Nguyn i ThAn ton Mng1 AN TON MNG TS. Nguyn i Th B mn Mng & Truyn thng My tnh Khoa Cng ngh Thng tin thond_cn@vnu.edu.vn Nm hc 2007-2008 I HC QUC GIA H NI TRNG I HC CNG NGH Nguyn i ThAn ton Mng2 Ti liu tham kho Sch tham kho chnh William Stallings. Cryptography and Network Security : Principles and Practice, Fourth Edition. Prentice Hall, 2005. Sch tham kho ph Charlie Kaufman, Radia Perlman, Mike Speciner. Network Security: Private Communication in a Public World, Second Edition. Prentice Hall, 2002. Matt Bishop. Computer Security: Art and Science. Addison Wesley, 2002. Man Young Rhee. Internet Security: Cryptographic principles, algorithms and protocols. John Wiley & Sons, 2003. Website http://williamstallings.com Nguyn i ThAn ton Mng3 Chng 1 Gii thiu Nguyn i ThAn ton Mng4 Bi cnh Nhu cu m bo an ton thng tin c nhng bin i ln Trc y Ch cn cc phng tin vt l v hnh chnh T khi c my tnh Cn cc cng c t ng bo v tp tin v cc thng tin khc lu tr trong my tnh T khi c cc phng tin truyn thng v mng Cn cc bin php bo v d liu truyn trn mng Nguyn i ThAn ton Mng5 Cc khi nim An ton thng tin Lin quan n cc yu t ti nguyn, nguy c, hnh ng tn cng, yu im, v iu khin An ton my tnh Cc cng c bo v d liu v phng chng tin tc An ton mng Cc bin php bo v d liu truyn trn mng An ton lin mng Cc bin php bo v d liu truyn trn mt tp hp cc mng kt ni vi nhau Nguyn i ThAn ton Mng6 Mc tiu mn hc Ch trng an ton lin mng Nghin cu cc bin php ngn cn, phng chng, pht hin v khc phc cc vi phm an ton lin quan n truyn ti thng tin Nguyn i ThAn ton Mng7 Kin trc an ton OSI Kin trc an ton cho OSI theo khuyn ngh X.800 ca ITU-T nh ra mt phng thc chung cho vic xc nh cc nhu cu v an ton thng tin Cung cp mt ci nhn tng quan v cc khi nim mn hc s cp n Ch trng n cc hnh ng tn cng,cc c ch an ton, v cc dch v an ton Nguyn i ThAn ton Mng8 Hnh ng tn cng L hnh ng ph hoi an ton thng tin ca mt t chc An ton thng tin l nhng cch thc ngn nga cc hnh ng tn cng, nu khng c th pht hin v khc phc hu qu Cc hnh ng tn cng c nhiu v a dng Ch cn tp trung vo nhng th loi chung nht Lu : nguy c tn cng v hnh ng tn cng thng c dng ng ngha vi nhau Nguyn i ThAn ton Mng9 Cc hnh ng tn cng Cc hnh ng tn cng th ng Nghe trm ni dung thng tin truyn ti Gim st v phn tch lung thng tin lu chuyn Cc hnh ng tn cng ch ng Gi danh mt thc th khc Pht li cc thng bo trc Sa i cc thng bo ang lu chuyn T chi dch v Nguyn i ThAn ton Mng10 Dch v an ton L mt dch v nng cao an ton ca cc h thng x l thng tin v cc cuc truyn d liu trong mt t chc Nhm phng chng cc hnh ng tn cng S dng mt hay nhiu c ch an ton C cc chc nng tng t nh m bo an ton ti liu vt l Mt s c trng ca ti liu in t khin vic cung cp cc chc nng m bo an ton kh khn hn Nguyn i ThAn ton Mng11 Cc dch v an ton Theo X.800 Dch v an ton l dch v cung cp bi mt tng giao thc ca cc h thng m kt ni nhm m bo an ton cho cc h thng v cc cuc truyn d liu C 5 loi hnh Theo RFC 2828 Dch v an ton l dch v x l hoc truyn thng cung cp bi mt h thng bo v ti nguyn theo mt cch thc nht nh Nguyn i ThAn ton Mng12 Cc dch v an ton X.800 Xc thc m bo thc th truyn thng ng l n iu khin truy nhp Ngn khng cho s dng tri php ti nguyn Bo mt d liu Bo v d liu khi b tit l tri php Ton vn d liu m bo nhn d liu ng nh khi gi Chng chi b Ngn khng cho bn lin quan ph nhn hnh ngNguyn i ThAn ton Mng13 C ch an ton L c ch nh ra pht hin, ngn nga v khc phc mt hnh ng tn cng Khng mt c ch n l no c th h tr tt c cc chc nng m bo an ton thng tin C mt yu t c bit hu thun nhiu c ch an ton s dng hin nay l cc k thut mt m Mn hc s ch trng lnh vc mt m Nguyn i ThAn ton Mng14 Cc c ch an ton X.800 Cc c ch an ton chuyn bit M ha, ch k s, iu khin truy nhp, ton vn d liu, trao i xc thc, n tin truyn, iu khin nh tuyn, cng chng Cc c ch an ton ph qut Tnh nng ng tin, nhn an ton, pht hin s kin, du vt kim tra an ton, khi phc an ton Nguyn i ThAn ton Mng15 M hnh an ton mng Thng bo an ton Thng tin b mt Chuyn i lin quan n an ton Thng bo Thng bo Thng tin b mt Chuyn i lin quan n an ton Thng bo an ton i th Bn th ba ng tin Bn giBn nhn Knh thng tin Nguyn i ThAn ton Mng16 M hnh an ton mng Yu cu Thit k mt gii thut thch hp cho vic chuyn i lin quan n an ton To ra thng tin b mt (kha) i km vi gii thut Pht trin cc phng php phn b v chia s thng tin b mt c t mt giao thc s dng bi hai bn gi v nhn da trn gii thut an ton v thng tin b mt, lm c s cho mt dch v an tonNguyn i ThAn ton Mng17 M hnh an ton truy nhp mng Cc ti nguyn tnh ton (b x l, b nh, ngoi vi) D liu Cc tin trnh Phn mm Knh truy nhp Chc nng gc cng Cc iu khin an ton bn trong i th - Con ngi - Phn mm Nguyn i ThAn ton Mng18 M hnh an ton truy nhp mng Yu cu La chn cc chc nng gc cng thch hp nh danh ngi dng Ci t cc iu khin an ton m bo ch nhng ngi dng c php mi c th truy nhp c vo cc thng tin v ti nguyn tng ng Cc h thng my tnh ng tin cy c th dng ci t m hnh ny Nguyn i ThAn ton Mng19 Chng 2 M HA I XNG Nguyn i ThAn ton Mng20 Hai k thut m ha ch yu M ha i xng Bn gi v bn nhn s dng chung mt kha Cn gi l M ha truyn thng M ha kha ring / kha n / kha b mt L k thut m ha duy nht trc nhng nm 70 Hin vn cn c dng rt ph bin M ha kha cng khai (bt i xng) Mi bn s dng mt cp kha Mt kha cng khai + Mt kha ring Cng b chnh thc nm 1976 Nguyn i ThAn ton Mng21 Mt s cch phn loi khc Theo phng thc x l M ha khi Mi ln x l mt khi nguyn bn v to ra khi bn m tng ng (chng hn 64 hay 128 bit) M ha lung X l d liu u vo lin tc (chng hn mi ln 1 bit) Theo phng thc chuyn i M ha thay th Chuyn i mi phn t nguyn bn thnh mt phn t bn m tng ng M ha hon v B tr li v tr cc phn t trong nguyn bn Nguyn i ThAn ton Mng22 M hnh h m ha i xng Kha b mt dng chung bi bn gi v bn nhn Kha b mt dng chung bi bn gi v bn nhn Gii thut m haGii thut gii m Nguyn bn u vo Nguyn bn u ra Bn m truyn i M ha Y = EK(X) Gii m X = DK(Y) Nguyn i ThAn ton Mng23 M hnh h m ha i xng Gm c 5 thnh phn Nguyn bn Gii thut m ha Kha b mt Bn m Gii thut gii m An ton ph thuc vo s b mt ca kha, khng ph thuc vo s b mt ca gii thut Nguyn i ThAn ton Mng24 Ph m L n lc gii m vn bn c m ha khng bit trc kha b mt C hai phng php ph m Vt cn Th tt c cc kha c th Thm m Khai thc nhng nhc im ca gii thut Da trn nhng c trng chung ca nguyn bn hoc mt s cp nguyn bn - bn m mu Nguyn i ThAn ton Mng25 V l thuyt c th th tt c cc gi tr kha cho n khi tm thy nguyn bn t bn m Da trn gi thit c th nhn bit c nguyn bn cn tm Tnh trung bnh cn th mt na tng s cc trng hp c th Thc t khng kh thi nu di kha ln Phng php ph m vt cn Nguyn i ThAn ton Mng26 Thi gian tm kim trung bnh Kch thc kha (bit) S lng kha Thi gian cn thit (1 gii m/s) Thi gian cn thit (106 gii m/s) 32 56 128 168 26 k t (hon v) 232 = 4,3 x 109 256 = 7,2 x 1016 2128 = 3,4 x 1038 2168 = 3,7 x 1050 26! = 4 x 1026 231 s = 35,8 pht 255 s = 1142 nm 2127 s = 5,4 x 1024 nm 2167 s = 5,9 x 1036 nm 2 x 1026 s = 6,4 x 1012 nm 2,15 ms 10,01 gi 5,4 x 1018 nm 5,9 x 1030 nm 6,4 x 106 nm Tui v tr : ~ 1010 nmKha DES di 56 bit Kha AES di 128+ bit Kha 3DES di 168 bitNguyn i ThAn ton Mng27 Cc k thut thm m Ch c bn m Ch bit gii thut m ha v bn m hin c Bit nguyn bn Bit thm mt s cp nguyn bn - bn m Chn nguyn bn Chn 1 nguyn bn, bit bn m tng ng Chn bn m Chn 1 bn m, bit nguyn bn tng ng Chn vn bn Kt hp chn nguyn bn v chn bn m Nguyn i ThAn ton Mng28 An ton h m ha An ton v iu kin Bn m khng cha thng tin xc nh duy nht nguyn bn tng ng, bt k vi s lng bao nhiu v tc my tnh th no Ch h m ha n mt ln l an ton v iu kin An ton tnh ton Tha mn mt trong hai iu kin Chi ph ph m vt qu gi tr thng tin Thi gian ph m vt qu tui th thng tin Thc t tha mn hai iu kin Khng c nhc im Kha c qu nhiu gi tr khng th th ht Nguyn i ThAn ton Mng29 M ha thay th c in Cc ch ci ca nguyn bn c thay th bi cc ch ci khc, hoc cc s, hoc cc k hiu Nu nguyn bn c coi nh mt chui bit th thay th cc mu bit trong nguyn bn bng cc mu bit ca bn m Nguyn i ThAn ton Mng30 H m ha Caesar L h m ha thay th xut hin sm nht v n gin nht S dng u tin bi Julius Caesar vo mc ch qun s Dch chuyn xoay vng theo th t ch ci Kha k l s bc dch chuyn Vi mi ch ci ca vn bn t p = 0 nu ch ci l a, p = 1 nu ch ci l b,... M ha : C = E(p) = (p + k) mod 26 Gii m : p = D(C) = (C - k) mod 26 V d : M ha "meet me after class" vi k = 3 Nguyn i ThAn ton Mng31 Ph m h m ha Caesar Phng php vt cn Kha ch l mt ch ci (hay mt s gia 1 v 25) Th tt c 25 kha c th D dng thc hin Ba yu t quan trng Bit trc cc gii thut m ha v gii m Ch c 25 kha th Bit v c th d dng nhn ra c ngn ng ca nguyn bn V d : Ph m "GCUA VQ DTGCM" Nguyn i ThAn ton Mng32 H m ha n bng Thay mt ch ci ny bng mt ch ci khc theo trt t bt k sao cho mi ch ci ch c mt thay th duy nht v ngc li Kha di 26 ch ci V d Kha abc def ghijk lm n o p q rs tuv wxyz M N B V C X Z A S D F G H J K L P O I U Y T R E W Q Nguyn bn i love you Nguyn i ThAn ton Mng33 Ph m h m ha n bng Phng php vt cn Kha di 26 k t S lng kha c th = 26! = 4 x 1026 Rt kh thc hin Khai thc nhng nhc im ca gii thut Bit r tn s cc ch ci ting Anh C th suy ra cc cp ch ci nguyn bn - ch ci bn m V d : ch ci xut hin nhiu nht c th tng ng vi 'e' C th nhn ra cc b i v b ba ch ci V d b i : 'th', 'an', 'ed' V d b ba : 'ing', 'the', 'est' Nguyn i ThAn ton Mng34 Cc tn s ch ci ting Anh Tn s tng i (%) Nguyn i ThAn ton Mng35 V d ph m h n bng Cho bn m UZQSOVUOHXMOPVGPOZPEVSGZWSZOPFPESXUDBMETSXAIZ VUEPHZHMDZSHZOWSFPAPPDTSVPQUZWYMXUZUHSX EPYEPOPDZSZUFPOMBZWPFUPZHMDJUDTMOHMQ Tnh tn s ch ci tng i on P l e, Z l t on ZW l th v ZWP l the Tip tc on v th, cui cng c it was disclosed yesterday that several informal but direct contacts have been made with political representatives of the viet cong in moscow Nguyn i ThAn ton Mng36 H m ha Playfair (1) L mt h m ha nhiu ch Gim bt tng quan cu trc gia bn m v nguyn bn bng cch m ha ng thi nhiu ch ci ca nguyn bn Pht minh bi Charles Wheatstone vo nm 1854, ly tn ngi bn Baron Playfair S dng 1 ma trn ch ci 5x5 xy dng trn c s 1 t kha in cc ch ci ca t kha (b cc ch trng) in nt ma trn vi cc ch khc ca bng ch ci I v J chim cng mt ca ma trn Nguyn i ThAn ton Mng37 H m ha Playfair (2) V d ma trn vi t kha MONARCHY MONAR CH YBD E FGI/J K L PQS T UV W X Z M ha 2 ch ci mt lc Nu 2 ch ging nhau, tch ra bi 1 ch in thm Nu 2 ch nm cng hng, thay bi cc ch bn phi Nu 2 ch nm cng ct, thay bi cc ch bn di Cc trng hp khc, mi ch ci c thay bi ch ci khc cng hng, trn ct ch ci cng cp Nguyn i ThAn ton Mng38 Ph m h m ha Playfair An ton m bo hn nhiu h m ha n ch C 26 x 26 = 676 cp ch ci Vic gii m tng cp kh khn hn Cn phn tch 676 tn s xut hin thay v 26 Tng c qun i Anh, M s dng rng ri Bn m vn cn lu li nhiu cu trc ca nguyn bn Vn c th ph m c v ch c vi trm cp ch ci cn gii m Nguyn i ThAn ton Mng39 H m ha Vigenre L mt h m ha a bng S dng nhiu bng m ha Kha gip chn bng tng ng vi mi ch ci Kt hp 26 h Ceasar (bc dch chuyn 0 - 25) Kha K = k1k2...kd gm d ch ci s dng lp i lp li vi cc ch ci ca vn bn Ch ci th i tng ng vi h Ceasar bc chuyn i V d Kha :deceptivedeceptivedeceptive Nguyn bn : wearediscoveredsaveyourself Bn m :ZICVTWQNGRZGVTWAVZHCQYGLMGJ Nguyn i ThAn ton Mng40 Ph m h m ha Vigenre Phng php vt cn Kh thc hin, nht l nu kha gm nhiu ch ci Khai thc nhng nhc im ca gii thut Cu trc ca nguyn bn c che y tt hn h Playfair nhng khng hon ton bin mt Ch vic tm di kha sau ph m tng h Ceasar Cch tm di kha Nu di kha nh so vi di vn bn, c th pht hin 1 dy vn bn lp li nhiu ln Khong cch gia 2 dy vn bn lp l 1 bi s ca di kha T suy ra di kha Nguyn i ThAn ton Mng41 H m ha kha t ng Vigenre xut t kha khng lp li m c gn vo u nguyn bn Nu bit t kha s gii m c cc ch ci u tin S dng cc ch ci ny lm kha gii m cc ch cc tip theo,... V d : Kha :deceptivewearediscoveredsav nguyn bn : wearediscoveredsaveyourself M ha : ZICVTWQNGKZEIIGASXSTSLVVWLA Vn c th s dng k thut thng k ph m Kha v nguyn bn c cng tn s cc ch ci Nguyn i ThAn ton Mng42 n mt ln L h m ha thay th khng th ph c xut bi Joseph Mauborgne Kha ngu nhin, di bng di vn bn, ch s dng mt ln Gia nguyn bn v bn m khng c bt k quan h no v thng k Vi bt k nguyn bn v bn m no cng tn ti mt kha tng ng Kh khn vic to kha v m bo phn phi kha an ton Nguyn i ThAn ton Mng43 M ha hon v c in Che y ni dung vn bn bng cch sp xp li trt t cc ch ci Khng thay i cc ch ci ca nguyn bn Bn m c tn s xut hin cc ch ci ging nh nguyn bn Nguyn i ThAn ton Mng44 H m ha hng ro Vit cc ch ci theo ng cho trn mt s hng nht nh Sau c theo tng hng mt V d Nguyn bn : attack at midnight M ha vi cao hng ro l 2 a t c a m dih t a k t in gt Bn m : ATCAMDIHTAKTINGT Nguyn i ThAn ton Mng45 H m ha hng Vit cc ch ci theo hng vo 1 s ct nht nh Sau hon v cc ct trc khi c theo ct Kha l th t c cc ct V d Kha :431 2 5 67 Nguyn bn : a t t a c k p o st p o n e d untilt w oamx y z Bn m :TTNAAPTMTSUOAODWCOIXKNLYPETZ Nguyn i ThAn ton Mng46 M ha tch hp Cc h m ha thay th v hon v khng an ton v nhng c im ca ngn ng Kt hp s dng nhiu h m ha s khin vic ph m kh hn Hai thay th to nn mt thay th phc tp hn Hai hon v to nn mt hon v phc tp hn Mt thay th vi mt hon v to nn mt h m ha phc tp hn nhiu L cu ni t cc h m ha c in n cc h m ha hin i Nguyn i ThAn ton Mng47 M ha khi So vi m ha lung M ha khi x l thng bo theo tng khi M ha lung x l thng bo 1 bit hoc 1 byte mi ln Ging nh thay th cc k t rt ln (> 64 bit) Bng m ha gm 2n u vo (n l di khi) Mi khi u vo ng vi mt khi m ha duy nht Tnh thun nghch di kha l n x 2n bit qu ln Xy dng t cc khi nh hn Hu ht cc h m ha khi i xng da trn cu trc h m ha Feistel Nguyn i ThAn ton Mng48 Mng S-P Mng thay th (S) - hon v (P) xut bi Claude Shannon vo nm 1949 L c s ca cc h m ha khi hin i Da trn 2 php m ha c in Php thay th : Hp S Php hon v : Hp P an xen cc chc nng Khuch tn : Hp P (kt hp vi hp S) Pht ta cu trc thng k ca nguyn bn khp bn m Gy ln : Hp S Lm phc tp ha mi quan h gia bn m v kha Nguyn i ThAn ton Mng49 Hp S 0 1 2 3 4 5 6 7 u vo 3 bit 0 1 0 0 1 2 3 4 5 6 7 1 1 0 u ra 3 bit Lu : Hp S c tnh thun nghch Nguyn i ThAn ton Mng50 Hp P Lu : Hp P c tnh thun nghch u vo 4 bit 1 1 0 1 1 0 1 1 1 1 0 1 1 0 1 1 Nguyn i ThAn ton Mng51 M ha Feistel xut bi Horst Feistel da trn khi nim h m ha tch hp thun nghch ca Shannon Phn mi khi di 2w bit thnh 2 na L0 v R0 X l qua n vng Chia kha K thnh n kha con K1, K2,..., Kn Ti mi vng i Thc hin thay th na bn tri Li-1 bng cch XOR n vi F(Ki, Ri-1) F thng gi l hm chuyn i hay hm vng Hon v hai na Li v Ri Nguyn i ThAn ton Mng52 Nguyn bn (2w bit) w bitw bit L0 R0 Vng 1 K1 L1 R1 F + Kn Ln Rn F + Vng n ... ... Ln+1 Rn+1 Bn m (2w bit) Nguyn i ThAn ton Mng53 Cc c trng h Feistel di khi Khi cng ln cng an ton (thng 64 bit) di kha Kha cng di cng an ton (thng 128 bit) S vng Cng nhiu vng cng an ton (thng 16 vng) Gii thut sinh m con Cng phc tp cng kh ph m Hm vng Cng phc tp cng kh ph m nh hng n ci t v phn tch Nguyn i ThAn ton Mng54 Gii m Feistel Ging gii thut m ha, ch khc Bn m l d liu u vo Cc kha con c dng theo th t ngc li Ti mi vng kt qu u ra chnh l cc d liu u vo ca qu trnh m ha i vi qu trnh m ha Li = Ri-1 Ri = Li-1 F(Ri-1, Ki) i vi qu trnh gii m Ri-1 = Li Li-1 = Ri F(Li, Ki) Nguyn i ThAn ton Mng55 Chun m ha d liu DES (Data Encryption Standard) c cng nhn chun nm 1977 Phng thc m ha c s dng rng ri nht Tn gii thut l DEA (Data Encryption Algorithm) L mt bin th ca h m ha Feistel, b xung thm cc hon v u v cui Kch thc khi : 64 bit Kch thc kha : 56 bit S vng : 16 Tng gy nhiu tranh ci v an ton Nguyn i ThAn ton Mng56 Gii thut m ha DES Nguyn bn (64 bit) giao hon thun vng 1 K1 vng 2 K2 vng n Kn giao hon nghch Bn m (64 bit) hon i 32 bit Kha 56 bit ... giao hon dch vng trigiao hon dch vng tri giao hon dch vng trigiao hon ... Nguyn i ThAn ton Mng57 Mt vng DES Li-1 m rng g/hon hp S giao hon Ri-1 x Ki x Li Ri --- 48 bit --- 48 bit --- 32 bit --- 32 bit Nguyn i ThAn ton Mng58 Ph m DES Kha 56 bit c 256 = 7,2 x 1016 gi tr c th Phng php vt cn t ra khng thc t Tc tnh ton cao c th ph c kha 1997 : 70000 my tnh ph m DES trong 96 ngy 1998 : Electronic Frontier Foundation (EFF) ph m DES bng my chuyn dng (250000$) trong < 3 ngy 1999 : 100000 my tnh ph m trong 22 gi Vn cn phi nhn bit c nguyn bn Thc t DES vn c s dng khng c vn Nu cn an ton hn : 3DES hay chun mi AES Nguyn i ThAn ton Mng59 H m ha 3DES S dng 3 kha v chy 3 ln gii thut DES M ha : C = EK3[DK2[EK1[p]]] Gii m : p = DK1[EK2[DK3[C]]] di kha thc t l 168 bit Khng tn ti K4 = 56 sao cho C = EK4(p) V sao 3 ln : trnh tn cng "gp nhau gia" C = EK2(EK1(p)) X = EK1(p) = DK2(C) Nu bit mt cp (p, C) M ha p vi 256 kha v gii m C vi 256 kha So snh tm ra K1 v K2 tng ng Kim tra li vi 1 cp (p, C) mi; nu OK th K1 v K2 l kha Nguyn i ThAn ton Mng60 Chun m ha tin tin AES (Advanced Encryption Standard) c cng nhn chun mi nm 2001 Tn gii thut l Rijndael (Rijmen + Daemen) An ton hn v nhanh hn 3DES Kch thc khi : 128 bit Kch thc kha : 128/192/256 bit S vng : 10/12/14 Cu trc mng S-P, nhng khng theo h Feistel Khng chia mi khi lm i Nguyn i ThAn ton Mng61 Cc h m ha khi khc (1) IDEA (International Data Encryption Algorithm) Khi 64 bit, kha 128 bit, 8 vng Theo cu trc mng S-P, nhng khng theo h Feistel Mi khi chia lm 4 Rt an ton Bn quyn bi Ascom nhng dng min ph Blowfish Khi 64 bit, kha 32-448 bit (ngm nh 128 bit), 16 vng Theo cu trc h Feistel An ton, kh nhanh v gn nh T do s dng Nguyn i ThAn ton Mng62 Cc h m ha khi khc (2) RC5 Pht trin bi Ron Rivest Khi 32/64/128 bit, kha 0-2040 bit, 0-255 vng n gin, thch hp cc b x l c rng khc nhau Theo cu trc h Feistel CAST-128 Pht trin bi Carlisle Adams v Stafford Tavares Khi 64 bit, kha 40-128 bit, 12/16 vng C 3 loi hm vng dng xen k Theo cu trc h Feistel Bn quyn bi Entrust nhng dng min ph Nguyn i ThAn ton Mng63 Cc phng thc m ha khi ECB (Electronic Codebook) M ha tng khi ring r CBC (Cipher Block Chaining) Khi nguyn bn hin thi c XOR vi khi bn m trc CFB (Cipher Feedback) M phng m ha lung (n v s bit) s bit m ha trc c a vo thanh ghi u vo hin thi OFB (Output Feeback) s bit tri u ra trc c a vo thanh ghi u vo hin thi CTR (Counter) XOR mi khi nguyn bn vi 1 gi tr thanh m m ha Nguyn i ThAn ton Mng64 Phng thc ECB M ha p1 C1 K M ha p2 C2 K M ha pN CN K ... M ha Gii m C1 p1 K Gii m C2 p2 K Gii m CN pN K ... Gii m Nguyn i ThAn ton Mng65 nh gi ECB Nhng khi lp li trong nguyn bn c th thy c trong bn m Nu thng bo di, c th Gip phn tch ph m To c hi thay th hoc b tr li cc khi Nhc im do cc khi c m ha c lp Ch yu dng gi thng bo c t khi V d gi kha Nguyn i ThAn ton Mng66 Phng thc CBC M ha p1 C1 K M ha C2 K M ha CN K ... M ha Gii m C1 p1 K Gii m C2 p2 K Gii m CN pN K ... Gii m p2 pN IV CN-1 CN-1IV Nguyn i ThAn ton Mng67 nh gi CBC Mi khi m ha ph thuc vo tt c cc khi nguyn bn trc S lp li cc khi nguyn bn khng th hin trong bn m ha Thay i trong mi khi nguyn bn nh hng n tt c cc khi bn m v sau Cn 1 gi tr u IV bn gi v bn nhn u bit Cn c m ha ging kha Nn khc nhau i vi cc thng bo khc nhau Cn x l c bit khi nguyn bn khng y cui cng Dng m ha d liu ln, xc thc Nguyn i ThAn ton Mng68 M ha CFB Thanh ghi dch 64-s bit|s bit M ha Chn s bit B i 64-s bit p1 K 64 64 s s C1 IV Thanh ghi dch 64-s bit|s bit M ha Chn s bit B i 64-s bit p2 K 64 64 s s C2 Thanh ghi dch 64-s bit|s bit M ha Chn s bit B i 64-s bit pM K 64 64 s s CM ... s CM-1 Nguyn i ThAn ton Mng69 Gii m CFB Thanh ghi dch 64-s bit|s bit M ha Chn s bit B i 64-s bit p1 K 64 64 s s IV Thanh ghi dch 64-s bit|s bit M ha Chn s bit B i 64-s bit p2 K 64 64 s s C2 Thanh ghi dch 64-s bit|s bit M ha Chn s bit B i 64-s bit pM K 64 64 s s CM ... s CM-1 C1 Nguyn i ThAn ton Mng70 nh gi CFB Thch hp khi d liu nhn c theo tng n v bit hay byte Khng cn n thng bo lm trn khi Cho php s lng bit bt k K hiu CFB-1, CFB-8, CFB-64,... L phng thc lung ph bin nht Dng gii thut m ha ngay c khi gii m Li xy ra khi truyn 1 khi m ha s lan rng sang cc khi tip sau Nguyn i ThAn ton Mng71 M ha OFB Thanh ghi dch 64-s bit|s bit M ha Chn s bit B i 64-s bit p1 K 64 64 s s C1 IV Thanh ghi dch 64-s bit|s bit M ha Chn s bit B i 64-s bit K 64 64 Thanh ghi dch 64-s bit|s bit M ha Chn s bit B i 64-s bit K 64 64 ... s OM-1 p2 s s C2 pM s s CM Nguyn i ThAn ton Mng72 Gii m OFB Thanh ghi dch 64-s bit|s bit M ha Chn s bit B i 64-s bit p1 K 64 64 s s IV Thanh ghi dch 64-s bit|s bit M ha Chn s bit B i 64-s bit K 64 64 Thanh ghi dch 64-s bit|s bit M ha Chn s bit B i 64-s bit K 64 64 ... s OM-1 C1 p2 s C2 pM s CM Nguyn i ThAn ton Mng73 nh gi OFB Tng t CFB ch khc l phn hi ly t u ra gii thut m ha, c lp vi thng bo Khng bao gi s dng li cng kha v IV Li truyn 1 khi m ha khng nh hng n cc khi khc Thng bo d b sa i ni dung Ch nn dng OFB-64 C th tit kim thi gian bng cch thc hin gii thut m ha trc khi nhn c d liu Nguyn i ThAn ton Mng74 Phng thc CTR M ha M ha Bin m p1 K M ha Bin m + 1 p2 K M ha Bin m + N - 1 pN K ... Gii m C1 C2 CN M ha Bin m C1 K M ha Bin m + 1 C2 K M ha Bin m + N - 1 CN K ... p1 p2 pN Nguyn i ThAn ton Mng75 nh gi CTR Hiu qu cao C th thc hin m ha (hoc gii m) song song C th thc hin gii thut m ha trc nu cn C th x l bt k khi no trc cc khi khc An ton khng km g cc phng thc khc n gin, ch cn ci t gii thut m ha, khng cn n gii thut gii m Khng bao gi s dng li cng gi tr kha v bin m (tng t OFB)Nguyn i ThAn ton Mng76 B tr cng c m ha Gii php hu hiu v ph bin nht chng li cc mi e da n an ton mng l m ha thc hin m ha, cn xc nh M ha nhng g Thc hin m ha u C 2 phng n c bn M ha lin kt M ha u cui Nguyn i ThAn ton Mng77 M ha lin kt Cng c m ha c sp t 2 u ca mi lin kt c nguy c b tn cng m bo an ton vic lu chuyn thng tin trn tt c cc lin kt mng Cc mng ln cn n rt nhiu cng c m ha Cn cung cp rt nhiu kha Nguy c b tn cng ti mi chuyn mch Cc gi tin cn c m ha mi khi i vo mt chuyn mch gi c c a ch phn u Thc hin tng vt l hoc tng lin kt Nguyn i ThAn ton Mng78 M ha u cui Qu trnh m ha c thc hin 2 h thng u cui m bo an ton d liu ngi dng Ch cn mt kha cho 2 u cui m bo xc thc mc nht nh Mu lu chuyn thng tin khng c bo v Cc phn u gi tin cn c truyn ti tng minh Thc hin tng mng tr ln Cng ln cao cng t thng tin cn m ha v cng an ton nhng cng phc tp vi nhiu thc th v kha Nguyn i ThAn ton Mng79 Kt hp cc phng n m ha PSN : Packet-switching node Cng c m ha u cui Cng c m ha lin kt Nguyn i ThAn ton Mng80 Qun l kha b mt Vn i vi m ha i xng l lm sao phn phi kha an ton n cc bn truyn tin Thng h thng mt an ton l do khng qun l tt vic phn phi kha b mt Phn cp kha Kha phin (tm thi) Dng m ha d liu trong mt phin kt ni Hy b khi ht phin Kha ch (lu di) Dng m ha cc kha phin, m bo phn phi chng mt cch an ton Nguyn i ThAn ton Mng81 Cc cch phn phi kha Kha c th c chn bi bn A v gi theo ng vt l n bn B Kha c th c chn bi mt bn th ba, sau gi theo ng vt l n A v B Nu A v B c mt kha dng chung th mt bn c th gi kha mi n bn kia, s dng kha c m ha kha mi Nu mi bn A v B u c mt knh m ha n mt bn th ba C th C c th gi kha theo cc knh m ha n A v B Nguyn i ThAn ton Mng82 Phn phi kha t ng 1. Host gi gi tin yu cu kt ni 2. FEP m gi tin; hi KDC kha phin 3. KDC phn phi kha phin n 2 host 4. Gi tin m c truyn i FEP = Front End Processor KDC = Key Distribution Center Nguyn i ThAn ton Mng83 Chng 3 MT M KHA CNG KHAI Nguyn i ThAn ton Mng84 Gii thiu Nhng hn ch ca mt m i xng Vn phn phi kha Kh m bo chia s m khng lm l kha b mt Trung tm phn phi kha c th b tn cng Khng thch hp cho ch k s Bn nhn c th lm gi thng bo ni nhn c t bn gi Mt m kha cng khai xut bi Whitfield Diffie v Martin Hellman vo nm 1976 Khc phc nhng hn ch ca mt m i xng C th coi l bc t ph quan trng nht trong lch s ca ngnh mt m B xung ch khng thay th mt m i xng Nguyn i ThAn ton Mng85 c im mt m kha cng khai Cn gi l mt m hai kha hay bt i xng Cc gii thut kha cng khai s dng 2 kha Mt kha cng khai Ai cng c th bit Dng m ha thng bo v thm tra ch k Mt kha ring Ch ni gi c bit Dng gii m thng bo v k (to ra) ch k C tnh bt i xng Bn m ha khng th gii m thng bo Bn thm tra khng th to ch k Nguyn i ThAn ton Mng86 M ha kha cng khai Cc kha cng khai Nguyn bn u vo Nguyn bn u ra Bn m truyn i Gii thut m ha Gii thut gii m Kha cng khai ca Alice Kha ring ca Alice Ted Alice Mike Joy Nguyn i ThAn ton Mng87 Xc thc Cc kha cng khai Nguyn bn u vo Nguyn bn u ra Bn m truyn i Gii thut m ha Gii thut gii m Kha ring ca Bob Kha cng khai ca Bob Ted Bob Mike Joy Nguyn i ThAn ton Mng88 ng dng mt m kha cng khai C th phn ra 3 loi ng dng M ha/gii m m bo s b mt ca thng tin Ch k s H tr xc thc vn bn Trao i kha Cho php chia s kha phin trong m ha i xng Mt s gii thut kha cng khai thch hp cho c 3 loi ng dng; mt s khc ch c th dng cho 1 hay 2 loi Nguyn i ThAn ton Mng89 M hnh m bo b mt Ngun th. bo Gii thut m ha Gii thut gii m ch th. bo Ngun cp kha K ph m Ngun A ch B Nguyn i ThAn ton Mng90 M hnh xc thc Ngun th. bo Gii thut m ha Gii thut gii m ch th. bo Ngun cp kha K ph m Ngun A ch B Nguyn i ThAn ton Mng91 M hnh kt hp Ngun th. bo G. thut m ha G. thut gii m ch th. bo Ngun cp kha Ngun Ach B G. thut m ha G. thut gii m Ngun cp kha Nguyn i ThAn ton Mng92 Trao i kha AliceBob M haGii m Kha cng khai ca BobKha ring ca Bob Kha ngu nhinKha ngu nhin Nguyn i ThAn ton Mng93 Cc iu kin cn thit Bn B d dng to ra c cp (KUb, KRb) Bn A d dng to ra c C = EKUb(M) Bn B d dng gii m M = DKRb(C) i th khng th xc nh c KRb khi bit KUb i th khng th xc nh c M khi bit KUb v C Mt trong hai kha c th dng m ha trong khi kha kia c th dng gii m M = DKRb(EKUb(M)) = DKUb(EKRb(M)) Khng thc s cn thit Nguyn i ThAn ton Mng94 H m ha RSA xut bi Ron Rivest, Adi Shamir v Len Adleman (MIT) vo nm 1977 H m ha kha cng khai ph dng nht M ha khi vi mi khi l mt s nguyn < n Thng kch c n l 1024 bit 309 ch s thp phn ng k bn quyn nm 1983, ht hn nm 2000 An ton v chi ph phn tch tha s ca mt s nguyn ln l rt ln Nguyn i ThAn ton Mng95 To kha RSA Mi bn t to ra mt cp kha cng khai - kha ring theo cc bc sau : Chn ngu nhin 2 s nguyn t ln p = q Tnh n = pq Tnh u(n) = (p-1)(q-1) Chn ngu nhin kha m ha e sao cho 1 < e < u(n) v gcd(e, u(n)) = 1 Tm kha gii m d n tha mn e.d 1 mod u(n) Cng b kha m ha cng khai KU = {e, n} Gi b mt kha gii m ring KR = {d, n} Cc gi tr b mt p v q b hy b Nguyn i ThAn ton Mng96 Thc hin RSA m ha 1 thng bo nguyn bn M, bn gi thc hin Ly kha cng khai ca bn nhn KU = {e, n} Tnh C = Me mod n gii m bn m C nhn c, bn nhn thc hin S dng kha ring KR = {d, n} Tnh M = Cd mod n Lu l thng bo M phi nh hn n Phn thnh nhiu khi nu cn Nguyn i ThAn ton Mng97 V sao RSA kh thi Theo nh l Euler a, n : gcd(a, n) = 1 au(n) mod n = 1 u(n) l s cc s nguyn dng nh hn n v nguyn t cng nhau vi n i vi RSA c n = pq vi p v q l cc s nguyn t u(n) = (p - 1)(q - 1) ed 1 mod u(n) - s nguyn k : ed = ku(n) + 1 M < n C th suy ra Cd mod n = Med mod n = Mku(n) + 1 mod n = M mod n = M Nguyn i ThAn ton Mng98 V d to kha RSA Chn 2 s nguyn t p = 17 v q = 11 Tnh n = pq = 17 11 = 187 Tnh u(n) = (p - 1)(q - 1) = 16 10 = 160 Chn e : gcd(e, 160) = 1 v 1 < e < 160; ly e = 7 Xc nh d : de 1 mod 160 v d 187 Gi tr d = 23 v 23 7 = 161 = 1 160 + 1 Cng b kha cng khai KU = {7, 187} Gi b mt kha ring KR = {23, 187} Hy b cc gi tr b mt p = 17 v q = 11 Nguyn i ThAn ton Mng99 V d thc hin RSA M haGii m Nguyn bn Nguyn bn Bn m Nguyn i ThAn ton Mng100 Chn tham s RSA Cn chn p v q ln Thng chn e nh Thng c th chn cng gi tr ca e cho tt c ngi dng Trc y khuyn ngh gi tr ca e l 3, nhng hin nay c coi l qu nh Thng chn e = 216 - 1 = 65535 Gi tr ca d s ln v kh on Nguyn i ThAn ton Mng101 An ton ca RSA Kha 128 bit l mt s gia 1 v mt s rt ln 340.282.366.920.938.000.000.000.000.000.000.000.000 C bao nhiu s nguyn t gia 1 v s ny n / ln(n) = 2128 / ln(2128) 3.835.341.275.459.350.000.000.000.000.000.000.000 Cn bao nhiu thi gian nu mi giy c th tnh c 1012 s Hn 121,617,874,031,562,000 nm (khong 10 triu ln tui ca v tr) An ton nhng cn phng nhng im yu Nguyn i ThAn ton Mng102 Ph m RSA Phng php vt cn Th tt c cc kha ring c th Ph thuc vo di kha Phng php phn tch ton hc Phn n thnh tch 2 s nguyn t p v q Xc nh trc tip u(n) khng thng qua p v q Xc nh trc tip d khng thng qua u(n) Phng php phn tch thi gian Da trn vic o thi gian gii m C th ngn nga bng cch lm nhiu Nguyn i ThAn ton Mng103 Phn tch tha s RSA An ton ca RSA da trn phc tp ca vic phn tch tha s n Thi gian cn thit phn tch tha s mt s ln tng theo hm m vi s bit ca s Mt nhiu nm khi s ch s thp phn ca n vt qu 100 (gi s lm 1 php tnh nh phn mt 1 qs) Kch thc kha ln m bo an ton cho RSA T 1024 bit tr ln Gn y nht nm 1999 ph m c 512 bit (155 ch s thp phn)Nguyn i ThAn ton Mng104 H trao i kha Diffie-Hellman Gii thut mt m kha cng khai u tin xut bi Whitfield Diffie v Martin Hellman vo nm 1976 Malcolm Williamson (GCHQ - Anh) pht hin trc my nm nhng n nm 1997 mi cng b Ch dng trao i kha b mt mt cch an ton trn cc kch thng tin khng an ton Kha b mt c tnh ton bi c hai bn An ton ph thuc vo phc tp ca vic tnh log ri rc Nguyn i ThAn ton Mng105 Thit lp Diffie-Hellman Cc bn thng nht vi nhau cc tham s chung q l mt s nguyn t ln o l mt nguyn cn ca q o mod q, o2 mod q,..., oq-1 mod q l cc s nguyn giao hon ca cc s t 1 n q - 1 Bn A Chn ngu nhin lm kha ring XA < q Tnh kha cng khai YA = oXA mod q Bn B Chn ngu nhin lm kha ring XB < q Tnh kha cng khai YB = oXB mod q Nguyn i ThAn ton Mng106 Trao i kha Diffie-Hellman Tnh ton kha b mt Bn A bit kha ring XA v kha cng khai YB K = YBXA mod q Bn B bit kha ring XB v kha cng khai YA K = YAXB mod q Chng minh YAXB mod q = (oXA mod q)XB mod q = oXAXB mod q = oXBXA mod q = (oXB mod q)XA mod q = YBXA mod q Nguyn i ThAn ton Mng107 V d Diffie-Hellman Alice v Bob mun trao i kha b mt Cng chn q = 353 v o = 3 Chn ngu nhin cc kha ring Alice chn XA = 97, Bob chn XB = 233 Tnh ton cc kha cng khai YA = 397 mod 353 = 40(Alice) YB = 3233 mod 353 = 248(Bob) Tnh ton kha b mt chung K = YBXA mod 353 = 24897 mod 353 = 160(Alice) K = YAXB mod 353 = 40233 mod 353 = 160(Bob) Nguyn i ThAn ton Mng108 Hn ch ca kha cng khai Tc x l Cc gii thut kha cng khai ch yu dng cc php nhn chm hn nhiu so vi cc gii thut i xng Khng thch hp cho m ha thng thng Thng dng trao i kha b mt u phin truyn tin Tnh xc thc ca kha cng khai Bt c ai cng c th to ra mt kha cng b l ca mt ngi khc Chng no vic gi mo cha b pht hin c th c c ni dung cc thng bo gi cho ngi kia Cn m bo nhng ngi ng k kha l ng tin Nguyn i ThAn ton Mng109 Chng 4 XC THC & CH K S Nguyn i ThAn ton Mng110 Vn xc thc Cc tiu chun cn xc minh Thng bo c ngun gc r rng chnh xc Ni dung thng bo ton vn khng b thay i Thng bo c gi ng trnh t v thi im Mc ch chng li hnh thc tn cng ch ng (xuyn tc d liu v giao tc) Cc phng php xc thc thng bo M ha thng bo S dng m xc thc thng bo (MAC) S dng hm bm Nguyn i ThAn ton Mng111 Xc thc bng cch m ha S dng m ha i xng Thng bo gi t ng ngun v ch c ngi gi mi bit kha b mt dng chung Ni dung khng th b thay i v nguyn bn c cu trc nht nh Cc gi tin c nh s th t v m ha nn khng th thay i trnh t v thi im nhn c S dng m ha kha cng khai Khng ch xc thc thng bo m cn to ch k s Phc tp v mt thi gian hn m ha i xng Nguyn i ThAn ton Mng112 M xc thc thng bo (MAC) Khi kch thc nh c nh gn vo thng bo to ra t thng bo v kha b mt chung Bn nhn thc hin cng gii thut trn thng bo v kha so xem MAC c chnh xc khng Gii thut to MAC ging nh gii thut m ha nhng khng cn nghch c C th nhiu thng bo cng c chung MAC Nhng nu bit mt thng bo v MAC ca n, rt kh tm ra mt thng bo khc c cng MAC Cc thng bo c cng xc sut to ra MAC p ng 3 tiu chun xc thc Nguyn i ThAn ton Mng113 a) Xc thc thng bo b) Xc thc thng bo v bo mt; MAC gn vo nguyn bn c) Xc thc thng bo v bo mt; MAC gn vo bn m Ngun Ach B So snh So snh So snh Nguyn i ThAn ton Mng114 V sao dng MAC Nhiu trng hp ch cn xc thc, khng cn m ha tn thi gian v ti nguyn Thng bo h thng Chng trnh my tnh Tch ring cc chc nng bo mt v xc thc s khin vic t chc linh hot hn Chng hn mi chc nng thc hin mt tng ring Cn m bo tnh ton vn ca thng bo trong sut thi gian tn ti khng ch khi lu chuyn V thng bo c th b thay i sau khi gii m Nguyn i ThAn ton Mng115 MAC da trn DES (DAC) M haM haM haM ha (16 - 64 bits) Nguyn i ThAn ton Mng116 Hm bm To ra mt gi tr bm c kch thc c nh t thng bo u vo (khng dng kha) h = H(M) Hm bm khng cn gi b mt Gi tr bm gn km vi thng bo dng kim tra tnh ton vn ca thng bo Bt k s thay i M no d nh cng to ra mt gi tr h khc Nguyn i ThAn ton Mng117 Ngun Ach B So snh So snh So snh a) Xc thc thng bo v bo mt; m bm gn vo nguyn bn b) Xc thc thng bo; m bm c m ha s dng phng php i xng c) Xc thc thng bo; m bm c m ha s dng phng php kha cng khai Nguyn i ThAn ton Mng118 Ngun Ach B So snh So snh So snh d) Xc thc bng m ha kha cng khai v bo mt bng m ha i xng e) Xc thc khng cn m ha nh hai bn chia s mt gi tr b mt chung f) Xc thc nh mt gi tr b mt chung; bo mt bng phng php i xng Nguyn i ThAn ton Mng119 Yu cu i vi hm bm C th p dng vi thng bo M c di bt k To ra gi tr bm h c di c nh H(M) d dng tnh c vi bt k M no T h rt kh tm c M sao cho H(M) = h Tnh mt chiu T M1 rt kh tm c M2 sao cho H(M2) = H(M1) Tnh chng xung t yu Rt kh tm c (M1, M2) sao cho H(M1) = H(M2) Tnh chng xung t mnh Nguyn i ThAn ton Mng120 Cc hm bm n gin 16 bit XOR dch vng tri 1 bitXOR mi khi 16 bit Nguyn i ThAn ton Mng121 Kiu tn cng ngy sinh Nghch l ngy sinh Trong 23 ngi, xc sut tm ra 1 ngi khc c cng ngy sinh vi A l 6% Xc sut 2 trong 23 ngi c cng ngy sinh l 50% Cch thc tn cng m bm m bit To ra 2m/2 bin th ng ngha ca thng bo hp l To ra 2m/2 bin th ca thng bo gi mo So snh 2 tp thng bo vi nhau tm ra 1 cp c cng m bm (xc sut > 0,5 theo nghch l ngy sinh) ngi gi k bin th hp l, ri dng ch k gn vo bin th gi mo Nguyn i ThAn ton Mng122 An ton hm bm v MAC Kiu tn cng vt cn Vi hm bm, n lc ph thuc di m ca m bm phc tp ca tnh mt chiu v tnh chng xung t yu l 2m; ca tnh chng xung t mnh l 2m/2 128 bit c th ph c, thng dng 160 bit Vi MAC, n lc ph thuc vo di k ca kha v di n ca MAC phc tp l min(2k, 2n) t nht phi l 128 bit Kiu thm m Hm bm thng gm nhiu vng nh m ha khi nn c th tp trung khai thc im yu hm vng Nguyn i ThAn ton Mng123 Ch k s Xc thc thng bo khng c tc dng khi bn gi v bn nhn mun gy hi cho nhau Bn nhn gi mo thng bo ca bn gi Bn gi chi l gi thng bo n bn nhn Ch k s khng nhng gip xc thc thng bo m cn bo v mi bn khi bn kia Chc nng ch k s Xc minh tc gi v thi im k thng bo Xc thc ni dung thng bo L cn c gii quyt tranh chp Nguyn i ThAn ton Mng124 Yu cu i vi ch k s Ph thuc vo thng bo c k C s dng thng tin ring ca ngi gi trnh gi mo v chi b Tng i d to ra Tng i d nhn bit v kim tra Rt kh gi mo Bng cch to thng bo khc c cng ch k s Bng cch to ch k s theo mun cho thng bo Thun tin trong vic lu tr Nguyn i ThAn ton Mng125 Ch k s trc tip Ch lin quan n bn gi v bn nhn Vi mt m kha cng khai Dng kha ring k ton b thng bo hoc gi tr bm C th m ha s dng kha cng khai ca bn nhn Quan trng l k trc m ha sau Ch c tc dng khi kha ring ca bn gi c m bo an ton Bn gi c th gi v mt kha ring Cn b xung thng tin thi gian v bo mt kha kp thi Kha ring c th b mt tht K cp c th gi thng bo vi thng tin thi gian sai lch Nguyn i ThAn ton Mng126 Ch k s gin tip C s tham gia ca mt bn trng ti Nhn thng bo c ch k s t bn gi, kim tra tnh hp l ca n B xung thng tin thi gian v gi n bn nhn An ton ph thuc ch yu vo bn trng ti Cn c bn gi v bn nhn tin tng C th ci t vi m ha i xng hoc m ha kha cng khai Bn trng ti c th c php nhn thy hoc khng ni dung thng bo Nguyn i ThAn ton Mng127 Cc k thut ch k s gin tip (a) M ha i xng, trng ti thy thng bo (1) X A :M EKXA[IDX H(M)] (2) A Y :EKAY[IDX M EKXA[IDX H(M)] T] (b) M ha i xng, trng ti khng thy thng bo (1) X A :IDX EKXY[M] EKXA[IDX H(EKXY[M])] (2) A Y : EKAY[IDX EKXY[M] EKXA[IDX H(EKXY[M])] T] (c) M ha kha cng khai, trng ti khng thy thng bo (1) X A :IDX EKRX[IDX EKUY[EKRX[M]]] (2) A Y :EKRA[IDX EKUY[EKRX[M]] T] K hiu : X = Bn giM = Thng bo Y = Bn nhnT = Nhn thi gian A = Trng ti Nguyn i ThAn ton Mng128 Chng 5 CC NG DNG XC THCNguyn i ThAn ton Mng129 Gii thiu Mc ch ca cc ng dng xc thc l h tr xc thc v ch k s mc ng dng Phn lm 2 loi chnh Da trn m ha i xng Dch v Kerberos Giao thc Needham-Schroeder Da trn kha cng khai c chng thc Dch v X.509 H thng PGP Nguyn i ThAn ton Mng130 Kerberos H thng dch v xc thc pht trin bi MIT Nhm i ph vi cc him ha sau Ngi dng gi danh l ngi khc Ngi dng thay i a ch mng ca client Ngi dng xem trm thng tin trao i v thc hin kiu tn cng lp li Bao gm 1 server tp trung c chc nng xc thc ngi dng v cc server dch v phn tn Tin cy server tp trung thay v cc client Gii phng chc nng xc thc khi cc server dch v v cc client Nguyn i ThAn ton Mng131 K hiu C : Client AS : Server xc thc V : Server dch v IDC : Danh tnh ngi dng trn C IDV : Danh tnh ca V PC : Mt khu ca ngi dng trn C ADC : a ch mng ca C KV : Kha b mt chia s bi AS v V : Php ghp TGS : Server cp th TS : Nhn thi gian Nguyn i ThAn ton Mng132 Mt hi thoi xc thc n gin Giao thc (1) C AS :IDC PC IDV (2) AS C :Th (3) C V : IDC Th Th = EKV[IDC ADC IDV] Hn ch Mt khu truyn t C n AS khng c bo mt Nu th ch s dng c mt ln th phi cp th mi cho mi ln truy nhp cng mt dch v Nu th s dng c nhiu ln th c th b ly cp s dng trc khi ht hn Cn th mi cho mi dch v khc nhau Nguyn i ThAn ton Mng133 Hi thoi xc thc Kerberos 4 (a) Trao i vi dch v xc thc : c th cp th (1) C AS :IDC IDtgs TS1 (2) AS C :EKC[KC,tgs IDtgs TS2 Hn2 Thtgs] Thtgs = EKtgs[KC,tgs IDC ADC IDtgs TS2 Hn2] (b) Trao i vi dch v cp th : c th dch v (3) C TGS :IDV Thtgs DuC (4) TGS C :EKC,tgs[KC,V IDV TS4 ThV] ThV = EKV[KC,V IDC ADC IDV TS4 Hn4] DuC = EKC,tgs[IDC ADC TS3] (c) Trao i xc thc client/server : c dch v (5) C V :ThV DuC (6) V C :EKC,V[TS5 + 1] DuC = EKC,V[IDC ADC TS5] Nguyn i ThAn ton Mng134 M hnh tng quan Kerberos Mi phin ngi dng mt ln Mi dch v mt ln Mi phin dch v mt ln AS TGS Client Server dch v Nguyn i ThAn ton Mng135 Phn h Kerberos Mt phn h Kerberos bao gm Mt server Kerberos cha trong CSDL danh tnh v mt khu bm ca cc thnh vin Mt s ngi dng ng k lm thnh vin Mt s server dch v, mi server c mt kha b mt ring ch chia s vi server Kerberos Mi phn h Kerberos thng tng ng vi mt phm vi hnh chnh Hai phn h c th tng tc vi nhau nu 2 server chia s 1 kha b mt v ng k vi nhau iu kin l phi tin tng ln nhau Nguyn i ThAn ton Mng136 1 2 3 4 5 67 Phn h A Phn h B 1. Yu cu th cho TGS cc b 2. Th cho TGS cc b 3. Yu cu th cho TGS xa 4. Th cho TGS xa 5. Yu cu th cho server xa 6. Th cho server xa 7. Yu cu dch v xaNguyn i ThAn ton Mng137 Kerberos 5 Pht trin vo gia nhng nm 1990 (sau Kerberos 4 vi nm) c t trong RFC 1510 C mt s ci tin so vi phin bn 4 Khc phc nhng khim khuyt ca mi trng Ph thuc gii thut m ha, ph thuc giao thc mng, trt t byte thng bo khng theo chun, gi tr hn dng th c th qu nh, khng cho php y nhim truy nhp, tng tc a phn h da trn qu nhiu quan h tay i Khc phc nhng thiu st k thut M ha hai ln c mt ln tha, phng thc m ha PCBC m bo tnh ton vn khng chun d b tn cng, kha phin s dng nhiu ln c th b khai thc tn cng lp li, c th b tn cng mt khu Nguyn i ThAn ton Mng138 Dch v xc thc X.509 Nm trong lot khuyn ngh X.500 ca ITU-T nhm chun ha dch v th mc Servers phn tn lu gi CSDL thng tin ngi dng nh ra mt c cu cho dch v xc thc Danh b cha cc chng thc kha cng khai Mi chng thc bao gm kha cng khai ca ngi dng k bi mt bn chuyn trch chng thc ng tin nh ra cc giao thc xc thc S dng mt m kha cng khai v ch k s Khng chun ha gii thut nhng khuyn ngh RSA Nguyn i ThAn ton Mng139 Khun dng X.509 Nguyn i ThAn ton Mng140 Nhn chng thc C c kha cng khai ca CA (c quan chng thc) l c th xc minh c chng thc Ch CA mi c th thay i chng thc Chng thc c th t trong mt th mc cng khai Cu trc phn cp CA Ngi dng c chng thc bi CA ng k Mi CA c hai loi chng thc Chng thc thun : Chng thc CA hin ti bi CA cp trn Chng thc nghch : Chng thc CA cp trn bi CA hin ti Cu trc phn cp CA cho php ngi dng xc minh chng thc bi bt k CA noNguyn i ThAn ton Mng141 Phn cp X.509 Nguyn i ThAn ton Mng142 Thu hi chng thc Mi chng thc c mt thi hn hp l C th cn thu hi chng thc trc khi ht hn Kha ring ca ngi dng b tit l Ngi dng khng cn c CA chng thc Chng thc ca CA b xm phm Mi CA phi duy tr danh sch cc chng thc b thu hi (CRL) Khi nhn c chng thc, ngi dng phi kim tra xem n c trong CRL khngNguyn i ThAn ton Mng143 Cc th tc xc thc Nguyn i ThAn ton Mng144 Chng 6 AN TON TH IN TNguyn i ThAn ton Mng145 Gii thiu Th in t l dch v mng ph dng nht Hin nay cc thng bo khng c bo mt C th c c ni dung trong qu trnh thng bo di chuyn trn mng Nhng ngi dng c quyn c th c c ni dung thng bo trn my ch Thng bo d dng b gi mo bi mt ngi khc Tnh ton vn ca thng bo khng c m bo Cc gii php xc thc v bo mt thng dng PGP (Pretty Good Privacy) S/MIME (Secure/Multipurpose Internet Mail Extensions) Nguyn i ThAn ton Mng146 PGP Do Phil Zimmermann pht trin vo nm 1991 Chng trnh min ph, chy trn nhiu mi trng khc nhau (phn cng, h iu hnh) C phin bn thng mi nu cn h tr k thut Da trn cc gii thut mt m an ton nht Ch yu ng dng cho th in t v file c lp vi cc t chc chnh ph Bao gm 5 dch v : xc thc, bo mt, nn, tng thch th in t, phn v ghp Ba dch v sau trong sut i vi ngi dngNguyn i ThAn ton Mng147 Xc thc ca PGP Ngun Ach B So snh M = Thng bo gcEP = M ha kha cng khai H = Hm bmDP = Gii m kha cng khai = GhpKRa = Kha ring ca A Z = Nn KUa = Kha cng khai ca A Z-1 = Ci nn Nguyn i ThAn ton Mng148 Bo mt ca PGP Ngun Ach B EC = M ha i xng DC = Gii m i xng Ks = Kha phin Nguyn i ThAn ton Mng149 Xc thc v bo mt ca PGP Ngun Ach B Nguyn i ThAn ton Mng150 Nn ca PGP PGP nn thng bo s dng gii thut ZIP K trc khi nn Thun tin lu tr v kim tra, nu k sau khi nn th Cn lu phin bn nn vi ch k, hoc Cn nn li thng bo mi ln mun kim tra Gii thut nn khng cho kt qu duy nht Mi phin bn ci t c tc v t l nn khc nhau Nu k sau khi nn th cc chng trnh PGP cn s dng cng mt phin bn ca gii thut nn M ha sau khi nn t d liu s khin vic m ha nhanh hn Thng bo nn kh ph m hn thng bo th Nguyn i ThAn ton Mng151 Tng thch th in t ca PGP PGP bao gi cng phi gi d liu nh phn Nhiu h thng th in t ch chp nhn vn bn ASCII (cc k t c c) Th in t vn ch cha vn bn c c PGP dng gii thut c s 64 chuyn i d liu nh phn sang cc k t ASCII c c Mi 3 byte nh phn chuyn thnh 4 k t c c Hiu ng ph ca vic chuyn i l kch thc thng bo tng ln 33% Nhng c thao tc nn b li Nguyn i ThAn ton Mng152 Bng chuyn i c s 64 Nguyn i ThAn ton Mng153 Phn v ghp ca PGP Cc giao thc th in t thng hn ch di ti a ca thng bo V d thng l 50 KB PGP phn thng bo qu ln thnh nhiu thng bo nh Vic phn on thng bo thc hin sau tt c cc cng on khc Bn nhn s ghp cc thng bo nh trc khi thc hin cc cng on khc Nguyn i ThAn ton Mng154 Danh tnh kha PGP Vi mt thng bo nht nh cn xc nh s dng kha no trong nhiu kha cng khai / kha ring C th gi kha cng khai cng vi thng bo nhng lng ph ng truyn khng cn thit Gn cho mi kha mt danh tnh ring Gm 64 bit bn phi ca kha Xc sut cao l mi kha c mt danh tnh duy nht S dng danh tnh kha trong ch k Nguyn i ThAn ton Mng155 Qun l kha PGP Thay v da trn cc CA (c quan chng thc), i vi PGP mi ngi dng l mt CA C th chng thc cho nhng ngi dng quen bit To nn mt mng li tin cy Tin cc kha c chng thc Mi kha c mt ch s tin cy Ngi dng c th thu hi kha ca bn thn Nguyn i ThAn ton Mng156 S/MIME Nng cp t chun khun dng th in t MIME c thm tnh nng an ton thng tin MIME khc phc nhng hn ch ca SMTP (Simple Mail Transfer Protocol) Khng truyn c file nh phn (chng trnh, nh,...) Ch gi c cc k t ASCII 7 bit Khng nhn thng bo vt qu kch thc cho php ... S/MIME c xu hng tr thnh chun cng nghip s dng trong thng mi v hnh chnh PGP dng cho c nhn Nguyn i ThAn ton Mng157 Cc chc nng ca S/MIME Bao bc d liu M ha ni dung thng bo v cc kha lin quan K d liu Ch k s to thnh nh m ha thng tin tng hp thng bo s dng kha ring ca ngi k Thng bo v ch k s c chuyn i c s 64 K v nguyn d liu Ch ch k s c chuyn i c s 64 K v bao bc d liu Kt hp k v bao bc d liu Nguyn i ThAn ton Mng158 X l chng thc S/MIME S/MIME s dng cc chng thc kha cng khai theo X.509 v3 Phng thc qun l kha lai ghp gia cu trc phn cp CA theo ng X.509 v mng li tin cy ca PGP Mi ngi dng c mt danh sch cc kha ca bn thn, danh sch cc kha tin cy v danh sch thu hi chng thc Chng thc phi c k bi CA tin cy Nguyn i ThAn ton Mng159 Chng 7 AN TON IP Nguyn i ThAn ton Mng160 Gii thiu L do cn IPSec C nhng vn an ton cn gii quyt mc thp hn tng ng dng c bit cc hnh thc tn cng tng IP rt ph bin nh gi mo IP, xem trm gi tin An ton mc IP s m bo an ton cho tt c cc ng dng Bao gm nhiu ng dng cha c tnh nng an ton Cc c ch an ton ca IPSec Xc thc Bo mt Qun l kha Nguyn i ThAn ton Mng161 Cc ng dng ca IPSec Xy dng mng ring o an ton trn Internet Tit kim chi ph thit lp v qun l mng ring Truy nhp t xa an ton thng qua Internet Tit kim chi ph i li Giao tip an ton vi cc i tc m bo xc thc, bo mt v cung cp c ch trao i kha Tng cng an ton thng mi in t H tr thm cho cc giao thc an ton c sn ca cc ng dng Web v thng mi in t Nguyn i ThAn ton Mng162 Minh ha ng dng IPSec Nguyn i ThAn ton Mng163 ch li ca IPSec Ti tng la hoc b nh tuyn, IPSec m bo an ton cho mi lung thng tin vt bin Ti tng la, IPSec ngn chn thm nhp tri php t Internet vo IPSec nm di tng giao vn, do vy trong sut vi cc ng dng IPSec c th trong sut vi ngi dng cui IPSec c th p dng cho ngi dng n l IPSec bo v an ton kin trc nh tuyn Nguyn i ThAn ton Mng164 Kin trc an ton IP c t IPSec kh phc tp nh ngha trong nhiu ti liu Bao gm RFC 2401 (tng quan kin trc), RFC 2402 (m t m rng xc thc), RFC 2406 (m t m rng m ha), RFC 2408 (c t kh nng trao i kha) Cc ti liu khc c chia thnh 7 nhm Vic h tr IPSec l bt buc i vi IPv6, ty chn i vi IPv4 IPSec c ci t nh cc phn u m rng sau phn u IP Phn u m rng cho xc thc l AH Phn u m rng cho m ha l ESP Nguyn i ThAn ton Mng165 Tng quan ti liu IPSec Nguyn i ThAn ton Mng166 Cc dch v IPSec Bao gm iu khin truy nhp Ton vn phi kt ni Xc thc ngun gc d liu T chi cc gi tin lp Mt hnh thc ca ton vn th t b phn Bo mt (m ha) Bo mt lung tin hu hn S dng mt trong hai giao thc Giao thc xc thc (ng vi AH) Giao thc xc thc/m ha (ng vi ESP) Nguyn i ThAn ton Mng167 Cc lin kt an ton Khi nim lin kt an ton (SA) L quan h mt chiu gia bn gi v bn nhn, cho bit cc dch v an ton i vi lung tin lu chuyn Mi SA c xc nh duy nht bi 3 tham s Ch mc cc tham s an ton (SPI) a ch IP ch nh danh giao thc an ton Cc tham s khc lu trong CSDL SA (SAD) S th t, cc thng tin AH v ESP, thi hn,... CSDL chnh sch an ton (SPD) cho php iu chnh mc p dng IPSec Nguyn i ThAn ton Mng168 Phn u xc thc m bo ton vn v xc thc cc gi IP Cho php mt h thng u cui hay mt thit b mng xc thc ngi dng hoc ng dng Trnh gi mo a ch Chng li hnh thc tn cng lp li S dng m xc thc thng bo Bn gi v bn nhn phi c mt kha b mt dng chung Nguyn i ThAn ton Mng169 Khun dng AH Nguyn i ThAn ton Mng170 Ch giao vn v ng hm Nguyn i ThAn ton Mng171 Phn u ESP m bo bo mt ni dung v bo mt lung tin hu hn C th cung cp cc dch v xc thc ging nh vi AH Cho php s dng nhiu gii thut m ha, phng thc m ha, v cch n khc nhau DES, 3DES, RC5, IDEA, CAST,... CBC,... n cho trn kch thc khi, kch thc trng, che du lu lng lung tin Nguyn i ThAn ton Mng172 Khun dng ESP Nguyn i ThAn ton Mng173 Giao vn v ng hm ESP Ch giao vn ESP dng m ha v c th c thm chc nng xc thc d liu IP Ch m ha d liu khng m ha phn u D b phn tch lu lng nhng hiu qu p dng cho truyn ti gia hai im cui Ch ng hm m ha ton b gi tin IP Phi b xung phn u mi cho mi bc chuyn p dng cho cc mng ring o, truyn ti thng qua cu ni Nguyn i ThAn ton Mng174 Kt hp cc lin kt an ton Mi SA ch c th ci t mt trong hai giao thc AH v ESP ci t c hai cn kt hp cc SA vi nhau To thnh mt gi lin kt an ton C th kt thc ti cc im cui khc nhau hoc ging nhau Kt hp theo 2 cch Gn vi giao vn To ng hm theo nhiu bc Cn xem xt th t xc thc v m haNguyn i ThAn ton Mng175 V d kt hp cc SA Nguyn i ThAn ton Mng176 Qun l kha C chc nng sn sinh v phn phi kha Hai bn giao tip vi nhau ni chung cn 4 kha Mi chiu cn 2 kha: 1 cho AH, 1 cho ESP Hai ch qun l kha Th cng Qun tr h thng khai bo cc kha khi thit lp cu hnh Thch hp vi cc mi trng nh v tng i tnh T ng Cho php to kha theo yu cu cho cc SA Thch hp vi cc h phn tn ln c cu hnh lun thay i Gm cc thnh phn Oakley v ISAKMP Nguyn i ThAn ton Mng177 Oakley L mt giao thc trao i kha da trn gii thut Diffie-Hellman Bao gm mt s ci tin quan trng S dng cookie ngn tn cng gy qu ti Cookie cn ph thuc vo cc bn giao tip, khng th sinh ra bi mt bn khc vi bn sinh cookie, c th sinh v kim tra mt cch nhanh chng H tr vic s dng cc nhm vi cc tham s Diffie-Hellman khc nhau S dng cc gi tr nonce chng tn cng lp li Xc thc cc trao i Diffie-Hellman chng tn cng ngi gia Nguyn i ThAn ton Mng178 ISAKMP Vit tt ca Internet Security Association and Key Management Protocol Cung cp mt c cu cho vic qun l kha nh ngha cc th tc v cc khun dng thng bo cho vic thit lp, tha thun, sa i, v hy b cc lin kt an ton c lp vi giao thc trao i kha, gii thut m ha, v phng php xc thc Nguyn i ThAn ton Mng179 Cc khun dng ISAKMP Nguyn i ThAn ton Mng180 Chng 8 AN TON WEB Nguyn i ThAn ton Mng181 Vn an ton Web (1) Web c s dng rng ri bi cc cng ty, t chc, v cc c nhn Cc vn c trng i vi an ton Web Web d b tn cng theo c hai chiu Tn cng Web server s gy tn hi n danh ting v tin bc ca cng ty Cc phn mm Web thng cha nhiu li an ton Web server c th b khai thc lm cn c tn cng vo h thng my tnh ca mt t chc Ngi dng thiu cng c v kin thc i ph vi cc him ha an ton Nguyn i ThAn ton Mng182 Vn an ton Web (2) Cc him ha i vi an ton Web Tnh ton vn Tnh bo mt T chi dch v Xc thc Cc bin php an ton Web Nguyn i ThAn ton Mng183 SSL L mt dch v an ton tng giao vn Do Netscape khi xng Phin bn 3 c cng b di dng bn tho Internet Tr thnh chun TLS Phin bn u tin ca TLS SSLv3.1 tng thch ngc vi SSLv3 S dng TCP cung cp dch v an ton t u cui ti u cui Gm 2 tng giao thc Nguyn i ThAn ton Mng184 M hnh phn tng SSL Nguyn i ThAn ton Mng185 Kin trc SSL (1) Kt ni SSL Lin kt giao tip t im nt ti im nt Mang tnh nht thi Gn vi mt phin giao tc Cc tham s xc nh trng thi kt ni Cc s ngu nhin chn bi server v client Kha MAC ca server Kha MAC ca client Kha m ha ca server Kha m ha client Cc vector khi to Cc s th t Nguyn i ThAn ton Mng186 Kin trc SSL (2) Phin SSL Lin kt gia client v server To lp nh giao thc bt tay C th bao gm nhiu kt ni Xc lp mt tp cc tham s an ton s dng bi tt c cc kt ni trong phin giao tc nh danh phin Chng thc im nt Phng php nn c t m ha Kha b mt ch C c th tip tc hay khng Nguyn i ThAn ton Mng187 Giao thc bn ghi SSL Cung cp cc dch v bo mt v xc thc Kha b mt chung do giao thc bt tay xc lp Nguyn i ThAn ton Mng188 Khun dng bn ghi SSL Nguyn i ThAn ton Mng189 Giao thc i c t m ha SSL Mt trong ba giao thc chuyn dng SSL s dng giao thc bn ghi SSL Ch gm mt thng bo cha mt byte d liu c gi tr l 1 Khin cho trng thi treo tr thnh trng thi hin thi Cp nht c t m ha cho kt ni Nguyn i ThAn ton Mng190 Giao thc bo ng SSL Dng chuyn ti cc bo ng lin quan n SSL ti cc thc th im nt Mi thng bo gm 2 byte Byte th nht ch mc nghim trng Cnh bo : c gi tr l 1 Tai ha : c gi tr l 2 Byte th hai ch ni dung bo ng Tai ha : unexpected_message, bad_record_mac, decompression_failure, handshake_failure, illegal_parameter Cnh bo : close_notify, no_certificate, bad_certificate, unsupported_certificate, certificate_revoked, certificate_expired, certificate_unknown Nguyn i ThAn ton Mng191 Giao thc bt tay SSL Cho php server v client Xc thc ln nhau Tha thun cc gii thut m ha v MAC Tha thun cc kha mt m s c s dng Gm mt chui cc thng bo trao i gia client v server Mi thng bo gm 3 trng Kiu (1 byte) di (3 byte) Ni dung (> 0 byte) Nguyn i ThAn ton Mng192 TLS L phin bn chun Internet ca SSL M t trong RFC 2246 rt ging vi SSLv3 Mt s khc bit nh so vi SSLv3 S phin bn trong khun dng bn ghi SSL S dng HMAC tnh MAC S dng hm gi ngu nhin khai trin cc gi tr b mt C thm mt s m bo ng Khng h tr Fortezza Thay i trong trao i chng thc Thay i trong vic s dng d liu m