N TPAN NINH MNG THNG TIN1. Cc kiu thc c bn v k thut an ton mng thng tin1.1 Cc c tnh an ninh mng vin thng. Nhn thc (Authentication): Nhn thc l qu trnh kim tra s hp l ca cc i tng tham gia thng tin. Xc nhn rng i tng (con ngi hay phn mm) c cp php truy cp vo h thng. (mt khu, sinh trc hc). Cch nhn thc n gin nht nhng cng km an ninh nht l kt hp tn ngi s dng v mt khu. Cc phng php tin tin hn l s dng cc chng nhn s hay cc ch k in t. Cm t chi (Non repudiation): Yu cu cc bn c trch nhim vi giao dch c tin hnh v bao gm c nhn dng i tng tham gia nhm trnh chi b. Chng pht li (Non-replay): Trnh cc bn tham gia pht li cc bn tin gy ra hin tng t chi dch v ca bn nhn. Ton vn s liu (Integrity): l s m bo rng s liu truyn khng b thay i hay b ph hoi trong qu trnh truyn dn t ni pht n ni thu. iu ny c th c thc hin bng kim tra mt m hay MAC (Message Authentication Code: m nhn thc bn tin). M ha (Encryption): Mc ch ca bo mt l m bo tnh ring t ca s liu chng li s nghe hoc c trm s liu t nhng ngi khng c php. Qu trnh ny bao gm m ha bn tin vo dng khng th c c i vi bt k my thu no khc tr my thu ch nh. Trao quyn (Authorization): l c ch kim tra rng ngi s dng c quyn truy nhp mt dch v c th v quyt nh mc truy nhp ca ngi s dng: ngi s dng c quyn thc hin mt s hnh ng. Trao quyn thng lin h cht ch vi nhn thc. Mt khi ngi s dng c nhn thc, h thng c th quyt nh ngi s dng c lm g.1.2 Khi nim mt m ho i xng: m khi v m dng: Khi nim mt m kho i xng: cn c gi l mt m bng kha b mt qu trnh mt m c s bao gm nhn s liu (Plaintext: vn bn th) s dng kho ring duy nht (mt lung s liu khc) thc hin mt php tnh no (chng hn cng hai lung s to ra mt lung th ba (vn bn mt m). Sau s liu mt m c th c gi qua mng. Kiu mt m ny cn c gi l m mt ln. M khi: Khi x l s liu, trc ht b mt m khi chia s liu thnh cc khi (c gi l chunk) c kch thc bng nhau. Kch thc ca mi chunk c xc nh da trn kch thc khi ca b m ha. V khng th m bo rng di ca u vo l bi s kch thc khi ca b mt m ha, nn c th phi n thm. M dng: mi ln b mt m dng tnh ton cho mt bit s liu. S dng mt kho lm ht ging, chng to ra mt lung bit sau XOR vi s liu u vo. B mt m v b gii mt m phi ng b vi nhau m bo cng mt bt lung c s dng mt m vn bn th gii mt m bit tng ng ca vn bn th.Note: Khi s dng m ha khi, mt mt gi khng nh hng n x l cc gi sau, nhng s dng mt m dng iu ny s nh hng.1.3 Khi nim v mt m ha kha i xng v mt m ha kha cng khai Khi nim v mt m ha kha i xngCn c gi l mt m bng kha b mt qu trnh mt m c s bao gm nhn s liu (Plaintext: vn bn th) s dng kho ring duy nht (mt lung s liu khc) thc hin mt php tnh no (chng hn cng hai lung s to ra mt lung th ba (vn bn mt m). Sau s liu mt m c th c gi qua mng. Kiu mt m ny cn c gi l m mt ln. Nhc im: Trc ht khng thc t khi phi c di kho bng di s liu mc d kho cng di cng cho tnh an ninh cao hn v cng kh m kho. th hai l c hai pha cn s dng chung mt kho (kha ny thng c gi l kha chia s). iu ny lm ny sinh cu hi: lm cch no pht kho n pha thu mt cch an ton? khc phc, ngi ta s dng mt m kho cng khai. Khi nim mt m ha kha cng khaiTrong mt m kho cng khai hai kho c s dng. Mt kho cng khai v mt kho ring ng thi c tao lp bng cng mt gii thut (gii thut thng dng l RSA). Ngi s dng gi kho ring ca mnh nhng a ra kho cng khai cho mi ngi. Kho ring khng bao gi c chia s vi mt ngi khc hoc truyn trn mng. C th s dng kho cng khai mt m ho s liu nhngbit v kho ny cng khng th gii m s liu ny v cn phi bit kho ring. S d nh vy v cc php ton c s dng trong kiu mt m ny khng i xng. V d: Ngi s dng A mun pht s liu c bo v n ngi s dng B, ngi s dng A s dng kho cng khai ca ngi s dng B mt m ho s liu v an tm rng ch c ngi s dng B l c th c c s liu ny.1.4 Hot ng ca m khi mc xch CBCCh CBC nhn khi vn bn mt m trc v XOR n vi khi vn bn th mt m. V khng c khi trc i vi khi u tin nn khi ny c XOR vi mt vect khi u (IV: Initial Vector). di ca IV phi bng di ca khi mt m m bo x l ton b khi th nht. IV phi c cc thuc tnh ngu nhin mnh m bo rng vn bn th ging nhau khng to ra vn bn mt m ging nhau. Gii mt m l qu trnh ngc ca mt m: mi khi c gii mt m v tnh ton XOR (Exclisive Or: hoc loi tr) vi khi trc cha gii mt m. Khi u tin c gii mt m v tnh ton XOR vi IV.

1.5 Hot ng ca gii thut tiu chun m ha tin tin AESAES c xy dng da trn gii thut Rijindael. y l mt phng php mt m ha lp lin kt c coi rng c cc thuc tnh mt m mnh. Ngoi vic cung cp mt m mnh, AES cn cho php thc hin nhanh v d rng trong phn cng cng nh phn mm v i hi b nh nh hn so vi cc s mt m tng ng khc.Hot ng:1. Trong thao tc Subytes, tng byte trong trng thi S c thay th bng mt byte khc bng cch s dng mt bng tra cu c gi l hp S (S-Box). Hp S c s dng rt ra hm o trn trng GF() c bit l c cc thuc tnh phi tuyn tt. Thao tc ny l thao tc duy nht m bo tnh phi tuyn cho mt m ny. Mc d c th rt ra bng S bng phng php ton hc, nhng hu ht cc ng dng s dng bng thay th lu trong b nh.2. Trong thao tc ShiftRows, mi hng c dch vng theo mt s bc c nh. Chng hn, cc phn t ca hng th nht c nguyn, cc phn t ca hng th hai dch tri tri mt ct, cc phn t ca hng th ba dch tri hai ct v cc phn t ca hng th t dch tri ba ct. Thao tc ny m bo rng mi ct ca trng thi u ra trong bc ny bao gm cc byte ca mi ct ca trng thi u vo.3. Trong thao tc MixColumns, mi ct c chuyn i tuyn tnh bng cch nhn vi mt ma trn trong trng hu hn. Ni chnh xc hn, mi ct c x l nh l mt a thc to m trn GF() sau c nhn modul +1 vi mt a thc c nh C(x)=3++x+2. Chuyn i tuyn tnh kh o ny cng vi thao tc ShiftRows m bo s ri rm trong b mt m.4. Trong thao tc AddRoundKey, trong mi trng thi c hoc loi tr (XOR) vi kha vng. Qu trnh AES bao gm vic rt ra 11 kha vng t kha mt m a n u my mt m. Bn thn m kha mt m c chuyn n cng l kt qu ca mt s bin i nh: lm ri (Hashing) c thc hin trn kha b mt ch. 11 kha vng c rt ra t kha mt m bng cch s dng gii thut tnh ton n gin.

c im:M ha AES vi kha c kch thc 256 bt (an ton). M ha AES l mt m khi gm nhiu vng. M ha AES khng phi l mt m ha Feistel. Cho php la chn kch thc khi m ha l 128, 192 hay256 bt. Cho php la chn kch thc ca kha mt cch c lp vi kch thc khi: l 128, 192 hay 256 bt. S lng vng c th thay i t 10 n 14 vng ty thuc vo kch thc kha.1.6 Gii thut RSA v phn tch u, nhc im.Phng php RSA l mt phng php m ha kha cng khai v l phng php m ho theo khi trong bn r M v bn m C l cc s nguyn t 0 n vi i l s bit ca khi. Kch thc ca i thng dng l 1024 bt. RSA s dng hm mt chiu l phn tch mt s thnh tha s nguyn t.Nguyn tc thc hin: thc hin m ha v gii m, RSA dng php ly tha modulo ca l thuyt s.1. Tm 2 s nguyn t p v q, sao cho N=p.q. N thng c gi l modulus.2. Chn E (kho cng khai) sao cho 1