tran quang thuan_k51mmt_khoa luan tot nghiep dai hoc
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I HC QUC GIA H NI TRNG I HC CNG NGH
Trn Quang Thun
NGHIN CU V XY DNG H TNG KHA CNG KHAI
KHO LUN TT NGHIP I HC H CHNH QUY Ngnh : Cng ngh thng tin
H NI - 2010
I HC QUC GIA H NI TRNG I HC CNG NGH
Trn Quang Thun
NGHIN CU V XY DNG H TNG KHA CNG KHAI
KHO LUN TT NGHIP I HC H CHNH QUY Ngnh : Cng ngh thng tin Cn b hng dn: PGS TS.H S m Cn b ng hng dn: TS.L c Phong
H NI - 2010
LI CM NTi xin gi li cm n chn thnh nht ti PGS.TS H S m, TS. L c Phong. Nhng ngi thy cho ti nhng nh hng v nhng kin rt qu bu ti hon thnh c kha lun tt nghip ny. Ti xin t lng bit n su sc ti cc thy c, bn b du dt, gip ti tin b trong sut qu trnh lm kha lun tt nghip. Xin cm n gia nh v b bn, nhng ngi lun khuyn khch v gip ti trong mi hon cnh kh khn. Ti xin cm n b mn Truyn Thng v Mng My Tnh, khoa Cng Ngh Thng Tin trng i Hc Cng Ngh-i Hc Quc Gia H Ni ht sc to iu kin cho ti trong qu trnh hc, lm v hon thnh kha lun ny.
M C L CTrn Quang Thun...........................................................................................................................1 H NI - 2010...........................................................................................................................1 Trn Quang Thun...........................................................................................................................2 Kha lun H tng kha cng khai (PKI), vn cp pht chng thc s v ng dng trong thng mi in t. H tng kha cng khai l mt b khung c bn xy dng m hnh an ninh, bo mt trong thng mi in t. Tm hiu vai tr ca chng thc s trong h tng kha cng khai. Vai tr ca chng thc s trong cc giao dch trc tuyn. Ngi s dng, ngoi hnh thc bo mt thng thng nh mt khu, cng phi dng mt chng thc s c nhn khng nh danh tnh ca mnh, xc nhn cc hot ng giao dch ca mnh vi dch v ngn hng, thng mi in t, dao dch chng khon... Chng thc s s gip nh qun l m bo rng khch hng khng th chi ci cc giao dch ca mnh, khi h dng chng thc s. T t ra cc vn qun l (cp pht,xc thc) thu hi v cp pht li chng thc s............................5 Trong kha lun ti s trnh by v cc vn chnh xoay quanh vn h tng kha cng khai (PKI). Phn u ca kha lun (chng 1) gii thiu vn v cch tip cn gii quyt vn s trnh by khi qut v mt vi khi nim c bn v mt m hc kha cng khai, h tng kha cng khai ; cc khi nim c bn v thut ton v l thuyt phc tp; mt vi cng c nn tng ca mt m hc kha cng khai (m ha thng tin, hm bm, ch k s). Chng 2 ca kha lun s lm r hn cc khi nim, cc vn c bn bn trong mt h tng kha cng khai (chng thc s, cc dch v ng k, cp pht, xc thc, thu hi, kha cng khai); ng dng ca h tng kha cng khai trong giao dch in t ngy nay ; v mt vi h thng h tng kha cng khai trong thc t. Chng 3 c t mt h tng kha cng khai n gin v Kt Lun.................................................................................................................................................5
TM TT KHA LUNKha lun H tng kha cng khai (PKI), vn cp pht chng thc s v ng dng trong thng mi in t. H tng kha cng khai l mt b khung c bn xy dng m hnh an ninh, bo mt trong thng mi in t. Tm hiu vai tr ca chng thc s trong h tng kha cng khai. Vai tr ca chng thc s trong cc giao dch trc tuyn. Ngi s dng, ngoi hnh thc bo mt thng thng nh mt khu, cng phi dng mt chng thc s c nhn khng nh danh tnh ca mnh, xc nhn cc hot ng giao dch ca mnh vi dch v ngn hng, thng mi in t, dao dch chng khon... Chng thc s s gip nh qun l m bo rng khch hng khng th chi ci cc giao dch ca mnh, khi h dng chng thc s. T t ra cc vn qun l (cp pht,xc thc) thu hi v cp pht li chng thc s. Trong kha lun ti s trnh by v cc vn chnh xoay quanh vn h tng kha cng khai (PKI). Phn u ca kha lun (chng 1) gii thiu vn v cch tip cn gii quyt vn s trnh by khi qut v mt vi khi nim c bn v mt m hc kha cng khai, h tng kha cng khai ; cc khi nim c bn v thut ton v l thuyt phc tp; mt vi cng c nn tng ca mt m hc kha cng khai (m ha thng tin, hm bm, ch k s). Chng 2 ca kha lun s lm r hn cc khi nim, cc vn c bn bn trong mt h tng kha cng khai (chng thc s, cc dch v ng k, cp pht, xc thc, thu hi, kha cng khai); ng dng ca h tng kha cng khai trong giao dch in t ngy nay ; v mt vi h thng h tng kha cng khai trong thc t. Chng 3 c t mt h tng kha cng khai n gin v Kt Lun.
DANH MC T VIT TT
PKI CA RSA DSA MD5 RA SHA SHS H RFC
Public Key Infrastructure Certificate Authority Rivest Shamir Adleman Digital Signature Algorithm Message Digest 5 Registration Authority Secure Hash Algorithm Secure Hash Standard Hash function Request For Comments
DANH MC HNH V V BNGHnh 1.1: Cp pht kha ring kha cng khai Hnh 1.2: M ha thng tin Hnh 1.3: To v xc thc ch k s Hnh 1.4 : M hnh xy dng PKI c bn Bng 1.5 : m hnh x dng xc thc Hnh 2.1 : c im ca cc thut ton bm SHA Bng 2.2 :So snh thi gian to kha, to ch k v xc nhn ch k ca RSA vi DSA Hnh 2.3 : Thi gian xc nhn ch k ca RSA v DSA Hnh 2.4 : Thi gian to ch k ca RSA v DSA Hnh 2.5 : Thi gian xc nhn ch k ca RSA v DSA Hnh 2.6 : M hnh phn cp Hnh 3.1 : Hm to cp kha ring v kha cng khai Hnh 3.2 : M phng to kha Hnh 3.3 : To ch k s Hnh 3.4 : Form nhp thng tin ca client Hnh 3.5 : Thng bo tr v khi kt qu gi thng tin thnh cng Hnh 3.6 : Xc thc kha cng khai v ch k s Hnh 3.7 : cp pht chng thc s Hnh 3.8 : Kim tra thng tin v cp pht chng thc s Hnh 3.9 : Xc thc chng thc s Hnh 3.10 : Form tm kim, sa, xa thng tin chng thc s Hnh 3.11 : Kim tra v thu hi chng thc s ht hn s dng
M u
Trong k nguyn ca cng ngh thng tin, tnh ph bin rng ri ca Internet mt mt em li nhiu ng dng tin li, th v v dn thay th cc hot ng truyn thng trong th gi thc; mt khc n t ra cc vn v s an ton, tnh tin cy ca nhng giao dch trn Internet. C s h tng kha cng khai (PKI) c th p ng, gii quyt nhng vn c bn nht cho nhng yu cu trn. Da trn cc dch v c bn v chng thc s v ch k s, mt PKI chnh l b khung ca cc chnh sch, dch v v phn mm m ha, p ng nhu cu bo mt ca ngi s dng. Khng ch nm trong lnh vc thng mi in t, chng thc s hin cn c s dng nh mt dng chng minh th c nhn. Ti cc nc cng ngh pht trin, chng thc s CA c tch hp vo cc chip nh nm trong th cn cc, th tn dng tng cng kh nng bo mt, chng gi mo, cho php ch th xc thc danh tnh ca mnh trn nhiu h thng khc nhau, chng hn nh xe bus, th rt tin ATM, kim sot hi quan, ra vo chung c .v.v. Vi cc c im ni bt nh khng th gi mo, chng thc ngun gc xut x, cc quc gia pht trin u s dng chng thc s nh mt bng chng php l t rt sm. y l yu t rt quan trng c th pht trin thng mi in t, v khng ai dm mo him vi tin ca mnh, khi h cha chc chn c rng cc hot ng c c m bo, v c c php lut cng nhn hay khng. Trong bn kha lun tt nghip ny, tc gi xin trnh by tng qut v c s h tng kha cng khai v ng dng ca n trong thng mi in t. Qua trnh by mt bn platform m phng hot ng ca mt h tng kha cng khai (PKI) c bn.
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Chng 1 : Gii Thiu1.1. Tm hiu Mt m hc kho cng khai1.1.1. Mt m hc kho cng khaiMt m hc kha cng khai (Phi i xng) l g
1.1.1.1.
- l mt chuyn ngnh ca mt m hc cho php ngi s dng trao i cc
thng tin mt m khng cn phi trao i cc kha chung b mt trc . iu ny c thc hin bng cch s dng mt cp kha c quan h ton hc vi nhau l kha cng khai v kha c nhn (hay kha b mt).-
Trong mt m hc kha cng khai, kha c nhn phi c gi b mt trong khi kha cng khai c ph bin cng khai. Trong 2 kha, mt dng m ha v kha cn li dng gii m. iu quan trng i vi h thng l khng th tm ra kha b mt nu ch bit kha cng khai.[1] Mc ch ca h thng m ho cng khai :
1.1.1.2.-
Cp pht kho ring v kho cng khai :
Hnh 1.1: Cp pht kha ring kha cng khai
Vic cp pht kho cng khai v kho b mt thng qua thut ton RSA (ph bin). Thut ton RSA to ra cp kho bng cc phng thc ton hc t 2 s nguyn t bt k ln.2
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M ho :
Hnh 1.2: M ha thng tin
Bob m ha thng tin gi cho Alice bng kha cng khai ca Alice. Alice nhn c tin nhn t Bob kim tra tin nhn v gii m bng kha b mt ca Alice.
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To v xc thc ch k s :
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Hnh 1.3: To v xc thc ch k s S = H(m)^d mod n (To ch k s) Cho php kim tra mt vn bn c phi c to vi mt kha b mt no hay khng. To ch k s bng kha b mt ca Alice. V k vo tin nhn Alive gi cho Bob Bob kim tra ch k s bng kha cng khai ca Alice: S^e mod n =H(m) vi H(m) l gi tr sau khi bm tin nhn Alice gi cho Bob. Ch k s ng n ng ngha vi vic cc thng tin Alice gi bob l ng n.
1.1.2. ng dngng dng r rng nht ca mt m ha kha cng khai l trong lnh vc bo mt, an ton thng tin: Mt vn bn c m ha bng kha cng khai ca mt ngi s dng th ch c th gii m vi kha b mt ca ngi .Cc thut ton to ch k s kha cng khai cho php nh danh mt tin nhn hay 1 ti liu . Mt ngi s dng c th m ha vn bn vi kha b mt ca mnh. Nu mt ngi khc c th gii m vi kha cng khai ca ngi gi th c th tin rng vn bn thc s xut pht t ngi gn vi kha cng khai (y l nguyn l sinh & xc thc ch k s, ngi gi s dng kha b mt ca mnh sinh ra 1 ch k s cho 1 tin nhn, ti liu. Bn nhn c th xc thc tnh ng n ca4
ch k s nh vo kha cng khai ca ngi gi).Cc c im trn cn c ch cho nhiu ng dng khc nh: tin in t, tha thun kha... Cc vn v mc ch ca ti.
1.2. Thut ton v phc tp thut ton1.2.1. Thut tonThut ton c hiu l s c t chnh xc ca mt dy cc bc c th c thc hin mt cch my mc gii quyt mt vn . Cn nhn mnh rng, mi thut ton c mt d liu vo (Input) v d liu ra (Output); khi thc hin thut ton (thc hin cc bc m t) , thut ton cn cho ra cc kiu d liu ra tng ng vi cc d liu vo.[2]
1.2.2.
Phn tch thut ton
1.2.2.1. Tnh hiu qu ca thut ton Khi gii mt vn , chng ta cn chn trong s cc thut ton, mt thut ton m chng ta cho l tt nht. C s nh chn la thut ton :
Thut ton n gin, d hiu, d ci t(d vit chng trnh)
Thut ton s dng tit kim nht cc ngun ti nguyn ca my tnh v c bit chy nhanh nht c th c. Tnh hiu qu ca thut ton bao gm 2 nhn t c bn :
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Dung lng khng gian nh cn thit lu gi cc d liu vo, cc kt qu tnh ton trung gian v cc kt qu ca thut ton
Thi gian cn thit thc hin thut ton(hay thi gian chy) [3] nh gi thi gian thc hin thut ton5
1.2.2.2.
Thi gian chy chng trnh ph thuc vo cc nhn t chnh sau: Cc d liu vo Chng trnh dch chuyn chng trnh ngun thnh m my.
Tc thc hin ca cc php ton ca my tnh c s dng chy chng trnh.
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Gi s T(n) l thi gian thc hin thut ton v f(n) l hm xc nh dng.T(n)=O(f(n)) nu cc hng s dng c v n0 sao cho T(n) c.g(n) vi mi n>= n 0 .
1.3. H tng kha cng khai (PKI)1.3.1. PKI l g hiu r v vic xy dng c PKI v vn cp pht chng thc s c vai tr v ng dng nh th no trong thng mi in t. Chng ta s i phn tch tng kha cnh xung quanh PKI.-
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Trc tin chng hiu th no l PKI v tnh cp thit ca PKI hin nay : PKI : vit tt ca Public Key Infrastructure tc l h tng c s kha cng khai. L mt c ch cho mt bn th 3 (thng l nh cung cp chng thc s) cung cp v xc thc nh danh cc bn tham gia vo qu trnh trao i thng tin. C ch ny cng cho php gn cho mi ngi s dng trong h thng mt cp kha cng khai/kha b mt.
Trong k nguyn bng n ca cng ngh thng tin, mi giao dch t xa c th thng qua internet. Tuy nhin, mt khc kh m bo m rng nhng giao dch trn Internet lun an ton. C s h tng kha cng khai (PKI) p ng nhng yu cu cp thit . Da trn cch s dng ca cha kha mt m cng cng v ch k in t, mt PKI chnh l b khung ca cc chnh sch, dch v v phn mm m ha, p ng nhu cu bo mt ca ngi s dng.
1.3.2. C s h tng kha cng khai
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Hnh 1.4 : M hnh xy dng PKI c bn-
PKI cung cp mt cp cha kha, trong c mt cha l cha kha cng khai (Public key) c th s dng dch v, cha cn li l cha kha b mt (Private key) m ngi s dng phi gi b mt. Hai cha kha ny c lin quan mt thit n nhau, sao cho mt thng ip c m ha bi mt cha kha mt m cng khai th ch gii m c bi mt cha kha b mt tng ng. V d v m hnh x dng xc thc : Gi s c 2 ngi dng Bob v Alice mun chuyn th in t cho nhau m bo tnh xc thc v bo mt h dng 1 phn mm PKI
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Hnh ng
Trng thi ca h thng PKI
Bob mun chuyn mt th in t n Phn mm PKI dng cha kha c nhn cho Alice, vi yu cu rng giao dch ca Bob to ra mt ch k in t cho phi chng minh c chnh anh gi bc th n i v ni dung bc th khng b thay i. Bob mun chc chn rng khng ai ngoi Phn mm PKI ca Bob dng cha kha7
Alice c c bc th ny
cng cng ca Alice m ha thng ip ca Bob. Phn mm PKI dng cha kha c nhn ca Alice gii m thng ip.
Alice mun c th do Bob gi
Alice mun kim chng rng chnh Bob Phn mm PKI ca Alice dng cha kha gi i thng ip v ni dung cng cng ca Bob kim chng ch thng ip khng b chnh sa. k in t ca anh ta. Bng 1.5 : M hnh s dng xc thc
1.4. Mt vi kin trc v cng ngh PKI hin hnh1.4.1. Mt s ng dngMc tiu chnh ca PKI l cung cp kha cng khai v xc nh mi lin h gia kha v nh dng ngi dng. Nh vy ngi dng c th s dng trong mt s ng dng nh: M ho Email hoc xc thc ngi gi Email (OpenPGP hay S/MIME). M ha hoc nhn thc vn bn (Cc tiu chun Ch k XML* hoc m ho XML* khi vn bn c th hin di dng XML). Xc thc ngi dng ng dng (ng nhp bng th thng minh smartcard, nhn thc ngi dng trong SSL). Cc giao thc truyn thng an ton dng k thut Bootstrapping (IKE, SSL): trao i kha bng kha bt i xng, cn m ha bng kha i xng.
1.4.2. Mt s h thng PKIDi y l danh sch mt s h thng PKI, trong mt s nh cung cp chng thc s hng u (v d VeriSign) khng c lit k v cc phn mm ca h khng c cng b cng khai :8
H thng qun l chng thc Red Hat Computer Associate eTrust PKI
Microsoft OpenCA (Mt m hnh PKI m ngun m) RSA Security IDX-PKI Simple CA
1.5. Mc ch ca ti-
Mt vi nm tr li y PKI l 1 ch nng i vi cc doanh nghip ln. Vit Nam y vn l mt ti kh mi m. Do vy tm hiu v xy dng h tng c s xc thc kha cng khai(PKI) l mt cch tip cn cho mt nn tng mi. T nu r vai tr v ng dng ca h tng kha cng khai trong thng mi in t. Tm hiu v cc thut ton(sinh s ngu nhin trong vic to kha, hm bm, m ha, to ch k s...)
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1.6. t vn ? xy dng mt c s h tng chng ta phi gii quyt s b nhng vn sau y :
Lm sao cp pht kha cng khai v kha b mt cho tng ngi. Vn ng k kha cng khai vi mt CA Vn thu hi/cp pht li kha cng khai Vn kim chng kha cng khai
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Lm sao t kha cng khai ca 1 ngi h thng PKI phi xc nh xem ch k s c phi ca ngi hay khng. Vn ton vn d liu. H thng PKI phi xc nh xem liu tin nhn gi i gia client v server c b thay i hay khng? Mt thng ip c m ha bi mt cha kha mt m cng khai th ch gii m c bi mt cha kha b mt tng ng. Kha ca bn th 3 bn thm nh s do cp hay t chc no gim inh. Hay phi c c ch no chng gi mo bn chng thc. Cc Vn lin quan n chng thc s cp pht, xc thc v qun l ti server ra sao.
1.7. Cc vn s gii quyt trong kha lunVi nhng yu cu v mt h thng PKI nh trn chng ta phi xy dng bi ton nh th no.Chng trnh thit k phi bao gm 3 i tng : Server : Cho php ngi dng trong h thng ng k kha cng khai. Cp pht 1 chng thc s (certificat) cho ngi dng nu kha cng khai hp l Qun l kha cng khai, Thu hi/cp pht li chng thc s Cho php bn th 3 kim tra tnh ng n ca 1 chng thc s bt k
User : H thng PKI cp pht mt kha cng khai cho user v kha b mt (Kha ring) do PKI client cp pht v user phi gi b mt. To ch k s cho tng vn bn ngu nhin. Bn th 3 l bn thm nh v nh gi : Cp pht v bo mt Kha ring v kha cng khai ca CA.
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Chng 2 : Xy dng h tng kha cng khai(PKI), vn cp pht chng thc s v ng dng trong thng mi in t
2.1. Hm bm mt m hc2.1.1. Hm bmHm bm (ting Anh: hash function) l hm sinh ra cc gi tr bm tng ng vi mi khi d liu (c th l mt chui k t, mt on tin nhn...). Gi tr bm ng vai tr gn nh mt kha phn bit cc khi d liu, tuy nhin, ngi ta chp nhn hin tng trng kha hay cn gi l ng v c gng ci thin gii thut gim thiu s ng . Hm bm thng c dng trong bng bm nhm gim chi ph tnh ton khi tm mt khi d liu trong mt tp hp (nh vic so snh cc gi tr bm nhanh hn vic so snh nhng khi d liu c kch thc ln).
2.1.2. Hm bm mt m hc-
Trong ngnh mt m hc, mt hm bm mt m hc (ting Anh: 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).[4]
2.1.3. m bo tnh ton vn d liu-
Hm bm mt m hc l hm bam v c tnh cht l hm 1 chiu. T khi d liu hay gi tr bm u vo ch c th a ra 1 gi tr bm duy nht. Nh chng
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ta bit i vi tnh cht ca hm 1 chiu. Mt ngi no d bt c gi tr bm h cng khng th suy ngc li gi tr, on tin nhn bm khi im.-
Hm bm thng c dng trong bng bm nhm gim chi ph tnh ton khi tm mt khi d liu trong mt tp hp. Gi tr bm ng vai tr gn nh mt kha phn bit cc khi d liu Gi tr u vo(tin nhn, d liu...) b thay i tng ng gi tr bm cng b thay i. Do vy nu 1 k tn cng ph hoi, chnh sa d liu th server c th bit ngay lp tc.
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2.1.4. Mt s hm bm thng dng2.1.4.1. Thut ton hm bm MD5 a. Thut ton hm bm MD5 MD5 (Message-Digest algorithm 5) l mt hm bm mt m c s dng ph bin, c thit k bi Gio s Ronald L. Rivest ti trng MIT vo nm 1991 thay th cho hm bm trc l MD4 (1990). L mt chun Internet (RFC 1321), MD5 c dng trong nhiu ng dng bo mt v cng c dng ph bin kim tra tnh ton vn ca tp tin. Cng nh cc hm bm khc nh MD4 v SHS (Secure Hash Standard), MD5 l phng php c u im tc x l rt nhanh, thch hp vi cc thng ip di v cho ra gi tr bm di 128 bit. Trong MD5, thng ip ban u X s c m rng thnh dy bit X c di l bi ca 512. Dy bit X gm cc thnh phn c sp th t nh sau: Dy bit X ban u, mt bit 1, dy d bit 0 (d c tnh sao cho dy X cui cng l bi ca 512), dy 64 bit l biu din chiu di ca thng ip. n v x l trong MD5 l cc t 32-bit, nn dy bit X trn s c biu din thnh dy cc t X[i] 32-bit sau: X=X[0] X[1] X[2] X[N1] , vi N l bi ca 16.[5] b. Phng php MD5 c nhng u im sau so vi phng php MD4
- Thay v c 3 chu k bin i nh trong MD4, MD5 b sung thm chu k th4 tng mc an ton.12
- Trong mi thao tc ca tng chu k, MD5 s dng hng s ti phn bit, trongkhi MD4 s dng hng s chung cho mi thao tc trong cng chu k bin i.
- Hm G chu k 2 ca MD4: G(X,Y,Z) = ((X Z) (X Y) (Y Z ))c thay th bng G(X,Y,Z) = (X Z) xng.
(Y ( Z )) gim tnh i
- Mi bc bin i trong tng chu k chu nh hng kt qu ca bc bini trc, v vy lm tng nhanh tc ca hiu ng lan truyn (avalanche).
- Cc h s dch chuyn xoay vng trong mi chu k c ti u ha nhmtng tc hiu ng lan truyn. Ngoi ra, mi chu k s dng 4 h s dch chuyn khc nhau.
- L do MD5 c thit k thay th cho MD4 l v cc phn tch ch ra rngphng php MD4 c v khng an ton. Den Boer v Bosselaers ch ra cc im yu trong MD4 trong mt bi bo c ng vo nm 1991v mt tn cng xung t u tin c tm thy bi Han Dobbertin vo nm 1996 .
- Tuy nhin, cc n lc tn cng, phn tch ca cc nh nghin cu cho thyMD5 cng khng cn an ton v cn c thay th bng mt thut ton bm khc nh cc cng b ca Den Boer v Bosselaers nm 1993; ca Hans Dobbertin nm 1996; ca nhm tc gi Xiaoyun Wang, Dengguo Feng, Xuejia Lai, v Hongbo ngy 19/8/2004; ca Arjen Lenstra, Xiaoyun Wang, v Benne de Weger ngy 1/3/2005; v ca Vlastimil Klima, 2.1.4.2. Chun bm an ton SHS
- SHS (Secure Hash Standard) l chun gm tp hp cc thut ton bm mtm an ton (Secure Hash Algorithm SHA) nh SHA-1, SHA-224, SHA256, SHA-384, SHA-512 do NIST 2 v NSA 3 xy dng.
- Phng php SHA-1 (cng nh SHA-0) c xy dng trn cng c s viphng php MD4 v MD5. Tuy nhin, phng php SHA-1 s dng trn h thng Big-endian 5 thay v Little-endian 6 nh phng php MD4 v MD5. Ngoi ra, hm bm SHA-1 to ra thng ip rt gn kt qu c di 160 bit nn thng c s dng13
- Phng php SHA-1 ging vi MD5 (ci tin t MD4) nhng thng ip tmtt c to ra c di 160 bit. Di y l mt s im so snh gia MD5 v SHA-1:
Ging nh MD5, SHA-1 cng thm chu k th 4 tng mc an ton cho thut ton. Tuy nhin, chu k 4 ca SHA-1 s dng li hm f ca chu k th 2. Trong SHA-1, 20 bc bin i trong cng mt chu k s dng cng mt hng s K[t] . Trong khi , mi bc bin i trong cng mt chu k ca MD5 s dng cc hng s khc nhau. So vi MD4, hm G trong MD5 c thay th thnh hm mi lm gim tnh i xng. Trong khi SHA-1, hm G trong SHA-1 vn gi li hm G ca MD4. C MD5 v SHA-1, mi bc bin i trong tng chu k chu nh hng kt qu ca bin i trc, v vy lm tng nhanh tc ca hiu ng lan truyn.
Hnh 2.1: c im ca cc thut ton bm SHA
2.2. M ha thng tin
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C rt nhiu thng tin m chng ta khng mun ngi khc bit khi gi i nh: thng tin v Credit-Card, thng tin v kinh doanh ca cng ty, thng tin v ti khon c nhn, thng tin v c nhn nh s chng minh th, s th...-
Cc thng tin b mt c cung cp cho cc my tnh quan mng Internet bng nhiu phng thc khc nhau v d : Mt cch bo mt n gin nhng minh bch nht l lu cc thng tin b mt trn cc b nh c th xo c (Removable Storage) nh a mm. Tuy nhin dng bo mt ph bin nht vn l da vo qu trnh m ho d liu (Encryption).
Cc h thng m ho trong my tnh ph bin nht thuc mt trong hai loi sau: M ho vi kho i xng (Symmetric-key Encryption) : Trong phng php m ho vi kho i xng, mi my tnh c mt kho b mt (dng m) dng m ho cc gi thng tin trc khi chng c gi qua mng ti cc my tnh khc. Phng php m ho vi kho i xng i hi ngi s dng phi xc nh c nhng my tnh no ang lin lc trao i thng tin vi nhau ci t kho ny trn mi my. M ho vi kho cng khai (Public-key Encryption).[6]
2.3. Ch k s2.3.1.-
Ch k s
Ch k s (Digital Signature) ch l tp con ca ch k in t. Ch k s l ch k in t da trn k thut m ha vi kha cng khai, trong , mi ngi c mt cp kha (mt kha b mt v mt kha cng khai). Kha b mt khng bao gi c cng b, trong khi , kha cng khai c t do s dng. trao i thng ip b mt, ngi gi s dng kha cng khai ca ngi nhn m ha thng ip gi, sau , ngi nhn s s dng kha b mt tng ng ca mnh gii m thng ip. Ch k in t l thng tin c m ho bng Kho ring ca ngi gi, c gi km theo vn bn nhm m bo cho ngi nhn nh danh, xc thc ng ngun gc v tnh ton vn ca ti liu nhn c. Ch k in t th hin vn bn gi i l c k bi chnh ngi s hu mt Kho ring tng ng vi mt Chng ch in t no .15
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Ch k s kha cng khai (hay h tng 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 2 qu trnh: to ch k v kim tra ch k. [7]
2.3.2. To v kim tra ch k s2.3.2.1. Cc thut ton ch k s thng dng Ch k s gip xc nh c ngi to ra hay chu trch nhim i vi mt thng ip c k. Mt phng php ch k s phi bao gm t nht 3 thut ton chnh, l thut ton dng to kha, thut ton dng to ra ch k s v thut ton tng ng xc nhn ch k s. 2.3.2.2. Thut ton ch k s RSA-
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Phng php ch k s RSA c xy dng da trn thut ton m ha kha cng khai RSA. to mt cp kha, RSA thc hin cc bc sau: Chn 2 s nguyn t ln ngu nhin p, q. Nhm c s an ton ti a nn chn p v q c di bng nhau. Tnh n=pq v =(p1)(q1). Chn ngu nhin mt s nguyn e (1