n chuyn ngnh

n chuyn ngnh

LI CM N

Em xin chn thnh cm n :

Thy Nguyn Kim Tun, ging vin hng dn trc tip gip em rt nhiu trong thi gian nghin cu v thc hin n chuyn ngnh.Cc thy c b mn Cng Ngh Thng Tin i hc Duy Tn tn tnh dy bo, truyn t kin thc v nhiu kinh nghim qu bu cho em trong sut thi gian qua.

Gia nh v bn b quan tm, khuyn khch v gip em trong sut qu trnh honh thnh n.

Sau cng em xin chc ton th qu thy c trong khoa Cng Ngh Thng Tin, thy Nguyn Kim Tun mt li chc sa khe, lun thnh cng trong cng vic v cuc sng.

Do kin thc cn hn ch nn chc n chuyn ngnh cn nhiu sai st. Em rt mong nhn c s gp t cc qu thy c v bn b n c hon thin hn.

Mt ln na em xin chn thnh cm n!

Sinh vin thc hin

Nguyn Th Thy

LI CAM OAN

Em xin cam oan :

Nhng ni dung trong ti ny l do em thc hin di s hngdn trc tip ca thy Nguyn Kim Tun.

Mi tham kho dng trong lun vn u c trch dn r rng v trung thc tn tcgi, tn cng trnh, thi gian, a im cng b.

Mi sao chp khng hp l, vi phm quy ch o to, hay gian tr,em xin chu hon ton trch nhim.

Sinh vin thc hin

Nguyn Th Thy

MC LC

1LI CM N

2LI CAM OAN

3MC LC

6DANH MC HNH

8DANH MC CC T VIT TT

1LI M U

2CHNG I: TNG QUAN V BO MT

21.1. AN TON THNG TIN L G

21.2. CC MI E DA VI MT H THNG V CC BIN PHP NGN CHN

21.2.1. Cc mi e da vi mt h thng

41.2.2. Cc bin php ngn chn

41.3. MC TIU V NGUYN TC CHUNG CA AN TON BO MT THNG TIN

51.3.1. Tnh b mt

51.3.2. Tnh ton vn

51.3.3. Tnh sn sng

61.4 M HA

61.4.1. Khi nim

61.4.2. Cc k thut m ha

9CHNG II: CH K S TRONG TRONG TH IN T

92.1.GII THIU V CH K S V NHNG CNG C LIN QUAN

102.1.1. Khi nim v ch k s

102.1.2. So snh ch k s vi ch k thng thng (ch k vit tay) trn vn bn

102.1.3. V tr vai tr ca ch k s

112.1.4. Phn loi ch k s

122.1.5. nh ngha lc ch k s

132.1.6. Lc ch k s RSA

132.2. C S HNH THNH CH K S

132.2.1. C s ton hc

132.2.1.1. Sinh s nguyn t v phn tch tha s nguyn t

152.2.1.2. Php m ha v khai cn Modul

162.2.2. Hm bm mt m

162.2.2.1.Gii thiu

172.2.2.2.nh ngha

182.2.2.3. Cu trc c bn ca thut ton bm

192.2.2.4. Gii thut MD4

192.2.2.5. Gii thut MD5

222.2.2.6. Gii thut SHA-1

232.2.3 H m ha RSA

27CHNG III: TRIN KHAI V CI T

273.1. CI T MY CH CA V CP CHNG CH S CHO MY TRM

393.2 TO CH K IN T V M HA TH IN T BNG OUTLOOK EXPRESS

44KT LUN

46TI LIU THAM KHO

DANH MC HNH

12Hnh 1.1: M hnh h m ha i xng

13Hnh 1.2: M hnh m ha kha cng khai

23Hnh 2.1: nh minh ha lm vic ca mt hm bm

27Hnh 2.2: Gii thut MD5

29Hnh 2.3: SHA-1

33Hnh 3.1 M hnh bo mt CA

34Hnh 3.2 Ci dt chng ch s gc (Chng ch s CA)

34Hnh 3.3 Chn chng ch s gc (chng ch s CA)

35Hnh 3.4 Ci t chng ch s gc (Chng ch s CA)

36Hnh 3.5 Kt thc vic ci t chng ch s gc (Chng ch s CA)

36Hnh 3.6 Ci dt chng ch s vo my trm

37Hnh 3.7 Chn yu cu v yu cu chng ch s

37Hnh 3.8 La chn thng tin m rng v yu cu chng ch s

38Hnh 3.9 To chng ch s c chp nhn t CA

38Hnh 3.10 La chn thng s v cc thut ton ca chng ch s

39Hnh 3.11 Ci t chng ch s ca ngi dng

39Hnh 3.12 Kim tra chng ch s ca ngi dng c ci t

40Hnh 3.13 Kim tra tnh hp l ca ch k s

41Hnh 3.14 Kt xut cp kha Public v Private

41Hnh 3.15 Chn nh dng cho kha Public ca ngi dng

42Hnh 3.16 t tn cho kha Public ca ngi dng

42Hnh 3.17 Hon thnh vic to kha Public cho ngi s dng

43Hnh 3.18 t tn cho kha Private ca ngi dng

43Hnh 3.19 Chn nh dng cho kha Private ca ngi s dng

44Hnh 3.20 Nhp Password kha Private ca ngi s dng

44Hnh 3.21 Hon Thnh vic to kha Private cho ngi s dng

45Hnh 3.22 Biu tng kha Public ca ngi s dng

45Hnh 3.23 Biu tng kha Private ca ngi s dng

46Hnh 2.24 Thit lp ch k v m ha vi Outlook Express bc 1

46Hnh 2.25 Thit lp ch k v m ha vi Outlook Express bc 2

47Hnh 2.26 Thit lp ch k v m ha vi Outlook Express bc 3

47Hnh 2.27 Thit lp ch k v m ha vi Outlook Express bc 4

48Hnh 2.28 To ch k s cho Outlook Express

49Hnh 2.29 S dng ch k s cho tt c cc th gi i

49Hnh 2.30 S dng m ha cho tt c cc th gi i

50Hnh 2.31 Nhn bit th k hoc m ha

DANH MC CC T VIT TTT vit ttT y ngha

DoSDenial of serviceTn cng t chi dch v

MD4Message Digest 4Thut ton MD4

MD5Message Digest 5Thut ton MD5

SHASecure Hash AlgorithmThut gii bm an ton

SMTPSimple Mail Transfer ProtocolGiao thc truyn ti th tn n gin

POPPoint of presenceim truy cp truyn thng

DCDomain ControllerMy ch Domain Controller

CACertificate AuthorityNh phn phi chng thc s

DNSDomain Name SystemH thng phn gi tn min

DHCPDynamic Host Configuration ProtocolGiao thc cu hnh host ng

VPNVirtual Private NetworkMng ring o

L2TPLayer 2 Tunneling ProtocolGiao thc ng ngm lp 2

IPSecInternet Protocol SecurityGiao thc an ninh Internet

PKIPublic Key InfrastructureC s h tng kho cng khai

PPPPoint to Point ProtocolGiao thc im ti im

PPTPPoint to Point Tunneling ProtocolGiao thc ng ngm im ti im

TCPTransmission Control ProtocolGiao thc iu khin ng truyn

UDPUser Datagram ProtocolGiao thc UDP

LI M UMt m hc l mt trong nhng vn quan trng trong lnh vc bo mt v an ton thng tin. Trn th gii, mt m hc c ra i t thi La M c i v ngy cng c nghin cu, pht trin t c nhng thnh tu to ln. Trong mt m hc vn bo mt lun i i vi vn xc thc thng tin, c bit l trong h thng m ha kha cng khai vn xc thc l v cng quan trng. Vi s bng n ca mng Internet hin nay, khi m ng dng trn mng my tnh cng tr nn ph bin, thun li v quan trng th yu cu v an ton mng, bo mt d liu cng tr nn cp bch v cn thit. Ngun ti nguyn mng rt d b nh cp hoc ph hng nu khng c mt c ch cho chng hoc s dng c ch bo mt qu lng lo. Thng tin trn mng, d ang truyn hay lu tr cn c bo v. Cc thng tin y phi c gi b mt; Cho php ngi ta kim tra tin tng rng chng khng b sa i so vi dng nguyn thy ca mnh v chng ng l ca ngi nhn n gi n. gii quyt vn trn ngi ta a ra mt cch gii quyt hiu qu, l ch k s. Vic s dng ch k s l mt gii php hu hiu, ngy cng c ng dng nhiu trong thc t. l l do em chn ti Ch k s v ng dng lm n chuyn ngnh ca mnh. n s tp trung nghin cu v cch thc bo mt, m bo mail ca mnh s khng b c trm hay mt mt cc d liu nh km khi c truyn i trong mng bng ch k.

CHNG I: TNG QUAN V BO MT1.1. AN TON THNG TIN L GThng tin c lu tr bi cc sn phm v h thng CNTT l mt ti nguyn quan trng cho s thnh cng ca t chc , l ti sn ca mt c nhn hay t chc. Cc thng tin c nhn lu tr trong h thng thng tin cn c gi b mt, bo v v khng b thay i khi khng c php. Trong khi cc sn phm v h thng CNTT thc hin cc chc nng ca chng, cc thng tin cn c kim sot m bo chng c bo v chng li cc nguy c, v d nh vic ph bin v thay i thng tin khng mong mun v tri php, nguy c mt mt thng tin. An ton thng tin l an ton k thut cho cc hot ng ca cc c s h tng thng tin, trong bao gm an ton phn cng v phn mm theo cc tiu chun k thut do nh nc ban hnh; duy tr cc tnh cht b mt, ton vn, chnh xc, sn sng phc v ca thng tin trong lu tr, x l v truyn ti trn mng (theo nh ngha trong Ngh nh 64-2007/N-CP).Thut ng an ton CNTT thng s dng ch vic ngn chn v lm gim nh cc mi nguy hi tng t i vi cc sn phm v h thng CNTT.1.2. CC MI E DA VI MT H THNG V CC BIN PHP NGN CHN

1.2.1. Cc mi e da vi mt h thngTrong thi gian gn y, s v xm nhp tri php cc h thng thng tin qua mng Internet v Intranet ngy cng tng. C nhiu nguyn nhn dn n vic cc mng b tn cng nhiu hn, trong s nhng nguyn nhn chnh c th k n xu hng chuyn snag mi trng tnh ton client/server (khch/ch), cc ng dng thng mi in t, vic hnh thnh mng Intranet ca cc cng ty vi vic ng dng Internet vo cc mng kiu ny dn ti xa nha ranh gii gia phn bn ngoi (Internet) v phn bn trong (Intranet) ca mng, ta nn nhng nguy c mi v an ton thng tin. Cng cn lu rng nhng nguy c mt an ton thng tin khng ch do tn cng t bn ngoi m mt phn ln li chnh l t ni b: nhn vin bt mn, sai st ca ngi s dng, thc bo mt km,

Cc phng php tn cng vo h thng thng tin ca nhng k ph hoi (hacker) ngy cng tr nn tinh vi, li dng nhng im yu c bn ca mi trng tnh ton phn tn. Mt s cc phng php tn cng thng gp:

Cc th thut quan h:Hacker mo nhn l ngi trong c quan, ngi ph trch mng hoc nhn vin an ninh hi mt khu ca ngi s dng. Vi nhng mng c ngi s dng t xa th hacker ly l do qun mt khu hoc b hng a cng yu cu cp li mt khu.

B mt khu:Hacker tm cch ly file mt khu v sau tn cng bng t in, da trn cc thut ton m ha m cc h diu hnh s dng. Nhng mt khu yu rt d b pht hin bng cch ny.

Virus v cc chng trnh tn cng t bn trong:Hacker c th s dng chng thc hin nhng vic nh: bt cc k t g vo bn phm tm mt khu, chp trm file mt khu, thay i quyn ca ngi s dng

Cc cng c tn cng gi mo a ch (IP spoofing):Hacker c th s dng nhng cng c ny lm h thng tng lm my tnh ca hacker l mt my trong mng ni b, hoc xa du vt trnh pht hin.

Tn cng t chi dch v (DoS- Denial of Service):

y l kiu tn cng lm t lit h thng, lm mt kh nng cung cp dch v (Denial of Service - DoS) khng cho h thng thc hin c cc chc nng m n c thit k. Kiu tn cng ny rt kh ngn chn bi chnh nhng phng tin dng t chc tn cng li chnh l nhng phng tin dng lm vic v truy cp thng tin trn mng. Mt th d v trng hp c th xy ra l mt ngi trn mng s dng chng trnh y ra nhng gi tin yu cu v mt trm no . Khi nhn c gi tin, trm lun lun phi x l v tip tc thu cc gi tin n sau cho n khi b m y, dn ti tnh trng nhng nhu cu cung cp dch v ca cc my khc n trm khng c phc v.

iu ng s l cc kiu tn cng DoS ch cn s dng nhng ti nguyn gii hn m vn c th lm ngng tr dch v ca cc site ln v phc tp. Do vy loi hnh tn cng ny cn c gi l kiu tn cng khng cn xng (asymmetric attack). Chng hn nh k tn cng ch cn mt my tnh PC thng thng vi mt modem tc chm vn c th tn cng lm ngng tr cc my tnh mnh hay nhng mng c cu hnh phc tp. Nghe trm trn mng

Thng tin gi i trn mng thng c lun chuyn t my tnh ny qua hng lot cc mytnh khc mi n c ch. iu , khin cho thng tin ca ta c th b k khc nghe trm.Ti t hn th, nhng k nghe trm ny cn thay th thng tin ca chng ta bng thng tin doh t to ra v tip tc gi n i. Vic nghe trm thng c tin hnh sau khi cc hacker chim c quyn truy nhp h thng hoc kim sot ng truyn. May mn thay, chng tavn cn c mt s cch bo v c ngun thng tin c nhn ca mnh trn mng bng cchm ho ngun thng tin trc khi gi i qua mng Internet. Bng cch ny, nu c ai nc thng tin ca mnh th cng ch l nhng thng tin v ngha.1.2.2. Cc bin php ngn chnThng c 3 bin php ngn chn:

iu khin thng qua phn mm: da vo cc c ch an ton bo mt ca h thng nn (h iu hnh), cc thut ton mt m hc.

iu khin thng qua phn cng: cc c ch bo mt, cc thut ton mt m hc c cng ha s dng.

iu khin thng qua cc chnh sch cu t chc: ban hnh qui nh ca cc t chc nhm m bo tn an ton ca mt h thng1.3. MC TIU V NGUYN TC CHUNG CA AN TON BO MT THNG TINAn ton thng tin yu cu nhm m bo ba c im quan trng nht ca thng tin, l: tnh b mt, tnh ton vn, tnh sn sng. Cc c im ny bao trm ton b an ton cc h thng thng tin. Cc c im ny cng ng vi mi t chc, khng l thuc vo vic chng chuia s thng tin nh th no.1.3.1. Tnh b mtTnh b mt l tm im chnh ca mi gii php an ton cho mt sn phm/h thng CNTT. Mt gii php an ton l tp hp cc quy tc xc nh quyn c truy cp n vi thng tin ang tm kim, i vi mt s lng ngi s dng thng tin nht nh v mt s lng thng tin l ti sn nht nh. Trong trng hp kim sot truy cp cc b, nhm ngi truy cp s c kim sot xem l h truy cp nhng s liu no. Tnh b mt l s m bo rng cc chc nng kim sot truy cp c hiu lc.

m bo tnh b mt l nhm loi b nhng s truy cp khng c php vo cc khu vc l c quyn ca cc c nhn, t chc.1.3.2. Tnh ton vn

Tnh ton vn, khng b sa i l c tnh phc hp nht v d b hiu lm ca thng tin. Mt nh ngha khi qut hn c s dung trong ti liu ny l vn cp l cht lng ca s liu (thng tin), ch khng phi l con ngi c/ hoc khng c php truy cp. c tnh ton vn c hiu l cht lng ca thng tin c xc nh cn c vo xc thc khi phn nh thc t. S liu cng gn vi thc t bao nhiu th cht lng thng tin cng chun by nhiu.

m bo tnh ton vn ca thng tin l mt lot cc cc bin php ng b nhm h tr v m bo tnh thi s kp thi v s y trn vn, cng nh s bo mt hp l cho thng tin.

1.3.3. Tnh sn sng

Tnh sn sng ca thng tin cng l mt c tnh quan trng, khng khc g cc c tnh cp n trn. l kha cnh sng cn ca an ton thng tin, m bo cho thng tin n ng a ch (ngi c php s dng) khi c nhu cu, hoc c yu cu.

Tnh sn sng m bo n nh ng tin cy ca thng tin, cng nh m nhim chc nng l thc o, xc nh phm vi ti hn ca an ton mt h thng thng tin.1.4 M HA1.4.1. Khi nim

bo mt thng tin truyn trn mng, ngi ta s dng cc phng php m ha (Encryption). M ha l qu trnh bin i thng tin (phim, hnh nh, vn bn) dng c c sang dng khng c c bng mt thut ton no (to mt m) v s c bin i ngc li (gii m) bn nhn.1.4.2. Cc k thut m haa. M ha i xngThut ton i xng hay cn gi thut ton m ho c in l thut ton mti kho m ho c th tnh ton ra c t kho gii m. Trong rt nhiutrng hp, kho m ho v kho gii m l ging nhau. Thut ton ny cnc nhiu tn gi khc nh thut ton kho b mt, thut ton kho n gin,thut ton mt kho. Thut ton ny yu cu ngi gi v ngi nhn phitho thun mt kho trc khi thng bo c gi i, v kho ny phi cct gi b mt. an ton ca thut ton ny vn ph thuc v kho, nu l ra kho ny ngha l bt k ngi no cng c th m ho v gii mthng bo trong h thng m ho.S m ho v gii m ca thut ton i xng biu th bi : M ha:Y = EK(X) Gii m:X = DK(Y)

Hnh 1.1: M hnh h m ha i xngb. M ha kha cng khaiVo nhng nm 1970 Diffie v Hellman pht minh ra mt h m ho mic gi l h m ho cng khaihay h m ho phi i xng.Thut ton m ho cng khai l khc bit so vi thut ton i xng. Chngc thit k sao cho khos dng vo vic m ho l khc so vi khogii m. Hn na kho gii m khng th tnh ton c t kho m ho.Chng c gi vi tn h thng m ho cng khai bi v kho m hoc th cng khai, mt ngi bt k c th s dng kho cng khai m hothng bo, nhng ch mt vi ngi c ng kho gii m th mi c khnng gii m. Trong nhiu h thng, kho m ho gi l kho cng khai(public key), kho gii m thng c gi l kho ring (private key).

Hnh 1.2: M hnh m ha kha cng khaic trng ni bt ca h m ha kha cng khai l c kha cng khai (Public key) v bn tin m ha (Ciphertext) u c th gi i trn mt knh thng tin khng an ton.

Diffie v Hellman xc nh r cc iu kin ca mt h m ha kha cng khai nh sau: Vic tnh ton ra cp kha cng khai KB v b mt kBda trn c s cc iu kin ban u phi c thc hin mt cch d dng ngha l thc hin trong thi gian a thc. Ngi gi A c c kha cng khai ca ngi nhn B v c bn tin P cn gi i th c th d dng to ra c bn m C.

C = EKB (P) = EB (P)Cng vic ny cng trong thi gian a thc. Ngi nhn B khi nhn c bn tin m ha C vi kha b mt kB th c th gii m bn tin trong thi gian a thc.

P = DkB (C) = DB[EB(M)]

Nu k ch bit kho cng khai KB c gng tnh ton kho b mt th khi chng phi ng u vi trng hp nan gii, trng hp ny i hi nhiu yu cu khng kh thi v thi gian.

Nu k ch bit c cp (KB,C) v c gng tnh ton ra bn r P th gii quyt bi ton kh vi s php th l v cng ln, do khng kh thi.

CHNG II: CH K S TRONG TRONG TH IN T2.1.GII THIU V CH K S V NHNG CNG C LIN QUANTrong i sng hng ngy, ch k (vit tay) trn mt vn bn l mt chng minh v bn quyn hay t nht cng l s tn ng, tha nhn cc ni dung trong vn bn. Chng hn nh trn vic k vo phiu nhn tin ca ngn hng, hp ng mua bn, chuyn nhng, tha k, t tng... Ch k vit tay c chnh tay ngi k nn khng th sao chp c. Thng thng ch k vit tay trn vn bn th c dng xc nhn ngi k n. Nhng yu t no lm nn sc thuyt phc ca n?. V mt l tng th: Ch k l bng chng th hin ngi k c ch nh khi k vn bn

Ch k th hin ch quyn, n lm cho ngi nhn vn bn bit ai ch th l ngi d k vn bn Ch k khng th ti s dng, tc l n l mt phn ca vn bn m khng th sao chp sang cc vn bn khc

Vn bn k khng th thay i c

Ch k khng th gi mo v cng l th khng th chi b( ngi k vn bn khng th ph nh vic mnh k vn bn v ngi khc khng th to ra ch k ).

Trong cuc sng i thng, to ra mt m hnh l tng nh trn lkhng d v vic k trn bn giy l c th b gi mo ch k, nhng vi kh nng kim nh st sao th vic lm thay i khng phi d. Tuy nhin trong th gii my tnh th vn k nh trong thc t gp rt nhiu kh khn: cacsdongf thng tin trn my tnh c th thay i d dng, hnh nh ca ch k tay ca mt ngi cng d dng cho sang truyn t mt vn bn ny sang mt vn bn khc, v vic thay i ni dung mt vn bn in t (sau khi k) cng chng li du vt g v phng din ty xa c c nhng c tnh nh trn, giao thc k trong th gii in t cn phi c h tr ca cng ngh m ha. S ch k s l phng php k mt thng bo di dng in t. Giao thc c bn ca ch k s da trn tng ca Diffie v Hellman:

Ngi gi (ch nhn ca vn bn) k vn bn bng cch m ha n vi kha b mt ca mnh.

Ngi gi chuyn vn bn k cho ngi nhn

Ngi nhn vn bn kim tra ch k bng cch s dng cha kha cng khai ca ngi gi gii m vn bn

2.1.1. Khi nim v ch k sCh k s (kha cng khai) l m hnh s dng cc k thut mt m gn vi mi ngi s dng mt cp kha cng khai b mt v qua c th k cc vn bn in t cng nh trao i cc thng tin mt. Kha cng khai thng c phn phi thng qua chng thc kha cng khai. Qu trnh s dng ch k s bao gm hai qu trnh: to ch k v kim tra ch k.Cc thut ton ch k s cho php xc nh ngun gc, bo m tnh ton vn ca du liu c truyn i, ng thi n cng bo m tnh khng th ph nhn ca thc t k thng tinh.

2.1.2. So snh ch k s vi ch k thng thng (ch k vit tay) trn vn bn

Ch k s v ch k thng c nhiu im khc nhau:

Vi ti liu c k: Vi ti liu thng thng, n l mt phn vt l ca ti liu. Ngc li, ch k s khng phi theo kiu vt l gn vo thng bo nn khng nhn thy trn bc in

V vn kim tra ch k: Ch k thng thng c kim tra bng cch so snh n vi cc ch k xc thc khc (ch k mu). im yu cu ch k thng thng l khng an ton, v d c th gi mo. Ngc li, ch k s li c kim tra nh dng thut ton kim tra cng khai, bt k ai cng c th kim tra c. Vic dng mt s ch k an ton c th ngn chn c gi mo.

2.1.3. V tr vai tr ca ch k s

Xu hng quc t ha v ton cu ha v ang nh hng n s pht trin ca th gii. Vic trao i thng tin cng t yu cu nhanh gn, chnh xc v c bit l phi an ton. Vic trao i thng tin, chng thc thng tin theo phong cch truyn thng lm gim tc , cng nh s chnh xc ca thng tin. Nhng cng vic mang tnh cht th cng gy ra s chm ch v thiu chnh xc trong trao i.Chnh kh khn ny sinh s pht trin mnh m ca cng ngh thng tin v cng ngh m ha . Hin nay, tt c cc nc pht trin cng nh ang pht trin, mng my tnh ang ngy cng ng vai tr thit yu trong mi lnh vc hot ng ca ton x hi v nhu cu bo mt thng tin c t ln hng u. in hnh l vic m ho bo mt cc thng tin s ca doanh nghip, dng ch k s xc thc email trao i thng tin, kim sot truy cp vo cc sn thng mi in t v cc n t hng, ngn hng in t, mua sm trc tuyn... m vai tr ch yu l ch k s in t.Trn thc t, ch k s khng ch c thc hin cho cc giao dch in t trn mng internet m cn qua h thng mng vin thng di ng.c bit, hin nay nhiu nc trn th gii khng ch trin khai ng dng ch k s trn mng my tnh m cn p dng trn mng in thoi di ng thc hin cc giao dch in t. Hng i ny gip y nhanh giao dch, n gin ho mua sm trc tuyn v gip ngi dng c th truy cp mi lc, mi ni.

S ra i ca ch k s khng inh c li ch to ln v chin lc v kinh t, ng thi cc vn lin quan n ch k s cng l nhng ch quan trng nht ca mt m hc.2.1.4. Phn loi ch k s

Chng ta c th chia ch k s ra 2 loi: K thut k m ch k s l mt phn nh vo thng ip gi i, c 2 u l u vo cho qu trnh xc minh tnh ng n ca ch k v loi ch k m t n c th phc hi li thng ip ban u trc khi k, thng ip ban u ny khng phi l u vo cho qu trnh xc minh ch k.

Do tnh thc t ca ch k s m lun vn ch yu tp trung vo k thut k th 2, ch k s nh mt phn nh km thm cho qu trnh xc minh thng ip. Nhng c im c bn ca ch k ny l : Ch k in t i km vi thng ip gc

Cn c thng ip (gc) cho qu trnh kim tra ch k in t

S dng hm bm mt m. V d: RSA, DSA

Da trn thut ton m ha. V d: ch k s Full Domain Hash, RSA-PSS da theo thut ton m ha RSA, ch k s DSA da vo thut ton DSA

2.1.5. nh ngha lc ch k sMt s ch k s bao gm hai thnh phn ch cht l thut ton k v thut ton xc minh.Mt s ch k s l mt b 5 (P,A,K,S,V) tha mn cc iu kin sau: P l mt tp hp cc bn r c th

A l tp hu hn cc ch k c th K l tp hu hn cc kha c th S l tp cc thut ton k V l tp cc thut ton xc minh

Vi mi k thuc K, tn ti mt thut ton k sigk thuc S v mt thut ton xc minh verk thuc V, trong sigk v verk l cc nh x : sigk l mt nh x t P sang A v Verk l mt nh x t A sang tp biu din {True, False} tha mn vi mi x thuc P, y thuc A,ver (x,y)= true nu y=sig(x) v ver(x,y) = false nu y khc sig(x). Vi mi k thuc K, hm sigk v verk l cc hm thi gian a thc, verk l hm cng khai cn sigk l hm mt. ngha ca s Khi mt ngi dng mun k ln mt thng bo x th ngi dng thut ton an ton to ra ch k y =sig(x) nhn c v gi cho ngi nhn. Ngi nhn nhn c ch k sig(x) th dng thut ton xc minh ver(x,y) xc nh tnh ng n ca ch k s ( tr v true hoc false).2.1.6. Lc ch k s RSA

Cho N = P x Q vi P v Q l cc s nguyn t khc nhau. Cho P = A = ZN v nh ngha P = {(N, P, Q, A, B) vi N = PQ, AB mod((N)))}. Cc gi tr N v B l cng khai. Ta nh ngha : sigk(x) = x(mod N)

V

verk(x,y) = true x y B(mod N)

Trong s ny, (N) l phi hm Euler (s gii thch chng 2 : (N) = (P-1)x(Q-1)). Thng ip x c k theo php tnh ng d vi kha ring vi kha ring ca ngi gi v qu trnh xc thc ch k cng da vo php tnh ng d nhng vi kha cng khai ca ngi gi.

2.2. C S HNH THNH CH K S2.2.1. C s ton hc

S hc l mt nhnh ca ton hc, nhng n li tr thnh mt trong nhng cng c hu hiu nht ca ngnh an ninh my tnh. Nh l s khi u, s hc gip bo v nhng d liu nhy cm nh s th tn dng khi gip ngi dng mua sm trc tuyn. chnh l kt qu ca mt s thnh tu nghin cu ng ghi nhn t nhng nm 1970 ti nay, c p dng rng ri trn th gii. Nhng giao thc m ha c bit l ch k s in t u da trn l thuyt s hc to kha, m ha v gii m. An ton ca nhng giao thc ny u lin quan ti vn trong s hc : gii thut cng khai v phn tch tha s nguyn t.2.2.1.1. Sinh s nguyn t v phn tch tha s nguyn t

Hai h qu v mt c lng trong thuyt s hc l tin cho h thng kha cngkhai RSA ngy nay.H qu 1 : Sinh s nguyn t th d. Vic tm ra mt s nguyn t ngu nhin vi kchc cho trc l d dng.N l kt qu ca hai im khc : S nguyn t vi kch thc bt k th rt ph binv vic kim tra s nguyn t th khng kh thm ch vi c s nguyn t rt ln.

sinh s nguyn t ngu nhin, n gin nht l ch vic sinh ra mt s nguynngu nhin vi ln cho v kim tra tnh nguyn t cho n khi mt s nguyn tc tm thy. Da vo iu kin s nguyn t, mt s k vng c kim tra da vo th t ca lnx( thut ton t nhin ca x) khi m x l mt s in hnh vi ln mongmun.Vic kim tra mt s l s nguyn t l khng d. Trong thc t, dng nh vic kimtra tnh nguyn t s yu cu mt s khc ngoi chnh s v s 1 l c ca s nguyn cn kim tra. Hu ht cc h m ha kha cng khai ngy nay ph thuc vo vic sinh s nguyn t.

Cho p, v q l 2 s nguyn t ln c sinh ngu nhin.(kch c trung bnh trong cch m ha thng l 512 bits hoc ln hn).H qu 2 : Php tnh nhn l d : Vi p v q cho trc, vic tnh kt qu ca phpnhn n = p.q l d dng.c lng 3 : Phn tch tha s l kh : Vi mt s nguyn n l kt qu ca phpnhn s nguyn t ln, vic tm li cc s nguyn t tha s p, q l rt kh.

Bt chp hng trm nm nghin cu trong vn ny, vic phn tch ra tha s ca mt s nguyn ln vn mt rt mt thi gian di. Phng php nhanh nht gn y nhanh hn rt nhiu so vi nhng cch n gin l tm tt c cc cc tha s cng mt thi im. Tuy nhin, phng php ny rt t. Cho v d, vic phn tch ra tha s nguyn t ca mt s 1024bit mt mt nm vi mt my gi 10 triu USD. Vi mt s 2048 bit th thi gian hon thnh cn gp vi t ln.Nhng c lng ny th t hn so vi d kin nhng nm 1970 khi vn u tin c xut trong ngnh mt m hc. ln khuyn co tng nhanh trong nhng nm gn dy, bi s khm ph ra nhng phng thc phn tch tha s nhanh hn cng nh s ph trin trong sc mnh tnh ton ca my tnh. Khng ai bit nhng phng thc nhanh hn s c pht hin trong nhng nm ti s xy ra bao gi. Nhng mt khc, khng ai c th chng minh n s khng xy ra. C hai kha cnh u tn ti thnh nhng lnh vc nghin cu ca ton hc.2.2.1.2. Php m ha v khai cn Modul

Nh trn ta khai bo n l kt qu ca php nhn hai s nguyn t ln c sinh ngu nhin. Cho m v c l nhng s nguyn nm trong khong (0,n-1) v e l mt s nguyn l trong khong (3,n-1) v nguyn t cng nhau vi p-1 v q-1.

Thao tc m ha v gii m trong h m ha kha cng khai RSA c thc hin da trn 2 h qu v 1 c lng sau :

H qu 4: Php tnh m ha modul l d : Cho n,m v e. Vic tnh c = me mod n l d dng

Gi tr me mod n chnh thc l kt qu ca nng ly tha e ca m, chia cho n v lyphn d. iu ny c th l mt php tnh ton phc tp lin quan ti vic nhn (e-1) s m v kt qu tr v l mt s nguyn ln, trc khi vic thc hin php chia cho n.Tuy nhin hai cch ti u ha sau lm cho vic tnh ton tr nn d dng :

Nhn vi mt trnh t thch hp ca cc gi tr trung gian trc , thay v hn ch bng m, c th gim s lng cc php nhn khng qu hai ln kch thc ca e trong h nh phn

Chia v ly phn d sau khi mi php nhn gi kt qu trung gian c cng kch thc nh n

H qu 5 : Php khai cn module nghch o ca php ly tha module. Cho n,e,c v nhng tha s nguyn t p, q, vic khi phc li gii tr m sao cho c = me mod n l d dng.

Gi tr m c th khi phc t c bi thao tc m ha modul vi mt s nguyn l d nm trong khong (3,n-1). c bit, vi s d ny, biu thc sau th hin cho tt c m : m= (me)d mod n.S nguyn d ny th d dng tnh vi e, p, q cho trc.

c lng 6: Php khai cn modul li kh mt hon cnh khc Cho n,e,nhng khng bit nhng tha s nguyn t, vic khi phc li m l kh khn.

Phng php nhanh nht th c sn trong vic tnh ton khai cn modul di iu kin da l n v e l phn tch tha s n v p dng h qu 5 quyt nh d. Thc s, bt k phng thc no quyt nh d u b chuyn v mt cch khc ca vic phn tch tha s n. ng l c th khi m tn ti mt phng php m tnh ton khai cn modul m khng cn phn tch n hoc quyt nh d. Nhng cho n nay cha phng php no c th lm nh vy nhanh hn vic phn tch tha s n.

Nhn xt:

S hc, c bit l s nguyn ln v cc php tnh ng d l nhng cng c quan trng trong mt m hc c bit l trong vic tnh ton mt m hc kha cng khai, in hnh l RSA. Tuy nhin chng ny cng ch trnh by qua cc thut ton lm vic vi nhng s nguyn ln m hu ht u c ci t thnh th vin nn nhng h thng thc t ngi ta s s dng chng tin cho qu trnh ci t.

2.2.2. Hm bm mt m

2.2.2.1.Gii thiu

Trong ngnh mt m hc, mt hm bm mt m hc (cryptographic hash function) l mt hm bm vi mt s tnh cht bo mt nht nh ph hp vic s dng trong nhiu ng dng bo mt thng tin a dng, chng hn nh chng thc (authentication) v kim tra tnh nguyn vn ca thng ip (message integrity). Mt hm bm nhn u vo l mt xu k t di (hay thng ip) c di ty v to ra kt qu l mt xu k t c di c nh, i khi c gi l tm tt thng ip (message digest) hoc ch k s (digital fingerprint).

Cc hm bm nhn mt chui bit c chiu di ty ( hu hn) lm d liu u vo v to ra mt chui bit c chiu di c nh bng n bit, gi l m bm. S thay i nh ca chui u vo cng lm thay i gi tr bm. K hiu D l min xc nh, R l min gi tr ca hm bm h(x).

h(x) : D R

Ta c s lng phn t ca tp D ln hn gi tr ca tp R hm bm h(x) khng phi l n nh Lun tn ti cp u vo khc nhau c cng gi tr bm.

Gi s hn ch hm h(x) trn min xc nh ch bao gm cc chui bit c chiu di t (t>n). Nu h(x) l ngu nhin vi tt c cc gi tr u ra ca n c xc sut bng nhau th c khong 2(t-n)u nh x vo mi gi tr u ra. Xc sut hai gi tr( c chiu di bng nhau) u vo nh x vo cng mt gi tr l 2-n(khng ph thuc vo t) Nu n ln th 2-n s rt nh. Nh vy mc d bit trc gi tr bm nhng tm mt u vo c cng gi tr bm vi gi tr bm bit l rt kh nu chn c h(x) thch hp v n ln.

Trong lnh vc m ha thng tin, m bm c xem nh c trng thu gn ca mt chui bit ty v dng nhn ra chui bit . Hm bm chnh l cng c to ra ch k s v m bo an ton d liu.2.2.2.2.nh ngha

Hm bm l mt gii tht nhm sinh ra cc gi tr bm tng ng vi mi khi d liu. Gi tr bm ng vai tr gn nh mt kha phn bit cc khi d liu.

Hnh 2.1:nh minh ha lm vic ca mt hm bmPhn loi:Hm bm mt chiu : (one way hash functions) : L hm bm mang cht : vi mi m bm bit trc, khng th tnh ton tm c chui bit ban u vo c m bm bng vi m bm cho [8]Hm bm khng xung t : (collision resistant hash funtions) l hm bm mang tnh cht : khng th tnh ton tm ra hai chui bit c cng gi tr bm.

Mt s tnh cht c bn ca hm bm :

(i) C th p dng vi thng bo u vo c di bt k

(ii) To ra gi tr bm y = h(x) c di c nh

(iii) h(x) d dng tnh c vi bt k x no (iv) Tnh mt chiu : Vi mi u ra y cho trc khng th tm c x sao cho h(x) bng gi tr y cho trc

(v) Tnh chng xung t yu : Vi mi d liu u vo x1 cho trc khng th tm c bt k gi tr x2 no (x2 khc x1) m h(x2) = h(x1).

(vi) Tnh chng xung t mnh : Khng th tnh ton tm c hai d liu u vo x1 v x2 phn bit sao cho chng c cng gi tr bm (h(x1) = h(x2))

Nh vy da theo cc tnh cht trn ta thy hm bm mt chiu tha mn tnh cht (iv) v tnh cht (v), cn hm bm khng xung t tha mn tnh cht (iv) v (vi).2.2.2.3. Cu trc c bn ca thut ton bmKhi d liu u vo x c chiu di hu hn ty s c phn thnh cc khi conlin tip c chiu di c nh r, gi s c nh s l x1,x2,...,xm. Tuy nhin do chiu di ca khi d liu ban u x l ty , do cn phi thm vo d liu ban u mt s bit ph sao cho tng s bit ca khi d liu x sau khi thm vo s l bi s ca r. Ngoi ra khi bit thm vo thng cha mt khi bit (c chiu di c nh trc, thng l 64 bit) xc nh chiu di thc s ca khi bit d liu khi cha thm cc bit ph. Tip theo, ln lt ct cc khi con r bit t khi m rng x. Mi khi con r bit xi ln lt bc qua mt hm nn f ca hm bm h(x). Ti bc th i, hm nn f nhn d liu u vo l xi v kt qu trung gian ca bc trc (bc i 1) to u ra l kt qu u vo l xi v kt qu trung gian ca bc trc (bc i 1) to u ra l kt qu chui bit c di c nh bng n > 0.

Kt qu k hiu IV l gi tr ban u (cho H0 ), th qu trnh lp x l dy cc khicon x1,x2,..,xm c m t :

H0 = IV

Hi = f(Hi-1,xi) (i = 1,2,..,m)

h(x) = g(Hm)

Cc bin Hi l cc bin dy chuyn

Hm g(x) ly bin dy chuyn cui cng to ra m bm cui cng cn tm. Trong hu ht cc thut ton g(x) thng c chn l nh x ng nht tc l g(Hm) = Hm

Khu then cht trong xy dng hm bm l thit k hm nn f Gi tr ca hm bm mt m ca mt thng ip c gi l Message Digest (MD).Mt s hm bm mt m thng dng : MD4,MD5 v SHA-12.2.2.4. Gii thut MD4MD4 (Message-Digest algorithm4) l mt thng ip tiu ha thut ton (th t trong lot a) c thit k bi Gio s Ronald Rivest ca MIT vo nm 1990. N thc hin mt hm bm mt m s dng trong kim tra tnh ton vn thng ip. Chiu di ca gi tr bm l 128 bit.

Thut ton MD4 nhn d liu u vo l mt chui bit x c chiu di b >= 0 ty v sinh ra m bm ca x c chiu di c nh 128 bit. Trc tin chui bit x c nh dng li bng cch thm r > 0 bit ph thuc vo x sao cho chiu di ca chui bit mi l b = b + r l bi s ca 512.

Sau chia chui bit mi ny thnh m khi, mi khi c di ng bng 512 bit . Mi khi bit ny li chia thnh 16 t, mi t c 32 bit.

Thut ton MD4 tun t x l dy m khi trong m lt tnh ton. D liu u vo ti lt tnh ton th k (1