Security 844 22 Key Distribution Cen ier39 KDC CI Alice Bob need shared symme rr ic key CI KDC server shares differenf secr39e139 key wi rh each regis rer ed user39 many users CI Alice Bob know own symme rr39ic keys KAKDC KBKDC for communica ring wifh KDC E Netwurk Security 845 Key Distribution Cen ier39 KDC 039 How does KDC allow Bob Alice To defermine shared symme rr39ic secr39e139 key To communica re wifh each ofher KDC R11 KBKDCAVR1 Bob knows To use R1 To Alel communica ie wiTh Alice KBKDC Alice and Bob communicafe using R1 as session key for shared symme rr ic encr39yp rion E Netwurk Security 846 23 Cer l39ifica i39ion Au l39hori l39ies El CerTificaTion auThoriTy CA binds public key To parTicular enTiTy E El E person rouTer regisTers iTs public key wiTh CA 0 E provides proof of idenfifyquot1 o CA 0 CA creafes cerfificafe binding E To ifs public key 0 cerfificafe confaining E39s public key digifally signed by CA CA says this is E39s public keyquot Bob39s digital public signature K key KB EM P B b Privg cerfificafe for o s identifying 39 7 key Bob s public key information signed by CA a NeIWuik SEEUVW mi Cer l39ifica i39ion Au l39hori l39ies El When Alice wanTs Bob39s public key 0 geTs Bob39s cerTificaTe Bob or elsewhere 0 apply CA39s public key To Bob39s cerTificaTe geT Bob39s public key digital KB signature gt decrypt A a NeIWuik SEEUVW ma 24 Cer l39ifica i39ion Au l39hori l39ies El CerTificaTion auThoriTy CA binds public key To parTicular enTiTy E El E person rouTer regisTers iTs public key wiTh CA 0 E provides proof of idenfifyquot1 o CA 0 CA creafes cerfificafe binding E To ifs public key 0 cerfificafe confaining E39s public key digifally signed by CA CA says this is E39s public keyquot Bob39s digital public signature K key KB EM P B b Privg cerfificafe for o s identifying 39 7 key Bob s public key information signed by CA a NeIWuik SEEUVW mi Cer l39ifica i39ion Au l39hori l39ies El When Alice wanTs Bob39s public key 0 geTs Bob39s cerTificaTe Bob or elsewhere 0 apply CA39s public key To Bob39s cerTificaTe geT Bob39s public key digital KB signature gt decrypt A a NeIWuik SEEUVW ma 24 A certificate contains Serial number uni ue to issuer CI info aboutincluding algorithm and key valu itse not shown info about isquot EditA Certification Authority 7 Netscape KNEE C er f f C 016 This Certi mle belongs to This Certi cate was issued by ciass 1 Public Primary Ceru canon Class 1 Public Primary Certi cation Authonty Authority Issuer VeriSigrl Inc VeriSign Inc us us Serial number nucnaA7rsorumpEmacs4rE22Acaz72AAsi g Val Id doles This Ceni mle is 39 on Sun Jan 23 1996 to me Aiig in 2025 Certi cate Fingerp lt 39 39 I 97scitscastesismeiisiccisiaseaeaisz EI digita This certi cate belongs to a Certifying Authority 7 s nature r Accept unis Certi cate Aud mnty for Certifying network sites 47 Accept this Certi cate Authority for Certifying email users issUer r Accept unis Certi cate Aud imity for certifying sortiiiare developers r Warn before sending data to sites certi ed by this authority OK Cancel 8 Network Security 849 Chapter 8 roadmap 81 What is network security 82 Principles of cryptography 83 Authentication 84 Integrity 85 Key Distribution and certification 86 Access control firewalls 87 Attacks and counter measures 88 Security in many layers 8 Network Security 860 25 Firewalls irewall isola res organiza rion39s in rernal ne r from larger In rerne r allowing some packe rs To pass blocking o rhers adminisTered public ne rwork In rerne r firewall 8 Network Security 8751 Firewalls Why preven r denial of service a r racks O SYN flooding a r racker es rablishes many bogus TCP connec rions no resources lef r for quotrealquot connec rions preven r illegal modifica rionaccess of in rernal da ra O eg a r racker replaces CIA39s homepage wi rh some rhing else allow only au rhorized access ro inside ne rwork se r of au rhen rica red usershos rs rwo Types of firewalls O applica rionlevel o packe rfil rering 8 Network Security 8752 26 Should arriving packe r be allowed in Deparfing packe r le r ouf PackeT FilTer39ing CI in rernal ne rwork connec red ro In rerne r via rou rer firewall CI rou rer fil rers packe rbypacke r decision ro forwarddrop packe r based on 0 source IP address des rina rion IP address 0 TCPUDP source and des139ina139ion por139 numbers 0 ICMP message Type O TCP SYN and ACK bi139s 8 Network Security 8753 Packe i Filfering CI Example 1 block incoming and ou rgoing da ragrams wi rh IP pro rocol field 17 and wi rh ei rher source or des r por r 23 0 All incoming and ou rgoing UDP flows and relne r connec rions are blocked CI Example 2 Block inbound TCP segmen rs wi rh ACKO O Preven rs ex rernal clien rs from making TCP connec rions wi rh in rernal clien rs bu r allows in rernal clien rs ro connec r ro ou rside 8 Network Security 8754 27 Application gateways gmewaymmm host te net session hosttogateway telnet session CI Filters packets on application data as well as on IPTCPUDP fields CI Example allow select internal users to telnet outside 1 Require all telnet users to telnet through gateway 2 For authorized users gateway sets up telnet connection to dest host Gateway relays data between 2 connections 3 Router filter blocks all telnet connections not originating from gateway 8 Network Security 8755 Limitations of firewalls and qateways CI IP spoofing router CI filters often use all or can39t know if data nothing policy for UDP quotWallyquot 50m fmm CI tradeoff degree of Cla39med 5 r39ce communication with El if multiple app s need outside world level of special treatment each security has 0Wquot ClPP 9 leW0Y CI many highly protected CI client software must sites still suffer from know how to contact attacks gateway o eg must set IP address of proxy in Web browser 8 Network Security 8756 28 Chapter 8 roadmap 81 What is network security 82 Principles of cryptography 83 Authentication 84 Integrity 85 Key Distribution and certification 86 Access control firewalls 87 Attacks and counter measures 88 Security in many layers 8 Network Security 8757 Internet security threats Mapping 0 before attacking case the Jointquot find out what services are implemented on network 0 Use ping to determine what hosts have addresses on network 0 Portscanning try to establish TCP connection to each port in sequence see what happens 0 nmap httpwwwinsecureorgnmap mapper network exploration and security auditingquot Countermeasures 8 Network Security 8758 29 InTerneT securiTy ThreaTs Mapping coun iermeasures 0 record Traffic en rering ne rwork 0 look for suspicious ac rivi ry IP addresses por rs being scanned sequen rially 8 Network Security 8759 InTerneT securiTy ThreaTs Packe r sniffing O broadcas r media 0 promiscuous NIC reads all packe rs passing by O can read all unencryp red da ra eg passwords O 69 C sniffs B39s packe rs A gc I I B Coun rermeasures 8 Network Security 8760 30 Infernef securify Threafs Packef sniffinq coun rermeasures 0 all hos rs in organiza rion run sof rware rha r checks periodically if hos r inferface in promiscuous mode 0 one hos r per segmen r of broadcas r media swi rched E rherne r a r hub A QC I I Q 1 B 8 Network Security 8761 Infernef securify Threafs IP Spoofing O can genera re quotrawquot IP packe rs direc rly from applica rion puffing any value in ro IP source address field 0 receiver can39f Tell if source is spoofed O eg C pre rends To be B Coun rermeasures 8 Network Security 8762 31 InTerneT securiTy ThreaTs IP Spoofinq inqress fil rerinq O rou rers should no r forward ou rgoing packe rs wi rh invalid source addresses eg da ragram source address no r in rou rer s ne rwork O grea r bu r ingress fil rering can no r be manda red for all ne rworks 8 Network Securlty 8763 InTerneT securiTy ThreaTs Denial of service lDOS O flood of maliciously genera red packe rs quotswampquot receiver 0 Dis rribu red DOS DDOS mul riple coordina red sources swamp receiver 0 eg C and remo re hos r SYNaffack A A B Coun rermeasures SYN 8 Network Securlty 8764 32 Infernef securify Threafs Denial of service DOS counfermeasures O fil rer ou r flooded packe rs eg SYN before reaching hos r Throw ou r good wi rh bad 0 fraceback ro source of floods mos r likely an innocen r compromised machine A SYN 8 Network Security 8765 Chap rer 8 roadmap 81 Who is ne rwork securi ry 82 Principles of cryp l39ography 83 Aufhen rica rion 84 Infegri ry 85 Key Dis rribu rion and cer rifica rion 86 Access confrol firewalls 87 Affacks and counfer measures 88 Securi ry in many layers 881 Secure email 882 Secure socke rs 883 IPsec 884 Securi ry in 80211 8 Network Security 8766 33 Secure email a Alice wants to send confidential e rnail m to Bob KE Alice El generates random symmefrcprivate key K5 El encrypts message with K5 for efficiency El also encrypts K5 with Bob39s public key El sends both K5m and KBK5 to Bob 8 Nelwuvksecumv arm Secure email a Alice wants to send confidential e rnail m to Bob Bob El uses his private key to decrypt and recover K5 El uses K5 to decrypt K5m to recover m a Nelwuvksecumv area 34 Secure email continued Alice wan rs To provide sender au rhen rica rion message inTegri ry mg g K E Kit KHm KAHm Hm m b H K 1 l r3 Cojare Lg m H39 Hm m Alice digi rally signs message sends bo rh message in The clear and digi ral signa rure a Nelwuvksecumv area Secure email continued Alice wan rs To provide secrecy sender auThen rica rion message inTegriTy as H KRC 0400 B Alice uses Three keys her priva re key Bob39s public key newly crea red symmeTric key a Nelwuvksecumv mu 35 PreTTy qood privacy PGP Inferne r email encryp rion scheme defacfo sfandard A P6P signed message CI uses symme rric key cryp rography public key cryp rography hash funcfion and digi ral signa rure as described CI provides secrecy sender aufhen rica rion in regri ry CI inven139or Phil Zimmerman was Targef of 3year federal invesfigafion BEGIN PGP SIGNED MESSAGE Hash SHA1 BobMy husband is out of town tonightPasslonately yours Alice BEGIN PGP SIGNATURE Version PGP 50 Charset noconv thJRHhGJthglZEpJ108gE4VB3qu hFEVZP9t6n7G6m5Gw2 END PGP SIGNATURE 8 Network Security 8771 Secure sockeTs layer 55L CI Transpor r layer securi ry To any TCP based app using SSL services CI used be rween Web browsers servers for ecommerce sh r rp CI securi ry services 0 server au rhenficafion O dafa encryp rion O clien r au rhenficafion opfional CI server au rhen rica rion O SSLenabled browser includes public keys for rrus red CAs 0 Browser reques rs server cer rifica re issued by rrus red CA 0 Browser uses CA39s public key To ex rracf server39s public key from cer rifica re CI check your browser39s securi ry menu To see i rs rrus red CAs 8 Network Security 8772 36 55L continued Encryp red SSL session CI Browser genera res symmefn39c sessmn key encryp rs i r wi rh server39s public key sends encryp red key To server CI Using priva re key server decryp rs session key CI Browser server know session key 0 All dafa sen139 in ro TCP socke r by clien r or server encrypfed wi139h session key CI SSL basis of IETF Transpor r Layer Securi ry TLS CI SSL can be used for nonWeb applica rions eg IMAP CI Clien r au rhen rica rion can be done wi rh clien r cer rifica res 8 Network Security 8773 IPsec NeTwork Layer SecuriTy CI Ne rworklayer secrecy o sending hos r encrypts rhe dafa in IP da ragram O TCP and UDP segmen rs ICMP and SNMP messages CI Ne rworklayer au rhenficafion O desfinafion hos139 can au rhen rica re source IP address CI Two principle profocols O au rhenficafion header AH profocol O encapsula rion securi ry payload ESP profocol CI For bo139h AH and ESP source desfinafion handshake O creafe nefworklayer logical channel called a securi ry associafion SA CI Each SA unidirec rional CI Uniquely defermined by O securi ry pro rocol AH or ESP 0 source IP address 0 32bi1 connec rion ID 8 Network Security 8774 37 AuThenTicaTion Header AH ProTocol CI provides source auThenTicaTion daTa inTegriTy no confidenTialiTy CI AH header inserTed beTween IP header daTa field CI proTocoI field 51 CI inTermediaTe rouTers process daTagrams as usual IP header AH header AH header includes CI connecTion idenTifier CI auThenTicaTion daTa source signed message digesT calculaTed over original IP daTagram CI nexT header field specifies Type of daTa eg TCP UDP ICMP daTa eg TCP UDP segmenT 8 Network Security 8775 ESP ProTocoI CI provides secrecy hosT auThenTicaTion daTa inTegriTy CI daTa ESP Trailer encrypTed CI ESP auThenTicaTion field is similar To AH auThenTicaTion field CI ProTocol 50 CI nexT header field is in ESP Trailer 4 auThenTicaTed gt llt encrypTed gt IP header I TCPUDP segmenT ESP ESP Trailer auThenT 8 Network Security 8776 38 IEEE 80211 securiTy CI Wardn39whg drive around Bay area see wha r 80211 ne rworks available 0 More Than 9000 accessible from public roadways O 85 use no encryp rionau rhen rica rion O packe rsniffing and various a r racks easy CI Securing 80211 0 encryp rion au rhen rica rion O firs r a r remp r a r 80211 securi ry Wired Equivalen r Privacy WEP a failure 0 curren r a r remp r 80211i 8 Network Security 8777 Wired EquivalemL Privacy WEP CI au rhen rica rion as in pro rocol 0040 O hos r reques rs au rhen rica rion from access poin r 0 access poin r sends 128 bi r nonce O hos r encryp rs nonce using shared symme rric key 0 access poin r decryp rs nonce au rhen rica res hos r CI no key dis rribu rion mechanism CI au rhen rica rion knowing The shared key is enough 8 Network Security 8778 39 WEP daTa encrypfion CI Hos rAP share 40 bi r symme rr ic key semi permanen r CI Hos r appends 24bi r ini rializa rion vec ror IV To cr ea re 64 bi r key CI 64 bi r key used To genera re s rr eam of keys kiIV CI kiIV used To encr yp r i rh by re di in frame ci di XOR k3quot CI IV and encr yp red by res ci sen r in frame 8 Network Secu ty 8779 80211 WEP encrypTion IV L per frame Ks 40bit key sequence generator 80211 heada WEPencxypted data plus CRC secret I for given Ks IV ymm Ln39 5 e C li w lfzw lfzw lwa liNHxvH kINHw plainlext aa 9 frame data gtd d2 d3 plus CRC V V V C 92 0 CN om ow Senderside WEP encr yp rion d ckc CI39C4 i i V V V 8 Network Secu ty 8780 40 Breakinq 80211 WEP encryption Security hole CI 24bit IV one IV per frame gt IV39s eventually reused CI IV transmitted in plaintext gt IV reuse detected El Attack 0 Trudy causes Alice to encrypt known plaintext d1 d2 d3 d4 O Trudy sees ci di XOR kiIV O Trudy knows ci di so can compute kiIV O Trudy knows encrypting key sequence k1 0 Next time IV is used Trudy can decrypt 8 Network Security 8781 IV kzIV kSIV 80211i improved security El numerous stronger forms of encryption possible El provides key distribution El uses authentication server separate from access point 8 Network Security 8782 41 80211i four phases of operation 5 STA AP atcess point AS i client station Authentication W server Discovery of security capabilities I quott STA and AS mutually authenticate together generate Master Key MK AP servers as pass throughquot STA derives Pairwise Master AS dames Key PMK same PMK sends to AP 0 STA AP use PMK to derive Temporal Key TK used for message enCFYPtionr integrity 8 Network Security 8783 EAP extensible authentication protocol El EAP endend client mobile to authentication server protocol El EAP sent over separate links 0 mobiletoAP EAP over LAN 0 AP to authentication server RADIUS over UDP 8 Network Security 8784 42 Ne rwork Securi ry Summary Basic Techniques O cryp rography symme rric and public 0 au rhen rica rion 0 message in regri ry 0 key dis rribu rion used in many differen r securi39ry scenarios 0 secure email 0 secure Transpor r 55L 0 IP sec 0 80211 8 Network Security 8785 43
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