Final Report Cryptography NetworkSecurity

7/26/2019 Final Report Cryptography NetworkSecurity

1/23

1

Li Ni uTrong thi i cng nghngy cng pht trin th con ngi ta cng cn bo mt thng tin nhiu

hn. V thmt m ngy cng c ch trng trong ngnh cng nghthng tin.

Mt m hc l mt lnh vc lin quan vi cc kthut ngn ngv ton hc m bo an ton

thng tin, cthl trong thng tin lin lc. Vphng din lch s, mt m hc gn lin vi qu

trnh m ha; iu ny c ngha l n gn vi cc cch thc chuyn i thng tin tdng ny

sang dng khc nhng y l tdng thng thng c thnhn thc c thnh dng khng th

nhn thc c, lm cho thng tin trthnh dng khng thc c nu nh khng c cc kin

thc b mt.

Qu trnh m ha c sdng chyu m bo tnh b mt ca cc thng tin quan trng,

chng hn trong cng tc tnh bo, qun shay ngoi giao cng nh cc b mt vkinh t, thng

mi. Trong nhng nm gn y, lnh vc hot ng ca mt m ha c mrng: mt m ha

hin i cung cp c chcho nhiu hot ng hn l chduy nht vic gib mt v c mt lot

cc ng dng nh: chng thc kha cng khai, chk s, bu cin thay tin in t. Ngoi

ra, nhng ngi khng c nhu cu thit yu c bit vtnh b mt cng sdng cc cng ngh

mt m ha, thng thng c thit kv to lp sn trong cc c shtng ca cng nghtnh

ton v lin lc vin thng

Mt m hc l mt lnh vc lin ngnh, c to ra tmt slnh vc khc. Cc dng cnht ca

mt m ha chyu lin quan vi cc kiu mu trong ngn ng. Gn y th tm quan trng

thay i v mt m ha sdng v gn lin nhiu hn vi ton hc, cthl ton hc ri rc, bao

gm cc vn lin quan n l thuyt s, l thuyt thng tin, phc tp tnh ton, thng k v

thp. Mt m ha cng c coi l mt nhnh ca cng ngh, nhng n c coi l khng bnh

thng v n lin quan n cc schng i ngm (xem cng nghmt m ha v cng nghan

ninh). Mt m ha l cng cc sdng trong an ninh my tnh v mng.

Lnh vc c lin quan vi n l steganographyl lnh vc nghin cu vvic che giu stn

ti ca thng ip m khng nht thit phi che giu ni dung ca thng ip (v d: nh im,

hay mc khng mu).


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MC LC

I . GII TH IU CC GII THUT MT M ...................................................................................... 31. DES ................................................................................................................................................... 3

2. AES .................................................................................................................................................... 8

3. RSA .................................................................................................................................................. 12

4. So Snh Cc Gii Thut .................................................................................................................. 18

I I . MC TIU ..................................................................................................................................... 18

I I I . H IN THC .................................................................................................................................. 18

1. Gii thiu s lc ........................................................................................................................... 18

2. Cc cng vic cn lm: ................................................................................................................... 19

3. Qu trnh hin thc ng dng ......................................................................................................... 20

I V. Kt qut c ............................................................................................................................ 23


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I .

GII TH IU CC GII THUT MT M

1.

DES

DES (vit tt ca Data Encryption Standard, hay Tiu chun M ha Dliu) l

mt phng php mt m ha c FIPS (Tiu chun Xl Thng tin Lin bang

Hoa K) chn lm chun chnh thc vo nm 1976. Sau chun ny c sdng

rng ri trn phm vi thgii. Ngay tu, thut ton ca n gy ra rt nhiu

tranh ci, do n bao gm cc thnh phn thit kmt, di kha tng i ngn,

v cc nghi ngvca sau C quan An ninh quc gia Hoa K(NSA) c thb

kha. Do , DES c gii nghin cu xem xt rt klng, vic ny thc

y hiu bit hin i vmt m khi (block cipher) v cc phng php thm mtng ng.

Hin nay DES c xem l khng an ton cho nhiu ng dng. Nguyn nhn

chyu l di 56 bit ca kha l qu nh. Kha DES tng bph trong vng

cha y 24 gi. c rt nhiu kt quphn tch cho thy nhng im yu vmt

l thuyt ca m ha c thdn n ph kha, tuy chng khng khthi trong thc

tin. Thut ton c tin tng l an ton trong thc tin c dng Triple DES (thc

hin DES ba ln), mc d trn l thuyt phng php ny vn c thbph. Gny DES c thay thbng AES (Advanced Encryption Standard, hay Tiu

chun M ha Tin tin).

Khi nguyn ca thut ton c tu thp nin 1970. Vo nm 1972, sau khi

tin hnh nghin cu vnhu cu an ton my tnh ca chnh phHoa K, Cc Tiu

chun Lin bang Hoa K(National Bureau of Standard - NBS), hin nay i tn

thnh Vin Tiu chun v Cng ngh Quc gia Hoa K (National Institute of

Standards and Technology -NIST), nhn ra nhu cu vmt tiu chun ca chnhphdng mt m ha cc thng tin mt/nhy cm. Vo ngy 15 thng 5 nm

1973, sau khi tham kho vi NSA, NBS a ra ku gi thit kmt thut ton m

ha c thp ng c cc tiu chun nghim ngt.

M tthut ton :


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- DES l thut ton m ha khi: n xl tng khi thng tin ca bn r c

di xc nh v bin i theo nhng qu trnh phc tp trthnh khi thng

tin ca bn m c di khng thay i. Trong trng hp ca DES, di

mi khi l 64 bit. DES cng sdng kha c bit ha qu trnh chuyn i.

Nhvy, chkhi bit kha mi c thgii m c vn bn m. Kha dng

trong DES c di ton bl 64 bit. Tuy nhin chc 56 bit thc sc s

dng; 8 bit cn li chdng cho vic kim tra. V th, di thc tca kha

chl 56 bit.

- Ging nh cc thut ton m ha khi khc, khi p dng cho cc vn bn di

hn 64 bit, DES phi c dng theo mt phng php no . Trong ti liu

FIPS-81 chra mt sphng php, trong c mt phng php dng

cho qu trnh nhn thc.

- Cu trc tng thca thut ton c thhin hnh 1 di: c 16 chu trnh

ging nhau trong qu trnh xl. Ngoi ra cn c hai ln hon vu v cui

(Initial and final permutation - IP & FP). Hai qu trnh ny c tnh ch t i

nhau (Trong qu trnh m ha th IP trc FP, khi gii m th ngc li). IP v

FP khng c vai tr xt vmt m hc v vic sdng chng chc ngha

p ng cho qu trnh a thng tin vo v ly thng tin ra tcc khi phn

cng c tthp nin 1970. Trc khi i vo 16 chu trnh chnh, kh i thng tin

64 bit c tch lm hai phn 32 bit v mi phn sc xl tun t(qu

trnh ny cn c gi l mng Feistel).

- Cu trc ca thut ton (mng Feistel) m bo rng qu trnh m ha v gii

m din ra tng t. im khc nhau chchcc kha con c sdng

theo trnh tngc nhau. iu ny gip cho vic thc hin thut ton trnn

n gin, c bit l khi thc hin bng phn cng.

- K hiu sau: thhin php ton XOR. Hm F lm bin i mt na ca khi

ang xl vi mt kha con. u ra sau hm F c kt hp vi na cn li

ca khi v hai phn c tro i xl trong chu trnh ktip. Sau chu

trnh cui cng th 2 na khng btro i; y l c im ca cu trc Feistel

khin cho qu trnh m ha v gii m trnn ging nhau.


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Hnh 1


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- Hm F, nh c miu tHnh 2, hot ng trn khi 32 bit v bao gm bn

giai on:

+ Mrng: 32 bit u vo c mrng thnh 48 bit sdng thut ton

hon vmrng (expansion permutation) vi vic nhn i mt sbit. Giaion ny c k hiu l E trong s .

+ Trn kha: 48 bit thu c sau qu trnh mrng c XOR vi kha

con. Mi su kha con 48 bit c to ra tkha chnh 56 bit theo mt

chu trnh to kha con (key schedule) miu tphn sau.

+ Thay th: 48 bit sau khi trn c chia lm 8 khi con 6 bit v c x

l qua hp thay thS-box. u ra ca mi khi 6 bit l mt khi 4 bit theo

mt chuyn i phi tuyn c thc hin bng mt bng tra. Khi S-boxm bo phn quan trng cho an ton ca DES. Nu khng c S-box th

qu trnh sl tuyn tnh v vic thm m srt n gin.

+ Hon v: Cui cng, 32 bit thu c sau S-box sc sp xp li theo

mt thtcho trc (cn gi l P-box).

Qu trnh lun phin sdng S-box v shon vcc bt cng nh qu trnh

mrng thc hin c tnh cht gi l sxo trn v khuch tn (confusion

and diffusion). y l yu cu cn c ca mt thut ton m ho c Claude

Shannon pht hin trong nhng nm 1940.


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- Qu Trnh to kha con: Hnh 3 m t thut ton to kha con cho cc chu

trnh. u tin, t64 bit ban u ca kha, 56 bit c chn (Permuted Choice

1, hay PC-1); 8 bit cn li bloi b. 56bit thu c c chia lm hai phn

bng nhau, mi phn c xl c lp. Sau mi chu trnh, mi phn c

dch i 1 hoc 2 bit (ty thuc tng chu trnh, nu l chu trnh 1,2,9,16 th

l dch 1bit, cn li th sc dich 2bit). Cc kha con 48 bit c to

thnh bi thut ton la chn 2 (Permuted Choice 2, hay PC-2) gm 24 bit t

mi phn. Qu trnh dch bit (c k hiu l "


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An ton v sgii m: Mc d c nhiu nghin cu vph m DES hn bt k

phng php m ha khi no khc nhng phng php ph m thc tnht hin

nay vn l tn cng Brute-force. Nhiu c tnh mt m ha ca DES c xc

nh v t ba phng php ph m khc c xc nh vi mc phc tp

nhhn tn cng bo lc. Tuy nhin cc phng php ny i hi mt slng

bn r qu ln ( tn cng la chn bn r) nn hu nh khng th thc hin

c trong thc t.

2. AES

Trong mt m hc, AES (vit tt ca tting Anh: Advanced Encryption Standard,

hay Tiu chun m ha tin tin) l mt thut ton m ha khi c chnh ph

Hoa kp dng lm tiu chun m ha. Ging nh tiu chun tin nhim DES,

AES c kvng p dng trn phm vi thgii v c nghin cu rt klng. AES c chp thun lm tiu chun lin bang bi Vin tiu chun v cng

nghquc gia Hoa k(NIST) sau mt qu trnh tiu chun ha ko di 5 nm


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Thut ton c thit k bi hai nh mt m hc ngi B: Joan Daemen v

Vincent Rijmen. Thut ton c t tn l "Rijndael" khi tham gia cuc thi thit

kAES.

Qu trnh pht trin: Thut ton c da trn bn thit kSquare c trc caDaemen v Rijmen; cn Square li c thit kda trn Shark.

Khc vi DES sdng mng Feistel, Rijndael sdng mng thay th-hon v.

AES c thddng thc hin vi tc cao bng phn mm hoc phn cng v

khng i hi nhiu bnh. Do AES l mt tiu chun m ha mi, n ang c

trin khai sdng i tr.

M tthut ton : Mc d 2 tn AES v Rijndael vn thng c gi thay th

cho nhau nhng trn thc tth 2 thut ton khng hon ton ging nhau. AES chlm vic vi cc khi dliu (u vo v u ra) 128 bt v kha c di 128,

192 hoc 256 bt trong khi Rijndael c thlm vic vi dliu v kha c di

bt kl bi sca 32 bt nm trong khong t128 ti 256 bt. Cc kha con s

dng trong cc chu trnh c to ra bi qu trnh to kha con Rijndael. Mi kha

con cng l mt ct gm 4 byte. Hu ht cc php ton trong thut ton AES u

thc hin trong mt trng hu hn ca cc byte. Mi khi dliu 128 bit u vo

c chia thnh 16 byte (mi byte 8 bit),c thxp thnh 4 ct, mi ct 4 phn t

hay l mt ma trn 4x4 ca cc byte,n c gi l ma trn trng thi, hay vn tt

l trng thi (ting Anh: state, trang thi trong Rijndael c thc thm ct). Trong

qu trnh thc hin thut ton cc ton ttc ng bin i ma trn trng thi

ny.

Qu trnh m ha :

- Khi ng vng lp: AddRoundKeyMi ct ca trng thi u tin ln

lt c kt hp vi mt kha con theo thttu dy kha.

- Vng lp:

SubBytes : y l php th(phi tuyn) trong mi byte trong trng

thi sc thbng mt byte khc theo bng tra (Rijndael S-box).

ShiftRowsdch chuyn, cc hng trong trng thi c dch vng

theo sbc khc nhau.


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MixColumnsqu trnh trn lm vic theo cc ct trong khi theo

mt php bin i tuyn tnh.

Addroundkey

- Vng lp cui

SubBytes

ShiftRows

Addroundkey

Ti chu trnh cui th bc MixColumns khng thc hin.

Bc Subbytes: Cc byte c ththng qua bng tra S-box. y chnh l qu

trnh phi tuyn ca thut ton. Hp S-box ny c to ra tmt php bin i

khnghch trong trng hu hn GF (28) c tnh cht phi tuyn. chng li cc

tn cng da trn cc c tnh i s, hp S-box ny c to nn bng cch kt

hp php nghch o vi mt php bin i affine khnghch. Hp S-box ny

cng c chn trnh cc im bt ng (fixed point).

Bc ShiftRows: Cc hng c dch vng mt sbc nht nh. i vi AES,

hng u c ginguyn. Mi byte ca hng th2 c dch vng tri mt v

tr. Tng t, cc hng th3 v 4 c dch vng 2 v 3 vtr. Do vy, mi ct

khi u ra ca bc ny sbao gm cc byte 4 ct khi u vo. i vi

Rijndael vi di khi khc nhau th svtr dch chuyn cng khc nhau.

Bc MixColumns: Bn byte trong tng ct c kt hp li theo mt php bin

i tuyn tnh khnghch. Mi khi 4 byte u vo scho mt khi 4 byte u

ra vi tnh cht l mi byte u vo u nh hng ti c4 byte u ra. Cng

vi bc ShiftRows, MixColumns to ra tnh cht khuch tn cho thut ton.

Mi ct c xem nh mt a thc trong trng hu hn v c nhn vi a

thc c(x) = 3x^3 + x^2 + x + 2 (modulo x^4+1). V th, bc ny c thc xem

l php nhn ma trn trong trng hu hn

Bc AddRoundKey: Ti bc ny, kha con c kt hp vi cc khi. Kha

con trong mi chu trnh c to ra t kha chnh vi qu trnh to kha con

Rijndael; mi kha con c di ging nh cc khi. Qu trnh kt hp c thc

hin bng cch XOR tng bt ca kha con vi khi dliu.


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Ti u ha: i vi cc hthng 32 bt hoc ln hn, ta c thtng tc thc

hin thut ton bng cch st nhp cc bc SubBytes, ShiftRows, MixColumns

v chuyn chng thnh dng bng. C cthy 4 bng vi 256 mc, mi mc l 1

t32 bt, 4 bng ny chim 4096 byte trong bnh. Khi , mi chu trnh sc

bao gm 16 ln tra bng v 12 ln thc hin php XOR 32 bt cng vi 4 php

XOR trong bc AddRoundKey.

Hnh nh minh ha cho gii thut


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An ton ca gii thut:

- Vo thi im nm 2006, dng tn cng ln AES duy nht thnh cng l tn

cng knh bn (side channel attack]). Vo thng 6 nm 2003, chnh phHoa

ktuyn bAES c thc sdng cho thng tin mt.

-

Thit kv di kha ca thut ton AES (128, 192 v 256 bt) l an

ton bo vcc thng tin c xp vo loi TI MT (secret). Cc thng

tin TUYT MT (top secret) sphi dng kha 192 hoc 256 bt. Cc phin

bn thc hin AES nhm mc ch bo vh thng an ninh hay thng tin

quc gia phi c NSA kim tra v chng nhn trc khi sdng.

- iu ny nh du ln u tin cng chng c quyn tip xc vi thut ton

mt m m NSA ph chun cho thng tin TUYT MT. Nhiu phn mm

thng mi hin nay sdng mc nh kha c di 128 bt.

3. RSA

Thut ton c Ron Rivest, Adi Shamir v Len Adleman m tln u tin vo

nm 1977 ti Hc vin Cng nghMassachusetts (MIT). Tn ca thut ton ly t3

chci u ca tn 3 tc gi.

Trc , vo nm 1973, Clifford Cocks, mt nh ton hc ngi Anh lm vic ti

GCHQ, m tmt thut ton tng t. Vi khnng tnh ton ti thi im th

thut ton ny khng khthi v cha bao gic thc nghim. Tuy nhin, pht minh

ny chc cng bvo nm 1997 v c xp vo loi tuyt mt.

Thut ton RSA c MIT ng k bng sng chti Hoa Kvo nm 1983 (S

ng k 4.405.829). Bng sng chny ht hn vo ngy 21 thng 9 nm 2000. Tuy

nhin, do thut ton c cng btrc khi c ng k bo hnn sbo hhu


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nh khng c gi trbn ngoi Hoa K. Ngoi ra, nu nh cng trnh ca Clifford

Cocks c cng btrc th bng sng chRSA khng thc ng k.

M ts lc:Thut ton RSA c hai kha: kha cng khai (hay kha cng

cng) v kha b mt (hay kha c nhn). Mi kha l nhng scnh sdng trong qu trnh m ha v gii m. Kha cng khai c cng brng

ri cho mi ngi v c dng m ha. Nhng thng tin c m ha

bng kha cng khai chc thc gii m bng kha b mt tng ng. Ni

cch khc, mi ngi u c thm ha nhng chc ngi bit kha c nhn

(b mt) mi c thgii m c.

Ta c thm phng trc quan mt hmt m kho cng khai nh sau: Bob

mun gi cho Alice mt thng tin mt m Bob mun duy nht Alice c th

c c. lm c iu ny, Alice gi cho Bob mt chic hp c kha

msn v gili cha kha. Bob nhn chic hp, cho vo mt tgiy vit

th bnh thng v kha li (nh loi kho thng thng chcn sp cht li,

sau khi sp cht kha ngay cBob cng khng thmli c-khng c li

hay sa thng tin trong th c na). Sau Bob gi chic hp li cho Alice.

Alice mhp vi cha kha ca mnh v c thng tin trong th. Trong v d

ny, chic hp vi kha mng vai tr kha cng khai, chic cha kha chnh

l kha b mt.

To kha

Gi s Alice v Bob cn trao i thng tin b mt thng qua mt knh khng an ton

(v d nhInternet). Vi thut ton RSA, Alice u tin cn to ra cho mnh cp kha

gm kha cng khai v kha b mt theo cc bc sau:

1. Chn 2s nguyn tln v vi , la chn ngu nhin v c lp.

2.

Tnh: .

3. Tnh: gi tr hm s le .

4. Chn mt s t nhin sao cho v l s nguyn t cng

nhau vi .


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5. Tnh: sao cho .

Cc s nguyn t thng c chn bng phng php th xc sut.

Cc bc 4 v 5 c th c thc hin bng gii thut Euclid m rng (xem thm: s hc

mun).

Bc 5 c th vit cch khc: Tm s t nhin x \, sao cho d = \frac{x(p-1)(q-1)+1}{e}

Kha cng khai bao gm: n, mdun, e, s m cng khai

Kha b mt bo gm: n, mdun, xut hin c trong kha cng khai v kha b mt, d v

s m b mt

Mt dng khc ca kha b mt bao gm :p v q, hai s nguyn t chn ban u,d mod

(p-1) v d mod (q-1) (thng c gi l dmp1 v dmq1),(1/q) mod p (thng c gil iqmp)

Dng ny cho php thc hin gii m v k nhanh hn vi vic s dng nh l s d

Trung Quc (ting Anh: Chinese Remainder Theorem - CRT). dng ny, tt c thnh

phn ca kha b mt phi c gi b mt.

Alice gi kha cng khai cho Bob, v gi b mt kha c nhn ca mnh. y, p v q

gi vai tr rt quan trng. Chng l cc phn t ca n v cho php tnh d khi bit e. Nu

khng s dng dng sau ca kha b mt (dng CRT) th p v q s c xa ngay sau khi

thc hin xong qu trnh to kha.

M ha : GisBob mun gi on thng tin M cho Alice. u tin Bob chuyn

M thnh mt sm < n theo mt hm c tho ngc (tm c thxc nh li

M) c tha thun trc. Lc ny Bob c m v bit n cng nh e do Alice gi.

Bob stnh c l bn m ha ca m theo cng thc:

c = m^e mod n

Gii m : Alice nhn c t Bob v bit kha b mt d. Alice c th tm

c m tc theo cng thc sau:

Bit m, Alice tm li M theo phng php tha thun trc. Qu trnh gii m

hot ng v ta c


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.

Do ed 1 (modp-1) v ed 1 (modq-1), (theo nh l Fermat nh) nn:

v

Do p v q l hai snguyn tcng nhau, p dng nh l sd Trung Quc, ta

c:

.

hay:

.

Chuyn i vn bn r

Trc khi thc hin m ha, ta phi thc hin vic chuyn i vn bn r (chuyn i

tM sang m) sao cho khng c gi tr no ca M to ra vn bn m khng an ton. Nu khng

c qu trnh ny, RSA s gp phi mt s vn sau:

Num = 0 hocm = 1 s to ra cc bn m c gi tr l 0 v 1 tng ng

Khi m ha vi s m nh (chng hne = 3) v m cng c gi tr nh, gi tr cng

nhn gi tr nh (so vin). Nh vy php mun khng c tc dng v c th d dng tm

cmbng cch khai cn bce cac (b qua mun).

RSA l phngphpm ha xc nh(khng c thnh phn ngu nhin) nn k tn cng

c th thc hintn cng la chn bn rbng cch to ra mt bng tra gia bn r v bn

m. Khi gp mt bn m, k tn cng s dng bng tra tm ra bn r tng ng.

Trn thc t, ta thng gp 2 vn u khi gi cc bn tin ASCII ngn vi m l

nhm vi k tASCII. Mt on tin chc 1 k tNUL sc gn gi trm = 0 v

cho ra bn m l 0 bt kgi trca e v N. Tng t, mt k tASCII khc, SOH,

c gi tr1 slun cho ra bn m l 1. Vi cc hthng dng gi tre nhth tt c

k tASCII u cho kt qum ha khng an ton v gi trln nht ca m chl 255

v 2553 nhhn gi trn chp nhn c. Nhng bn m ny sddng bph m.
https://vi.wikipedia.org/w/index.php?title=M%C3%A3_h%C3%B3a_x%C3%A1c_%C4%91%E1%BB%8Bnh&action=edit&redlink=1https://vi.wikipedia.org/w/index.php?title=M%C3%A3_h%C3%B3a_x%C3%A1c_%C4%91%E1%BB%8Bnh&action=edit&redlink=1https://vi.wikipedia.org/w/index.php?title=M%C3%A3_h%C3%B3a_x%C3%A1c_%C4%91%E1%BB%8Bnh&action=edit&redlink=1https://vi.wikipedia.org/w/index.php?title=T%E1%BA%A5n_c%C3%B4ng_l%E1%BB%B1a_ch%E1%BB%8Dn_b%E1%BA%A3n_r%C3%B5&action=edit&redlink=1https://vi.wikipedia.org/w/index.php?title=T%E1%BA%A5n_c%C3%B4ng_l%E1%BB%B1a_ch%E1%BB%8Dn_b%E1%BA%A3n_r%C3%B5&action=edit&redlink=1https://vi.wikipedia.org/w/index.php?title=T%E1%BA%A5n_c%C3%B4ng_l%E1%BB%B1a_ch%E1%BB%8Dn_b%E1%BA%A3n_r%C3%B5&action=edit&redlink=1https://vi.wikipedia.org/w/index.php?title=T%E1%BA%A5n_c%C3%B4ng_l%E1%BB%B1a_ch%E1%BB%8Dn_b%E1%BA%A3n_r%C3%B5&action=edit&redlink=1https://vi.wikipedia.org/w/index.php?title=M%C3%A3_h%C3%B3a_x%C3%A1c_%C4%91%E1%BB%8Bnh&action=edit&redlink=1


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trnh gp phi nhng vn trn, RSA trn thc tthng bao gm mt hnh thc

chuyn i ngu nhin ha m trc khi m ha. Qu trnh chuyn i ny phi m

bo rng m khng ri vo cc gi trkhng an ton. Sau khi chuyn i, mi bn r

khi m ha scho ra mt trong skhnng trong tp hp bn m. iu ny lm gim

tnh khthi ca phng php tn cng la chn bn r (mt bn r sc thtng

ng vi nhiu bn m tuthuc vo cch chuyn i).

Mt stiu chun, chng hn nh PKCS, c thit kchuyn i bn r trc

khi m ha bng RSA. Cc phng php chuyn i ny bsung thm bt vo M. Cc

phng php chuyn i cn c thit kcn thn trnh nhng dng tn cng

phc tp tn dng khnng bit trc c cu trc ca bn r. Phin bn ban u

ca PKCS dng mt phng php c ng (ad-hoc) m vsau c bit l khng an

ton trc tn cng la chn bn r thch ng (adaptive chosen ciphertext attack). Cc

phng php chuyn i hin i sdng cc kthut nh chuyn i m ha bt i

xng ti u (Optimal Asymmetric Encryption Padding - OAEP) chng li tn cng

dng ny. Tiu chun PKCS cn c bsung cc tnh nng khc m bo an ton

cho chk RSA (Probabilistic Signature Scheme for RSA - RSA-PSS).

To chk scho vn bn

Thut ton RSA cn c dng to chk scho vn bn. GisAlice

mun gi cho Bob mt vn bn c chk ca mnh. lm vic ny, Alice

to ra mt gi trbm (hash value) ca vn bn cn k v tnh gi trm d

mod n ca n (ging nh khi Alice thc hin gii m). Gi trcui cng

chnh l chk in tca vn bn ang xt. Khi Bob nhn c vn bn

cng vi chk in t, anh ta tnh gi trm e mod n ca chk ng

thi vi vic tnh gi trbm ca vn bn. Nu 2 gi trny nh nhau th

Bob bit rng ngi to ra chk bit kha b mt ca Alice v vn bn

khng bthay i sau khi k. Cn ch rng cc phng php chuyn i bn r (nh RSA-PSS) gi

vai tr quan trng i vi qu trnh m ha cng nh chk in tv

khng c dng kha chung cho ng thi cho chai mc ch trn.

an ton


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an ton ca hthng RSA da trn 2 vn ca ton hc: bi ton phn

tch ra tha snguyn tcc snguyn ln v bi ton RSA. Nu 2 bi

ton trn l kh (khng tm c thut ton hiu qugii chng) th

khng ththc hin c vic ph m ton bi vi RSA. Ph m mt

phn phi c ngn chn bng cc phng php chuyn i bn r an

ton.

Bi ton RSA l bi ton tnh cn bc e mun n (vi n l hp s): tm s

m sao cho me=c mod n, trong (e, n) chnh l kha cng khai v c l bn

m. Hin nay phng php trin vng nht gii bi ton ny l phn tch n

ra tha snguyn t. Khi thc hin c iu ny, ktn cng stm ra s

m b mt d tkha cng khai v c thgii m theo ng quy trnh ca

thut ton. Nu ktn cng tm c 2 snguyn tp v q sao cho: n = pq

th c thddng tm c gi tr(p-1)(q-1) v qua xc nh d te.

Cha c mt phng php no c tm ra trn my tnh gii bi ton

ny trong thi gian a thc (polynomial-time). Tuy nhin ngi ta cng

cha chng minh c iu ngc li (skhng tn ti ca thut ton).

Xem thm phn tch ra tha snguyn tvvn ny.

Ti thi im nm 2005, s ln nht c thc phn tch ra tha s

nguyn tc di 663 bt vi phng php phn tn trong khi kha ca

RSA c di t1024 ti 2048 bt. Mt schuyn gia cho rng kha 1024

bt c thsm bph v(cng c nhiu ngi phn i vic ny). Vi kha

4096 bt th hu nh khng c khnng bph vtrong tng lai gn. Do

, ngi ta thng cho rng RSA m bo an ton vi iu kin n c

chn ln. Nu n c di 256 bt hoc ngn hn, n c thbphn tch

trong vi givi my tnh c nhn dng cc phn mm c sn. Nu n c

di 512 bt, n c thbphn tch bi vi trm my tnh ti thi im

nm 1999. Mt thit bl thuyt c tn l TWIRL do Shamir v Tromer

m tnm 2003 t ra cu hi van ton ca kha 1024 bt. V vy

hin nay ngi ta khuyn co sdng kha c di ti thiu 2048 bt.

Nm 1993, Peter Shor cng bthut ton Shor chra rng: my tnh lng

t(trn l thuyt) c thgii bi ton phn tch ra tha strong thi gian


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a thc. Tuy nhin, my tnh lng tvn cha thpht trin c ti mc

ny trong nhiu nm na.

Nm 2010, cc nh khoa hc thuc i hc Michigan cng bpht hin

mt khtrong hthng mt m ho RSA. Cch ph vhthng, ly kho

b mt RSA 1024 bit chtrong vi ngy thay v vi nm nu tn cng theo

cch thng thng - tn cng bng brute force (d tm ln lt). Cc nh

khoa hc to mt in thln gy li hthng, t gip tm ra kho

b mt. Vic tn cng c thc hin trn mt FPGA. Bo co c trnh

by ti hi nghDATE 2010 din ra ti Dresden, c thng 3 nm 2010.

4.

So Snh Cc Gii Thut

Gii thut Tc thc hin Khnng gii mCch thc hin

thut ton

DES Nhanh C th Di

AES Nhanh C th Di

RSA LuKhng th(vmt

thi gian)Dthc hin

I I .

MC TIU

1.

Hiu c cc gii thut m ha2. ng dng cc th vin m ha xy dng chng trnh

I I I .

HIN THC

1.

Gii thiu s lc

- Ngn ngsdng l java vi cc th vin jce v jca v mt sth vin lin quan

ti data


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19

2.

Cc cng vic cn lm:

No Task Chi tit

1 Tm hiu cc gii thut vmha i xng v bt i xng

Tm hiu vDES,AES,RSA

2Tm hiu cc th vin m ha

trong java

Jce v jca ,cryptography,security v

mt sth vin file,stream, sdng

swingui

3 Tin hnh mockup giao dinTo giao din trc quan cho ngi

dng

4

Hin thc cc gii thut m

haCoding

5 Test + debug Testing,debuging

6 deploy Xut file out put

7 Report + guideVit bo co chi tit vcc qu trnh

v kt qucui cng

Bng phn cng cng vic

Tn Cng vic Mc hon thin

Ph Quc Anh 1 2 3 4 6

Bi Tun Cnh 1 5 6

V nh Hu 1 6 7


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3.

Qu trnh hin thc ng dng

Thit kgiao din


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Phn tch cc method dng:

-

Trong qu trnh m ha vi input l mt file bt k. S s dng class

KeyGeneration to ngu nhin mt kha private i vi DES v AES v

slu mt ni c chn.

- Mt file key c sinh ra v chng trnh sdung key ny m ha cng

nh gii m. i vi DES key c khi to 56bit v 128bit vi AES.


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- Trong qu trnh gii m ngi dng scung cp key l mt file lu trn

thit bno khi tin hnh c chui file ny thnh dng stream cc

dng bit lin tc vo byte[] c ththchuyn chng vdng SecretKey.

- Th vin java htrclass Cipher dung cho vic m ha v gii m v trong

class ny nhm sdng 2 MODE chnh l ENCRYPT v DECRYPT

thc hin. V method doFinal() sthc hin qu trnh m ha cng nh gii

m.

- i vi gii thut RSA c bit hn DES v AES v y l kha bt i

xng nn nhm chn gii php cho chng trnh sinh ra mt cp kha

ring v kha cng khai ln lt c tn privateKey.RSAkey v

publicKey.RSAkey.

-

Bng cch tng ta hai kha ny vbyte[] v dung cc phng phpbin i X509EncodeKeySpec cho publicKey v PKCS8EncodeKeySpec

to li cp kha trn bng nhng file xut.

- Sau tin hnh m ha v gii m nh bnh thng

Qu trnh

- M ha:

1.Sinh Key

2.Chuyn input thnh dng bit

3.M ha tng khi

4.Sinh file output

- Gii m:

1.Nhn Key

2.Chuyn key vbyte[]

3.Chuyn byte[] vdng chng trnh hiu c bng cc hm Spec

4.Tin hnh gii m.

5.

Ghi cc dng bit ra file output

Coding

- Cc gii thut c hin thc bng cc c click vo cc nt nt nhn trn

giao din

- Sdng class file input stream cho qu trnh nhp xut file


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- Tin hnh chuyn a vmng [byte]

- Vi DES v AES ,y l m ha i xng ,to gi trkey bng hm key

generation ,lu key vo mc do ngi dng chn lu tr. M ha v gii

m bng hm dofinal sau xut file vo th mc do ngi dng chn.

- RSA ,to 1 cp kha gm kha cng khai v kha ring, sdng kha cng

khai m ha v dung kha ring m. Checksum vi MD5 v SHA-256

c hin thm 16bit(hecxa)

- Hin thqu trnh gii m v m ha.

I V.

Kt qut c

- Cc chc nng c bn ca cc gii thut.

- M ha c v gii m cc tp tin th mc,hnh nh,.ng thi to ra cc file

cha key ca gii thut .

- i vi RSA chm ha c cc file c dung lng nhhn 56 byte v tn nhiu

khng gian lu trv khng phi l gii thut m ha khi nn thng c sdng

m ha key trong qu trnh chia skha

- Bit c cch sdng cc hm th vin m ha c sn trong java

- Bng cch lu li cc file ha c thto ra c hm hybrid gia cc gii thut

phn phi kha

-

C thm ha c tt ccc file trong folder nhng cha khi to c ngdn.

-- HT --

Final Report Cryptography NetworkSecurity

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