Mn: Xy dng Chun Chnh Sch An Ton Thng Tin trong doanh nghipGVHD:
Nhm TH: Nguyn DuyMai c An Nguyn Cnh H Hong Ngc Tng Phm Ngc Thng Cao
Nguyn Trung Sang L Trung Trng Giang
Ni Dung I Gii Thiu II Cc Phng Php M Ha III Kt Lun
IV Ti Liu Tham Kho
I Gii Thiu Mt m ha c s dng t thi c i cho n ngy nay. Hin nay cc
giao dch ti chnh, chuyn khon, mua sm
trc tuyn, th tn, ti liu, ...c thc hin qua nhiu mi trng mng i hi
phi c bo mt tt.
I Gii Thiu(tt) Mt s khi nim: Thng bo, vn bn: l chui hu hn cc k t
c ly t mt bn ch ci Z no v c k hiu l m Mt m ha: l bin i mt thng bo
sao cho n khng th hiu ni vi bt k ngi khc ngoi ngi nhn mong mun. Php
mt m ha c k hiu l e(m), vi m l thng bo cn m ha.
I Gii Thiu(tt) Kha: l thng s u vo ca php m ha v gii m.
Kha dng m ha k hiu l: Ke Kha dng gii m k hiu l: Kd Chui mt m: l
chui thng bo qua php m ha, c k1y hiu l c , c = e (m, Ke). Php gii m
: l qu trnh xc nh thng bo t chui mt m c v kha Kd, c k hiu l : d(c,
Kd), d(c,Kd) = m.
I Gii Thiu(tt)
I Gii Thiu(tt) Mt m hc c 2 phn: Mt m hc c in : Caesar, Vigenere,
Substitution ., cc ch tng hnh ca Ai Cp c i, m ha thay th Atbash c
khon nm 500 600 tr.CN Mt m hc hin i : IDEA, RC4, DES, ASE ., cha ca
n l Claude Shannon. Cc yu cu c bn ca mt m ha l: + C tnh bo mt cao +
Cng khai, d hiu. Kh nng bo mt c cht vo kha c khng phi vo gii thut.
+ Trin khai c trn cc thit b in t.
II Cc phng php m ha Substitution Cipher (m ha thay th n gin).
Trong php ny, kha l 1 hon v h ca bn ch ci Z v mi k hiu thng bo c
thay th bng nh ca n qua hon v h Kha thng biu din bng 1 chui 26 k t
(bn ch ci ABC), c 26! (~4.10 26) hon v (kha). V d: kha l chui
UITPRO . , k hiu A trong chui thng bo thay bng U, k hiu B thay bng
I .
II Cc phng php m ha(tt) V d, chn 1 hon v p lm kha nh hnh sau, ta
c:
m ha Ep(a) = X v gii m Dp(A)= d
II Cc phng php m ha(tt) M rng: thay th n-gram. Thay v thay th cc
k t, ngi ta c th thay th cho tng cm 2 k t (diagram), 3 k t
(trigram), hay cho n k t (ngram) Vi bn ch ci gm 26 k t th php thay
th n-gram s c kha l 1 hon v ca 26n n-gram khc nhau.
II Cc phng php m ha(tt) V d thay th diagram th hon v ca n gm
262
diagram v c th biu din bng 1 dy 2 chiu trong cc hng biu din k
hiu u tin, cc ct biu din k hiu th 2, minh ha nh sau:
II Cc phng php m ha(tt) IDEA (International Data Encryption
Algorithm) l mt phng
php m khi, c a ra thay th ci c l DEA (Data Encryption
Algorithm), cng b nm 1991. Cch thc hin IDEA l h m thao tc trn tng
khi 64bit, m khi 64bit plantext thnh khi 64bit ciphertext, s dng
128bit lm kha bao gm 1 chui 8 ln bin i lin tip v tip theo l 1 ln
bin i u ra. Ln bin i th r s dng 6 khi kha con 16 bit Ki(r), 1 d4 d1
XOR d3 --> d5 d2 XOR d4 --> d6 d5 x s5 --> d7 d6 + d7
--> d8 d8 x s6 --> d9 d7 + d9 --> d10 d1 XOR d9 --> d11
d3 XOR d9 --> d12 d2 XOR d10 --> d13 d4 XOR d10 -->
d14
II Cc phng php m ha(tt) Sau khi thc hin xong bc ny, cc khi d12
,d 13 xut ra s
c trao i d11 v d13, d12 v d14 c dng lm u vo trong vng lp k tip
cng vi 6 kha ph tip theo ,bao gm t s7 n s12. Th tc ny c lp li trong
8 vng na cui cng xut ra tng cng 4 khi m chng ta gi l e1,e2,e3 v e4.
4 bc tip theo dng 4 kha ph trc hon thnh vic m ha e1 x s49 --> c1
e2 + s50 --> c2 e3 + s51 --> c3 e4 x s52 --> c4
II Cc phng php m ha(tt) Ch : Nhm p ng c tt c mc ch ca gii thut ,
1
kha ca mi ch s c nh ngha bng php nhn modulo 2^16 cho mi bc k
tip.4 khi xut ra cui cng,c1 ti c4, c gn thm to ra khi ciphertext 64
bit.C qu trnh c lp i lp li m ha khi plaintext 64 bit cho n khi qu
trnh m ha thnh cng.Qu trnh gii m cng tin hnh tng t qu trnh m kha
cho khi 64 bit ciphertext nhng vi 1 b kha ph khc.Nhng kha ph gii m
c lm ra t nhng kha ph m ha bng cch o ngc php nhn hoc cng .Nhng kha
ph gii m (tng t vi kha ph m ha t s1 ti s52) c trnh by bng bn di
:
II Cc phng php m ha(tt)
1st round s49* s50# s51# s52* s47 s48 2nd round s43* s45# s44#
s46* s41 s42 3rd round s37* s39# s38# s39* s35 s36 4th round s31*
s33# s32# s34* s29 s30 5th round s25* s27# s26# s28* s23 s24 6th
round s19* s21# s20# s22* s17 s18 7th round s13* s15# s14# s16* s11
s12 8th round s7* s9# s8# s10* s5 s6 S bin i cui cng.....s1* s2#
s3# s4* sXX* = php nhn o ngc ng d ca ((2^16)+1) sXX# = php cng o
ngc ng d ca sXX (2^16)
II Cc phng php m ha(tt) RC4: phng php hin i ,kha i xng,c thit k
bi
Ron Rivest vo nm 1987. RC4 pht sinh 1 lung m gi bit m ha , n c
kt hp vi plaintext bng php ton XOR , qu trnh gii m cng tng t. pht
sinh lung kha, thut ton chia lm 2 phn : 1. Han v tt c 256 bit (biu
th \ S \) 2. Hai con tr 8 bit (biu th \ i \ v \ j \).Qu trnh han v
ny
c khi to vi 1 kha c di thay i , thay i trong khong 40 256 bits ,
s dng thut tan RSA. Mt khi han thnh, lung bits ny c sinh ra dng gii
thut pht sinh m gi ngu nhin.
II Cc phng php m ha(tt) Gii thut Key-scheduleKey-schedule l 1
thut ton m tnh ton kha ph cho mi vng lp da trn kha chnh c cho trc.
Key-schedule c dng khi to hon v trong mng S. Chiu di kha c nh ngha
cng chnh l s byte trong kha v nm trong khong t : 1 chiu di 256, u
tin, mng S c khi to t 1 hon v ng nht. S sau c x l ,lp i lp li trong
256 ln theo cng 1 cch ca gii thut PRGA, nhng cng ng thi c trn trong
nhng bytes ca kha . for i from 0 to 255 S[i] := I endfor j := 0 for
i from 0 to 255 j := (j + S[i] + key[i mod keylength]) mod 256
swap(S[i],S[j]) endfor
II Cc phng php m ha(tt) Gii thut pht sinh m gi (PRGA) . Trong qu
trnh lp i lp li,
PRGA sa i trng thi v xut ra 1 byte ca lung kha.Trong mi qu trnh
lp , PRGA tng dn i, v tnh ra 2 gi tr ca S ti 2 byte i v j , sau cng
2 gi tr S[i] S[j] ,ri xut ra gi tr S chnh l kha k. Mi gi tr ca S c
thay i t nht 1 ln n 256 ln lp i lp li.i := 0 j := 0 while
GeneratingOutput: i := (i + 1) mod 256 j := (j + S[i]) mod 256
swap(S[i],S[j]) output S[(S[i] + S[j]) mod 256] endwhile
II Cc phng php m ha(tt) Thi gian test cc phng php trn
II Cc phng php m ha(tt)
II Cc phng php m ha(tt)
III Kt Lun Substitution Cipher l phng php m ha c in, hot
ng bng cch thay th k t nn thi gian m ha lu hn so vi 2 gii thut m
ha IDEA v RC4. IDEA: Nhanh hn 3DES, nhng chm hn Arcfour v Blowfish.
RC4 : Thut ton n gin, ngha tng bc r rng.
IV Ti Liu Tham KhoBooks:[1]: Slide An ton mng my tnh T Nguyn Nht
Quang HCNTT [2]: Cryptography And Network Security William
Stallings Internet: [1]: www.wikipedia.org [2]:
www.diendantinhoc.org [3]: www.slideshare.net
Cm n cc bn lng nghe!
Q&A
