Mã hóa trong .Net

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CHNG 1: GII THIU .NET FRAMEWORK

1.1. nh ngha.

.NET framework l mt nn tng lp trnh v cng l mt nn tng thc thi ng

dng ch yu trn h iu hnh Microsoft Windows c pht trin bi Microsoft.

Cc chng trnh c vit trn nn.NET Framework s c trin khai trong mi

trng phn mm (ngc li vi mi trng phn cng) c bit n vi tn

Common Language Runtime (CLR). Mi trng phn mm ny l mt my o trong

cung cp cc dch v nh an ninh phn mm (security), qun l b nh (memory

management), v cc x l li ngoi l (exception handling).

.NET framework bao gm tp cc th vin lp trnh ln, v nhng th vin ny

h tr vic xy dng cc chng trnh phn mm nh lp trnh giao din; truy cp,

kt ni c s d liu; ng dng web; cc gii thut, cu trc d liu; giao tip mng...

CLR cng vi b th vin ny l 2 thnh phn chnh ca.NET framework.

.NET framework n gin ha vic vit ng dng bng cch cung cp nhiu

thnh phn c thit k sn, ngi lp trnh ch cn hc cch s dng v ty theo

s sng to m gn kt cc thnh phn li vi nhau. Nhiu cng c c to ra

h tr xy dng ng dng .NET, v IDE (Integrated Developement Environment)

c pht trin v h tr bi chnh Microsoft l Visual Studio.[1]

1.2. Kin trc ca .Net framework

.Net framework c gii thiu bao gm 2 thnh phn chnh l Common

Language Runtime (CLR) v Base Class Libraries (BCL). Mt trong cc thnh phn

ny u c vai tr cc k quan trng trong vic pht trin cc dch v v cc ng

dng ca .Net.

Common Language Runtime (gi tt l b thc thi) c xy dng trn cc dc

v iu hnh. N chu trch nhim thc hin cc ng dng v m bo cc phn lin

quan n ng dng u c ap ng nh qun l b nh, an ninh bo mt, tch hp

ngn ng, B thc thi bao gm nhiu dch v h tr pht trin v trin khai ng

dng cng nh cu thin ng tin cy ca ng dng. Tuy vy, nhng nh pht trin

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trn thc t khng tng tc vi CLR. H s dng mt tp cc th vin c s c

xy dng bn trn b thc thi ny thng qua cc ngn ng lp trnh. Nh l mt

phn ca cc lp c s, .Net framework cn cung cp mt m hnh lp trnh ng

dng cho Web ASP.Net cung cp cc thnh phn v cc dch v mc cao hn

nhm mc ch pht trin cc dch v v cc ng dng Web XML.

Hnh 1.1: S kin trc .Net framework

1.2.1. Common Language Runtime CLR.

Common Langua Runtime trong .Net framework qun l s thc hin m v

cung cp s truy cp vo nhiu loi dch v gip cho qu trnh pht trin c d

dng hn. Common Language Runtime c kh nng tch hp cc ngn ng, bo mt

truy cp m, qun l thi gian sng ca i tng v h tr g li.

M c bin dch v hng ti CLR c tn managed code. Managed code

cung cp siu d liu cn thit cho CLR cung cp cc dch v h tr a ngn ng,

bo mt, qun l thi gian sng v qun l b nh.

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1.2.2. Base Class Libraries.

Th vin cc lp c s .Net framework cung cp mt tp cc lp, hng i

tng c th bc v c th m rng chng c s dng bi bt c ngn ng lp

trnh no. Nh vy, tt c cc ngn ng t Jscript ti C++ tr nn bnh ng v cc

nh pht trin c th t do la chn ngn ng m h vn quen dung.

Tp cc lp, cc kiu gi tr v giao din ny c t chc bng mt h thng

Namespace. khai bo mt Namespace ta dng:

namespace NamespaceName

{

// ni cha ng tt c cc class

}

Trong ,

Namespace: l t kha khai bo mt NameSpace

NamespaceName: l tn ca mt Namespace

1.2.3. ASP.Net.

ASP.Net l mt tp hp cac lp nm trong th vin lp c s. ASP.Net cung cp

mt m hnh ng dng Web di dng mt tp cc i tng iu khin v cung

cp c s h tng gip bn to ra cc ng dng Web mt cch d dng. Cc i

tng iu khin ny c xy dng cho cc ng dng trn my phc v phn nh

nhng i tng iu khin giao din ngi dng HTML c th nh listbox,

textbox, button,..vv.

ASP.Net cng cung cp nhng c tnh nh qun l trng thi v phc hi tin

trnh gip gim bt s lng m m mt ngi pht trin phi vit v tng tin cy

ca ng dng. Ngoi ra ASP.Net cho php cc nh pht trin chuyn giao phn mm

nh l mt dch v. Khi s dng nhng c tnh cc dch v Web XML ASP.Net,

cc nh pht trin ASP.Net c th vit nhng giao dch logic n gin v c s h

tng ASP.Net s chu trch nhim chuyn dch v theo ng SOAP v cc giao

thc khc. ASP.Net lm vic vi mi ngn ng v cng c.

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CHNG 2: .NET FRAMEWORK TRONG BO MT

2.1. .Net Framework v Common Language Runtime.

.Net framework v Common Language Runtime cho php ngi lp trnh lm

vic n gin hn vi cc phng php bo mt. Gi s nh chng li vic thng

tin b nh cp bng cch s dng phng php bo mt thch hp trong chng

trnh. Cc m c c th ngn chn bng vic phn quyn ngi s dng v bo v

truy cp m ngun.

Di y l mt s cc tnh nng c cung cp bi nn tng .Net framework

kh quan trng trong vn an ninh v m ha:

Thit lp cc chnh sch an ninh v tnh xc thc.

Quyn thi hnh da trn tnh xc thc v chnh sch an ninh.

Quyn truy cp thng qua vic xc thc ngi dng v vai tr ca ngi

dng.

Qun l v xc thc mi trng ng dng.

Lp Crytography cung cp cc thut ton m ha an ton.

2.2. .Net Framework v Common Language Runtime.

Mt vn ln trong lp trnh cc phng php an ninh s dng Win32 API l rt

kh khan trong hiu v s dng. Nhng dng m kh hiu c sp xp li s

l mt cch n gin nht, v d nh vic ly kha trong Cryptographic Service

Provider (CSP) m rt nhiu ngi pht trin thng b qua n. Nhng pht trin

thng p dng chnh sch an ninh bng vic dng Win32 API, h thng phi c

gng lm mt li lp trnh phc tp.

.Net framework cung cp nhiu phng php n gin bng cch a Win32

Security API vo mt i tng n gin hn. Rt nhiu php ton nh ly kha t

trong CSP gi c th t ng ly kha trong lp an ninh ca .Net Security

framework. Thm na mi lp trong .Net Security framework c tch hp cc tnh

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nng an ninh c v khai bo nh lp c nim phong khng th nh cp v b

l.

2.3. tin cy v nn tng ca .Net framework.

Khi s dng bt k mt bin php an ninh hay cc k thut m ha, phi chc

chn v tin cy ca chng trnh. Nn tng .Net tin xa mt bc gii quyt

vn v tin cy. .Net framework x l rt nhiu dch v an ninh t ng ng

tin cy nh:

Kim tra gii hn trong qu trnh chy chng trnh trnh s tht thot

b nh v trn stack.

Kim tra kiu d liu trong qu trnh chy chng trnh trnh a ra

kiu d liu sai.

i dc stack kim tra s cho php gi m.

T ng gom rc mt cch hiu qu tit kim b nh.

Kim sot li trnh nhng li bt thng trong qu trnh chy.

Bo v theo vai tr xc thc v gii hn thc thi cho ngi s dng.

Bo v theo chng thc qun l vic cho php s dng m c s.

2.4. Qun l kiu m v nh kiu an ton.

M c th s dng dch v ca CLR c tn l qun l m. CLR cung cp mt tp

hp dch v, nh kim tra nh kiu an ton v t ng thu gom rc, lm tng tnh

tin cy v tnh an ton. s dng c nhng dch v ca CLR, qun l m cn

phi d on trc, sp xp v kiu ng nht. nh kiu an ton hon ton c th

thc hin c v CLR hiu chi tit v loi d liu no ang c qun l. S dng

c s hiu bit , CLR c th p kiu chnh xc a ra cc lut trong vic

nh kiu an ton.

thc hin vic kim tra kiu an ton, .Net tch hp thm cc d liu ln

nh ngha m ngun v d liu cha trong chng trnh. Trnh qun l m c t

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ng chp nhn hoc t chi bi CLR. Trnh qun l b nh t ng ny gn ging

vi vic thu gom rc. Thu gom rc chng li vic r r b nh v tng tin cy.

2.5. Lp Cryptography v mt s hm m ha c ng dng trong .Net

Framework

2.5.1. Tng quan lp Cryptography.

Microsoft ng k bn quyn s hu Win32 Cryptography API (CryptoAPI) vo

nm 1996 tch hp trong Win NT. Mc d CryptoAPI cung cp y s h tr cho

ngnh lp trnh mt m, nhng n rt kh s dng. Phi tht s hiu r v mt m

hc v phi lm vic vi rt nhiu cc thnh phn cng nh nhng con s ln trong

API. .Net framework lm n gin ha vic s dng API bng cch cung cp mt

lp vi tn gi System.Security.Cryptography dng cho lp trnh m ha. Cch s

dng th vin Cryptography.

using System.Security.Cryptography;

System.Security.Cryptography c mt s lp chnh nh sau:

SymmetricAlgorithm: Lp m ha i xng. M ha theo cc thut ton

m ha i xng nh: DES, Rijndael, Triple DES, RC 2.

AsymmetricAlgorithm: Lp m ha bt i xng, n s m ha theo cc

thut ton RSA, DSA.

CryptoStream: Kt ni dng d liu ngun vi cc thut ton m ha.

CspParameters: Cha thng tin ca cc tham s trong nhng thut ton

c bit c th lu tr v ly li thng tin qua CSP.

HashAlgorithm: Lp c s h tr thut ton bm.

RandomNumberGenerator: Lp c s sinh s ngu nhin.

ToBase64Transform v FromBase64Transform: Dng chuyn i

cc dy Byte v Base64.

CryptographicException: Cha thng tin v li ca cc loi m khc

nhau.

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Hnh 2.1: Cc lp trong Cryptography

2.5.2. Cc thut ton m ha i xng trong .Net.

Cho thy cch mt m i xng hot ng. Lu rng ngi gi v ngi nhn

(v d, Bob v Alice) phi ng trc v nhng g cha kha v nhng thut ton

b mt c s dng. Cng vi cc thut ton, c nhng chi tit c lin quan, chng

hn nh cc vector khi to, phng thc hot ng v padding cng phi c

tho thun.

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Hnh 2.2: Qu trnh m ha v gii m thut ton m ha i xng

Cc lp .Net framework thc thi thut ton m ha i xng thng qua lp c

s SymmetricAlgorithm. Lp SymmetricAlgorithm c mt vi trng c khai bo

protected nn khng th truy vn trc tip vo phng thc khng c cung cp

bi lp. Tuy nhin nhng trng ny c th truy vn thng qua cc thuc tnh o,

thuc tnh o thc thi c th trn lp c th. V d nh trng s nguyn

BlockSizeValue c th truy vn thng qua thuc tnh BlockSize theo kiu thch hp,

da trn lp thc t ang s dng. Theo cch ny, vic c gng t c ca khi thnh

gi tr c th l khng hp php trong thut ton m ha i thnh gi tr c th l

khng hp php trong thut ton m ha i xng, s c cho php bi

CryptographicException, da trn thut ton c th ang c s dng. Trong mi

trng hp c khai bo protected v thuc tnh o s c chung kiu d liu v

tn s cng c loi b ch c gi tr gn lin vi trng c khai bo protected

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c gi li. Cc thuc tnh c trong lp SymmetricAlgorithm c th hin nh

sau:

Thuc tnh ngha

BlockSize Kiu int. Ly hoc t gi tr cho kch c khi di dng

cc bit cho thut ton, d liu tng th c th c m

ha hoc gii m trong mt bc. D liu m ln hn kch

c khi s c chia ra cc khi khc c kch c ging

nh khi to. Khi cui cng s c gn thm kch c

ca n

IV Kiu mng Byte. Ly hoc t gi tr ban u cho vector

trong thut ton m ha i xng, bt buc phi c mt

s ch Cirpher Mode.

Key Kiu mng Byte. Ly hoc t gi tr cho kha b mt s

dng trong thut ton m ha i xng m ha hoc

gii m.

KeySize Kiu int. Ly hoc t c cho kha b mt di dng cc

bit. Kch c thch hp s c phn bit bi

LegalKeySizes trong mi thut ton.

LegalKeySizes Ly kch c ca kha c h tr trong thut ton m ma

i xng.

LegalBlockSizes Ly kch c ca khi c h tr trong thut ton m ha

i xng..

Mode Kiu CipherMode. Ly hoc t ch thc hin trong

cc thut ton.

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Padding Kiu PaddingMode. Ly hoc t gi tr chn vo cc byte

cn trng ca khi cui cng.

Bng 2.1: Cc thuc tnh ca Symmetric Algorithm.

SymmetricAlgorithm c thit k l lp public v khng cha tham s. Kiu

thit k ny to ra cc kha b mt khc nhau. Tt nhin, SymmetricAlgorithm cng

h tr cc phng thc chun Equals, Finalize, GetHashCode, ToString, GetType

v MemberwiseClone nhng phng thc m c nh ngha lp Object c

s.

Phng thc chung ngha

Clear Phng thc tr v kiu void. S gi Dispose, gii phng

ngun c s dng trong thut ton m ha i xng.

Create Phng thc tr v i tng SymmetricAlgorithm. To

i tng SymmetricAlgorithm m ha hoc gii m.

CreateDecryptor To i tng gii m s dng kha v vector khi to.

Phng thc tham chiu n ICrptoTranform s dng

chuyn d liu thnh cc khi.

CreateEncryptor To i tng m ha s dng kha v vector khi to.

Phng thc tham chiu n ICrptoTranform s dng

chuyn d liu thnh cc khi.

Equals K tha t lp Object, s dng so snh 2 i tng

SymmetricAlgorithm cho bng nhau. Gi tr tr v c dng

bool.

GenerateIV Khi to gi tr vector bt k. Tr v kiu void.

GenerateKey Khi to kha bt k. Tr v kiu void.

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GetHashCode K tha t lp Object, cung cp gi tr bm cho i tng

SymmetricAlogrithm. Tr v kiu int.

GetType K tha t lp Object, s dng ly kiu cho i tng

SymmetricAlogrithm. Tr v kiu Type.

ToString K tha t lp Object, s dng cung cp chui hin th

cho i tng SymmetricAlogrithm.

ValidKeySize Phng thc ny quyt nh khi kch c kha ph hp vi

thut ton ang s dng. Tr v kiu bool.

Bng 2.2: Cc phng thc c trong SymmetricAlgorithm.

Chng ta khng lm vic trc tip vi i tng SymmetricAlgorithm, v y l

mt i tng tru tng. Bn s lm vic vi cc class c cung cp v n hot

ng nh mt phng thc o ca Symmetric Algorithm di y l s cc lp

trong SymmetricAlgorithm.

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Hnh 2.3: Cc thut ton m ha bt i xng c trong lp Symmetric

Algorithm.

Chng ta c th thy trong hnh 2.3 l cc lp c trong lp SymmetricAlgorithm,

chng cng l cc lp tru tng. By gi chng ta s tm hiu nha ca cc lp

v cch khai bo:

DES l lp tru tng ng gi theo thut ton m ha i xng. Cch

khai bo:

DESCryptoServiceProvider desCSP = new DESCryptoServiceProvider();

TripleDES l lp tru tng ng gi theo thut ton m ha i xng

Triple DES, thut ton ny c an ton cao hn DES. Cch khai bo:

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TripleDESCryptoServiceProvider tdesCSP = new

TripleDESCryptoServiceProvider();

Rijndael l lp tru tng ng gi theo thut ton m ha i xng.

Cch khai bo:

AesCryptoServiceProvider aesCSP = new AesCryptoServiceProvider();

RC 2 l lp tru tng ng gi theo thut ton m ha i xng. Cch

khai bo:

RC2CryptoServiceProvider rc2CSP = new RC2CryptoServiceProvider();

Kch thc kha v kha mc nh ca cc thut ton m ha i xng c s dng

trong .Net framework:

Thut ton Kch thc kha hp l Kch thc kha mc nh

DES 64 bit 64 bit

RC 2 T 40 n 128 bit 128 bit

Triple DES 128, 192 bit 192 bit

Rijndael 128, 192, 256 bit 256 bit

Bng 2.3: Kch thc kha ca cc thut ton m ha i xng

2.5.3. Cc thut ton m ha bt i xng trong .Net.

s dng mt m khng i xng, Bob ngu nhin to ra mt cp public v

private key. Bob cho php tt c mi ngi truy cp vo kha cng khai, trong

c Alice. Sau , khi Alice c mt s thng tin b mt m c mun gi cho Bob, c

m ha d liu bng cch s dng mt thut ton bt i xng thch hp v kha

cng khai c to ra bi Bob. Sau c gi bn m kt qu cho Bob. Bt c ai

khng bit kha b mt s mt mt thi gian di ly bn r t bn m ny, nhng

Bob c kha b mt v c th d dng gii m bn r ban u. Hnh 4-1 cho thy

cch m ha bt i xng c s dng.

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Hnh 2.4: Cch m ha bt i xng c s dng.

.Net framework thc thi thut ton m ha i xng thng qua lp c s

AsymmetricAlgorithm cng ging nh vic s dng cc thut ton m ha i xng

thng qua lp SymmetricAlgorithm. Sau y l s cc lp trong lp

AsymmetricAlgorithm:

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Hnh 2.5: Thut ton m ha i xng trong lp Asymmetric Algorithm.

Cc phng thc c th hin trong lp AsymmetricAlgorithm:

Phng thc chung ngha

KeySize Kch thc ca kha tnh theo bit

LegalKeySizes Gi tr kch thc kha hp l tnh the byte ca thut

ton m ha bt i xng hin ti

KeyExchangeAlgorithm Ch nh thut ton trao i kha c s dng v

cch thc trao i kha cng khai v kha b mt

SignatureAlgorithm Ch nh thut ton c s dng k trn i tng

hin thi

FromXmlString() Ti to li i tng thut ton m ha bt i xng

t 1 file XML

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ToXmlString() Tr v mt th hin XML cho i tng bt i xng

ang s dng

Bng 2.4: Cc phng thc chung ca lp Asymmetric Algorithm.

Cch khai bo thut ton m ha bt i xng RSA:

RSACryptoServiceProvider rsa = new RSACryptoServiceProvider();

Sinh cp kha b mt v cng khai lu di dng file .XML:

tbxPublicKeyAsym.Text = rsa.ToXmlString(false);

tbxPrivateKeyAsym.Text = rsa.ToXmlString(true);

trong thut ton m ha bt i xng, kha cng khai v kha b mt u c

lu di dng XML. Sau y l cu trc ca file XML gm:

Modulus: Gi tr m-un ca kha, n.

Exponent: Gi tr m ca kha, e.

D: Gi tr kha b mt, d.

P: c s dng tng hiu qu ca thut ton RSA.

Q

DP

DQ

InverseQ:

Kha cng khai:

rDfiEFFnSsTOckbA/gh7H75f7yQAGpsRNDFFuTxlepQA/oLoZVEdC

u4fyzNPzRl9Z5Lz25EDnOwliX2Py6vljxVIPQHC/H5n+yYSUvZtdiL9ELPxI2Tz

9807TWWDvKm7nx/4XeYvLc4/8swMnbaaUSktX3bHvaElLUV/DCQck/5XU+Q

49+/2+bF6IuwsNadNYOx3JgfkmYvPHmIEbLoqgKByBrKp4jnR+gOD7rzUPqvL

EfYLMvLGAPRCbYn4AvbA8Mnpo1s4PhypY3wW7O46WGElM7B/VWksltJ+h

9+/xCy2jptNlxmRJrB2sIf61EdK3TTFGlV6LnNE4LLpwQM9WQ==

AQAB

Kha b mt:

17

rDfiEFFnSsTOckbA/gh7H75f7yQAGpsRNDFFuTxl

epQA/oLoZVEdCu4fyzNPzRl9Z5Lz25EDnOwliX2Py6vljxVIPQHC/H5n+yYSU

vZtdiL9ELPxI2Tz9807TWWDvKm7nx/4XeYvLc4/8swMnbaaUSktX3bHvaElLU

V/DCQck/5XU+Q49+/2+bF6IuwsNadNYOx3JgfkmYvPHmIEbLoqgKByBrKp4j

nR+gOD7rzUPqvLEfYLMvLGAPRCbYn4AvbA8Mnpo1s4PhypY3wW7O46WG

ElM7B/VWksltJ+h9+/xCy2jptNlxmRJrB2sIf61EdK3TTFGlV6LnNE4LLpwQM9

WQ==

AQAB

1dVpO8WVUeCUI+8DmSZdAy6wLERPDaC/ntK+sRF0IFPRzkGUCexC7J4

SlCjmm7nmzY0OenpnyAh4X9Gamt9rpTSX765w0bdF8N9GyiZGKwi8H2AwY5

4giXPBFuOmfYkt1kDqEC/jg5nyeufITfWPH3lHBxMzlbzrwUuRqUuw0LE=

zi2tb/DxAfRyK6/LWuaCvZAeCDMUkfuuRnzwrgUBaeti41T8HfQRzLCpag

3p+nes4SSFm0KFuz6JO+tSSjEJ1Ee2v2PATEO6VC9M3PW9I/N31WPCR4gtzG

FTkSIM4KlrTiJbMq37RvkbuaLaoBi5c6HFH4OEyTEht8lEth47ISk=

quiI1KJGh4ulO9dEm/riqrF9U9RBDxZlMa8lhOb7Vv9HmMAnb4rrrq1lEhB

iySLby3yrjs8Y9fN3KragCJr8Ma4IpiRZvfTrLOt4bAgNW0X+/mDmLCjtvo7LTN

0la/7hqPZ3Xfq4sK2x9fQdz9mtzC0lzQzW1R6LnBInWRXLO/E=

ANvd2haF2n07MIVl8nX9W27LQTt9PXJv8mk403C/5cIOQmYrOrC2lkSy

H/f43os7FCED0XbAedwz1CURza9QnCrETx3KQkcR8qHTzyPS6uBrwl7NA2FE

15IcOAGNTi5GfSfVe2uQHWaSP/62rG4N77ZfzNbOacwjmNFk0OFlW6k=

NTNFwG5f/bA0paO6R7bgQnsAgM5R51BghexThn4dxlqXlU2QBHx

snPhV15IKJHwTEYQv+oUM5r5OiHWZxbtucqZemsD4PcUprjoaZaYqJ29fZ98S

d4xi96MZIDTFvU8YXfJyY55Bod4+/I3laNxg28U3DEoY/gu4u3HV99FmOcc=

CQhMS8FNOtNsJXu3AwvUU1OjifIYLE0OP6/G4aJ8iwuIqtCYWjoBHTHki

n6INLBdzqkbL5yhNSGAjX+/ozXCjjjWR1bYkHAbyYUTaHUCxDOtFKtvXgUd

M5W4wsQsfuBjFgMx/lDEkDE1UulnTv1FBjUz60IaU0SIo+F1eqBJPGzAReBm

BHSDKTjt+6xhpefjZRxTsH+um5zuRphBii8CvbOmTetNaMaIfvE7Huydy4eEc3y

nyFcZyxFiMzilxgDIS+Brr7Hm2za5v2dKeAleK0E2fWHWJ1tPwK0Re1XTDzTP

cYTrfpAJ2rPjpsOm4hqMLjt9ptb+VygPooNQYSV4YQ==

Cc bc thc hin thut ton RSA m ha file bng public key:

Chia nh bn r thnh cc khi d liu nh hn hoc bng 128 byte.

M ha cc khi nh d liu bng public key v hm m ha.

Ni cc khi m ha thnh bn m.

Thc hin gii m file bng private key.

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Chia nh bn m thnh cc khi d liu bng 128 byte.

Gii m tng khi nh bn m bng private key v hm gii m.

Ni cc khi gii m thnh bn r.

Gii thut k s (Digital Signature Algorithm, vit tt DSA) l chun ca chnh

ph M hoc FIPS cho cc ch k s. Gii thut ny c ngh bi Vin cc tiu

chun v cng ngh quc gia (NIST) vo thng 8/1991 s dng trong chun ch

k s (DSS), c ch ra trong FIPS 186, c chp nhn nm 1993. Mt sa i

nh c a ra nm 1996 trong FIPS 186-1, chun c m rng hn nm 2000,

c xem nh FIPS 186-2.[1]

Hot ng ca DSA:

To kha.

K ln bn r.

Kim tra tnh hp l ca ch k.

2.5.4. Cc thut ton hm bm trong .Net framework.

C 2 loi thut ton hm bm thng dng l SHA-1 (Secure Hash Algorithm)

v MD5 (Message Digest). Thm na, mt vi phin bn mi ca SHA c

cng b. Gii thut ton bm c kha cng rt quan trng trong vic xc thc thng

tin. Tt c nhng th u c h tr bi .Net framework di dng cc lp trong

HashAlgorithm:

MD5

SHA-1

SHA-256

SHA-384

SHA-512

KeyedHashAlgorithm

Tm tt cc thut ton bm ca .Net framework.

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Thut ton Kch thc khi

u vo (bit)

Tin nhn gii hn

(bit)

Kch thc m

bm (bit)

MD5 512 264 128

SHA-1 512 264 160

SHA-256 512 264 256

SHA-384 1024 2128 384

SHA-512 1024 2128 512

Bng 2.5: Cc thut ton hm bm.

Di y l s trong lp HashAlgorithm. Cc lp ny cng l lp tru tng

nn ta khng th thao tc trc tip ln lp. ng vi mi lp s c mt lp thc thi

c th v ta s s dng chng trc tip:

20

Hnh 2.6: Cc thut ton m ha bng hm bm.

Cch khai bo cc lp ca thut ton hm bm c trong .Net framework:

Khai bo MD5:

MD5CryptoServiceProvider md5 = new MD5CryptoServiceProvider();

byte[] hashKey = md5.ComputeHash(bytesKey);

21

Khai bo SHA-1:

SHA1CryptoServiceProvider sha1 = new SHA1CryptoServiceProvider();

byte[] hashKey = sha1.ComputeHash(bytesKey);

Khai bo SHA-256:



Khai bo SHA-384:



Khai bo SHA-512:



Khai bo lp KeyedHashAlgorithm, trong lp ny n thc thi c th da trn

lp HMACSHA1 v MACTripleDES. Nhng lp ny m ha thut ton hm bm

c kha da trn thut ton SHA-1 v TripleDES:

HMACSHA1 msha1 = new HMACSHA1 ();

MACTripleDES mtrdes = new MACTripleDES ();

Cc thuc tnh c trong lp hm bm.

Thuc tnh ngha

Hash Thuc tnh ny tr v gi tr ca m bm

tnh ton. N khng thng c s dng.

HashSize Thuc tnh ny tr v kch thc ca m

bm (bit) m thut ton bm to ra.

22

CanReuseTransform Cc thuc tnh t lp ICryptoTranform,

m khng lin quan trc tip n bm,

nhng c thc hin bi lp

HashAlgorithm

Bng 2.6: Cc thuc tnh c trong lp Hash Algorithm.

Cc phng thc ca lp Hash Algorithm:

Methods ngha

Create Phng thc tnh ny to ra mt th hin mi ca lp

HashAlgorithm bng tn.

ComputeHash Phng thc ComputeHash c s dng to ra m

bm t mng byte v lung d liu.

Initialize Lp ny c s dng bi cc lp hc thut ton thc hin

khi to trng thi ca h trc khi s dng.

Bng 2.7: Cc phng thc ca lp Hash Algorithm.

Nhng ngi lp trnh cn tha thun t tn chung hang tram cc chun,

thut ton v kiu d liu c t di mt ci tn duy nht. OIDs (Object

Identifiers) s c nh ngha v qun l bng s cc cu trc bao gm c ANSI

(American National Standards Institute) vi mc ch nh danh duy nht cc kiu

thng qua mt s phn cp logic. C s lng ln OIDs nh danh mi kiu

ring nh: giao thc, thut ton, cc kiu d liu. Phn ln cc thut ton m ha

c cng nhn bi ANSI u c ng k vi mt tn duy nht trong OIDs.

Chng ta s xem OIDs mt cch c th trong cc lp ca .Net Security Framework

nh SignHash v VerifyHash trong lp RSACryptoServiceProvider v

DSACryptoServiceProvider.

23

Cryptographic Hash Algorithm OIDs

MD5 1.2.840.113549.2.5

SHA-1 1.3.14.3.2.26

SHA-256 2.16.840.1.101.3.4.2.1

SHA-384 2.16.840.1.101.3.4.2.2

SHA-512 2.16.840.1.101.3.4.2.3

Bng 2.6: OIDs ca cc thut ton hm bm.

Sau y l mt v d minh ha vic s dng OIDs nh mt thnh phn trong

phng thc SignHash ca lp RSACryptoServiceProvider. Tt nhin n ch l gi

nh v bin hashbytes l mt mng byte c to ra bng cch gi hm

ComputerHash ca lp SHA-1.

RSACryptoServiceProvider rsa = new RSACryptoServiceProvider();

Signaturebytes = rsa.SignHash(hashbytes,1.3.14.3.2.26);

24

CHNG 3: LP TRNH M HA TRONG .NET

FRAMEWORK

3.1. Lp trnh m ha i xng trong .Net.

3.1.1. M ha v gii m file vi thut ton m ha i xng.

Chng ta s cng xem mt chng trnh demo v cng gii thch lm th no

m ha mt file vi cc thut ton m ha i xng. Di y l mt s giao din

ca chng trnh.

Hnh 3.1: Giao din Symmetric Algorithm.

Giao din chng trnh gm 3 GroupBox: Symmetric Algorithm, Modes,

Padding. Symmetric Algorithm bao gm 4 thut ton DES, RC2, TripleDES,

Rijndael (AES) v 4 Radiobutton i din cho 4 loi m ha , y chn ch

mc nh l DES. Cirpher Modes bao gm 5 Radiobutton i din cho 5 ch l

ECB, CBC, CFB, OFB, CTS, chn ch mc nh l CBC. Padding bao gm 3

25

Radiobutton i din cho 3 ch padding PKCS #7, Zeros, None chn ch mc

nh l PKCS #7.

Khi load form hoc c s thay i Radiobutton Symmetric Algorithm th s

gi n hm khi to thut ton m ha i xng.

private void rbtDES_CheckedChanged(object sender, EventArgs e)

{

if (rbtDES.Checked == true)

{

tbxCreateKeySym.Enabled = false;

sa = SymmetricAlgorithm.Create("DES");

}

}

private void rbtRC2_CheckedChanged(object sender, EventArgs e)

{

if (rbtRC2.Checked == true)

{

tbxCreateKeySym.Enabled = true;

sa = SymmetricAlgorithm.Create("RC2");

}

}

private void rbt3DES_CheckedChanged(object sender, EventArgs e)

{

if (rbt3DES.Checked == true)

{


sa = SymmetricAlgorithm.Create("TripleDES");

}

}

private void rbtAES_CheckedChanged(object sender, EventArgs e)

{

if (rbtAES.Checked == true)

{

tbxCreateKeySym.Enabled = true;

sa = SymmetricAlgorithm.Create("AES");

}

}

26

Modes, la chn ch mc nh CBC cho cc qu trnh m ha v gii m.

Khi c s thay i y s gi ti hm:

private void rbtEBC_CheckedChanged(object sender, EventArgs e)

{

if (rbtEBC.Checked == true)

{

sa.Mode = CipherMode.ECB;

}

}

private void rbtCBC_CheckedChanged(object sender, EventArgs e)

{

if (rbtCBC.Checked == true)

{

sa.Mode = CipherMode.CBC;

}

}

private void rbtCFB_CheckedChanged(object sender, EventArgs e)

{

if (rbtCFB.Checked == true)

{

sa.Mode = CipherMode.CFB;

}

}

private void rbtOFB_CheckedChanged(object sender, EventArgs e)

{

if (rbtOFB.Checked == true)

{

sa.Mode = CipherMode.OFB;

}

}

private void rbtCTS_CheckedChanged(object sender, EventArgs e)

{

if (rbtCTS.Checked == true)

{

MessageBox.Show("Not use!!!!");

rbtCBC.Checked = true;

}

}

27

Button Create Key v Create IV khi click vo s gi n GenKey() v GenIV()

dng sinh kha v sinh iv cho mi thut ton:

private void btnCreateKeySym_Click(object sender, EventArgs e)

{


{


tbxCreateKeySym.Text = GenKey();

}

tbxCreateKeySym.Text = GenKey();

}

private void btnCreateIV_Click(object sender, EventArgs e)

{

tbxCreateIVSym.Text = GenIV();

}

Hm GenKey() v GenIV().

public string GenKey()

{

sa.GenerateKey();

byte[] key = sa.Key;

string strKey = "";

foreach (int b in key)

strKey += b.ToString("X2") + " ";

return strKey;

}

public string GenIV()

{

sa.GenerateIV();

byte[] iv = sa.IV;

string strIV = "";

foreach (int b in iv)

strIV += b.ToString("X2") + " ";

return strIV;

}

28

Cc button Save Key v Save IV s lu key v iv thnh cc file c lu mc

nh .txt

private void btnSaveKey_Click(object sender, EventArgs e)

{

saveFD = new SaveFileDialog();

saveFD.DefaultExt = "txt";

saveFD.Title = "You want to save file?";

if (saveFD.ShowDialog() == DialogResult.OK)

{

SaveKey(saveFD.FileName);

}

}

private void btnSaveIV_Click(object sender, EventArgs e)

{


saveFD.DefaultExt = "txt";

saveFD.Title = "You want to save file?";


{

SaveIV(saveFD.FileName);

}

}

Khi mun m ha v gii m ngi dng phi ch ng dn ca Key, IV qua

cc ng dn Load Key, Load IV v ng dn Source File, Destination File.

Bc vo qu trnh gii m, khi ngi dng click vo button Encrypt, khi c

y cc thng tin cn thit qu trnh m ha s din ra.

private void btnEncryptSym_Click(object sender, EventArgs e)

{


{

EncryptData(4, tbxSourceFileSym.Text, tbxDesFileSym.Text,

HashKey(2, tbxCreateKeySym.Text), LoadIV(tbxLoadIVSym.Text));

MessageBox.Show("Encrypted!!!");

return;

}

29


{


LoadKey(tbxLoadKeySym.Text), LoadIV(tbxLoadIVSym.Text));


return;

}


{




return;

}


{


HashKey(1, tbxLoadKeySym.Text), LoadIV(tbxLoadIVSym.Text));


return;

}

}

V button Decrypt, thc hin qu trnh gii m vi key v iv c dng

m ha.

private void btnDecryptSym_Click(object sender, EventArgs e)

{


{

DecryptData(4, tbxSourceFileSym.Text, tbxDesFileSym.Text,

HashKey(2, tbxCreateKeySym.Text), LoadIV(tbxLoadIVSym.Text));

MessageBox.Show("Decrypted!!!");

return;

}


{



30


return;

}


{




return;

}


{


HashKey(1, tbxLoadKeySym.Text), LoadIV(tbxLoadIVSym.Text));


return;

}

3.1.2. M ha file bng thut ton m ha bt i xng.

Chng ta s cng xem mt chng trnh demo v cng gii thch lm th no

m ha mt file vi cc thut ton m ha i xng. Di y l mt s giao din

ca chng trnh.

31

Hnh 3.2: Giao din ca chng trnh Asymmetric Alogorithm.

y ch cung cp mt thut ton m ha bt i xng l RSA v cc padding:

PKCS #1 v1.5 v OAEP.

Khi click vo button Create Key, public key v private key c sinh ra di

dang file .XML.

private void btnCreateKeyAsym_Click(object sender, EventArgs e)

{

rsa = new RSACryptoServiceProvider();

tbxPublicKeyAsym.Text = rsa.ToXmlString(false);

tbxPrivateKeyAsym.Text = rsa.ToXmlString(true);

}

Cp kha public v private key s c lu khi ngi dng click vo button Save

Key.

private void btnSavePubKey_Click(object sender, EventArgs e)

32

{

if (tbxPublicKeyAsym.Text == "")

{

MessageBox.Show("You have not created key !!!");

return;

}


saveFD.DefaultExt = "xml";

saveFD.Title = "Do you want to save file?";


{

string pathSave = saveFD.FileName;

WriteFileText(pathSave, tbxPublicKeyAsym.Text);

}

saveFD.Dispose();

}

private void btnSavaPrivateKey_Click(object sender, EventArgs e)

{


saveFD.DefaultExt = "xml";

saveFD.Title = "Do you want to save file?";


{

string pathSave = saveFD.FileName;

WriteFileText(pathSave, tbxPrivateKeyAsym.Text);

}

saveFD.Dispose();

}

Bc vo qu trnh m ha, ngi dng phi ch ng dn ti ni lu kha

public key Load Key, nhp cc ng dn ti file cn m ha v lu file m ha.

Khi click vo button, Encrypt qu trnh m ha s bt u.

private void btnEncrypt_Click(object sender, EventArgs e)

{

if (tbxDesFileAsym.Text == "")

{

MessageBox.Show("Choose the source file to encrypt!!!");

33

return;

}


{

MessageBox.Show("Path wrong!");

return;

}

if (tbxLoadKeyAsym.Text == "")

{

MessageBox.Show("Choose the Public Key or Private Key to Encrypt

!!!");

return;

}

EncryptRSA(tbxLoadKeyAsym.Text, tbxSourceFileAsym.Text,

tbxDesFileAsym.Text);

MessageBox.Show("Encrypted !!!");

}

Button Decrypt, dng gii m file c m ha bng private key c

to ra cng public key. Kha private key s c c t ng dn Load Key.

private void btnDecrypt_Click(object sender, EventArgs e)

{


{

MessageBox.Show("Choose the source file to encrypt!!!");

return;

}


{

MessageBox.Show("Path wrong!!");

return;

}

if (tbxLoadKeyAsym.Text == "")

{

MessageBox.Show("Choose the Public Key or Private Key to Decrypt

!!!");

return;

}

34

DecryptRSA(tbxLoadKeyAsym.Text, tbxSourceFileAsym.Text,

tbxDesFileAsym.Text);

MessageBox.Show("Decrypted !!!");

}

3.1.4. M ha file bng thut ton hm bm.

m ha file bng thut ton hm bm s c h tr cc thut ton nh: MD5,

SHA-1, SHA-256, SHA-384, SHA-512, Keyed Hash Algorithm qua cc radiobutton

trong GroupBox Hash Algorithm.

Hnh 3.3: Giao din Hash Algorithm.

Thut ton Keyed Hash Algorithm l hm bm c key, nn khi chn thut ton

ny s cho php in key vo m ha trong khi cc thut ton khc th khng.

Ngi dng s phi in y ng dn v file cn m ha v file lu sau

khi m ha xong. Tip lc click vo button Hash, qu trnh m ha s bt u.

35

private void btnEncryptHash_Click(object sender, EventArgs e)

{

if (tbxSourceFileHash.Text == "")

{

MessageBox.Show("Choose source file!!!");

}

else if (tbxDesFileHash.Text == "")

{

MessageBox.Show("Choose destination file!!!");

}

else if (rbtKeyHash.Checked == true && tbxKeyHA.Text == "")

{

MessageBox.Show("Enter Key!!!");

}

else

{

FileInfo fiSource = new FileInfo(tbxSourceFileHash.Text);

if (fiSource.Exists)

{

if (hash == 6)

{

KeyedHashFile(tbxKeyHA.Text, tbxSourceFileHash.Text,

tbxDesFileHash.Text);

}

else

{

HashFile(hash, tbxSourceFileHash.Text, tbxDesFileHash.Text);

}

MessageBox.Show("Hash successfull!!!");

}

else

{

MessageBox.Show("Path wrong!!!");

return;

}

}

}

36

KT LUN

Sau qu trnh tm hiu ti bo co, nhm tm hiu v thc hin c mt

s vn d nh sau:

Tm hiu v .Net framework cng nh .Net framework trong bo mt

thng tin.

Tm hiu v lp Cryptopraphy trong .Net framework h tr trong lp trnh

bo mt

Xy dng c chng trnh demo v m ha file bng cc thut ton m

ha.

Bn cnh bi bo co cng c nhng mt hn ch:

Chng trnh cn kh n gin, cha thn thin vi ngi dng.

Cha bt ht cc li trong chng trnh.

Cha c h thng h tr ngi s dng.

Cha c phn to ch k s.

Chng trnh m ha cha m ha c cc file c dung lng ln.

Hng pht trin ca bo co:

Xy dng chng trnh hon thin hn,

Bt ht cc li cn thiu st.

B sung h thng h tr ngi s dng

37

TI LIU THAM KHO

1. http://vi.wikipedia.org/wiki/.NET_Framework

2. .Net Security and Cryptography.

3. Programing .Net Security.

4. V mt s ti liu khc trn internet.

Mã hóa trong .Net

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