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Computer Network Security

by: Stanford Cummings DDS

Computer Network Security ECPE 178

Stanford Cummings DDS
GPA 3.84


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This 47 page Class Notes was uploaded by Stanford Cummings DDS on Monday October 26, 2015. The Class Notes belongs to ECPE 178 at University of the Pacific taught by Staff in Fall. Since its upload, it has received 30 views. For similar materials see /class/229911/ecpe-178-university-of-the-pacific in ELECTRICAL AND COMPUTER ENGINEERING at University of the Pacific.

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Date Created: 10/26/15
Secure Communications the Internet WHY USE THE INTERNET The Internet offers Virtually universal worldwide coverage Access to anywhere from anywhere stationary or mobile Ease of use ease of E V bg 6sgggscnmw trai rm 7 V nlv Ruez FidoNel Con mdlvltl39 Cheap access i39na lly S39eVn39t p ersons i39I nis to b er Was rec1 of that m essage 1 st maehihesi i Iquot must be 7 With users 039 n SECURE COMMUNICATIONS Over the Internet T39O ensure the 39CONFIDENTIALIY of data we use TO 39ensure the of dzata we uise To the source of data use TO AI the identity network uSer s use 39DIGITAL CERTIFICATES Today all browsers Netscape IE come equipped With SSL Secure Sockets Layer Which establishes encrypted channels for passing private information 39su ch as credit rca39rd gtnumbiers to E commerce sites such as is a computers at remote lO39cVati ons vira39 the Internet not via private leased quotlines the way WideArea Networks 1 r been since 160 quot th39eir traf c to ensure that their communication s secret encryption schemes tci39overed39 in this talk users to encryted email to each other is 5 In the 5th Century BC the Greeks used 39a military cry ptographic d eVice called a Scytalequot The scy tale con sisteAd of a staff a strip leather or message written the strip in columns stjaff the two carried the mesfs39aige This technique Chraraeter H Ti a 39 7 cm W W 11m m WW 3169 ma W115 Wu 5 Ami maze m int5313 1 wig1amp9 52 W 311M rm W Gibggg WM 319 339 m Dag g q 31 GEE21 m wm W 533 3151 Crzm a ass a MWEQ cipher disk for its emblem curily Agency chose a gh www g CDT g m wampu f go EaZEJ EnyTQ GEQ The National Security Agency chose cipher disk for its rlnblem T acg mm 11 maggg 39e I Icw It Modern 1 ey cryptographic schemes rely on 3 main concepts quot Hp 39 39 f shuf ing of characters 9 a 4 haract eys with oth ri characters a 11th it 511 1 39 39 ENCRYPTION 39 r DECRTPTICIN quot quot PLAIHTEXT CIPHEFITEXT CIPHERTEXT PLnIHTEXT I Iew It Good schemes use a 128 bit key giving taker 1 Q t o ill a 39 atl ajst 19 Q 7 5017 the is 10110 years If you h utim39es t SEligFlE I KE I D E CR fF39TI O H EHCR I F TION 7 7 CIF39HEFITEXT CIF HEFITEXT PLAINTEXT F39 LAI TE KT DES Data Encryption Standard Private key Encrypts using a series of substitutions and With 39a 5 6 bit iorldWide39 sfta39n dard for more than ye ars Has a history of controversy later help interference longer considered secure for highly sensitive applications 39 39 Federal has prop 0sed Algorithmic St anidard 39as 39a replacement 39 DES 77quotquot 7 9 W m al Permutation C C C C C 64 bit 231 I llartext Ove rvi W 1teration perm mm a a a r 1 la nus I el39t shi I39l s lt13 PE ru 1 tinnicuntractiun 7 quot Permuttd Choice 2 I 43 dunc Moire s hn x I L Other Popular Symmetric Encryption Schemes 3D ES IDEA IPS ec 395 1 l g u 9 m In the seacallus paidquot Inky scum the Wheryisast ngofmdombitsg thatist hesmsizeusis tha massage To encrypt the plaintoxt message we morally XOR it with the key To decrypt tha amentext We merely XOR it again with the key 1111 0 0 l 1 l l l l l 01101111 01100101 i Jae in ASCII billale lPlaintext lI Zermf I10 10 1 ll 1 I 10 1 ll 10 10 1 10 1 lt a string of randoln bits I ip 11w ext 1111 MAM WM Mm 11019111 lt39 iegxu winging s yin 1 fE i EI Ef i g i 395 id ii f hniefs Eliny ji l ilili e ei Human tam1m 0111 it 1 f 39 Iiegn ll l ll l 01011010 10110010 lt hand carried to the receiver Plaintextz 101001011 011131111 ll l l i quotJO 3quot in ALS CH binary il k F WM t mtg tgg 5y o ot y g m EQLW M10311 magma gm m mm m m m m W W nm o W 132 6 m m gncc WE WW ing gq mg 9321 1th m w 161 mm 6mm cqmmmci gm agg mica m gm am a cgmgmi E93 7515 m m 319153 gw m 13538 M 3 1 lt Mg m arms E 6W2 mQEI Gt t l 6m CQL ET W 6W m 5233 W mm g m Lil DEEQ EQEEM JSJQA gt 331 W gig E i gigalg eg i 5mm e gram 335me m wig m m m TE 33 cm 3435 ili l fi li la mm mm 22CVamp 3 1 mm mm m gt egt I Altit l It atf 10100110 11110110 01010010 axe1111201 Iii 13391 3 14 01 paymnza puult gt 01001101 01011010 10110101 9151 sacqt su sumsD 19131195 9111 Io11 119542331 gt 101511 I 39I 39II a 1110011 1W1m11 113 Hammomratn 0 mums OMZI 311110 HOX 01 gt 11101017 Inforrao IIIoOIIII mac11911513 sayq town1 Jo Blunt Is a gt 01001101 01011010 10110101 L42651 ALIquottn 11 atr gt 10100110 11110110 01010010 ncanrpztct I IOVV II Worlgs 1 BOB39S compllter generates a public key pair When one it doesn39t matter which Ire is used to encrth a message 39 the ether message 39 2 gives a pfone L his keys called the 5 Z P39a39me 39quotj v t6 keeps b his ether 39 called the 4 sends gegg mallS 7 1 Z39LZTEJS her eiph efteXt to 3 encrypt quot1 7 7 5 decrypts the i 4 17 i 5 ciphertext using 1 1a if 1 s A Rivest Shamir Ad leman is th e most e n algorithm it c Dif e He l lman aIIIOSWS to a session key 39 Alngl39it39Ehlm is the U Sx stan dzard public algQrithm The The with f39 eff tijjv39j 391 3125 339 is the necessary mathematical relationship between39 the 7 i t f 39 quot and 3 i f i f a i quot quot This rielati dnship us from using just ol We do With symmetricA private cryto39graphye The39refore to igeft the ile zel of security provided by 13 1 g5 1 key secret key size we 11 1ust use a 1 f key 10 times l Onger Illsng 2 key public cryptoggrap39hy So are 2 p ossible keys the c39ryptanalyst39 need try July aout J of them Public Key 2 key Cryptography OK there are 21 24 possible keys but the cryptanalyst need try only about 2128 of them So then as With l key cryptography he is still left With 340000000000000000000000000000000000000 possible keys However use of stlch a large key 1024 bits slows the requisite number crunching and makes 2 key cryptography Therefore public key cryptography is generally used only to send the secret session key in 1 key private key cryptography Pretty Good Privacy PGP gives you secure pseudo anonyInous message service via your usual email service Alice creates a public key pair and gives Bob her public key Bob creates a random session key and l key encrypts his email With it Bob 2 key encrypts the session key With Alice s public key Bob sends to Alice both the encrypted email and the encrypted session key Alice receives Bob s email and reverses the process retrieving the original text E nclvpted Text gt l gt H Enciypted SeSion Key T 1 lt S E39Si ALICE S Key pueLe KEY Encrypted Text clear Text E L Se iun Key Encrypted ALlclas egiun K3 DRIVATE KEY Real World Use of 1 Key2 Key Cryptography Again 2 key cryptography is used primarily to istribute 56cret sessiOn that are then used With stand ardz old cryptogrlap39hy it a vm il itary venue is but also deal with th e issuequot of tautl39zentication WhijClI We heref 39 17 litary Applica a 2a I L A A hit mm m a 3 a W L g 33 rmac a g abica mm Riggs w 311 mg Sam M 13an Elai il roamvg gtmm Excavg 4i What x my 53 mmmf mtam mwmmk y 83g 1 83 mc m t a Isa wmwm g bcaymm w mm39 WWQQW 9quot 39 71 r 7 Q A Military Appliczlytio IE1 W ycmm km W thatgg 39 23137 1 V 3114quot 739x39i v1i Zn 39 imamga mg The Man in the Middle attack works like this I NTE RN ET I NTE RN ET The Man in the Middle attack works like this encrypts her messages public key then INTE RN ET INTE RN ET nor is any the SECURE COMMUNICATIONS Over the Internet T39O ensure the 39CONFIDENTIALIY of data we use TO 39ensure the of dzata we uise To the source of me ssages we use TO AI the identity network uSer s use 39DIGITAL CERTIFICATES Emums using at 1key and Zkey cryptography Ensures data integ t 9023 message digasts Authenticatcs message seams using digital signatures Amhenricatas network user samr identities using digital wai catcs For any given message text graphic etc a com puter program 1 comutes the 1 i 7 2 appends it to the end orquot the mesSageg receives the ial jso eomut es I does a 39 quothash 39739quot 901 In39essa39ger its c ornpu39tjed Is 4 39 verifies the is authentic 7 ijtr has not changed since its creation Yes x an in mid dle meSSage thrienr create a T I 1 We39 that n39ext39 D Mm ALICE MESSAGE ENCRYPTED SIGNED DIGEST I39u39ID MESSAGE 1 Ic o mpute s a me ssa gie Edi ge39st of message 2 Softwarei th en the using quotS L39 3 W 39 this encrypted been to the origrnal message the me ssfag39e is then can sidered Ws ggmea by ALICE j 7 L I39 397 39 ss decrypts g j 1 7 4 g 1 7 quot r39ei trievlzng of ALICEIS 39mferss age Then 39S its of the Orrigi7nal rmessagge 33 P RIUATE KEY f If BOB39s is identical to D mi ALICE39S g MESSAGE ENCRYPTED SIGNED DIGEST l39u39lD MESSAGE thing 1quot The alt Ife39 3 t 3 2 sent the mer39sj Sag 39 quot7 quot 39 39 Furthermorer cannot later c1 she Alice gains did SeIl39d the C r V quot 32 r ms mgg V s 39f7 i 2 7 quot 7 Them IL decry b the nme gsag lasing h g 7i9 22am ttfmcem 2 pr lt lteltdl 333 he a dl aquves amuthcemft ia 5g ftlhlc mE39Ssag s 34 To AUTHENTICATE the identity of network users we use DIGITAL CERTIFICATES M ost servers rconsider a correct I72 5 1 and I quot39quotI L th at the client is Who she claims to be IIOWe Ver can the client e sure that the 39s39erver is it 39clraims to be i a to authenticate the server befOrjer passin g on to it se39nsitive information Such as credit niumber s Note however that Digital Certificates can just as easily rused to39 authenticate a client to a 39s erver H W applications eg browsers use if f quot7 39 To AUTHENTICATE the identity Of network users we use DIGITAL CERTIFICATES fj a is like a driver39s license It id39entifies its 139 text A Cer tifieate Atlthority CA issu es the AIL quot 9 in elea r r certificate after verifying thequot cOntainedr in it Sigrn s digital signature to the Cer tificate before issuing it t39o lits normally a server person or est of the The digital signature is an encrypted m e ssage dig certificate the encryption being dene us ing the A39s Intended purpose ltAIIgt I Intermediate Certi cation Authorities I Trusted Root Lru u cuu Authorities Trusted Publ lt gt Issued To Issued By Expiretid Friendly Name Thewte Server CA UTN USERFirst Hardw UTN UsERFirst N I er gn Curlurn UBI iSigl l Commercial 5 12004 rti icate intended purposes Here is erisign s certificate It was Signed by Verisi 11 because there is 110 big er it A ll of e quotcerti 39c quott39eS iTn quotti 39 39Eiij39 39 1 110quot hl M1 7 39 oever Wrote th e brorwser We S 39 39 General Details I Certi cation Path Show ltAIIgt v Field V Value 3 ESerial number 1F 42 23 3F 3 33 3F 3e 3 39 Signature algorithm sha1RSA E Issuer VeriSign Trust Network c 19 Ewalid From Sunday May 1739 1993 5333 EEK and to Friday May 13 2313 43939 7 Subject 39v39e 39 39gn Trust Network c 19 8 315133 9 E39ngm Thumbprint algorithm J 30 El 39 02 El Ell CID a7 89 Ell 21 74 2 e A la 33 f3 93 31 97 3o Elf 21 33 f1 9e db 9 i 39 95 f1 2 D4 33 13 he 5f 52 3 1 Le 21 12 56 24 b8 91 69 21 CI 99 1f ad 130 96 le 79 04 f2 13 39 1 2 98 ha 03 2 BB 32 84 13 213 aa 69 39 09 f4 27 59 I32 54 42 12 23 4f 4a 318 EU De a2 f 31 3 19 e3 3 99 27 i 339 5 53 4 4 73 9e 31 I 43 33 Ea b9 33 C9 54 E2 132 C4 af d4 46 5a C9 15 30 ff vi Edit Properties Copy to File DIGITAL CERTIFICATES Authenticating the Machines Servers f 39 1 r 39 r 7 T In 1 r l requot39 g e 39 v1 394 171 ena ed W 01 mag w 39 3 0 2 9 brez Certificate Owner WWWamazoncom Seat e WA USA Certificate Issuer RSA Data Security Unc Valid From Tuesday March 119 20036 8 PM Valid To Thursday March 20 2907 75959 PM Public Key Algorithm BSA 1024 b t Server s Public Key 3G 81 87 02 81 81 063 08 1112 8k a 410 03 5b 1024 bits Signature Algorithm MDS 128 bit CA s Signature 62 89 a8 52 00 e6 8609 118 51 74 3a 413 43 m0 6 Que m 120 c e vex e m akes nry tnie 1 g n a 10 Cazg3 mm E 9 t J asse 33 33mg Ce rtificate I Details irQertiFicatior i Path Schwab s Digital Certi cate 7 w r L x Certificate Gen rai Details iCeritiFicaticrkinwbaith how ltAllgt v Certi cate Information This LI is 39 J J for the OEnsures the identity at a remote computer Double click on the ellow lock to get this Refer to the certi cation authority39s statement For details Issued to www5chwabcom er 39 I su Valid From nature algorithm k Subject Ty e Issued by Secure Server Certi cation nuth rity lEVElit From to Lnstell CertiFiEate I Ea I Constraints p AE Key Usage Digital Signature 37 30 81 89 Ell 31 DU 19 130 49 2b 94 61 A De TC El 45 SC US 25 f4 26 79 88 3 I31 if 66 39 6e 2a 19 71 ES 134 66 35 Be 11 elf 939 133 57 25 ed f 4 Ca Df 14 33 7 1 EC 133 I58 118 Ere 04 111 16 a2 4 83 16 C2 88 a3 ee 94 55 3e a4 1C1 2e a 16 59 16 da 5a 29 5 31 4f 7 9 fl da 2 393 23 de 14 b9 82 E4 30 23 b3 b0 49 39 12 Ce 2 b4 fe 3E 69 ED 97 26 9e 22 d5 J W 1 m1 ec i u g J imm m 1323 a mmcso J 1 AW 3212 mW digital m f j9 v amp1 1 i 1 mnp J 6 fm 395 779 36331231 almfslmcgmcn wa mmmm To m9 My W Ta 13 E 2231 1 a39 Awnm CCO kgx dam9 1 an Liz e m lt3m13lt 31 mo quotmagsusmhm x ova Emmkca v W Tile2m Cm ambc mi m g h39 in 1 mm r ALICE goes to Amazon giving it h er rusernam e land password reads the Certificate Authority 39 55L Encrypted I listeid in thve certificate Channel J7 s browser 11863 that 39S C 11 inclilded browSerb tquot deer pt the certificate39s quot quot i a fixif av th39e I ARIAZONC 0M browser compares the MD with its own MD of the certificate If the certi cate is aka39y using the Servers public key foun in its certi cate 1 A 1quotk y Le g39 R C42 cryptography 5539 Encrypted Channel ARIAZONC Um I A closed lt7quot is 1113 SSL Encrypted I Channel Jr 7 WONC01 7 session is secret that is use 0an Slngle 1 k4 y altyjptographie sess ibn dTieggfei sts 39d uses tall crypto mfessaige i gital anid digital Certi cates Secure Communications Over the Internet It 39 I orks Lllllr ID 3 r I I I I l I i I I I I I I I I E is The Data Encryption Standard a block cipher With 64 bit blocks and a 56 bit key Probably the most Widely used symmetric cipher ever devised DES has been a US government standard for use on unclassified data since the late 7039s It is seriously unsecure against current attacks a DES using threye when three different keys are used 3DES is considered a B elieved g bits Thquot 39 V 39 puma Enqryp encryptions on a single data block With at leakst two dif 168 bit key algo rithm ferent lt 4 39 39 s Iquot 39 ysing39 zli bit as many Priva 39MicroSp39ft I Hpi t to Point Eu quot1 quot 39 A quot ldry a quotquot 39 bn iIt into Microsoft A iciph39er Sgt bit and 39Vari39able length keys to SFO bit v k s ofiprohc39essing a algorithm all algorithm s lifsted here In Cit s 39c 1l1 r39rer1t 1 c r 139jril dsMGAS T lzs this St39a ndar di39ws39 main adx zant aj as over D ES are the 39 r 39y M A 091 size fhata110WSer higher Se urity CAST25 SuPPOrtS s veral K y siZ es 128 160 192222 4 and 256 bits and fa b1b k 39s i39ze of 128 bits 3915 several times rth a fir V V


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