7/26/2019 Huong Dan BT1

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HNG DN LM BI TP S 1

Cu 1:So snh cc bc trong quy trnh gi th tay & e-mail, nh gi bomt ca mi quy trnh.

Thy trnh by ti lp.

Cu 2:Ti sao cn phi bo mt thng tin c nhn?

V thng tin c nhn l ti sn ring c ca mi ngi. nh hng khng nhti i sng ca mi chng ta. C nhng k s hu thng tin c nhn ca mti tng c th li dng iu ny, bin n tr thnh cng c thc hin nhnghnh vi tiu cc, gy thit hi t nhiu cho nhng i tng h nhm vo.

Cu 3:Em lm g m bo an ton thng tin c nhn?

Nu nhng bin php quen thuc nhng hu hiu bo mt thng tin m bn thc hin trong i sng hng ngy, khi s dng my tnh & khai thcinternet.

Cu 4:Mt h thng m ha gm nhng thnh phn no? Cho v d?

Mt h m ha gm mt b (P, C, K, E, D)

-

P: tp bn r-

C: tp bn m-

Cu 5:H m Shift Cipher c bao nhiu kha tch cc?

H m Shift Cipher c 25 kha tch cc

Chn mt kha tch cc v m ha h tn ca bn theo phng php Shift

Cipher.Cu 6:Phng php Substitution Cipher c coi l tt hn Shift Cipher. Hylm sng t iu ny.

Da theo c ch ca Shift Cipher, ta thy rng y l h m khng c bomt tt bi khng gian kha cn hn hp. i phng ch cn d thm 1 trong25 kha K tch cc l c th gii m, thm ch trung bnh php th c th thnhcng vi 26/2 = 13 ln th.

7/26/2019 Huong Dan BT1

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trunglecntt

Ngc li, Substitution Cipher c khng gian kha kh ln, 26! kha, vic dthm l kh khn, cho nn n ti u hn Shift Cipher.

Cu 7:H thng m c in Affine cn iu kin g? Ti sao?

iu kin GCD(a, m) = 1 vi m l s modul.

Gii thch: tha mn phng trnh ng d l n nh, c nghim duy nht.

Cu 8:Trong h m c in, phng php Vigenre c gii hn chiu di khal bao nhiu?

Chiu di ti a ca bn kha l chiu di ca bn tin.

S dng kha l h tn ca bn, c th m ha d dng bn rhochocnnuahocmaiduphoclaiduoithixin.

Cu 9:Mt bn r:ROSESAREREDVIOLETSAREBLUESUGARISSWEETANDSOAREYOU(hoa hng mu , hoa violet mu xanh, ng th ngt ngo v em cng vy)

c m ho bng phng php Vigenre vi kho l DUYCOP sau lic m ho bng phng php Affine vi kho b mt thu c bn m l:KQMEETKITEFCVQJEXXZVGZBJXOYQAEVOMIYRWKVLEZZVGUGJ

Trnh by cc bc tm kho b mt ca phng php Affine?

Phng php:

- Da vo bn r ban u, ta tm c bn m sau qu trnh m ha bngphng php Vigenre vi kha y l:

DUYCOPDUYCOPDUYCOPDUYCOPDUYCOPDUYCOPDUYCOPDUYCOP

S dng bn m ny (l bn r trong qu trnh affine ha) kt hp vi bn mKQMEETKITEFCVQJEXXZVGZBJXOYQAEVOMIYRWKVLEZZVGUGJ

tm ra kha K(a, b)