nhan dang nguoi noi

I HC QUC GIA TP. HCM

TRNG I HC BCH KHOA

KHOA KHOA HC & K THUT MY TNH

BKTP.HCM

LUN VN TT NGHIP I HC

NGHIN CU S DNG GING NI TRONG

XC THC V M HA D LIU TRN THIT B

DI NG V XY DNG H THNG DEMO TRN

ANDROID

HI NG: H thng thng tin

GVHD: PGS. TS ng Trn Khnh

GVPB: ThS. Trng Qunh Chi

SVTH 1: L Phm Tuyn(50802487)

SVTH 2: Dng T Huy(50800768)

SVTH 3: L Tro Vit Cng(50800240)

TP. H CH MINH, THNG 12 NM 2012

ii

LI CM N

Chng em xin chn thnh cm n Khoa Khoa hc v K thut my tnh-trng

i hc Bch Khoa to iu kin cho chng em thc hin ti lun vn tt

nghip ny.

Chng em xin gi li cm n su sc n Thy ng Trn Khnh rt tn

tnh hng dn chng em trong sut thi gian thc hin ti, thy cung cp

khng t ti liu cng nh cho chng em nhng tng th v v y nhng

ng lc ln lao chng em thc hin lun vn ny.

Chng em xin chn thnh cm n n cc thy, c trong nhm nghin cu

DSTAR cho chng em nhng kin ng gp qu bu trong qu trnh thc

hin ti; xin gi li cm n chn thnh n cc Thy v cc C trong Khoa

truyn t cho chng em nhng kin thc b ch, gip chng em c c mt

nn tng l thuyt v nhng k thut cn bn thit yu.

Chng con xin c by t lng bit n su sc i vi ng b, cha m, ngi

lun lun quan tm chm sc, c v mt vt cht ln tinh thn, gip cho chng

con yn tm, tp trung vo cng vic hc tp v nghin cu.

Cui cng, xin c ni li cm n n cc anh ch, bn b gip , khch

l cng nh ph bnh, gp gip chng em hon thnh cng vic mt cch tt

nht.

Tp. H Ch Minh, 12/2012

SVTH

L Phm Tuyn

Dng T Huy

L Tro Vit Cng

iii

LI CAM OAN

Chng ti xin cam oan y l cng trnh nghin cu ca bn thn chng ti,

c xut pht t yu cu ca lun vn cng nh mong mun c nhn. Cc s

liu, t liu, m ngun tham kho c ngun gc r rng tun th ng nguyn tc

v kt qu trnh by trong lun vn thu thp c trong qu trnh nghin cu l

trung thc cha tng c ai cng b trc y.

iv

TM TT

Trong lun vn ny, chng ti trnh by nghin v cu sinh trc hc ging ni

v vic s dng ging ni xc thc v m ho d liu ngi dng.

Mt h thng xc thc in hnh gm hai qu trnh ng k v xc thc. Khi

s dng ging ni lm thng tin xc thc, h thng tri qua cc bc sau y:

Qu trnh ng k

o Thu d liu ging ni.

o Rt trch vector c trng t d liu ging ni.

o S dng mt gii thut sa li to ra thng tin tr gip, thng tin

ny l duy nht i mi c trng.

o To kho t vector c trng s dng cho m ho v gii m d

liu.

Qu trnh xc thc

o Thu d liu ging ni

o Rt trch vector c trng t d liu ging ni.

o Khi phc li vector c trng ban u bng cch s dng cng gii

thut sa li v thng tin tr gip sinh ra qu trnh ng k. Nu

khi phc thnh cng, xc thc thnh cng; ngc li, xc thc tht

bi.

o To kho t vector c trng s dng cho m ho v gii m d

liu.

Chng ti cng trnh by mt h thng ngh, s dng sinh trc hc ging

ni xc thc v m ho d liu trn thit b di ng s dng Android. H

thng c kim tra trn 295 mu ging ni (29 ngi) vi t l vi t l xc

thc thnh cng xp x 85%.

v

ABSTRACT

In this thesis, we present our research about using voice for authentication and

data encryption/decryption.

A typical authentication system involves two phases: enrollment and

authentication. When using voice as the trait for authentication, the following

steps are done:

Enrollment

o Capture the voice signal

o Extract the feature vector from input signal

o Apply an Error Correction Algorithm on feature vector to generate the

unique helper data.

o Generate key from this feature vector for data encryption/decryption.

Authentication

o Capture the voice signal

o Extract the feature vector from input signal

o Recover the original feature vector by applying the same Error

Correction Algorithm together with the helper data on the feature

vector. If the recover succeeds, the authentication succeeds;

otherwise fails.

o Generate key from this feature vector for data encryption/decryption.

We also present our proposed system which uses voice for authentication. This

system has been tested using our recorded audio library. The library contains 295

voice samples of 29 people. The correction rate of authentication is about 85%.

vi

MC LC

LI CM N .............................................................................................. ii

LI CAM OAN ......................................................................................... iii

TM TT ................................................................................................... iv

ABSTRACT ................................................................................................. v

MC LC................................................................................................... vi

DANH MC CC T VIT TT ................................................................. ix

DANH MC HNH ....................................................................................... x

DANH MC BNG ....................................................................................xiii

CHNG 1: GII THIU TI ...............................................................1

1.1 Gii thiu .......................................................................................1

1.1.1 nh ngha sinh trc hc ............................................................1

1.1.2 S cn thit ca sinh trc hc ....................................................3

1.2 Mc tiu ti ................................................................................4

1.2.1 Nhim v ...................................................................................4

1.2.2 Nhng vn khng thuc phm vi ti .................................5

1.2.3 Phng php thc hin .............................................................5

1.3 B cc lun vn ..............................................................................6

1.3.1 Chng 1: Gii thiu ti........................................................6

1.3.2 Chng 2: C s l thuyt ........................................................6

1.3.3 Chng 3: Cc nghin cu lin quan.........................................6

1.3.4 Chng 4: Phn tch v thit k h thng ..................................6

1.3.5 Chng 5: Tng kt nh gi ....................................................6

Chng 2: C S L THUYT ..................................................................7

2.1 Rt trch vector c trng t ging ni ............................................7

vii

2.1.1 Ly mu ging ni .....................................................................7

2.1.2 Tin x l mu ging ni .......................................................... 10

2.1.3 Rt trch vector c trng t mu tn hiu ging ni ................. 13

2.2 K thut sa li ............................................................................ 17

2.2.1 K thut lp (repetition) ............................................................ 17

2.2.2 K thut kim tra chn l.......................................................... 18

2.2.3 M Hamming ........................................................................... 18

2.2.4 M sa li Reed Solomon........................................................ 19

2.3 Tng quan v m ha................................................................... 28

2.3.1 Tng quan ............................................................................... 28

2.3.2 Cc m hnh m ha v gii m ............................................... 32

CHNG 3: CC NGHIN CU LIN QUAN .......................................... 38

3.1 H thng m ha bng cch to kha da trn trng mt ngi .. 38

3.1.1 M hnh h thng ..................................................................... 38

3.1.2 Qu trnh rt trch c trng ..................................................... 39

3.1.3 M ha v gii m ................................................................... 41

3.1.4 Kt qu thc nghim v phn tch ............................................ 42

3.2 Sinh trc hc khun mt v phng php nhn dng Eigenfaces . 43

3.2.1 Gii thiu ................................................................................. 43

3.2.2 Phng php Eigenfaces ........................................................ 44

CHNG 4: PHN TCH V THIT K H THNG ................................ 48

4.1 Phn tch, thit k h thng .......................................................... 48

4.1.1 M t h thng......................................................................... 48

4.2 Cc thnh phn ca h thng ....................................................... 52

4.2.1 Thnh phn thu nhn ging ni ................................................ 52

4.2.2 Thnh phn rt trch c trng sinh trc................................... 53

4.2.3 Thnh phn chun ha ............................................................ 56

viii

4.2.4 Thnh phn sa li .................................................................. 58

4.2.5 Thnh phn to kha ............................................................... 59

4.2.6 Thnh phn m ha v gii m d liu .................................... 59

4.3 Cc qu trnh ca h thng........................................................... 59

4.3.1 Qu trnh ng k (Enrollment) ................................................. 60

4.3.2 Qu trnh xc thc h thng (Authentication) ........................... 60

4.3.3 Qu trnh m ha v gii m .................................................... 61

Chng 5: TNG KT NH GI ......................................................... 62

5.1 Kt qu thc nghim .................................................................... 62

5.1.1 S dng gii thut LPC rt trch vector c trng ................ 62

5.1.2 Rt trch vector c trng bng gii thut FFT ......................... 64

5.1.3 So snh cc kt qu thu c ................................................. 68

5.2 Kt qu t c ......................................................................... 70

5.2.1 u im h thng .................................................................... 70

5.2.2 Nhc im h thng .............................................................. 70

5.3 Hng pht trin .......................................................................... 71

TI LIU THAM KHO .............................................................................. 72

PH LC .................................................................................................. 74

PH LC 1: DEMO CHNG TRNH BIO-CRYPT-ANDROID ................. 74

1. Yu cu v ci t ........................................................................... 74

2. Demo cc chc nng ...................................................................... 74

2.1 ng k thng tin....................................................................... 75

2.2 Xc thc ngi dng ................................................................. 77

2.3 M ha v gii m ..................................................................... 78

2.4 Phin bn thu ging ni trc tip ............................................... 78

PH LC 2: PHN CNG CNG VIC .................................................... 80

ix

DANH MC CC T VIT TT

LPC Linear Predictive Code

FFT Fast Fourier Transform

DFT Discrete Fourier Transform

MFCC Mel Frequency Cepstral Coefficient

PCM Pulse Code Modulation

DSP Digital Signal Processing

FRR False Reject Rate

FAR False Accept Rate

FMR False Match Rate

FNMR False Non-match Rate

ECC Error Correction Code

PCA Principle Component Analysis

MARF Modular Audio Recognition Framework

DES Data Encryption Standard

AES Advanced Encryption Standard

RSA Ron Rivest, AdiSharmir and Leonard Adleman

DSS Digital Signature Standard

IDEA International Data Encryption Algorithm

x

DANH MC HNH

Hnh 2.1-1 Biu din tn hiu ging ni theo thi gian ..........................................9

Hnh 2.1-2 Mu tn hiu ging ni sau khi c chun ha ............................... 10

Hnh 2.1-3 Mu tn hiu ging ni trc v sau khi kh khong lng ................. 11

Hnh 2.1-4 Mu tn hiu ging ni theo min tn s sau khi lc ly tn s thp .. 12

Hnh 2.1-5 M hnh rt trch ra vector c trng ................................................ 13

Hnh 2.1-6 Phn khung ..................................................................................... 14

Hnh 2.1-7 Ca s Hamming............................................................................. 15

Hnh 2.1-8 Ca s Hanning............................................................................... 15

Hnh 2.1-9 Ca s ch nht .............................................................................. 15

Hnh 2.2-1 nh x cc phn t c bn trong trng GF(8)................................ 21

Hnh 2.3-1 M ha v gii m............................................................................ 28

Hnh 2.3-2 M ha ............................................................................................ 29

Hnh 2.3-3 Khng gian kha .............................................................................. 30

Hnh 2.3-4 S m ha kha i xng ........................................................... 32

Hnh 2.3-5 Sc mnh ca cc gii thut kha i xng ..................................... 34

Hnh 2.3-6 M hnh m ha s dng kha bt i xng .................................... 35

Hnh 2.3-7 M hnh gii m s dng kha bt i xng ..................................... 35

Hnh 2.3-8 Cc nh dng thng ip ................................................................ 37

Hnh 3.1-1 M hnh h thng m ha ................................................................ 39

xi

Hnh 3.1-2 Tin x l trng mt ......................................................................... 40

Hnh 3.1-3 Hnh nh c lc ........................................................................... 41

Hnh 3.1-4 ng cong FAR v FRR ................................................................ 42

Hnh 3.2-1 Mt s Eigenface ............................................................................. 45

Hnh 4.1-1 M hnh use case ca h thng ....................................................... 48

Hnh 4.2-1 Rt trch vector c trng bng gii thut LPC ................................. 54

Hnh 4.2-2 Rt trch vector c trng bng gii thut FFT ................................. 55

Hnh 4.2-3 Cu trc MARF Framework.............................................................. 56

Hnh 4.2-4 Php bin i vector c trng LPC................................................. 57

Hnh 4.2-5 Php bin i vector c trng FFT ................................................. 57

Hnh 4.2-6 Encode trong R-S ............................................................................ 58

Hnh 4.2-7 Decode trong R-S ............................................................................ 59

Hnh 4.3-1 Qu trnh ng k ............................................................................. 60

Hnh 4.3-2 Qu trnh xc thc h thng............................................................. 61

Hnh 5.1-1 ng cong FAR v FRR ca gii thut LPC .................................. 63

Hnh 5.1-2 S phn b ca cc thnh phn vector vo 5 khong ...................... 64

Hnh 5.1-3 ng cong FAR v FRR ca gii thut FFT-32 .............................. 65

Hnh 5.1-4 S phn b ca cc thnh phn vector vo 20 khong .................... 65

Hnh 5.1-5 ng cong FAR v FRR ca gii thut FFT-64 .............................. 66


Hnh 5.1-7 ng cong FAR v FRR ca gii thut FFT-128 ............................ 68

xii


Hnh 5.1-9 So snh cc gii thut vi nhau ....................................................... 69

Hnh 1-1 Giao din ban u ca chng trnh ................................................... 75

Hnh 1-2 a) Giao din chn s sample. b) Giao din chn file ............................ 76

Hnh 1-3 Giao din confirm ng k li thng tin ................................................ 77

Hnh 1-4 a) Giao din qun l file. b) Option menu ............................................ 78

Hnh 1-5 Mn hnh thu ging ni ....................................................................... 79

xiii

DANH MC BNG

Bng 2.2-1 Chui d liu sau khi c thm vo cc bit chn l ....................... 18

Bng 2.2-2 Qu trnh kim tra tnh ng n chui d liu ................................ 19

Bng 2.2-3 Th vic cc php ton cng v nhn trong GF(8)........................... 22

Bng 3.1-1 FAR, FRR v ngng T .................................................................. 43

Bng 4.1-1 M t use case Enroll ................................................................... 49

Bng 4.1-2 M t use case Re-enroll .............................................................. 49

Bng 4.1-3 M t Use-case Login ................................................................... 50

Bng 4.1-4 M t use case Encrypt/Decrypt file .............................................. 51

Bng 5.1-1 FAR v FRR ca gii thut LPC ...................................................... 63

Bng 5.1-2 FAR v FRR ca gii thut FFT vi vector c trng 32 chiu ........ 64

Bng 5.1-3 FAR v FRR ca gii thut FFT vi vector c trng 64 chiu ........ 66

Bng 5.1-4 FAR v FRR ca gii thut FFT vi vector c trng 128 chiu....... 67

Chng 1: Gii thiu ti

GVHD: ng Trn Khnh 1 SVTH: L Phm Tuyn Dng T Huy L Tro Vit Cng

CHNG 1: GII THIU TI

1.1 Gii thiu

M u, ti s trnh by mt cch khi qut v sinh trc hc. Sinh trc hc

l g, cc phng thc sinh trc, cc yu t chn la phng thc sinh trc.

Tip theo, ti s trnh by ti sao v tm quan trng s dng sinh trc hc

trong cc h thng xc thc v m ha.

1.1.1 nh ngha sinh trc hc

Sinh trc hc (biometrics) l phng php xc thc con ngi da trn cc

c im sinh trc [1]. Cc c im sinh trc ny phi l ring bit v c th

nh gi tnh ton c. Cc c im sinh trc c chia thnh 2 loi: vt l v

hnh vi. Cc sinh trc vt l thng lin quan n khun mt, du vn tay, ging

ni Cc sinh trc hnh vi thng cp n cc hnh vi con ngi: ch k,

dng i Cc phng thc sinh trc:

Khun mt: Nhng hnh nh tnh hoc ng ca khun mt c dng

nhn dng. Nhng cch tip cn ngy nay da trn v tr, hnh dng v

nhng mi quan h gia cc c im trn khun mt nh mt, mi, mi

v cm Tuy nhin, qu trnh nhn dng da trn khun mt cng gp th

thch v khun mt s thay i theo thi gian.

Du vn tay: M hnh ca thung lng v i ni trn b mt u ngn tay,

c s dng trong cc lnh vc php l t hn mt th k. Du vn tay

c hnh thnh trong qu trnh pht trin bo thai, v ngay c nhng cp

sinh i ng nht cng khng c cng du vn tay. H thng nhn dng

c th nhn dng mt du vn tay hoc nhiu du vn tay. Hiu sut h

thng sinh trc s dng du vn tay thng cao v chnh xc.

Bn tay: cp n hnh dng bn tay, kch thc lng bn tay, v chiu

di v chiu rng cc ngn tay. u im ca phng thc ny l tng i

n gin v d s dng. Tuy nhin, v s khc nhau khng r rng hnh

dng bn tay trong phm vi ng dng ln, nn nhng h thng dng

phng thc bn tay thng dng xc minh (verification) hn l nhn

Chng 1: Gii thiu ti


dng (identification). Ngoi ra, v thit b ly d liu phi c kch thc ti

thiu l kch thc bn tay, qu ln so vi cc thit b nh laptop.

Ch tay (Palm Print): Ch tay kt hp cc c trng ca du vn tay v bn

tay. Ch tay cha cc vt ln v rnh ging du vn tay nhng ln hn. N

cng nh du vn tay thng c s dng trong cc h thng nhn dng

php l.

Trng mt (Iris): l mng mng c mu hnh trn bao bc con ngi

phc tp c ch trong vic nhn dng. Hiu sut h thng s dng

phng thc ny y trin vng. Tuy nhin, mc d h thng da trn

trng mt rt tt nhng FMR, FNMR li cao. Hn na, trng mt thay i

theo thi gian, nhng s thay i ny cha c nghin cu nhiu.

Ging ni: Ging ni kt hp trc tip cc c tnh sinh trc v hnh vi.

m thanh con ngi ni da trn nhiu yu t vt l ca c th (ming,

mi, mi, thanh qun) v b tc ng bi tui tc, cm xc, ngn ng v

tnh trng sc khe. Cht lng ca thit b ghi m v ting n cng tc

ng n hiu sut.

Ch k: Ch k con ngi thay i theo thi gian. N b tc ng mnh bi

cc yu t bn ngoi bao gm tnh trng sc khe, v cm xc ca ngi

k. Ngoi ra, ch k cng tng i d gi mo. Tuy nhin, ch k c

chp nhn nh mt phng thc nhn dng trong mt thi gian di.

Dng i: Dng i cng l mt phng thc nhn dng. Cc h thng nhn

dng dng i da trn qu trnh x l hnh nh pht hin hnh bng

ngi dng v cc thuc tnh thi gian khng gian lin quan. Dng i b tc

ng bi nhiu yu t, bao gm s la chn giy dp, b mt i, qun o.

Cc h thng nhn dng dng i vn cn ang trong qu trnh pht trin.

H thng sinh trc hc l h thng xc thc ngi dng s dng cc c im

sinh trc. Vic la chn sinh trc hc no nh danh ngi dng ph thuc

vo cc yu t sau y:

Tnh ph thng (Universality): mi ngi dng h thng u phi s hu

c im sinh trc c th.

Tnh duy nht (Uniqueness): cc c im sinh trc phi khc nhau v duy

nht.

Chng 1: Gii thiu ti


Tnh bn vng (Permanence): lin quan n cch thc m mt c im

sinh trc bin i theo thi gin. C th hn, mt c im sinh trc bn

vng tt phi bt bin theo thi gian i vi cc thut ton so snh c th.

S o lng (Measurability): Cc c im sinh trc c th thu c v s

ha bng cch s dng cc thit b thch hp m khng gy bt tin cho

ngi dng.

Hiu sut (Performance): lin quan n s chnh xc, tc v mnh m

ca cng ngh c s dng.

S chp nhn (Acceptability): cp n vic ngi dng c chp nhn

cng ngh ny v sn sng cho c im sinh trc ca h cho h thng.

S gi mo (Circumvention): cc c im sinh trc phi kh c th

gi mo.

Tuy nhin, cc h thng sinh trc khng nht thit phi tng tc vi tt c

mi ngi trong thi gian di, chng ch cn tng tc vi mt nhm ngi nh

trong thi gian ngn. Do c th tm c cc c im sinh trc n nh v

phn bit s dng trong thc t.

1.1.2 S cn thit ca sinh trc hc

Ngy nay, thit b di ng tr thnh vt khng th thiu trong cuc sng

hng ngy ca mi ngi v dn thay th cc thit b truyn thng nh my tnh

c nhn. Theo , thit b di ng s cha ng mt lng ngy cng nhiu d

liu c nhn ca ngi dng. V vy, nhu cu bo mt trn nhng d liu ny tr

nn quan trng.

Nm bt c nhu cu , nhiu phn mm c xy dng trn thit b

di ng m ha d liu ca ngi dng. Phn ln nhng phn mm ny u

s dng cch tip cn truyn thng l s dng mt mt khu kt hp vi cc

phng php m ha m ha d liu. Vi cch tip cn ny, ngi s dng

phi ghi nh mt khu ca mnh trong u hoc ghi vo mt ni no . Nu mt

khu qu di th s kh cho ngi s dng c th nh. Ngc li, nu mt khu

qu ngn th phn mm d b crack. Mc khc, vi cch tip cn s dng mt

khu ny, d liu dng xc thc phi c lu vo mt ch trn thit b v

Chng 1: Gii thiu ti


nu hacker c th ly c d liu ny th vic m ha gii m d liu ngi

dng tr nn d dng.

C hai vn cn phi gii quyt y l lm sao ngi s dng khng

cn phi nh mt khu ca mnh na v d liu xc thc d c b hacker nh

cp cng khng th no s dng c. Vi yu cu , cc h thng sinh trc

hc ra i gii quyt vn trn. truy cp vo h thng, ngi dng

phi dng thng tin sinh trc ca mnh xc thc thay v nhp mt khu. Do ,

ngi dng khng cn phi nh v s ngi khc bit mt khu ca mnh.

Thng tin sinh trc ny khng nhng c dng xc thc m cn m ha d

liu. Ngoi ra, h thng ch lu gi cc thng tin cng khai (public data) c

dng trong qu trnh xc thc ngi dng. Nu hacker c th nh cp c

thit b th cng khng th khai thc c thng tin g t thng tin ny. Do

khng th gii m c nhng thng tin mt c m ha ca ngi dng.

1.2 Mc tiu ti

Trong phn ny ti s nu ra nhim v c bn c th, phm vi ca ti-

l nhng g phi lm v nhng g khng thuc phm vi ca ti

1.2.1 Nhim v

Lun vn ny trnh by cho ngi c nhng kin thc c bn v chuyn su

v qu trnh xc thc v m ha bng cc thng tin sinh trc, xy dng mt bc

tranh tng qut v h thng c p dng sinh trc hc trn thit b di ng.

Th nht: ti s tp trung xy dng mt h thng xc thc v m ha d

liu tng qut, m t y cc thnh phn ca h thng. ti s dng ging

ni lm phng thc sinh trc xc thc v m ha d liu v hu ht thit b di

ng ngy nay u c thit b thu nhn ging ni. Ngoi ra, dng ging ni thun

tin cho ngi s dng hn cc phng thc sinh trc khc.

Th hai: xy dng h thng trn thit b di ng c h iu hnh Android. V

cc in thoi thng minh (smartphones) s dng h iu hnh Android hin nay

chim t l rt cao. Ngoi ra, h iu hnh Android l h iu hnh m ngun m,

ta c th ci t h thng ln thit b mt cch d dng.

Chng 1: Gii thiu ti


Nhng l thuyt phi tm hiu qua:

Nhng k thut rt trch ra vector c trng

K thut sa li

M ha - m ha i xng, bt i xng, cc gii thut m ha

K thut bm (hash) - dng to kha

H iu hnh android

1.2.2 Nhng vn khng thuc phm vi ti

Hin ti, phm vi nghin cu ca ti phn ln tp trung vo vic xy dng

mt h thng xc thc v m ha d liu v to ra mt ng dng c h thng

sinh trc ny trn thit b di ng. ti s khng qu tp trung vo cc vn

nghip v ca h thng cng nh xy dng mt ng dng tht s hon chnh v

y l qu trnh rt lu di cn nhiu k thut v kinh nghim tt trong vic thit

k v lp trnh di ng.

Hn na, ci m ti mun nhn mnh l vn xc thc v m ha d

liu ch khng phi l vn lm sao c mt ng dng di ng hon chnh v

iu ny nm mt kha cnh khc.

1.2.3 Phng php thc hin

Da vo thng tin t nhng bi bo co nghin cu khoa hc, nhng eBooks,

nhng website ng tin cy, chng ti tm hiu, phn tch v la chn ging ni

lm phng thc sinh trc cho h thng. Tt c nhng thng tin s dng u l

nhng thng tin hp php, c php s dng cho mc ch hc tp v nghin

cu.

Da vo nhng cng ngh c sn nh Java, h iu hnh Android, cc k

thut sa li, cc k thut m ha(i xng, bt i xng) xy dng mt ng

dng xc thc v m ha d liu trn thit b di ng Android.

Chng 1: Gii thiu ti


1.3 B cc lun vn

1.3.1 Chng 1: Gii thiu ti

Gii thiu v ti, tm tt mc tiu, nhim v, phng php thc hin ca

ti. Chng gii thiu mt cch tng qut v sinh trc hc v cc phng thc

sinh trc.

1.3.2 Chng 2: C s l thuyt

Chng ny trnh by c s l thuyt v vn xc thc v m ha d liu

bng ging ni. Cc k thut rt trch thng tin t ging ni, tng quan v m

ha, v cc k thut sa li. Cc l thuyt ny c p dng vo qu trnh hin

thc chng trnh ca ti.

1.3.3 Chng 3: Cc nghin cu lin quan

Vn sinh trc hc c nghin cu t lu. Cc nh khoa hc nghin

cu v ng dng nhiu loi phng thc sinh trc vo cc h thng sinh trc

ny. Chng ny trnh by mt s nghin cu lin quan n vn xc thc v

m ha d liu bng cc c im sinh trc.

1.3.4 Chng 4: Phn tch v thit k h thng

Trnh by c th v vic hin thc chng trnh. Bao gm cc s phn tch

chc nng h thng, cc thnh phn trong chng trnh, gii thch v cch thc

hot ng ca cc thnh phn.

1.3.5 Chng 5: Tng kt nh gi

Trnh by phng php thc nghim v kt qu thc nghim. Mt s nh gi

v kt qu thc nghim. Phn tch u nhc im ca chng trnh. Mt s kt

lun v hng m rng ca ti.

Chng 2: C s l thuyt


Chng 2: C S L THUYT

chng ny, chng ti tp trung vo cc k thut c dng hin thc

ti lun vn - h thng xc thc v m ha d liu trn thit b di ng s

dng ging ni. Ni dung c trch dn v sng lc t cc ti liu [2] [3]

2.1 Rt trch vector c trng t ging ni

Ging ni t lu l phng tin gip mi ngi c th giao tip, trao i

thng tin vi nhau. kha cnh loi ngi, ging ni c th gip ngi nghe xc

nh chnh xc ngi ang ni l ai, hoc t nht l phn bit ngi l nam

hay n bng cch ghi nhn li nhng c trng ca ging ni kt hp vi kh

nng phn on suy lun. Cn trong h thng my tnh, vic phn bit ngi ny

vi ngi khc bng ging ni ch n gin l thu li tn hiu ging ni sau

bin i n da vo mt trong nhng c trng vn c ca ging ni nh min

tn s, min nng lng, c trng cc h s cepstral tn s Mel (MFCC), c

trng m d on tuyn tnh (LPC)

Tng ng vi mi c trng ca ging ni ta thu c mt vector c

trng. Vector c trng ny gip gim s lng d liu ca ging ni, gip vic

tnh ton trong h thng gim i ng k. Bn cnh , vit rt trch c trng

cn lm r s khc bit ca ting ni ngi ny so vi ngi khc v lm m i

s khc bit ca hai ln ni khc nhau ca cng mt ngi. Trong gii hn ca

lun vn khng i su vo vic phn tch chi tit tng c trng sinh trc ca

ging ni m ch xin a ra cc k thut c bn rt trch ra c cc vector

c trng cng vi nhng k thut tin x l tn hiu ging ni. Nhng k thut

ny s c gii thiu theo trnh t t lc thu mu tn hiu ging ni cho n lc

rt trch c mt vector c trng.

2.1.1 Ly mu ging ni

Mc ch ca bc ny l lm sao chuyn ging ni ca ngi s dng thnh

mt dng thng tin m my tnh c th x l. Cht lng ca ging ni thu li c

Chng 2: C s l thuyt


nh hng rt ln n kt qu phn tch ging ni sau ny. Nhng yu t nh

hng n cht lng ca mu ging ni thu c bao gm:

2.1.1.1 Nhn t bn ngoi

Mi trng xung quanh khu vc thu ging ni c nh hng ln n cht

lng ca tn hiu ging ni. Thng khi ging ni c thu, n ln vo trong

m thanh nn ca nhng vt xung quanh. Vic loi b chng ra khi m thanh

gc s gip cht lng m thanh c tt hn.

Cht lng ca thit b thu nhn m cng l mt yu t gp phn tng cht

lng ca mu tn hiu ging ni. Mt s thit b cao cp cn chc nng gip lc

bt nhng tn hiu c cho l m thanh nn, gy nhiu.

Trng thi, thi hp tc ca ngi ni lc cng nh hng n cht

lng ging ni thu c. Ging ni lc ngi ni trng thi bnh thng vi

trng thi lc khng bnh thng (m, vim hng) s c nhng khc bit nht

nh. Mc khc khi ngi ni vn trong trng thi bnh thng nhng li c tnh

lm cho ging ni gc ca mnh khc i bng cch gi ging th mu tn hiu

ging ni thu c cng b nh hng rt nhiu.

Vic xc nh nhng nhn t bn ngoi gy nh hng gip ta c th a ra

nhng iu kin ban u cho ngi ni, v mi trng v v thit b c th

thu c mu tn hiu tt hn.

2.1.1.2 Nhn t bn trong

Tn hiu ging ni l mt dng ca tn hiu m thanh v khi mun lu vo

thit b lu tr lu tr th cng phi theo mt chun m ha no khi cc

chng trnh c d liu ln c th hiu. Nhng chun m ha ny gi l nh

dng ca m thanh (Audio Format). n gin nht l chun m ha PCM dng

cho WAV file. Trong k thut ny, tn hiu ging ni thu c s c biu din

nh mt chui ca nhng gi tr cng (amplitude). Phm vi ca gi tr bin

ph thuc vo thng s kch thc mu (sample size). Vi kch thc mu l

16-bit, th phm vi ca gi tr cng nm trong khong t 0 216 (65536). Khi

s dng chun m ha PCM-signed th phm vi ny s nm trong khong t -215

(32768) n 215 (32768). Vi kch thc mu ny gi tr cng s c biu

Chng 2: C s l thuyt


din mt khong rng hn so vi khi chn kch thc mu l 8-bit ( gi tr

cng ch nm trong khong t [-128, 128] ). V vy kch thc mu 16-bit

c chn thu c mu ging ni c cht lng tt hn.

Tn s ly mu (sample rate) ca mt file m thanh ni n s gi tr

cng thu c trong mt n v thi gian (thng l giy). Theo l thuyt

Nyquist, tn s ly mu phi t nht gp hai ln tn s ti a ca tn hiu tun t,

Ngc li, tn hiu tun t s khng to ra c tn hiu s mt cch chnh xc.

Mt v d n gin l nu tn s mu c chn l 8000Hz, th tn s ca tn

hiu tun t ca mi mu b gii hn c 4000Hz. Vi ging ni bnh thng ca

con ngi c tn s t 300 Hz n 3400 Hz th tn s ly mu 8000 Hz c th

chp nhn c.

S knh m thanh (number of channel) cng l mt thnh phn trong vic

thu li mu tn hiu ging ni v khng nh hng n u vo ca tn hiu

ging ni. N ch nh hng n u ra ca tn hiu ging ni. Mt s loi knh

c bn thng gp l mono (tn hiu m thanh nh nhau gia cc ngun pht)

hay stereo (tn hiu m thanh khc nhau gia cc ngun pht). n gin

trong vic x l tn hiu ging ni th knh mono c s dng. Hnh sau m t

biu din ca tn hiu ging ni theo thi gian.

Hnh 2.1-1 Biu din tn hiu ging ni theo thi gian

Chng 2: C s l thuyt


2.1.2 Tin x l mu ging ni

Cht lng ca tn hiu ging ni thu c c th c ci thin thng qua

cc gii thut tin x l. Mt s k thut l yu cu bt buc trc khi tin hnh

rt trch thng tin sinh trc nh chun ha (normalization), kh nhiu (remove

noise), kh khong lng (remove silence). Cng c nhng k thut ch c p

dng cho tng gii thut rt trch c th ty thuc vo gii thut da trn c

im sinh trc no ca ging ni.

2.1.2.1 Chun ha (Normalization)

Khng phi tt c cc mu ging ni u c thu cng mt trng thi. V

d mt ngi lc ni ln, ni nh, thit b thu m lc t gn lc t xa. iu ny

lm cho cng ging ni thu c c gi tr nm trong mt khong khng

ng nht vi nhau. V vy, vic chun ha d liu cho mu ging ni m

bo rng cc c trng c th so snh c vi nhau l ht sc quan trng. Khi

d liu m thanh c chuyn sang ht cc gi tr du chm ng nm trong

khon t -1 n 1. Vic chun ha c tin hnh bng cch tm cng m

ln nht trong mu tn hiu ging ni ri sau ly t l nhng cng m

khc trong mu tn hiu ging ni vi cng m ny. Vic ny s m bo

rng mi mu tn hiu s tht s bao ph ton b khong t -1 n 1. Hnh sau

m t d liu trc v sau khi chun ha

Hnh 2.1-2 Mu tn hiu ging ni sau khi c chun ha

Chng 2: C s l thuyt


2.1.2.2 Kh khong lng (Remove silence)

Khong lng l nhng khong trong mu tn hiu ging ni m ngi ni

khng ni g. N khng c ngha trong rt trch vector c trng ging ni, i

khi li km theo nhiu nn vic loi b n khi mu tn hiu ging ni l vic cn

thit. Thng cng ca khong lng ca khong lng rt thp (xp x 0) nn

cch loi b n ra khi mu tn hiu l loi i nhng phn t tn hiu c cng

nh hn mt ngng cng no cho trc (ngng ny xp x 0).

Phn cn li c xem l phn m thanh do ngi ni pht ra v c th a vo

mt s gii thut tin x l khc cho ra kt qu cui cng tt hn.

Hnh 2.1-3 Mu tn hiu ging ni trc v sau khi kh khong lng

2.1.2.3 Kh nhiu (Remove noise)

Ln trong mu tn hiu ging ni cng cha ng cc tn hiu khng mong

mun khc chng hn nh ting ni ca nhng ngi xung quanh, ca xe c

chy ngoi ng. Cc tn hiu ny lm gim ng k cht lng ca tn hiu.

C nhiu phng php loi b nhiu khi mu tn hiu da vo mt s c

trng nht nh. Trong s l k thut s dng mt b lc tn hiu da vo tn

s thp (FFT Low Pass Filter). Cng vic ca b lc ny l bin i mu tn

hiu ging ni t min thi gian sang min tn s ri sau n gin loi b

nhng gi tr tn s ln hn mt ngng no cho trc. Ging ni bnh

thng ca con ngi ch quanh qun quanh khong tn s t 300Hz n

Chng 2: C s l thuyt


3400Hz nn nhng m thanh thu c khong tn s trn 3400 s ch l

nhng tn hiu nhiu thu c cn phi c loi b.

Hnh 2.1-4 Mu tn hiu ging ni theo min tn s sau khi lc ly tn s thp

2.1.2.4 Gii thut d tm im cui (End-point detection)

D tm im cui l mt k thut c gng tm ra chnh xc khi no ngi ta bt

u v kt thc ni. N cn c dng xc nh khi m ngi ta khng tht

s ni g hoc ni nhng iu khng mong i. Khi , d tm im cui gip

gim mt s lng d liu cn phi x l, dn n gim ti vic tnh ton. Tuy

nhin, vic d tm im cui khng d nh ngi ta tng, bi v c s tn ti

ca ting n nn, ting ni nn. Vic xc nh im cui da vo gi tr cng

ca d liu thu c. C bn trng hp c xem l im cui:

im u hoc im cui ca mu tn hiu ging ni.

Nhng im c cng cao hn nhng im cn li xung quanh n (max

local)

Nhng im c cng thp hn nhng im cn li xung quanh n (min

local)

Nhng im c cng bng nhng im xung quanh n.

Chng 2: C s l thuyt


K thut d tm im cui c thc hin sau khi mu tn hiu ging ni

c x l kh nhiu v khong lng. N c p dng cho cc gii thut rt

trch vector c trng da vo min cng ca ging ni.

2.1.3 Rt trch vector c trng t mu tn hiu ging ni

Ging ni vi nhng c trng khc nhau, sau khi thng qua nhng b rt

trch khc nhau s cho ra vector c kch thc v min tr khc nhau. Di y l

hai gii thut rt trch ra vector c trng m nhm tm hiu c cng vi

nhng k thut phi lm trc khi rt trch.

Hnh 2.1-5 M hnh rt trch ra vector c trng

Chng 2: C s l thuyt


2.1.3.1 Phn khung (framing)

Trong nhiu k thut s l tn hiu s (DSP techniques) th vic x l c

thc hin trn mt khong cc gi tr ca mu ging ni hn l cho tng gi tr

ring l. K thut ct mu ging ni thnh nhng mu nh hn c gi l qu

trnh phn khung. iu ny gip gim bt chi ph tnh ton cho chng trnh.

rng ca khung v cch ly khung cng nh hng n nh hng n u ra

ca vector c trng. Hnh di m t cch phn chia cc khung thnh F1, F2,

F3, F4nhng khung ny chng lp ln nhau mt khong bng 1/3 rng ca

khung. iu ny lm cho kt qu php rt trch c trng c tng quan t

khung ny sang khung kia.

Hnh 2.1-6 Phn khung

2.1.3.2 Ca s Hamming

Sau khi phn khung, tng khung gi tr s c em i ly ca s. K thut

ny l mt phng php iu chnh d liu d liu tr nn thch hp hn

nhiu cho x l tn hiu. Vi mt ca s bnh thng, nhng phn t k nhau s

c xu hng thay i t ngt t ni c bin cao n ni c bin thp.

Vic ly ca s nh vy s lm cho d liu ging nh tun hon v khng c s

gin on t ngt. Trong s l tn hiu s, cc ca s thng c biu din

thng qua ca s Hamming tng qut:

Chng 2: C s l thuyt


{ (

) | |

| |

Ty vo cc gi tr khc nhau ca m ta c cc ca s khc nhau. Vi = 1,

ta c ca s ch nht, = 0.5 ta c ca s hanning v vi = 0.54 ta c ca s

hamming v cng l loi ca s c dng nhiu trong s l tn hiu s.

Hnh 2.1-7 Ca s Hamming

Hnh 2.1-8 Ca s Hanning

Hnh 2.1-9 Ca s ch nht

2.1.3.3 Gii thut bin i Fourier nhanh (Fast Fourier Transform FFT)

Ging ni ca con ngi c th c trng bng min tn s. Tuy nhin, mu

tn hiu ging ni thu c li c c trng theo min thi gian. Do nu

Chng 2: C s l thuyt


mun rt trch c vector c trng theo min tn s cn phi c mt phng

php chuyn mu tn hiu ging ni t min thi gian sang min tn s, v

php bin i Fourier ri rc (DFT) lm c iu . DFT l php bin i

thun nghch t min thi gian sang min tn s v ngc li. Cng thc:

Php bin i thun:

, k =0, 1, 2, , N -1.

Php bin i nghch:

, n =0, 1, 2, , N -1.

Nu bin i ny nu c tnh ton theo nh ngha th i hi O(N2) php

tnh. T phng php bn i Fourier nhanh (FFT) c s dng tnh

ton DFT cho ra cng kt qu nhng ch mt O(NlogN) php tnh.

K thut bin i ny cng phn chia mu d liu ging ni thnh cc khung

ri sau p dng ca s hamming. Tng ng vi mi ca s ta thu c c

trng min tn s ca n. Nu kt hp tt c window ca ging ni bng cch

ly trung bnh gia chng, ta c th ly c c trng tn s trung bnh cho

mu t ngi ni

2.1.3.4 Gii thut m d on tuyn tnh LPC (Linear Predictive Code)

y l mt trong cc phng php phn tch tn hiu ting ni mnh nht v

c s dng ph bin. im quan trng ca phng php ny nm kh nng

c th cung cp cc c lng chnh xc ca cc tham s tn hiu ging ni v

kh nng thc hin tnh ton tng i nhanh. tng c bn ca phng

php LPC l ti thi im n, mu ting ni S(n) c th c xp x bi mt t

hp tuyn tnh ca p mu trc . Cng thc:

Vi

l gi tr d bo ca S(n). Gi s ak l hng s

trn khung d liu c xem xt. Tp cc h s ak s l c trng ca tn hiu

Chng 2: C s l thuyt


ting ni. tm c tp cc h s ny ngi ta dng phng php phn tch

t tng quan (autocorrelation) nh sau:

Mi khung sau khi ly ca s s c a qua bc phn tch t tng

quan v cho ra (p + 1) h s t tng quan. Cng thc:

Trong gi tr t tng quan cao nht, p, c gi l cp ca phn

tch LPC. Thng thng, ta s dng cc gi tr p trong khong t 8 n

16.

Chuyn mi khung gm (p + 1) h s t tng quan thnh p h s LPC

bng thut ton Levinson Durbin. Lc ny, ta c th dng cc h s LPC

lm vector c trng cho tng khung.

2.2 K thut sa li

Trong qu trnh truyn d liu qua cc knh giao tip, cc tn hiu nhiu s

lm d liu c truyn b h hoc b mt i. Trong c hai trng hp, ta cn

phi x l phc hi d liu tr v trng thi ng ban u. T cc phng

php sa li ra i.

2.2.1 K thut lp (repetition)

y l phng php n gin nht. Vi mi bit ta lp n ln v sau quyt

nh gi tr bit ng da trn s ng. V d, vi n = 3 d liu l 101 s c

truyn i l 111000111. phng php ny c hiu qu, d liu phi c lp

t nht 3 ln.

Nu s li <

trong mi nhm th d liu s c gii m chnh xc. S lng

lp cho mi bit tng bao nhiu th xc sut khng gii c gim by nhiu.

Nhng k thut ny li lm tng lng d liu cn truyn i.

y l phng php n gin ca k thut sa li. N ch lm vic hiu qu

khi khng c s gii hn bng thng v quan trng l d liu c th khi phc

Chng 2: C s l thuyt


c. Nu ngi dng cn m ha d liu bo mt, vic bit thng tin c

lp li lm cho vic b kha d dng hn.

2.2.2 K thut kim tra chn l

Mt k thut khc l bit kim tra chn l. Bit kim tra chn l xc nh mt tp

bit l chn hay l. Thng thng, bit chn l s lm s lng bit 1 l chn. V d,

nu tao truyn chui 001, ta s ni vo cui chui bit kim tra chn l sao cho s

bit 1 l chn, do chui bit mi s l 0011.

V vy khi c 1 bit b sai, ta s bit c chui b thay i. Tuy nhin, k

thut ny khng xc nh c bit no b sai. Hoc nu c 2 bit b sai, k thut

ny khng th xc nh c d liu ny l ng hay sai. Do , vi 1 bit kim

tra chn l khng th kim tra tha ng s chnh xc ca d liu v khng th

sa cha d liu c. V vy, nhng phng php phc tp hn vi nhiu bit

chn l ra i khc phc nhc im ny.

2.2.3 M Hamming

Nm 1950, R.W.Hamming to ra m Hamming v nhng ci tin ca m

Hamming vn c s dng cho n ngy nay. M Hamming truyn m bit thng

tin cng vi k bit chn l. Chng c kh nng sa c 1 bit li bt k. Cc bit

chn l c xp vo cc v tr 1,2,,2k-1 v kim tra cc bit m v tr ca chng

dng nh phn c gi tr 1 ti v tr ki - 1. V d, bit chn l v tr K3= 4 s kim

tra cc bit c v tr l 100, 101, 110, 111, 1100, 1101, = 4,5,6,7,12,13,

Gi s rng chui d liu l 100110.Ta s thm vo chui cc bit chn l ti

cc v tr nh sau k1k21k3001k410.

Bng 2.2-1 Chui d liu sau khi c thm vo cc bit chn l

Th t bit 1 2 3 4 5 6 7 8 9 10

V tr bit chn l v bit d liu K1 K2 1 K3 0 0 1 K4 1 0

K1 1 1 0 1 1

K2 0 1 0 1 0

K3 1 0 0 1

Chng 2: C s l thuyt


K4 1 1 0

Chui m ha 1 0 1 1 0 0 1 0 1 0

Vy chui bit c truyn i l 1011001010. Gi s chui b sai v tr

5.Vy chui khi l 1011101010.Qu trnh gii m nh sau

Bng 2.2-2 Qu trnh kim tra tnh ng n chui d liu

Th t bit 1 2 3 4 5 6 7 8 9 10 Kim tra

chn l

Bit chn

l V tr bit kim tra v

bit d liu

K1 K2 1 K3 0 0 1 K4 1 0

D liu nhn c 1 0 1 1 1 0 1 0 1 0

K1 1 1 1 1 1 Sai 0

K2 0 1 0 1 0 ng 1

K3 1 1 0 1 Sai 0

K4 1 1 0 ng 1

Gi tr s nguyn cc bit chn l l 0101 = 5. Vy bit sai v tr 5. K thut ny

hiu qu hn hn k thut lp. Ta ch cn thm vo logn bit thay v xn, nhng n

ch c th sa c 1 li. Nu 2 li xy ra, m Hamming s sa ra mt chui sai.

2.2.4 M sa li Reed Solomon

Nm 1960, Irving Reed v Gus Solomon to ra mt loi m sa li - m Reed

Solomon. [4]

2.2.4.1 Trng hu hn

Khi nim

hiu c nguyn l m ha v gii m cc m khng nh phn, nh m

Reed-Solomon (R-S), ta cn phi tm hiu khi nim trng hu hn - Galois

Field (GF). Cho mt s nguyn t p, s tn ti mt trng hu hn, k hiu l

GF(p) c p phn t. Ta c th m rng GF (p) thnh pm phn t, c gi l

trng m rng ca GF(p), k hiu l GF(pm) vi m l s nguyn dng. Ch

Chng 2: C s l thuyt


rng GF(pm) cha tp con ca GF(p). Cc k hiu (symbol) trong trng GF(2m)

c s dng trong vic xy dng m Reed-Solomon (R-S).

Trng nh phn GF(2) l tp con ca trng m rng GF(2m). Ngoi cc s 0

v 1, cn c cc phn t duy nht trong trng m rng GF(2m) c biu din

bng k hiu . Mi phn t khc 0 trong GF(2m) c biu din bng ly tha

ca . Mt tp F v hn c cu thnh bng vic bt u vi cc phn t {0, 1,

}, cc phn t tip theo c to ra bng cch nhn phn t cui vi . Kt

qu l:

F = {0, 1, 1 , 2, , j, } (2.1)

thu c tp hu hn cc phn t ca GF(2m) t F, mt iu kin c

t ra n ch c 2m phn t l:

+ 1 = 0 hoc tng ng

= 1 = 0 (2.2)

Vi iu kin ny, cc phn t c ly tha ln hn hoc bng 2m-1 c th

c rt gn vi ly tha nh hn 2m-1, nh sau:

=

n+1= n+1 (2.3)

T (2.2), ta c th biu din 1 tp hu hn F* t tp v hn F nh sau:

F* = { 0, 1,

}

= { 0, } (2.4)

T (2.4), ta c th thy c cc phn t hu hn ca trng hu hn

GF(2m):

GF(2m) = { 0,

} (2.5)

Cc php ton trong trng hu hn

Chng 2: C s l thuyt


Mi phn t trong trng hu hn GF(2m) c th c biu din bng mt a

thc ring bit c bc m -1 hoc nh hn. Ta k hiu phn t khc 0 trong

GF(2m) l mt a thc ai(X), trong c ti thiu mt h s m khc 0. Vi i = 0,

1, 2, ,2m - 2

i = ai(X) = ai,0 + ai,1X + ai,2X2 + + ai,m-1X

m-1 (2.6)

Trng hp m = 3, trng hu hn s l GF(23). Hnh 2.2-1 th hin vic nh

x 7 phn t { i } v phn t 0 theo cc phn t c s {X0, X1, X2} nh phng

trnh (2.6). Phng trnh (2.2) cho bit 7= 0, do c 7 phn t khc 0 hoc c

tt c 8 phn t trong trng ny. Hnh 2.2-1, mt chui gi tr nh phn biu din

cc h s ai,0, ai,1, ai,2 trong phng trnh (2.6). Mt trong nhng li ch ca vic

s dng cc phn t trng m rng l vic thay th cc phn t nh phn thnh

cc k hiu nh gn to iu kin cho cc biu din ton hc ca qu trnh m

ha v gii m. Vic cng hai phn t trong trng hu hn c nh ngha l

tng modul-2 ca mi h s a thc.

i+j = (ai,0 + aj,0) + (ai,1+ aj,1) X + (ai,2 + aj,2) X2 + + (ai,m-1+ aj,m-1) X

m-1

Hnh 2.2-1 nh x cc phn t c bn trong trng GF(8)

Chng 2: C s l thuyt


Bng 2.2-3 Th vic cc php ton cng v nhn trong GF(8)

Php cng hai phn t bt k trong trng hu hn bng cch cng cc h s

tng ng trong a thc ca chng. Php nhn ca hai phn t bng cch cng

s m ca chng modul-(2m -1), trong trng hp ny l modul-7.

2.2.4.2 M Reed-Solomon

Khi nim: M Reed-Solomon l m vng khng nh phn vi mt chui

cc symbol m bit, trong m l mt s nguyn dng ln hn 2. M R-S(n,

k) vi cc symbol m bit vi

n = 2m - 1, k = 2

m -1 - 2t

Trong k l s symbol d liu hay s lng thng tin c m ha, n l tng

s symbol gm symbol d liu v symbol kim tra, t l kh nng sa li ca m,

v n - k = 2t l s lng symbol kim tra.

D liu c truyn i l lng thng tin c m ha. B m ho ly k

symbol d liu, mi symbol m bit, ri thm vo (n-k) symbol kim tra to thnh

mt t m n symbol. Sau khi nhn c, b m ha s gii m t m n symbol

ny phc hi li thng tin ban u.

Mt m R-S(n, k) c kh nng sa li ti a

li. Ngoi sa li, m R-S

cn c kh nng sa sai cc erasure (hin tng mt symbol). Cc th tc m

ho v gii m R-S(n,k) c th m bo sa c ti a (n-k) erasure. Mt cch

tng qut, mt m RS(n,k) c kh nng sa c e li v r erasure vi iu kin:

2e+r< (n k).

Chng 2: C s l thuyt


Qu trnh m ha

a thc sinh ca m R-S(n, k) c dng nh sau:

g(X) = g0+ g1X+ g2X2 + + g2t-1X

2t-1 + X

2t

Bc ca a thc sinh bng vi s lng symbol kim tra trong m R-S. V a

thc sinh c bc 2t, do s c 2t ly tha ca - nghim ca a thc. Ta k

hiu nghim ca g(X) l , 2, 3, , 2t. V d, a thc ca m R-S(7, 3) sinh c

2t = n - k = 4 nghim, c biu din nh sau:

g(X) = (X - ) (X - 2) (X - 3) (X - 4)

= ( X2 - ( + 2) X + 3) (X2 - ( 3 + 4) X + 7)

= (X2 - 4X + 3) ( X2 - 6X + 0)

= X4 - ( 4 + 6)X3 + ( 3 + 10 + 0) X2 - ( 4 + 9) X + 3

= X4 - 3X3 + 0X2 - 1X + 3

Theo th t t thp ln cao v thay du "-" thnh du "+", v trong trng nh

phn +1 = -1, g(X) c biu din li nh sau:

g(X) = 3 + 1X + 0X2 + 3X3 + X4

Vi d liu ban u m(X), ta m ha d liu bng cch nhn m(X) vi g(X)

to ra 1 t m (code word) U(X): U(X) = m(X) g(X)

V d: chui d liu 3-symbol, mi symbol c 3-bit

010 110 111

Ta c a thc m(X) = 1 + 3X + 5X2

Ta c t m:

U(X) a= m(X) g(X) (2.7)

= ( 1 + 3X + 5X2) ( 3 + 1X + 0X2+ 3X3 + X4)

Chng 2: C s l thuyt


= 0 + 2X + 4X2 + 6X3 + 1X4 + 3X5 + 5X6

= (100) + (001) X + (011) X2 + (101)X

3 + (010)X

4 + (110)X

5 + (111)X

6

Vi mt t m bt k, nghim ca a thc sinh chnh l nghim ca t m.

U( ) = U( 2) = U( 3) = U( 4) = 0

Tht vy:

U( ) = + + + + + +

= + + + + + +

= + + +

= + = 0

U( ) = + + + + + +

= + + + + + +

= + + +

= + = 0

U( ) = + + + + + +

= + + + + + +

= + + +

= + = 0

U( ) = + + + + + +

= + + + + + +

= + + +

= + = 0

Chng 2: C s l thuyt


Qu trnh gii m

Mt thng ip c m ha bng cch s dng m R-S (7, 3) to ra t

m c biu din bi (2.7). Gi s trong qu trnh truyn d liu, t m b lm

h sao cho 2 symbol nhn c b li ( y l s li tng ng kh nng sa li

ti a ca m). Vi t m 7-symbol, mt a thc li c biu din nh sau:

V d, a thc li b 2 li trong qu trnh truyn d liu, 1 symbol kim tra v

mt symbol d liu

e(X) = 0 + 0X + 0X2 + 2 X3 + 5X4 + 0X5 + 0X6

= (000) + (000)X + (000)X2 + (001)X

3 + (111)X

4 + (000)X

5 + (000)X

6

a thc t b li nhn c r(X) c biu din bng tng ca a thc t

c truyn i v a thc li nh sau:

r(X) = U(X) + e(X)

= (100) + (001) X + (011) X2 + (100)X

3 + (101)X

4 + (110)X

5 + (111)X

6

= 0 + 2X + 4X2 + 0X3 + 6X4 + 3X5 + 5X6 (2.9)

Trong v d trn, c 4 n s cn tm: 2 gi tr li v 2 v tr li. C s khc bit

quan trng gia gii m nh phn v khng nh phn. Trong gii m nh phn, b

gii m ch cn tm v tr li v gi tr li s b thay i t 1 thnh 0 v ngc li.

Nhng y, cc symbol khng nh phn i hi khng nhng tm thy v tr li

m cn phi xc nh cc gi tr ng ti nhng v tr . V c 4 n s trong v d

ny, do cn 4 phng trnh tm ra 4 n s ny.

Tnh Syndrome

Syndrome S l kt qu ca vic kim tra r(X) xc nh r(X) c phi l t m

hp l hay khng. Nu ng, syndrome phi bng 0. Nu tn ti mt gi tr ca S

khc 0, chng t c li xut hin. Syndrome S c n - k symbol, {Si} (i = 1, ,n -

k). Nh ta ni trong qu trnh m ha

Chng 2: C s l thuyt


U(X) = m(X) g(X)

Ta thy mi t m hp l U(X) chia ht cho a thc sinh g(X). Cho nn,

nghim ca g(X) cng l nghim ca U(X).V r(X) = U(X) + e(X), nu cc nghim

ca g(X) c th vo r(X) ch cho ra kt qu bng 0 th r(X) l t m hp l.

Nu c li s cho ra mt hoc nhiu kt qu khc 0.Vic tnh ton mt symbol

syndrome c biu din nh sau:

|

V d, r(X) cha 2 symbol li nh phng trnh (2.9). Nu r(X) l t m hp l,

mi symbol Si u bng 0. V d:

S1 = r( ) = + + + + + +

= + + + + + +

=

S2 = r( ) = + + + + + +

= + + + + + +

=

S3 = r( ) = + + + + + +

= + + + + + +

=

S4 = r( ) = + + + + + +

= + + + + + +

=

Kt qu cho thy t m nhn c cha li v S0.

Chng 2: C s l thuyt


Ta c:

|

[ ]|

Si = r( ) = U( ) + e( ) = 0 + e( ) (2.10)

T (2.10) ta thy gi tr syndrome bng vi gi tr ca a thc li khi th cc

nghim ca g(X). Gi s c v li trong t m ti cc v tr , , , . Khi

a thc li e(X) trong phng trnh (2.8) c vit li nh sau:

e(X) = +

+ +

sa t m b li, mi gi tr li v v tr li ca n phi c xc nh,

trong l = 1, 2, , v. Tip theo, ta tnh n - k = 2t symbol syndrome bng cch

thay th i vo a thc nhn vi i = 1, 2, , 2t:

S1 = r( ) = + + +

S2 = r( ) =

+ + +

S2t = r( ) =

+ + +

Ta c 2t n s ( t gi tr li v t v tr li tng ng), v 2t phng trnh. Do

ta c th tm ra nghim ca phng trnh. Bi bo co ny khng i su chi tit

qu trnh gii phng trnh.

T cc nghim tm c ta xc nh c a thc li e(X). T tnh c t

m hp l. Phng trnh (2.9)

r(X) = U(X) + e(X)

=> U(X) = r(X) - e(X)

Chng 2: C s l thuyt


V trong trng hu hn php "-" l php cng "+", nn ta c

U(X) = r(X) + e(X)

Vi t m hp l ny, ta c th khi phc li d liu ban u bng phng

trnh

U(X) = r(X) g(X)

2.3 Tng quan v m ha

M ha v gii m l mt phn trong h thng ang hng n. Mt s gii

thut m ha, gii m cng nh l u nhc im ca chng s c chng ti

gii thiu tip sau y. Ni dung c trch lc t mt ti liu [5] v [6]

2.3.1 Tng quan

M ha (encryption) l phng php bin i d liu ban u (plaintext) thnh

dng d liu khng th c c (ciphertext). D liu ban u l d liu c th

c hiu bi con ngi hoc l cc dng d liu m my tnh c th hiu v thc

thi (executable code). Khi d liu c m ha, c ngi v my u khng hiu

c cho n khi n c gii m. Vic m ha nhng d liu nhy cm khi lu

tr chng trn my tnh l vic lm cn thit trnh nhng truy cp ca k xu.

c bit, m ha rt cn thit khi truyn ti d liu qua mng nht l qua cc

knh truyn khng an ton.

Hnh 2.3-1 M ha v gii m

Mt h thng h tr m ha v gii m d liu c gi l mt cryptosystem.

H thng ny c xy dng da trn phn cng hoc h tr thng qua code

trong ng dng. Cryptosystem s dng cc gii thut m ha, cc gii thut ny

cho bit mc phc tp ca h thng. Hu ht cc gii thut u l nhng hm

ton hc phc tp c p dng trn plaintext. Cc gii thut m ha s dng

mt gi tr gi l kha (key), thng l mt chui bit, m ha v gii m (Hnh

2.3-2).

Chng 2: C s l thuyt


Hnh 2.3-2 M ha

Gii thut m ha l tp hp cc lut ton hc phc tp m ha v gii m

d liu. Hin nay, c ch m nhiu gii thut lm vic khng cn c gi b mt

na. Phn b mt ca mt qu trnh m ha d liu chnh l kha. Kha l mt

gi tr bt k c to nn t mt chui ln cc bit ngu nhin. Tuy nhin khng

phi bt k gi tr no cng c th l kha. Mi gii thut s c mt min gi tr

nht nh (gi l khng gian kha - keyspace), trong mi gi tr c th lm

kha cho gii thut . Keyspace cng ln ng ngha vi vic tm ra kha chnh

xc m gii thut s dng cng kh khn hn (hay ni cch khc l an ton

hn).

2.3.1.1 Substitution Cipher - Transposition Cipher

chuyn mt plaintext thnh mt ciphertext, c hai k thut c bn l

thay th (substitution cipher) v hon v (transposition cipher hay permutation

cipher).

Phng php thay th s thay cc bit, k t hoc mt nhm k t bi cc bit,

k t hoc nhm k t khc. Phng php hon v khng thay th cc gi tr hin

ti bi cc gi tr khc m n dch chuyn (hon v) cc bit hay cc k t vi nhau

nhm to thnh mt d liu mi.

Chng 2: C s l thuyt


Hnh 2.3-3 Khng gian kha

Substitution Cipher

K thut ny s dng kha dn hng cho qu trnh thay th. Trng hp

n gin nht l gii thut Caesar Cipher pht minh bi Julius Caesar, mi k t

c thay th bi mt k t khc nm v tr th 3 ngay sau n trong k t trong

bng ch ci alphabet. V d,

plain: meet me after the toga party

cipher: PHHW PH DIWHU WKH WRJD SDUWB

Ta c th thy rng, Caesar Cipher rt yu v keyspace ca Caesar Cipher ch

gm 25 gi tr. Tt nhin, y ch l v d n gin cho phng php thay th.

Thc t phng php ny c s dng trong cc gii thut nhng vi s phc

tp gp nhiu ln, hn na chng thng s dng nhiu hn mt bng ch ci.

Transposition Cipher

Chng 2: C s l thuyt


Nh ni, phng php ny s hon chuyn v tr cc k t trong mu ban

u. Kha s c s dng ch ra v tr m cc k t c di chuyn ti.

V d, ta c th sp xp cc k t ca plaintext thnh mt mng nhiu dng,

sau hon v cc ct v ghi li theo th t ct ta c ciphertext:

Key: 4 3 1 2 5 6 7

Plaintext: a t t a c k p

o s t p o n e

d u n t i l t

w o a m x y z

Ciphertext: TTNAAPTMTSUOAODWCOIXKNLYPETZ

Trn thc t, vic cc hon chuyn v tr ny c xc nh bi nhng hm

ton hc phc tp hn rt nhiu.

Hu ht cc gii thut hin nay s dng mt chui cc thao tc thay th v

hon v phc tp chuyn plaintext thnh ciphertext. Chui thao tc ny c

mt gii thut to ra nh vo mt gi tr kha c th.

2.3.1.2 Block Cipher - Stream Cipher

Block cipher m ha plaintext theo tng khi (block). Thng th mi khi c

kch thc khong 64 bit hoc 128 bit. Cc khi ny c m ha mt cch

ring bit khng ph thuc ln nhau cng nh trng thi hin ti ca qu trnh m

ha. Do , n cn c gi l stateless cipher.

Stream cipher cng c th xem l mt block cipher vi kch thc khi tng

i nh (thng l 1 bit). Vic m ha bit hin ti ph thuc vo trng thi ca

qu trnh m ha (cc bit c m ha trc ). Do , n cn c gi l

state cipher.

Chng 2: C s l thuyt


2.3.2 Cc m hnh m ha v gii m

Hin nay, cc m hnh m ha c th chia lm loi c bn sau: m ha kha

i xng (symmetric key cryptography), m ha kha bt i xng (asymmetric

key cryptography).

2.3.2.1 M ha kha i xng

M ha kha i xng l k thut m ha m trong qu trnh m ha v gii

m cng s dng chung mt kha (shared key). M hnh ny gm 5 thnh phn

sau y:

Plaintext: D liu ban u, l u vo ca gii thut m ha.

Encryption algorithm: Gii thut m ha thc thi cc tc v thay th v

hon v trn plaintext.

Hnh 2.3-4 S m ha kha i xng

Secret key: Kha cng l mt u vo ca gii thut m ha. Kha l gi

tr c lp vi plaintext cng nh gii thut m ha. Gii thut s to ra

output khc nhau ty vo gi tr kha c s dng ti mi thi im. Cc

thao tc thay th v hon v m gii thut thc hin trn plaintext c quy

nh bi kha.

Ciphertext: Output ca gii thut, thng ip dng khng hiu c. N

ph thuc vo gi tr ca plaintext v kha s dng. i vi mt thng ip

cho trc, hai kha khc nhau s dng cho cng gii thut s to ra 2

ciphertext khc nhau.

Chng 2: C s l thuyt


Decryption algorithm: Gii thut m ha c thc thi theo chiu ngc

li. u vo ca n l ciphertext v kha v to ra plaintext.

V m hnh kha i xng s dng chung kha cho c m ha v gii m nn

h thng s dng kha i xng c th m bo tnh ring t (confidentiality)

nhng khng m bo tnh xc thc (authentication) v tnh chng thoi thc

(non-repudiation) v khng c cch no xc nh ai l ngi to ra thng ip khi

m c hai cng s hu kha.

M hnh ny c mt s u im v khuyt im sau y:

u im:

- Nhanh hn rt nhiu ln so vi m hnh kha bt i xng.

- An ton nu s dng kha c kch thc ln.

Khuyt im:

- Phn phi kha (key distribution): cn c c ch an ton lm vic

ny.

- Tnh m rng (scalability): mi cp ngi dng cn c mt kha ring,

do , s lng kha s rt ln khi cn trao i vi nhiu ngi.

- Tnh bo mt (security): khng m bo tnh xc thc (authentication)

v tnh chng thoi thc (non-repudiation).

Vi li ch v tc thc thi nhanh, m hnh kha i xng c s dng kh

rng ri trong thc t. C nhiu gii thut lm vic theo m hnh ny. in hnh

nht l cc gii thut sau y:

Data Encryption Standard (DES)

Triple DES (3DES)

Advanced Encryption Standard (AES)

Blowfish

IDEA

RC4, RC5 v RC6

an ton ca cc gii thut (kha c kch thc khc nhau) i vi phng

php tn cng brute-force c cho hnh sau:

Chng 2: C s l thuyt


Hnh 2.3-5 Sc mnh ca cc gii thut kha i xng

2.3.2.2 M ha kha bt i xng

Trong nhiu trng hp, ngi ta mong mun s dng cc kha khc nhau

cho qu trnh m ha v gii m. Khi , m hnh kha bt i xng s c s

dng. M hnh ny c 6 thnh phn sau y:

Plaintext: D liu ban u, l u vo ca gii thut m ha.

Encryption algorithm: Gii thut m ha thc thi cc tc v thay th v

hon v trn plaintext.

Public and private keys: Cp kha c s dng cho m ha v gii m.

Cc thao tc thay th v hon v to ra bi gii thut m s ph thuc vo

vic s dng private key hay public key lm u vo cho gii thut.

Ciphertext: Output ca gii thut, thng ip dng khng hiu c. N

ph thuc vo gi tr ca plaintext v kha s dng. i vi mt thng ip

cho trc, hai kha khc nhau s dng cho cng gii thut s to ra 2

ciphertext khc nhau.

Decryption algorithm: gii thut nhn vo ciphertext v private key tng

ng v to ra plaintext.

Chng 2: C s l thuyt


Hnh 2.3-6 M hnh m ha s dng kha bt i xng

Hnh 2.3-7 M hnh gii m s dng kha bt i xng

Trong m hnh ny, mt thng ip khi c m ha bng public key th ch c

th c gii m bi private key tng ng v ngc li. Public key l kha

c cng khai cho tt c mi ngi, private key l kha m ch ch nhn ca n

c bit. Public key v private key c lin quan n nhau v mt ton hc

Chng 2: C s l thuyt


nhng c mt c im quan trng l khng th xc nh c private key

(public key) nu ch bit c gii thut m ha v public key (private key).

M hnh ny c th m bo c tnh ring t (confidentiality), tnh xc thc

(authentication) v tnh chng thoi thc (non-repudiation).

Nu ngi gi mun m bo tnh ring t (confidentiality) ca thng ip, h

s s dng public key ca ngi nhn m ha thng ip (secure message

format), khi thng ip ch c th c gii m bi ngi nhn.

Nu ngi gi mun m bo tnh xc thc (authentication), h s s dng

private key ca mnh m ha thng ip (open message format), khi ngi

nhn s s dng public key ca ngi gi gii m. Nu gii m c ngi

nhn s bit chc rng thng ip c gi i t chnh ngi s hu private

key.

Trong trng hp mun m bo c tnh ring t v tnh xc thc, ngi gi

s m ha thng ip bng public key ca ngi nhn, sau , m ha tip bi

private key ca mnh (secure and signed format). Khi ngi nhn nhn c

thng ip, h s xc thc bng cch gii m thng ip vi public key ca

ngi gi, sau gii m vi private key ca mnh.

Tm li, m hnh ny c nhng u im v khuyt im sau y:

u im:

- Vic phn phi kha n gin hn nhiu so vi m hnh kha i xng.

- C tnh m rng cao.

- m bo tnh ring t, tnh xc thc v tnh chng thoi thc.

Khuyt im:

- im yu ln nht ca m hnh ny l lm vic chm hn rt nhiu ln

do phc tp tnh ton cao.

Cc gii thut sau y l mt s v d cho m hnh ny:

RSA

Elliptic Curve Cryptosystem (ECC)

Diffie-Hellman

El Gamal

Chng 2: C s l thuyt


Digital Signature Standard (DSS)

Hnh 2.3-8 Cc nh dng thng ip

Chng 3: Cc nghin cu lin quan


CHNG 3: CC NGHIN CU LIN QUAN

c nhiu h thng c a ra [7] [8] [9] s dng ging ni lm c

trng sinh trc to xc thc, to kha m ha. Chng ny trnh by cc

nghin cu v vn xc thc v m ha d liu bng cc phng thc sinh

trc khc nh trng mt, khun mt.

3.1 H thng m ha bng cch to kha da trn trng mt

ngi

H thng m ha bng cch to kha da trn trng mt ngi c a ra

trong ti liu [10] l mt m hnh c s dng mt s k thut dng trong h thng

ang xy dng nh m sa li Reed-Solomon v mt s gii thut m ha (DES

AES)

3.1.1 M hnh h thng

Vi h thng m ha i xng truyn thng, kha gii m phi ging chnh xc

vi kha m ha. Tuy nhin, nhng c trng ny c trch xut t cng mt

trng mt qua nhiu ln khc nhau lun lun khc nhau do nhng nguyn nhn

nh: nhiu im nh, s bp mo trng mt, s che khut ca mi mt, m

mt Do , nhng c trng ca trng mt khng c s dng mt cch trc

tip lm kha. gii quyt vn ny, bi nghin cu ny s dng gii

thut sa li loi tr s khc nhau.

Trong qu trnh m ha, vector c trng c rt trch t trng mt. Ti thi

im , m sa li (Error Correction Code) c to ra bi gii thut Reed-

Solomon. Sau vector c trng ny c bin i thnh kha mt m bng

cch s dng hm bm (hash). Mt vi gii thut m ha tng qut s dng

kha ny m ha d liu nh: DES, AES

Trong qu trnh gii m, vector c trng c rt trch t trng mt ca ngi

dng v c sa li bi m sa li. Sau , s dng cng hm bm trong qu

trnh m ha bin i vector c trng thnh kha mt m. Cui cng, gii



thut m ha tng ng s dng kha mt m ny khi phc d liu c

m ha.

Hnh 3.1-1 M hnh h thng m ha

3.1.2 Qu trnh rt trch c trng

Cc phng php tin x l c s dng nh v v chun ha trng mt.

M mt trn, m mt di v lng mi thng bao ph trng mt, ta xc nh vng

quan tm (region of interesting- ROI) l 3/4 vng bn trong ca na di trng

mt, n cha thng tin phn bit cc trng mt khc. Ta chun ha ROI l

mt khi hnh ch nht 256 x 64 im nh



Hnh 3.1-2 Tin x l trng mt

B lc Gabor (Gabor filter) 2-D c xc nh nh sau:

[ ] [

] [

]

Trong , f l tn s ca bc sng phng hnh sin, v l hng s khng

gian ca hnh bao Gaussian dc theo trng x' v y' tng ng, biu th s nh

hng ca Gabor filter.

nh trng mt c chun ha c lc bi Gabor filter vi

. Hnh 3.1-3 cho v d v hnh nh c lc. Sau , cc nh

ny c chia thnh cc khi 16x4.Ta tnh trung bnh (mean) cho mi khi. Ta

nhn c 16x4x4 = 256 gi tr t mt nh trng mt to nn mt vector 256

chiu. V nhng yu t khng r rng nh nhiu, s bp mo trng mt, s che

khut mi mt, m mt nhng nh khc nhau ca cng 1 trng mt s khng

ging nhau chnh xc. Do , cc vector ca nhng nh ny s hi khc. Ta

chun ha mi thnh phn ca vector thnh mt s nguyn trong min [0, 15]

loi b hu ht s khc nhau. Vector c chun ha ny c gi l vector c

trng trng mt, c trnh by nh sau:

V = (M1, M2,,M256)



Tuy nhin, s chun ha khng loi b c tt c s khc nhau gia cc

vector c trng c to nn t nhiu nh ca cng mt trng mt v vn cn

vi thnh phn ca vector c trng l khc nhau. Nu s lng cc thnh phn

khc nhau ca 2 vector c trng nh hn 1 ngng T no , chng s c

xem l nhng nh ca cng 1 trng mt. Ngc li, chng c xem l nhng

nh ca cc trng mt khc.

Hnh 3.1-3 Hnh nh c lc

3.1.3 M ha v gii m

Nhng vector c trng ny c dng to ra kha mt m cho qu trnh

m ha v gii m.

Trong qu trnh m ha, nhng vector c trng ny c dng m ha d

liu. Gi s rng chiu di ca vector trng mt l N v ngng khc nhau l T,

qu trnh m ha d liu s nh sau:

1. Tnh m Reed-Solomon (N+2T, N, T) ca vector c trng. M Reed-

Solomon cha 2 phn: d liu vector v m sa li. Ta ch gi li m

sa li.

2. Bin i vector c trng thnh kha c chiu di c nh bng cch

dng hm bm (v d. MD5).

3. Ta s dng kha mt m v mt vi gii thut m ha i xng (v d.

AES) m ha d liu.

Trong qu trnh gii m, vector c trng c dng gii m d liu. Qu

trnh gii m c thc hin nh sau:



1. S dng gii thut gii m Reed-Solomon sa vector c trng vi

m sa li (ECC) thu c trong qu trnh m ha.

2. Bin i vector c sa li thnh kha bng cch dng cng hm

bm ging qu trnh m ha.

3. S dng kha ny v gii thut gii m tng ng (v d. AES) gii

m d liu.

Nu vector gii m c s sai khc nh hn T vi vector m ha, 2 vector ny

s c xem l c trch xut t cng 1 trng mt, gii thut gii m Reed-

Solomon c th bin i vector gii m thnh vector m ha. Ngc li, vic gii

m tht bi.

3.1.4 Kt qu thc nghim v phn tch

Hnh 3.1-4 th hin kt qu ca thc nghim

Hnh 3.1-4 ng cong FAR v FRR

ngn nhng k mo danh gii m d liu thnh cng, FAR phi bng

0.Theo Hnh 3.1-4 v Bng 3.1-1, s li c chn l 107 v FAR, FRR tng

ng l 0%, 5.5556%. Theo l thuyt m Reed-Solomon, m RS(570, 256, 107)

c chn sa li.



Bng 3.1-1 FAR, FRR v ngng T

3.2 Sinh trc hc khun mt v phng php nhn dng

Eigenfaces

Sinh trc hc khun mt v phng php nhn dng Eigenfaces c

nghin cu v pht trin t rt lu. Di y l mt s nghin cu v n c

rt trch t mt s ti liu ti [11] [12] [13] [14].

3.2.1 Gii thiu

Khi gp mt ngi no , khun mt c l l im gy ch u tin i vi

chng ta. Kh nng ghi nh v nhn dng khun mt ca con ngi rt c bit.

Ngi ta c th ghi nh v nhn ra khun mt ca hng trm, thm ch hng

ngn ngi m h tng bit, d sau mt khong thi gian rt lu khng gp; hay

d h c thay i kiu tc, hay gi i Rt nhiu nghin cu lin quan n vic

nhn dng khun mt c thc hin cho n nay.

Hin nay, c hai cch tip cn c bn nhn dng khun mt.



Phng php da trn c trng (feature-based): tp trung vo vic

phn tch v trch xut cc c trng ring bit nh mt, mi, ming v b

cc khun mt t nh ngha mt m hnh khun mt da trn v tr,

kch thc v quan h ca chng. Phng php ny i hi cc tnh ton

v m hnh ha rt phc tp, bn cnh , vic nhn dng t nhiu gc

nhn khc nhau cng c chng minh l rt kh kh thi cng nh n rt

nhy cm vi cc thay i trn gng mt. Tuy nhin, cch tip cn ny

vn ph bin nht trong lnh vc th gic my tnh hin nay.

Phng php da trn nh (image-based): da trn cc khi nim ca

l thuyt thng tin v phng php phn tch thnh phn chnh (Principle

Component Analysis PCA). Trong phng php ny, thng tin trn ton

b nh khun mt u cn thit (khng phi ch vi c trng ring bit).

Cc nh khun mt s c thu gim chiu bng cch chiu vo khng

gian cc khun mt (eigenfaces) c trch xut t mt tp hun luyn

(training set) v sau c phn loi bng cch so snh v tr ca n vi

v tr ca cc c nhn bit.

3.2.2 Phng php Eigenfaces

i vi cc nh khun mt, d c khc nhau nh th no i na th chng vn

c chung cc mu (pattern) thng tin nht nh, gi l cc eigenfaces. Cc mu

thng tin ny c ng gp vo cc khun mt khc nhau vi t l khc nhau, mi

khun mt c th xp x thnh mt t hp tuyn tnh cc eigenfaces v vector

cc h s l c trng cho khun mt trong tp hp cc khun mt hin ti.



Hnh 3.2-1 Mt s Eigenface

Vic tnh ton eigenfaces c thc hin s dng mt cng c ton hc l

Principal Component Analysis - PCA. PCA mt phng php thng k c trnh

by chi tit [11]. Phng php ny thng c dng thu gim s chiu

ca mt i tng d liu no nhm gim phc tp tnh ton. Trong mt

tp d liu nhiu chiu phn b hn n, PCA c gng tm ra cc vector c bn

(eigenvector), mi eigenvector s tng ng vi mt eigenvalue (eigenvalue

cng ln th s ng gp ca eigenvector vo s phn b d liu cng ln), sau

chn ra cc eigenvector c eigenvalue ln nht. Cc eigenvector ny s to

ra mt khng gian con (sub space) c s chiu nh hn nhiu v d liu ban u

s c chiu ln v tnh ton trn sub space ny.

Mattew Turk v Alex Pentland thuc hc vin Massachusetts (M) s dng

phng php ny trong mt nghin cu nhn dng khun mt v c trnh by

[12]. Theo bi bo ny, vic nhn dng khun mt i qua cc bc sau:

Chun b mt tp cc nh hun luyn (training set),



Tnh ton cc eigenfaces t tp hun luyn v gi li M eigenfaces c

eigenvalue ln nht, M eigenfaces ny nh ngha face space cho vic

nhn dng,

Chiu cc nh khun mt bng vo trong face space ta c cc vector

c trng cho mi khun mt l cc vector ca cc h s.

Chiu khun mt cn c nhn dng vo face space v xc nh xem n

ph hp nht vi khun mt bit no bng cch so snh vector h s ca n

vi cc vector trong tp hun luyn.

3.2.2.1 Tnh ton eigenfaces

Cc eigenfaces l tp cc eigenvector ca ma trn hip phng sai xy dng

t tp nh hun luyn.

Gi s ta c tp hun luyn gm M nh c kch thc h x w = N pixel. Mi nh

i trong tp ny c th c biu din thnh mt vector N chiu.

Vic tnh ton eigenfaces tri qua cc bc sau y:

Tnh vector khun mt trung bnh (mean image):

= 1

M iMi=1 (3.1)

Tnh vector sai s cho mi vector khun mt

i = i (3.2)

Cc vector sai s ny c sp xp to thnh mt ma trn d liu kch

thc N x M

A = [ 1 2 M] (3.3)

To ma trn hip phng sai (covariance matrix) bng cch nhn ma trn

(1.4) vi ma trn chuyn v ca n (transpose matrix)



C =AAT (3.4)

Tnh ton cc eigenvector v eigenvalue

Mt vector u c gi l eigenvector ca ma trn hip phng sai C khi:

Cu= u

Trong , c gi l eigenvalue tng ng vi u.

Ma trn C c kch thc N2 x N2 s c N2 eigenvectors, mi eigenvector tng

ng vi mt eigenvalue. Tuy nhin, khi M

Chng 4: Phn tch v thit k h thng


CHNG 4: PHN TCH V THIT K H THNG

Chng ny trnh by v vic phn tch v thit k h thng, cc thnh phn

ca h thng, cc qu trnh s dng ca h thng v cc cng ngh c s

dng.

4.1 Phn tch, thit k h thng

4.1.1 M t h thng

Cng ging nh a s cc h thng xc thc v m ha khc, h thng chng

ti ang xy dng v mt nghip v khng qu phc tp. M hnh sau th hin

cc use case ca h thng:

Hnh 4.1-1 M hnh use case ca h thng



4.1.1.1 Actor

H thng c 1 actor: User

nh ngha: l ngi trc tip tng tc vi h thng.

Chc nng:

- ng k c trng sinh trc vi h thng

- ng k li c trng sinh trc sau khi ng k

- Xc thc vo ng nhp vo h thng

- Duyt h thng file

- M ha v gii m file

4.1.1.2 Cc use case

1. Enroll

Bng 4.1-1 M t use case Enroll

Tn Use-case Enroll

Actor User

Khung cnh Ngi dng ng k thng tin ging ni vi h

thng

M t Ln u s dng h thng ngi dng phi ng

k thng tin ging ni ca mnh

iu kin ban u Khng

iu kin lc sau

Thng tin cn thit xc thc ngi dng c

lu trong h thng. H thng s chuyn n mn

hnh duyt file

Dng s kin

Actor H thng

Duyt chn file ging

ni thu sn, c th

chn nhiu file tng

chnh xc

Tnh ton thng tin tr

gip cn thit cho qu

trnh xc thc sau ny

v lu xung file. To

kha t thng tin sinh

ging ni thu c

2. Re-enroll

Bng 4.1-2 M t use case Re-enroll



Tn Use-case Re-enroll

Actor User

Khung cnh Ngi dng mun ng k li thng tin ging ni

vi h thng

M t

Ngi dng chn chc nng Enroll, sau xc

thc vi h thng; sau ng k li thng tin

ging ni.

iu kin ban u Ngi dng ng k ging ni vi h thng v

xc thc thnh cng

iu kin lc sau

Thng tin cn thit xc thc ngi dng c

lu trong h thng. H thng s chuyn n mn

hnh duyt file

Dng s kin

Actor H thng

Duyt chn file ging

ni thu sn, c th

chn nhiu file tng

chnh xc

Tnh ton thng tin tr

gip cn thit cho qu

trnh xc thc sau ny

v lu xung file. To

kha t thng tin sinh

ging ni thu c

3. Login

Bng 4.1-3 M t Use-case Login

Tn Use-case Login

Actor User

Khung cnh Ngi dng ng nhp vo h thng

M t

Ngi dng chn chc nng Authentication, sau

duyt chn file ging ni xc thc vi h

thng

iu kin ban u Ngi dng ng k ging ni vi h thng

iu kin lc sau H thng s chuyn n mn hnh duyt file



Dng s kin

Actor H thng

Duyt chn file ging

ni thu sn, c th

chn nhiu file tng

chnh xc bng cch

ch nh Number of

samples

Rt trch c trng

ging ni v tnh ton

xem thng tin ny c

khp vi thng tin ng

k hay khng nh vo

thng tin tr gip lu

trong h thng.

4. Encrypt/Decrypt file

Bng 4.1-4 M t use case Encrypt/Decrypt file

Tn Use-case Encrypt/Decrypt file

Actor User

Khung cnh Ngi dng mun m ha file d liu

M t

Sau khi ng k ging ni hoc xc thc thnh

cng, ngi dng c quyn thao tc trn h thng

file v m ha/gii m file d liu

iu kin ban u Ngi dng phi xc thc thnh cng vi h

thng

iu kin lc sau D liu c m ha/gii m v lu vo file

Dng s kin

Actor H thng

Ngi dng long-touch

vo file d liu mong

mun, sau chn

Encrypt hoc

Decrypt trn option

menu.

H thng s dng kha

m ha hoc gii m

file d liu.



4.2 Cc thnh phn ca h thng

Da vo nhng hiu bit t c v rt trch thng tin sinh trc, m sa

li, v m ha/gii m, chng ti xy dng h thng xc thc v m ha d

liu trn android. C hai h thng c xy dng song song vi nhau. Mt h

thng s dng file ging ni v mt h thng thu ging ni trc tip. im khc

bit ln nht ca hai h thng ny l cch nhn mu tn hiu ging ni. i vi

h thng s dng file ging ni, mu tn hiu ging ni c ly t file audio, cn

h thng cn li, ging ni c thu nhn trc tip t micro ca thit b. H thng

c phn thnh nhng thnh phn chnh sau y.

4.2.1 Thnh phn thu nhn ging ni

Thnh phn thu nhn ging ni trn hai h thng khc nhau c s khc nhau.

i vi h thng s dng file ging ni thu sn, mu tn hin ging ni s c

ly gin tip thng qua file audio c record trc . Vi h thng cn li

th ging ni s c thu trc tip t micro v chuyn thnh mng tn hiu ging

ni. Th vin Android [15] h tr hai cch ly ging ni thng qua hai lp

MediaRecorder v AudioRecorder. MediaRecorder l mt lp trong Android h

tr thu nhn audio, video t cc cm bin ca thit b. Nhng nh dng audio

m n c th h tr bao gm MP3, FLAC, AAC, MIDI v cha h tr nh dng

PCM/WAVE (Android di 4.1). Vic khng h tr nh dng PCM/WAVE cho

android di 4.1 gy tr ngi cho vic hin thc h thng v mu tn hiu m

thanh c thu nhn di dng PCM/WAVE m vic chuyn tn hiu t nhng

nh dng khc v PCM/WAVE cng phc tp. khc phc vn ny, lp

AudioRecorder c chn v s dng v u th h tr nh dng PCM/WAVE

ca n cng nh l kh nng c x l vi mu tn hiu ging ni ngay trong lc

thu nhn.

c hai h thng, ging ni c thu vi tn s ly mu l 8000 Hz nn theo

l thuyt Nyquist th tn s ti a ca tn hiu ging ni c th thu gi c l

4000 Hz. Nhng nhiu cng qu vi ging ni ca mt ngi bnh thng

c tn s t 300 Hz n 3400 Hz. Kch thc mu c chn l 16-bit v nh

dng ca m thanh l PCM-signed nn cng ca tn hiu ging ni c th

biu din trong khong t -215 (-32768) n 215 (32768). Loi knh c chn



cho mu tn hiu l mono gim s phc tp trong qu trnh thu nhn tn hiu

v n khng nh hng trong vic nhn dng ging ni.

4.2.2 Thnh phn rt trch c trng sinh trc

Vic rt trch ra vector c trng i theo mt ng ng (pipeline) t khu x

l mu tn hiu ging ni ra tn hiu s n vic p dng cc gii thut rt trch

to ra vector c trng cho ging ni. C nhiu k thut v gii thut rt trch

c p dng, di y l hai gii thut c chng ti p dng ly vector

c trng.

4.2.2.1 Rt trch c trng bng gii thut LPC

Rt trch vector c trng bng phng php LPC i qua cc bc:

i mu tn hiu ging ni t dng byte sang dng s: Mu tn hiu ging

ni d c c t file hay thu trc tip u di dng mt chui byte. Vic

cn lm l i chui byte ny sang dng s. Cch lm y l i 2 byte

(16-bit) ra gi tr nguyn ca n sau ly t l cho 32768 (216 gi tr). Ty

vo h thng lu gi tr di dng big-endian hay little-endian m th t

c 2 byte c hon i cho nhau. Gi tr ca mu tn hiu sau khi i

s nm trong min tr t -1 n 1.

p dng k thut chun ha mu tn hiu ging ni nh trnh by trong

phn 2.1.2.1 cho ra nhng mu tn hiu c th so snh c vi nhau.

Kh khong lng bng cch loi b nhng phn t tn hiu c ln nh

hn ngng 0.002 (di 0.002 c xem l khong lng).

p dng gii thut d tm im cui nh trnh by trong phn 2.1.2.4

S dng gii thut rt trch LPC vi u ra l mng vector c trng 16

chiu. rng ca khung c chn l 128 v cc khung chng ln nhau

mt khong bng mt na rng ca khung.



Hnh 4.2-1 Rt trch vector c trng bng gii thut LPC

4.2.2.2 Rt trch c trng bng gii thut FFT

Rt trch vector c trng bng phng php FFT i qua cc bc:

Cc bc i tn hiu ging ni sang tn hiu s sau chun ha n l

nhng bc bt buc phi lm trc khi rt trch vector c trng. Hin

thc ca n tng t nh hin thc ca gii thut LPC

Kh khong lng bng cch loi b nhng phn t tn hiu c ln nh

hn ngng 0.002 (di 0.002 c xem l khong lng)

Kh nhiu bng cch lc b nhng phn t tn hiu ging ni c tn s cao

hn ngng 2853 Hz.

S dng gii thut rt trch FFT vi u ra l mng vector c trng ln

lt 32, 64, 128 chiu. rng ca khung c chn l 128 v cc khung

chng ln nhau mt khong bng mt na rng ca khung.



Hnh 4.2-2 Rt trch vector c trng bng gii thut FFT

4.2.2.3 Cng ngh c s dng

Modular Audio Recognition Framework (MARF) [16] l mt th vin m ngun

m tp hp cc gii thut x l ngn ng t nhin, ging ni, m thanh c

vit bng ngn ng Java v c thit k thnh nhng module. Mi module

tng ng vi mt qu trnh trong tin trnh rt trch ra vector c trng. Vi cu

trc module, ta c th m rng th vin bng cch thm mi nhng gii thut

mi module mt cch d dng. Th vin ny c dng ch yu hc tp v

nghin cu. Hin ti, bn release cui cng ca n l vo nm 2007 v mt s

gii thut trong vn cha c hin thc. Kt qu tt nht ca th vin thu

nhn c l 82.76%. H thng ang xy dng da mt phn vo th vin

MARF v c mt cht ci tin thu c tn hiu ging ni c cht lng tt

hn. Nhng thnh phn s dng li l Loader (WAV), Preprocessing (Low-Pass,

Endpoint), Feature Extraction (FFT, LPC).



Hnh 4.2-3 Cu trc MARF Framework

4.2.3 Thnh phn chun ha

Trc khi i qua thnh phn sa li (Reed-Solomon), vector c trng phi i

qua mt bc bin i (transform) cho ra mt vector m cc gi tr ch l

nhng gi tr nguyn dng (khc vi vector ban u l nhng gi tr thc).

Bc ny c thc hin bi thnh phn chun ha vector. Vic chun ha

vector c trng gip cho min gi tr ca cc phn t ca vector thch hp hn

cho qu trnh sa li. Hin ti, gii thut sa li ch p dng cho vector m nhng

gi tr ca n l s nguyn dng v vn cha c cch bin i no ti u. Ty

vo mi phng php rt trch vector c trng khc nhau (cho ra vector c

trng vi min tr khc nhau) m phng php bin i khc nhau.

Vi phng php rt trch vector c trng LPC, min gi tr ca cc phn t

vector chy t -1 n 1. Cch bin i c p dng l chia khong gi tr t -1

n 1 ca vector c trng sang min s nguyn t 1 n 5 sao cho cc gi tr

phn b vo nm khong ng u nhau.



Hnh 4.2-4 Php bin i vector c trng LPC

Vi phng php rt trch vector c trng FFT, th min gi tr ca vector c

trng c sinh ra rng hn t 0 n v cng. Phng php bin i c p

dng l chia khong gi tr t 0 n v cng ca vector c trng sang min s

nguyn t 1 n 20 bng cch bin i phn nguyn sau khi lm trn. Thc t

gi tr sau khi bin i ch n 13 l ti a.

Hnh 4.2-5 Php bin i vector c trng FFT



4.2.4 Thnh phn sa li

Mc ch ca thnh phn ny l t vector c trng c th sinh ra cc thng

s sa li. Nh vo cc thng s ny, ta khng cn phi lu tr kha trong my.

lm c vic ny, thnh phn to kha s dng gii thut Reed-Solomon

[17]. C th chia thnh phn to kha ra lm hai nhim v chnh da vo gii

thut ca Reed-Solomon:

Encode: c thc hin trong qu trnh ng k (enrollment). Vector c

trng sau khi c chun ha, thng qua gii thut Reed-Solomon s to

ra m sa li. H thng s lu tr m sa li ny trong my s dng

trong qu trnh xc thc.

Hnh 4.2-6 Encode trong R-S

Decode: c s dng trong cc ln s dng h thng tip theo (qu trnh

xc thc). H thng s s dng m sa li sinh trc kt hp vi

vector c trng ( qua chun ha) a vo gii thut gii m ca

Reed-Solomon. Gii thut ny s

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