Bo co cui k An Ton Thng Tin Mng GVHD: TS.Nguyn Tn Khi

Bo co cui k An Ton Thng Tin Mng GVHD: TS.Nguyn Tn Khi

TRNG I HC BCH KHOAKHOA CNG NGH THNG TINB MN MNG V TRUYN THNG

BO CO MN HC AN TON THNG TIN MNG ti:C CH S DNG CH K IN T TRONGEMAIL V M HA D LIU

Sinh vin: Trn Th Th : L nh PhLp: 11TLTCn b hng dn : TS.Nguyn Tn Khi

Nng 2013

LI CM NNgy nay cng ngh thng tin ngy cng pht trin mnh m, vic hc tp v nm bt kin thc cng ngh thng tin l yu cu nht thit i vi mi ngi ni chung, v sinh vin cng ngh thng tin ni ring. An ton thng tin v mng l kin thc m bt buc mi mt sinh vin khoa cng ngh thng tin cn nm vng . Sau mt thi gian hc tp l thuyt trn lp vi s ging dy tn tnh ca thy Nguyn Tn Khi, chng em c giao lm bo co nhm nm vng kin thc tip thu c . Trong qua trnh thc hin s khng trnh khi nhng thiu st, knh mong thy gp chng em hon thin hn bi lm ca mnh. Cui cng chng em xin gi li cm n n thy Nguyn Tn Khi gip chng em hon thin bi lm ny. Chng em xin chn thnh cm n! Nhm sinh vinL nh PhTrn Th Th

CHNG 1: M U

1.1 L do chn tiNgy nay, cc ng dng ca cng ngh thng tin ngy cng khng th thiu c i vi cc thnh phn nh x hi, kinh t, chnh tr, qun s... Mt lnh vc quan trng m cng ngh thng tin c ng dng rt mnh m v khng th thiu l lnh vc truyn thng. Rt nhiu thng tin lin quan n nhng cng vic hng ngy u do my vi tnh qun l v truyn gi i trn h thng mng, ko theo l vn v xc thc ngun thng tin nhn c. V vn c t ra l lm th no xc thc c mt cch chnh xc ngun thng tin nhn l ca mt ngi, mt my ch hay ca mt thc th no gi tin trn h thng mng?

AINTERNETBDHnh 1.1 M hnh trao i thng tin qua mng INTERNET.V d: khi A gi mt thng tin in t cho D, v gi s B gi mo A cng gi mt thng tin cho D, hoc mt ngi C trn mi trng truyn bt c v sa i thng tin A gi sau cc thng tin ny c gi li cho D. Vy thng tin D nhn c khng chnh xc v ngi nhn D cng khng th xc thc c thng tin l do ngi A gi, hay B gi, hay mt ngi no khc gi.Vn t ra l ngi D sau khi nhn c bn tin phi xc thc c rng thng tin l ca chnh mt i tng c th gi v thng tin khng b tit l cng nh b khng thay i trn mi trng truyn thng.

ti C ch s dng ch k in t trong eMail v m ha d liu s tm hiu vn nu trn v ci t chng trnh minh ha.1.2 Mc tiu Tm hiu cc phng php m ha d liu. Hiu c c ch s dng ch k in t trong email. Demo minh ha

CHNG 2: TNG QUAN V CH K IN T

2.1 Ch k in t l g?Trong cuc sng hng ngy, ta cn dng ch k xc nhn cc vn bn ti liu no v c th dng con du vi gi tr php l cao hn i km vi ch k.Cng vi s pht trin nhanh chng ca cng ngh thng tin, cc vn bn ti liu c lu di dng s, d dng c sao chp, sa i. Nu ta s dng hnh thc ch k truyn thng nh trn s rt d dng b gi mo ch k. Vy lm sao c th k vo cc vn bn, ti liu s nh vy?Cu tr li l s dng ch k in t! Ch k in t i km vi cc thng tin ch s hu v mt s thng tin cn thit khc s tr thnh Chng ch in t. Ch k in t (ting Anh: electronic signature) l thng tin i km theo d liu (vn bn, hnh nh, video...) nhm mc ch xc nh ngi ch ca d liu .2.2 Chc nng Ch k in t c th s dng trong cc giao dch th in t, mua bn hng trc tuyn, chuyn tin ngn hngm bo an ton thng tin c nhn. Dng k khai, np thu trc tuyn, khai bo hi quan trc tip m khng mt thi gian cho cc th tc. Gip cho cc i tc c th k hp ng lm n trc tuyn, ch cn k vo file hp ng v gi qua e-mail. Xc nh ngi ch ca d liu m bo an ton d liu truyn trn mng Ngn chn vic thay i d liu2.3 M ha d liu2.3.1 M ha l g?S pht trin chng mt ca Internet tc ng n c cng vic kinh doanh v ngi tiu dng vi s ha hn v vic thay i cch m con ngi sng v lm vic. Nhng mi lo ngi ln nht c cp n l vic bo mt trn Internet, c bit khi cc thng tin mang tnh nhy cm v ring t c gi i trn mng.

M ha l s dng mt phng php bin i d liu t dng bnh thng sang mt dng khc, m mt ngi khng c thm quyn, khng c phng tin gii m th khng th c hiu c. Gii m d liu l qu trnh ngc li, l s dng mt phng php bin i d liu c m ha v dng thng tin ban u.

Hnh 1: Quy trnh m ha d liu2.3.2 Phn loi M ha b mt hoc m ha i xng (sysmmetric cryptography) M ha cng khai hoc m ha bt i xng (asymmetric) M ha mt chiu (hm bm)2.3.3 M ha b mta. Khi nimPhng php m kha b mt (secret key cryptography) cn c gi l m ha i xng (sysmmetric cryptography).L mt lp cc thut ton mt m ha trong cc kha dng cho vic mt m ha v gii m c quan h r rng vi nhau (c th d dng tm c mt kha nu bit kha kia). Kha dng m ha c lin h mt cch r rng vi kha dng gii m c ngha chng c th hon ton ging nhau, hoc ch khc nhau nh mt bin i n gin gia hai kha. Trn thc t, cc kha ny i din cho mt b mt c phn hng bi hai bn hoc nhiu hn v c s dng gi gn s b mt trong knh truyn thng tin.Trc khi m ha d liu truyn i trn mng, hai bn gi v nhn phi c kha v thng nht thut ton gii m. Mt s thut ton ng dng cho m ha kha b mt nh: DES (Data Encrytion Standard), 3DES (triple strength DES), RC2 (Rons Cipher 2), RC4,.b. Nhn xt u im: tc m ha v gii m nhanh Nhc im: kha c truyn trn m trng mng nn tnh bo mt khng cao. Ngi gi v ngi nhn phi bit gi b mt v kha.2.3.4 M ha cng khaia. Khi nimMt m ha kha cng khai l mt dng mt m ha 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).Phng php m ha cng khai (public key cryptography) cn gi l m ha bt i xng (asymmetric cryptography) v n s dng hai kha khc nhau public key v private key. Public key c cng khai trn mng v dng m ha, trong khi private key c gi kn v c dng gii m. iu quan trng i vi h thng l khng th tm ra kha b mt nu ch bit kha cng khai.H thng mt m ha kha cng khai c th s dng vi cc mc ch:- M ha: gi b mt thng tin v ch c ngi c kha b mt mi gii m c. - To ch k s: cho php kim tra mt vn bn c phi c to vi mt kha b mt no hay khng.- Tha thun kha: cho php thit lp kha dng trao i thng tin mt..Nhng ngi c kha cng khai c th m ha thng tin, nhng ch nhng ngi c kha b mt mi c c thng tin. Phng php ny s dng thut ton m ha RSA (Ron Rivest, Adi Shamir v Leonard Adleman) v thut ton DH (Diffie-Hellman)b. Nhn xt u im: phng php cho php trao i kha d dng v thun li. Nhc im: tc m ha chm, ch c s dng cho cc d liu nh.2.3.5 M ha mt chiu (hm bm)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 v kim tra tnh nguyn vn ca thng ip. Hm bm (hash) chng thc v kim tra tnh nguyn vn ca thng ip.Hm bm l cc thut ton khng s dng kha m ha, n c u vo l mt xu k t di ty , h thng s tin hnh bm thnh nhng xu k t c di c nh. Do ngi nhn khng bit c ni dung hay di ban u ca thng ip c bm bng hm bmKha m ha c to ra da trn tng on v kha b mt.Cc on thng tin c th c m ha hoc khng trc khi truyn qua mng. Ch ngi nhn c kha m ha mi gii m c cc thng tin.

2.3.6 Hm bm MD5 (Message Digest algorithm 5)Ronald Rivest la ngi a phat minh ra cac ham Bm MD2, MD4 (1990) va MD5 (1991). Do tinh cht tng t cua cac ham Bm nay, sau y chung ta se xem xet hm Bm MD5, y la mt cai tin cua MD4 va la ham Bm c s dung rng rai nht, nguyn tc thit k cua ham bm nay cung la nguyn tc chung cho rt nhiu cac ham bm khac. MD5 l mt chun internet dng kim tra tnh ton vn ca tp tin, c s dng ph bin vi gi tr Hash di 128 bit.

MD5 rt kh c th gii m ngc chiu.Cch n gin v hiu qu nht ca vic gii m MD5 l dng cc database ca cc gi tr m ha MD5.Miu t MD5:Mt bng bm MD5 thng c din t bng mt s thp lc phn 32 k t. u vo l nhng khi 512 bit, c chia cho 16 khi con 32 bit. u ra ca thut ton l mt thit lp ca 4 khi 32 bit to thnh mt hm bm 128 bit.u tin, ta chia tin nhn thnh nhng khi 512 bit, vi khi cui cng (t l x v x < 512 bit) ca tin nhn, chng ta cng thm bit 1 vo cui ca x, theo sau l cc bit 0 c di cn thit (512 bit). Kt qu tin nhn vo l mt chui M c di chia ht cho 512, v vy ta c th chia M thnh N khi con 32 bit (N khi ny s chia ht cho 16).2.3.7 RSAPhng php s dng thut ton m ha cng khai RSA c t tn t ba nh pht minh l Ron Rivest, Adi Shamir v Leonard Adleman, thut ton s dng biu thc vi hm m m ha bn gc thnh cc khi, mi khi c mt gi tr nh phn nh hn n.Thut ton RSA c hai kha: kha cng khai v kha b mt. Kha cng khai c cng b rng ri cho mi ngi v c dng m ha. Nhng thng tin c m ha bng kha cng khai ch c th c gii m bng kha b mt tng ng. to mt cp kha RSA thc hin cc bc sau: Chn hai s nguyn t ngu nhin p, q (nn chn p v q c di bng nhau) Tnh n = pq v (n) = (p-1)(q-1) Chn ngu nhin s nguyn e (1