2007.MScThesis

TP. H Ch Minh 02/2007

I HC QUC GIA THNH PH H CH MINH TRNG I HC BCH KHOA

WX

NGUYN VIT HNG

NHNG VN BO MT KHI TRUY VN C S D LIU XML NG C

OUTSOURCED

CHUYN NGNH: CNG NGH THNG TIN M S NGNH: 60.48.01

LUN VN THC S

ti: Security Issues in Querying Dynamic Outsourced XML Databases Trang 2/93

SV: Nguyn Vit Hng HD: TS ng Trn Khnh

CNG TRNH C HON THNH TI TRNG I HC BCH KHOA

I HC QUC GIA THNH PH H CH MINH

Cn b hng dn khoa hc: Tin s NG TRN KHNH

Cn b chm nhn xt 1: Tin s NGUYN C CNG

Cn b chm nhn xt 2: Tin s TRN VN HOI

Lun vn thc s c bo v ti HI NG CHM BO V LUN VN

THC S TRNG I HC BCH KHOA, ngy 03 thng 02 nm 2007

TRNG I HC BCH KHOA CNG HA X HI CH NGHA VIT NAM PHNG O TO SH C LP T DO HNH PHC

Tp. HCM, ngy . . . . thng . . . . nm 200. .

NHIM V LUN VN THC S H tn hc vin: Nguyn Vit Hng Phi: Nam Ngy, thng, nm sinh: 14 thng 01 nm 1981 Ni sinh: Kin Giang Chuyn ngnh: Cng ngh thng tin MSHV: 00703170 I- TN TI: Cc vn bo mt trong vic truy vn CSDL XML ng c outsourced. II- NHIM V V NI DUNG:

- Tm hiu tng quan cc vn lin quan bo mt CSDL c outsourced. - Tm hiu cc nghin cu lin quan kha cnh Query Assurance. - xut gii php kim tra query assurance cho CSDL XML c outsourced. - Xy dng chng trnh hin thc gii php, o c v nh gi gii php ra.

III- NGY GIAO NHIM V : ..................................................................................... IV- NGY HON THNH NHIM V: ...................................................................... V- CN B HNG DN: Tin s ng Trn Khnh. CN B HNG DN CN B MN (Hc hm, hc v, h tn v ch k) QL CHUYN NGNH

Ni dung v cng lun vn thc s c Hi ng chuyn ngnh thng qua. Ngy thng nm 2006 TRNG PHNG T SH TRNG KHOA QL NGNH



ACKNOWLEDGEMENT

I would like to express my gratefulness

To my mom and dad who has brought me up and done everything for my life;

To my advisor, Dr. DangTran Khanh, who has advised me with all his heart;

To my friends who are always in my side, and especially, to my colleagues

who are willing to help me complete some parts of the work.



ABSTRACT

With the impressive improvement of the network technologies, database outsourcing

is emerging as an important trend beside the application-as-a-service. In this model,

data owners ship their data to external service providers. Service providers do data

management tasks and offer their clients a mechanism to manipulate outsourced

database. Since a service provider is not always fully trusted, security and privacy of

outsourced data are important issues. These problems are referred as data

confidentiality, user privacy, data privacy and query assurance. Among them, query

assurance takes a crucial role to the success of the database outsourcing model. To the

best of our knowledge, however, query assurance, especially for outsourced XML

database, has not been concerned reasonably in any previous work.

In this paper, we propose a novel index structure, Nested Merkle B+ Tree, combining

the advantages of B+ tree and Merkle Hash Tree to completely deal with three issues

of query assurance known as correctness, completeness and freshness in outsourced

XML database. Experimental results with real dataset prove the effeciency of our

proposed solution.



TM TT

Vi s pht trin vt bc trong lnh vc cng ngh mng cho ra i nhiu dch v

t xa, c bit l s ra i ca dch v application as a service. Dch v ny gip

cho mi ngi c th tip cn mt cch hp php vi cc phn mm mi nht vi mt

chi ph thp nht. Thi gian gn y, xut hin xu th mi cho php lm gim chi ph

v qun l d liu qua mt dch v gi l database outsourcing. Vi dch v ny,

cc n v, t chc lu tr thng tin, d liu ca mnh ti my ch ca cc nh cung

cp dch v. Cc nh cung cp dch v s m nhn cc cng tc bo tr my ch, bo

tr phn mm DBMS cng nh bo tr CSDL ca khch hng. Bn cnh , h cung

cp cc c ch cho php cc n v, t chc c th thao tc trn CSDL ca mnh. Tuy

nhin, thng tin vn l mt ti sn ht sc qu bu, nn cc n v hon ton khng

th tin cy c cc nh cung cp dch v trong vic m bo an ton cho CSDL. Do

pht sinh cc yu cu bo mt v CSDL outsourced. Cc vn c th tm

gn trong bn yu cu bo mt, bao gm: data confidentiality, data privacy, user

privacy v query assurance.

Ngoi phn gii thiu tng quan v cc kt qu t c trong lnh vc data

outsourcing, ti liu a ra mt cu trc ch mc mi cho d liu XML. Da trn cu

trc ny, ti liu trnh by phng php m bo truy vn cho CSDL XML

outsourced cng nh mt s kt qu thc nghim hin thc cho phng php ny.



MC LC

ACKNOWLEDGEMENT ................................................................................................................ 4ABSTRACT ................................................................................................................................. 5

Chng 1 GII THIU ..................................................................................................... 81.1 Data Confidentiality ............................................................................................ 121.2 User Privacy v Data Privacy ............................................................................. 131.3 Query Assurance ................................................................................................. 171.4 Nhn xt .............................................................................................................. 19

Chng 2 CC NGHIN CU LIN QUAN ............................................................... 222.1 Khi nim ............................................................................................................ 222.2 Hng tip cn dng ch k in t ................................................................... 232.3 Hng tip cn s dng cu trc d liu c bit ............................................... 252.4 Hng tip cn Challenge Response. .............................................................. 282.5 Hng tip cn da vo c th ca bi ton ..................................................... 302.6 Bo m truy vn cho d liu dng cy .............................................................. 312.7 Nhn xt .............................................................................................................. 33

Chng 3 D LIU XML ............................................................................................... 353.1 M hnh lu tr ................................................................................................... 353.2 Ch mc cho ti liu XML .................................................................................. 40

Chng 4 M BO TRUY VN ................................................................................. 424.1 Phng php ....................................................................................................... 424.2 Nested B+ Tree ................................................................................................... 434.3 Tc v chn ......................................................................................................... 454.4 Cc tc v cp nht d liu ................................................................................. 49

Chng 5 PHN TCH .................................................................................................... 51Chng 6 THC NGHIM ............................................................................................. 58Chng 7 KT LUN ...................................................................................................... 63Chng 8 PH LC ......................................................................................................... 67

8.1 Cu trc lu tr XML ......................................................................................... 678.2 Gii thut gn nhn (labeling) ............................................................................. 678.3 Chng trnh th nghim .................................................................................... 688.4 Lc ti liu mondial.xml .............................................................................. 718.5 K hoch thc thi truy vn .................................................................................. 728.6 Tm lc cc nghin cu lin quan .................................................................... 738.7 Bi bo lin quan ................................................................................................ 83



Chng 1

GII THIU

Thng tin l mt ngun ti nguyn rt quan trng trong mi t chc. Qun l v x l

thng tin hiu qu v ang tp trung s quan tm ca mi ngi. Vi s ra i ca

my tnh in t (eclectronic computer) v cc my tnh c nhn (personal computer

PC), ngnh khoa hc my tnh mang n k nguyn mi, k nguyn ca thng

tin, tc ng mnh m n mi lnh vc trong i sng.

D liu c lu tr thnh cc cc c s d liu (CSDL), thng thng, c t

trong ni b t chc (in-house database). iu ny i hi mi t chc phi u t

mt khon chi ph cho vic qun l h thng CSDL, bao gm: thit b phn cng

(my mc, h thng mng), phn mm (h qun tr CSDL DBMS, cc chng trnh

ng dng c th,), nhn s (nhn vin qun tr mng, nhn vin qun tr CSDL,).

Cng vi s pht trin ca x hi ni chung v t chc ni ring, nhu cu lu tr v

x l ngy cng gia tng v phc tp hn. Nhng yu cu ny lm tng tng chi ph

trong qun l. Mc d, gi thnh phn cng gim rt nhiu, nhng chi ph bn

quyn phn mm, chi ph cho i ng nhn vin qun tr c trnh cao qun l

cc h thng thng tin ngy mt phc tp tht s l mt vn ng quan tm trong

tng chi ph s hu (total cost of ownership) ca t chc. iu ny c bit quan

trng i vi cc t chc va v nh, t chc phi li nhun,

Trong nhng nm gn y, s tin b vt bc trong cng ngh mng v truyn thng

cho ra i h thng mng tc cao, bng thng rng, khai sinh ra khi nim

application as a service. Ngi dng ch cn phi tr mt khon ph nh cho nh

cung cp dch v l c th s dng c cc phn mm mi m khng cn phi quan

tm n chi ph bn quyn, chi ph ci t v bo tr h thng.



Bn cnh , mt dch v khc cng dn c hnh thnh, l database as a

service, cung cp cho ngi dng ni lu tr v truy xut d liu ch vi mt chi ph

thp, m khng cn phi mua sm thit b, cng nh i hi phi c i ng chuyn

trch. iu ny s gip gim ng k chi ph qun l thng tin cho cc t chc.

Hnh 1.1. M hnh Database as a Service.

Trong m hnh database as a service, ngi s hu d liu (data owner DO) t CSDL ca mnh ti nh cung cp dch v (service provider SP) cho cc khch hng (clients, queriers C, Q) thc hin cc tc v trn CSDL nh select, insert update. M hnh cn c gi l outsourced database services (ODBS).

Thng tin l ti sn quan trng ca t chc. Vic t CSDL lu tr cc thng tin

mt ni khng tin cy bn ngoi t chc (nh cung cp dch v) lm ny sinh cc

vn bo mt. Chnh nhng vn ny s quyt nh tnh kh thi ca Dch v CSDL

outsource (outsourced database services ODBS). Cc CSDL outsourced phi c

m bo an ton, ngn cm s truy cp ca cc t chc/c nhn khng c thNm quyn,

k c nh cung cp dch v. Khi , chnh nh cung cp dch v tr thnh i tng

nguy him nht trong vic m bo bo mt ca d liu. Do cc xm nhp t bn

ngoi, cao nht, cng ch t c kh nng truy cp h thng nh cc nh cung cp

dch v. V vy cc nghin cu ch yu tp trung vo vic ngn chn hnh vi xm

nhp ca chnh cc nh cung cp dch v (service provider SP).

V mt c bn, vn bo mt CSDL ti cc SP c th chia thnh bn lnh vc nh

sau [1]:



Data confidentiality tnh ni b ca d liu. Ch s hu d liu (data owner

DO) khng mun nhng ngi khc khng c thNm

quyn c kh nng truy cp CSDL ca mnh, k c cc

SP.

User privacy tnh ring t ca ngi dng. Thng tin l hng ha.

Do n c th s c bn cho cc cng ty khc. Cc

cng ty khch hng khng mun l nhng thng tin

m h khai thc, k c i vi DO v SP.

Data privacy tnh bo mt d liu. DO khng mun khch hng ca

mnh c th khai thc c nhiu hn nhng thng tin

m h c php khai thc.

Query Assurance tnh bo m truy vn. Khch hng (Client) phi c

m bo ra d liu m mnh nhn c l chnh xc,

y v mi nht t CSDL nguyn thy do DO cung

cp, m khng b nhng thay i ngoi mun.

Bng 1.1. Cc vn bo mt trong ODBS.

Song song vi vic m bo cc yu cu bo mt, ta cn phi quan tm n hiu nng

thc hin truy vn (performance) cng nhng kh nng m rng ca CSDL

(scalability, usability).

m bo data confidentiality, d liu c m ha trc khi c outsourced.

Tuy nhin iu ny lm tng tnh phc tp ca vic x l cc truy vn trn d liu m

ha m vn phi m bo cc yu cu bo mt khc.



Hnh 1.2. M hnh ODBS

Trong m hnh ODBS, data owner t CSDL ca mnh ti cc server bn ngoi (SP) v thc hin truy vn lu tr thng qua ng truyn mng bo mt. Clients tr chi ph cho data owner c quyn truy cp d liu, v thc hin truy cp d liu trc tip t SP cng thng qua ng truyn bo mt.

Trong thc t, khng phi lc no cng cn thit phi m bo tt c cc yu cu bo

mt trn. Ty thuc vo tnh hung m mt s yu cu c th c b qua nhm gim

thiu mc phc tp tng hiu nng x l ca h thng. Quay tr li m hnh ca

ODBS, ta c bn m hnh bo mt nh sau [1].

- M hnh UP-DP (User privacy Data privacy): trong m hnh ny DO ng

thi l ngi cung cp dch v SP. DO bn thng tin t CSDL ca mnh cho

cc khch hng khc. y chnh l m hnh CSDL in-house truyn thng.

Do , m hnh ny ch quan tm n user privacy v data privacy.

- M hnh UP-nDP (User privacy non Data privacy): m hnh ny tng t

m hnh trn, ch khc l d liu c bn l ph bin, khng cn phi bo mt

d liu. Ch cn che du nhng g m ngi dng ly t CSDL.

- M hnh DC-UP (Data confidentiality User privacy): trong m hnh ny DO

ng thi l khch hng duy nht ca h thng. y l m hnh kh ph bin.

Cng ty thu nh cung cp dch v lu tr d liu ni b ca mnh v thc hin

truy cp trn CSDL ny. Do , ch xem xt confidentiality v user privacy.



- M hnh DC-UP-DP: y l m hnh y v phc tp nht. DO thu nh

cung cp dch v lu tr CSDL ca mnh. ng thi, thc hin bn thng tin

cho cc khch hng khc. DO cn c m bo data confidentiality v data

privacy trong khi ngi dng cn c m bo user privacy.

Trong tt c cc m hnh trn, query assurance lun l mt vn cn c quan

tm v xem xt.

Phn tip theo im qua cc nghin cu cng nh cc kt qu lin quan n cc vn

bo mt trong bng 1.

1.1 Data Confidentiality Data Confidentiality l yu cu m bo CSDL khng b truy cp bt hp php, k c

cc SP. t c yu cu ny, CSDL thng c m ha trc khi outsourced.

Tuy nhin, chnh vic m ha ny lm gia tng s phc tp trong truy vn d liu, nh

hng rt nhiu n hiu nng ca CSDL. Vic la chn c ch m ha c th dung

ha gia nhu cu bo mt v yu cu v hiu nng l rt cn thit. Hin nay, c ch

m ha kha b mt i xng (symmetric private key encryption) thng c s

dng, chng hn nh gii thut Rijndael, DES, TripleDES,....

Thc thi truy vn trn d liu m ha Hacigm [5] xut mt gii php thc thi cy truy vn trn d liu m ha.

tng chnh ca gii php ny l tch cu truy vn thnh hai phn: mt phn s c

thc thi ti server, phn cn li s c thc thi ti client.

Kenny C.K.Fong [6] ch ra nm l hng bo mt nghim trng ca phng php

ny:

1. Khng tha mn tnh bo mt v mt ng ngha (semantically secure). Tnh

cht ny khng tha mn nu ta c th tm c hai thng ip m0 v m1 m c

th on c kt qu m ha l ca m0 hay m1 vi xc sut > .

2. N u min gi tr ca cc trng d liu nh v ri rc, th hm bm ca gii

thut khng m bo an ton.



3. Gii thut cha m bo tnh xc thc ca kt qu truy vn tr v.

4. Cha che du cu truy vn mt cch hon ho. Server c th on bit c

loi truy vn m ngi dng thc hin.

5. Thc hin m ha theo record, do , phi gii m theo record. V vy, ngi

dng c th bit nhiu thng tin hn l h c php (khng tha mn data

privacy).

Tm kim d liu m ha trn d liu XML R. Brinkman [9] gii thiu mt cch thc cho php tm kim so trng cc tag ca mt

ti liu XML c m ha da trn gii thut Linear Search Strategy for Full Text

Documents (1), gi l Tree Search Strategy for XML Documents (2).

Gii thut (1) chia lm 3 giai on: lu tr (storage), tm kim (search), nhn d liu

(retrieval). giai on lu tr, ton b d liu c chia thnh nhiu khi nh c

nh, sau thc hin m ha cc khi ny trc khi lu tr trn server. DO cn phi

ghi nhn mt s thng tin v m ha c th gii m sau ny. Do , gii thut ny

ch ph hp vi m hnh DP-UP. giai on tm kim, chui d liu cn tm s c

m ha v chuyn n cho server so trng trn cc khi d liu xc nh ra v tr

ca on d liu m ha kt qu. Giai on nhn d liu, kt qu m ha s c gii

m da theo cc thng tin m ha c ghi nhn ti giai on lu tr.

Gii thut (2) c xy dng da trn gii thut (1). Tuy nhin, d liu l mt ti liu

XML thay v file text phi cu trc. Kch thc ca cc khi chia ra cng khng u

nhau m phc thuc vo kch thc ca tng node (hay mi node l mt khi). (2) ch

p ng cc cu truy vn dng tm kim so trng cc tag name trong ti liu XML m

khng x l n ni dung d liu bn trong node.

1.2 User Privacy v Data Privacy N gi s dng CSDL yu cu h thng phi m bo user privacy/data privacy v

yu cu truy vn cng nh kt qu tr v. SP, v k c DO, khng c php bit cc

thng tin ny.



Mt khc, ngi dng ch c php truy vn nhng g m h c php. Kt qu tr

v ch gii hn trong phm vi thng tin m h yu cu. N gi dng khng c php

thy cc d liu khng thuc thNm quyn ca mnh.

PIR-like protocols t c user-privacy, Chor gii thiu giao thc PIR (private information

retrieval). V mt l thuyt, PIR cho php ngi dng c th che du cu truy vn v

kt qu tr v. Tuy nhin, CSDL cn phi c nhn bn (replicate) sang nhiu ni.

N u khng, chi ph phi tr l rt ln (c th cn ly v ton b CSDL ti client). Mc

d vy, ngay c khi c nhn bn, chi ph phi tr cng ln PIR khng th

p dng vo thc t.

PIR ch dng truy xut d liu ch c (read-only). N otably v Ostrovsky pht

trin gii thut PIR cho php h tr cc thao tc cp nht d liu m bo user

privacy, giao thc PIS (private information storage).

ng dng PIR/PIS vo thc t, Asonov ci tin PIR thnh giao thc RIR

(repudiative information retrieval). RIR gim bt mt s rng buc bo mt gim

bt chi ph I/O m vn m bo user privacy. Tng t, giao thc RIS ci tin t PIS

vi chi ph thp v kh thi hn.

Tt c cc giao thc trn u c xy dng da trn nn tng ca PIR, do , chng

cn c gi l cc giao thc h PIR (PIR-like protocols). Tuy nhin, cc giao thc

ny ch h tr user privacy m khng m bo data privacy. Gertner pht trin

mt giao thc xy dng trn mt giao thc h PIR bt k cho php tha mn c hai

yu cu data privacy v user privacy, gi l SPIR (symmetrically private information

retrieval).

D liu dng cy (tree-structured data) Lin v Candan [2] ra mt gii thut cho php ngi dng c th che du d liu v

cc truy vn trn d liu dng cy. Lin v Candan a ra hai k thut: redundancy

access v node swapping.



- Redundancy access: khi ngi dng truy cp mt node d liu, h thng tr v

m node, trong m-1 node l ngu nhin hn ch khng cho server c th

bit c ngi dng thc s truy cp vo node no. Tuy nhin, nu mt node

c truy cp thng xuyn, node root, server c th giao cc redandancy set

pht hin ra node ny.

- Node swapping: mt node sau khi c truy xut s c hon chuyn sang

mt node khc. lm c iu ny, trong m-1 node ngu nhin c mt node

trng (empty node), node cn c s c hon chuyn vi node trng ny v

cp nht xung CSDL. K thut ny gii quyt c vn m redundancy

access gp phi.

[2] cng ch ra nm vn cn gii quyt v gii php cho chng:

1. Qun l danh sch cc empty nodes. Bng cch s dng mt node c bit

snode qun l cc eheads, etails bit c danh sch empty nodes.

2. Phng php chn ngu nhin cc node cho redundancy set.

3. m bo tnh ton vn ca mi quan h cha-con ca node b hon chuyn. Lin

v Candan ra hai gii php: (1) xc nh empty node s hon chuyn node

cha v cp nht lin kt vo node cha trc khi c node con ln. (2) ghi nh

ng dn cc node t root n node cn truy cp, sau mi thc hin hon

chuyn t di ln. [2] cng ch ra rng: gii php (1) l kh thi trong khi (2) l

khng kh thi.

4. Cc vn khi c s truy cp d liu ng thi. Trong [2], tc gi ra gii

php kha cc node khi truy cp. T , a ra nhng iu chnh m bo gii

thut khng b deadlock.

5. Vic chn gi tr cc thng s bo mt nh th no l hp l (m kch thc

ca cc tp d tha, redundancy set, s kch thc ca node).



Lin v Candan xy dng gii thut oblivious traversal algorithm, v chng

minh trong [2], nu tn sut truy cp ca cc node c phn b u (uniform

distribution) th gii thut ny t c user privac.

Trong trng hp tn sut cc node khng u nhau (iu ny thng gp trong thc

t), Lin v Candan cng nu ra mt s gii php trong [4]: dummy node access,

replicate frequently accessed nodes, clique approach. Tuy nhin, [4] cng nu ra cc

yu im ca tng gii php nh sau: s lng dummy node access, s lng

replicated nodes, kch thc redundancy set phi kh ln.

T , [4] xy dng mt gii php t c tnh privacy trong trng hp tn sut

truy cp khng u m trnh c cc hn ch trn, c gi l clustering node

acceses into uniform chains.

Hai giao thc extreme protocols Gii php ca Lin v Candan trong [2] ch ph hp cho m hnh UC-UP. ng thi,

vn cn tn ti mt s gii hn [3, 22]:

- Cha ch ra r rng cch thc cp nht danh sch cc empty nodes, ng thi

cng cha ch ra c vic tn dng li cc empty node.

- Gii thut ny khng h tr cc thao tc insert, delete mt cch trc tip. c

bit l khi xy ra trng hp over-full v under-full i vi cc node.

- Redundancy set ch c mt empty node nn khng h tr c khi xy ra over-

full v under-full.

[1] ra hai extreme protocol gii quyt cho hai m hnh DC-UP v DC-UP-DP.

M hnh DC-UP

DC + UP = Encryption + PIR protocol

Trong trng hp cn cp nht CSDL, PIR protocol c thay bng PIS protocol. V

m bo tnh thc thi, PIR/PIS protocol c thay bng RIR/RIS protocol.

M hnh DC-UP-DP



[1] xut s dng K nh l mt t chc ng tin cy th 3 (trusted third-party) lm

cu ni gia khch hng v nh cung cp dch v. Khi m hnh DC-UP-DP quay

tr li m hnh DC-UP uc gii quyt trc . Tuy nhin, do thng tin l mt

vn ht sc nhy cm, nn tm c mt t chc nh th ny trong thc t l mt

iu ht sc kh khn.

Oblivious operations on dynamic outsourced search trees N h trnh by, gii thut ca Lin v Candan trong [2] khng h tr cc thao tc

insert/delete v mt s gii hn ca gii thut. [3, 22]

[3, 22] cch gii quyt cc gii hn ca gii thut ca Lin v Candan. ng

thi, cng ra gii thut h tr thao tc insert/delete.

Tuy nhin, gii thut oblivious insert ch h tr B+-tree, m cha h tr cc cu trc

cy c bit khc nh: SH-trees, UB-trees, R+-trees, rd-trees [3, 22].Gii thut

oblivious delete c th c m rng h tr cc cy c bit ny, tuy nhin trong

trng hp cu trc cy chp nhn node under-full th gii thut khng th p dng.

Mt iu chnh ca gii thut ny c th gii quyt tt vn under-full node tuy

nhin ch c p dng cho B+-tree.

1.3 Query Assurance Query Assurance m bo kt qu truy vn tr v t server l ng (correctness) v

y (completeness) v mi nht (freshness).

- Tnh ng l cc kt qu tr v l chnh xc c ly t CSDL hay c dn

xut t (trung bnh, tng,) m khng b thay i.

- Tnh m bo kt qu truy vn tr v l y , khng b b st v mt

nguyn nhn no (do server thc hin khng ht cu truy vn, hoc khng

tr v y tp kt qu, hay do tht lc trn ng truyn).

- Tnh mi m bo kt qu tr v t server l d liu mi nht c cp nht t

cc DO. Tnh mi thng c quan tm trong trng hp d liu outsource

c th c thay i.



Einar Mykletun [7] ra mt gii php m bo tnh ng cho cc cu truy vn

dng ch c (read-only) v khng c tnh ton gp (nh SUM, AVERAGE,). Mi

dng d liu (record) c lu km theo ch k in t ca dng . Kt qu tr v

km theo vi ch k in t. Client kim tra ni dung d liu vi ch k km theo

xc nhn c tnh ng ca d liu. Tuy nhin, do s lng record tr v c th ln,

v vy vic kim tra mt s lng ln ch k in t cho tng dng dn n lng ph

thi gian v l mt chi ph nng n cho client. gii quyt vn ny, [7] ngh

m hnh Condensed-RSA. Theo , thay v kim tra ring l tng ch k ca tng

record, client ch cn kim tra tt c cc record cng lc da trn ch k tng hp

(condensed signature) do server tr v l c th xc nh c tnh ng ca d liu.

[7, 14] cng nu ra mt gii php khc nhm t c tnh ng l s dng Merkle

Hash Tree (MHT). MHT l cy m cc l ca n l kt qu bm ca d liu ca tng

dng tng ng trong CSDL. V nh du node gc bng mt ch k in t chuNn.

N u km theo hai record hai bin kt qu, ta c th chng minh c kt qu tr v

y .

Cu trc MHT i hi phi lu tr km theo mt cu trc d liu chuyn dng

phc v cho query assurance. Mi cu trc ny thng ch p dng cho mt thuc

tnh, nh vy, trong trng hp CSDL c nhiu thuc tnh dng tm (searchable

attribute) i hi nhiu cu trc tng ng, iu ny c th lm tng ph tn lu

tr ti server. Maithili N arasimha [10, 21] ngh mt hng tip cn mi da

trn chui ch k in t. Khi , trong ch k ca mt record c bao gm ni dung

ca record lin trc n (c sp xp theo mt thuc tnh cho trc). N h vy, to

thnh mt chui lin tip nhau. Trong kt qu tr v, server tr km thm hai record

bin c th m bo c tnh ng v y . Hng tip cn ca [10, 21] khng

i hi phi tn thm nhiu khng gian lu tr trn server. Mi dng d liu ch cn

lu thm mt ch k. ln ca mt ch k thng thng l 128 byte, i vi RSA

(64 byte cho BGLS).



Tuy nhin, chi ph xy dng, to cc ch k v kim tra cc ch k i khi cng ng

k, thng chm hn t 100 1,000 ln so vi vic bm (hashing). [15] xut gii

php da trn Embedded Merkle B-tree (EMB) cho php m bo tnh ng, y

v mi. Vic m bo truy vn ch yu da vo cc php bm. T , c th gim bt

thi gian thc hin tnh ton ch k khi CSDL c thay i cng nh thi gian kim

tra kt qu tr v. [15] ng thi cng l gii php u tin gii quyt c y cc

vn ca query assurance.

Radu Sion [8] a ra mt hng tip cn mi cho php m bo tnh y i vi

kt qu tr v t mt tp cc cu truy vn cn c thc hin (batch of queries).

Hng tip cn ny xy dng mt giao thc da trn vic m rng giao thc ringer.

Da trn cc challenge-token, gi km theo, mt cch ngu nhin, xen k vi cc cu

truy vn cn thc hin, client bit trc kt qu ca nhng cu truy vn ny v so

snh n vi kt qu tr v t server. N u trng khp th m bo kt qu tr v t

server y .

1.4 Nhn xt Phn trn ca ti liu trnh by mt cch tng quan nhng nghin cu v nhng kt

qu hin ti trong ODBS. Cc kt qu ny c tm tt theo dng cy phn ph lc.

Qua , ta c th rt ra mt s nhn xt nh sau:

- Vic m bo data confidentiality c th d dng t c bng cch m ha

d liu trc khi thc hin outsourced.

- Vic m bo user privacy/data privacy trn d liu m ha c rt nhiu

nghin cu trn cc dng d liu khc nhau (XML, RDB) v t c

nhng kt qu rt kh quan c th ng dng c vo thc t.

- Vic m bo query assurance trn ODB. D hin nay c nhiu nghin cu

nhm m bo query assurance tuy nhin kt qu t c vn cn mc hn

ch so vi cc kt qu t c cc lnh vc khc. Cc nghin cu hin nay

c th p ng c tnh ng, tnh y v tnh mi trong vic thc hin

cc cu truy vn. Tuy nhin, hu nh cc cch tip cn hin ti vn cha cp



trc tip n vn query assurance trn CSDL XML. Do tnh cht c th

ca mnh, CSDL XML i hi cn phi c mt s iu chnh c th m

bo query assurance.

Qua nhng ni dung tm hiu trn, chng ti c ra mt s hng nghin cu

tip theo nh sau:

1. Cc n lc nghin cu nhm xy dng cc giao thc cho php che du ngi

dng trong vic khai thc thng tin (nh danh, truy vn ci g, uc tr ci g)

i ngc li vi nguyn tc khng th ph nh trong cc h thng. c bit l

i vi cc h thng thng tin mt, c tnh nhy cm cao, c th to c s cho

cc ti phm tin hc c nhng hnh ng xu. N n chng xy dng mt giao

thc va m bo tnh ring t m vn c th, khi cn thit, chng thc c ai

ly thng tin g? [1]

2. Hu ht cc nghin cu hin nay ch tp trung gii quyt cho m hnh DC-UP.

Mc d [1] trnh by mt giao thc ton din (extreme protocol) h tr m

hnh DC-UP-DP, nhng giao thc ny i hi phi c mt ngi trung gian tin

cy (trusted third-party server) K c th chuyn i m hnh DC-UP-DP

sang tr li DP-UP. Vic nghin cu loi b K cng l mt vn ng

c quan tm. [1]

3. Cc gii thut h tr oblivious operation (insert/delete) vn cn mt s im

cha hon thin. Gii thut insert cha h tr cy c bit nh: SH-tree, UB-

tree, R+-tree, kd-tree. Gii thut delete ban u c th h tr cc cy ny, tuy

nhin nu cu trc cy cho php cc under-full node, th phin bn hiu chnh

ca n ch h tr B+-tree [3, 22]. Mt vn khc cn quan tm l cc gii

thut ny c chng minh l m bo tnh privacy trong trng hp tn sut

truy cp cc node l phn b u. Trong khi, th gii thc, tn sut ny l

khng u v c s chnh lch kh ln v tn sut gia cc node [4].



4. Chin lc thc thi cu SQL trn d liu m ha ca Hacigm vn cn nhiu

l hng bo mt [6]. Vic nghin cu v khc phc vn ny vn l mt iu

ng c quan tm.

5. m bo tnh query assurance i vi kt qu tr v t server mi ch dng

mc x l cc cu truy vn n gin [7, 8] v ch h tr m hnh DC-UP.

c th thc thi cc cu truy vn cp nht d liu v cc cu truy vn phc tp

hn i hi phi cng sc hn na [8].

Trong cc hng nghin cu va nu: (1) c nghin cu v pht trin rt nhiu,

p dng tt vo thc t. (2) l mt vn rt kh khn, hin ti hu ht cc giao

thc u trnh m hnh ny do tnh phc tp ca n. Xt thy trong thi gian gii hn,

cng nh vn cn thiu cc kin thc cn thit v bo mt v ODB; mt khc vn

ny hu nh khng lin quan n CSDL XML nh nu trong ti nn ti liu ny

s khng cp n. (3) (4) ch l nhng kha cnh rt nh v hu nh c gii

quyt. (5), nh trnh by, tuy c nhiu nghin cu nhng kt qu t c vn

cn nhiu hn ch, mt khc cha c nghin cu no v query assurance lin quan

n CSDL XML.

N h vy, trong phm vi ca mnh, ti liu ny trnh by mt hng tip cn nhm

gii quyt vn query assurance trong CSDL XML. Phn tip theo ca ti liu s

trnh by chi tit hn v cc kt qu lin quan trong lnh vc query assurance.



Chng 2

CC NGHIN CU LIN QUAN

2.1 Khi nim N h trnh by, query assurance l mt yu cu bo mt cn c quan tm trong

hu ht tt c cc m hnh ca ODBS. Query assurance c th c nh ngha thng

qua ba tnh cht cn c tha mn, bao gm: tnh ng, tnh y v tnh mi.

Vic gii quyt trit cc vn ca query assurance vn cn l mt bi ton kh,

i hi nhiu cng sc hn na. Hin nay, hnh thnh cc hng tip cn khc nhau

gii quyt vn ny, bao gm:

- S dng ch k in t (digital signature) chng thc tng dng d liu tr

v t server l ng n, khng b thay i bi server hay thay i trn ng

truyn [7]. Phng php ny ch c th m bo tnh ng m khng th m

bo hai yu cu cn li. Mt s nghin cu gn y m rng vic s dng

ch k in t th gii quyt c tnh y [10, 21]. Tuy nhin, n vn

cha th gii quyt c yu cu th ba (tnh mi) ca query assurance.

- S dng cc cu trc d liu chuyn bit gii quyt c bi ton v tnh

ng v tnh y . Merkle Hash Tree (MHT) l mt cu trc kh in hnh

ca khuynh hng ny [11, 14].

- p dng mt s kt qu trong bi ton tnh ton phn b [13] gii quyt cc

yu cu t ra. Mt kt qu ca hng ny l s dng m hnh challenge-

response m bo tnh y trong vic x l tp cc cu truy vn (batch of

queries). u im ca hng tip cn ny l c th x l c cho dng cu

truy vn bt k [8]. Tuy nhin, hng tip cn ny, nh trnh by, ch c th



p dng cho vic x l tp cc cu truy vn do khng ph hp trong vic x

l cc cu truy vn n l.

- Da vo tnh c th ca d liu, cng nh tnh chuyn bit ca cc cu truy

vn pht trin mt giao thc ring gii quyt cc yu cu ca query

assurance. Truy vn d liu m ha da vo cc t kha (keyword) l mt

v d [12].

Phn tip theo ca ti liu s trnh by chi tit hn v cc hng tip cn ny.

2.2 Hng tip cn dng ch k in t Vic s dng ch k in t chng minh tnh ng ca d liu l mt gii php

ang c s dng hin nay [7]. Trong m hnh unified client model, do ch c duy

nht mt Client ng thi l DO, nn vic s dng ch k in t c th c thay

th bng hm bm mt chiu khng th o trong thi gian tuyn tnh [8].

Vic chng thc d liu c th c thc hin nhiu cp khc nhau, granularity.

C th thc hin chng thc trn mt bng (ton b quan h), mt ct (thuc tnh ca

quan h) hay mt dng d liu (record). Vic chng thc cp bng i hi ton

b d liu ca bng phi c tr v mi c th thc hin chng thc c. iu ny

l khng th kh thi, v hu ht cc cu truy vn d liu ch tr v mt phn (mt s

dng) ca bng m thi. iu ny cng xy ra tng t nu thc hin vic chng thc

cp ct. V vy, vic chng thc cp dng c th c xem l mt chn la

tt nht1. N h vy, mi dng, ngoi cc d liu ca quan h, cn cn c lu tr

thm thng tin v ch k ca dng ny.

Vic thit k mt giao thc chng thc cn phi ch n cc yu t sau [7]:

- Tnh ton ti client: chi ph tnh ton ti client xc nh tnh ng ca dng

d liu.

- Bng thng ng truyn n client.

1 Mt gii php khc l s dng vic chng thc cp trng (field). Tuy nhin, iu ny s dn n s qu ti v mt lu tr cng qu ti v tnh ton trong vic chng thc (do thi gian kim tra ch k in t cng kh ln).



- Tnh ton ti server: bao gm vic truy sut, tr v cc thng tin dng kim

tra tr v cho cu truy vn.

- Tnh ton i vi Data Owner: chi ph tnh ton cc thng tin dng kim tra

trc khi lu tr vo CSDL.

- Yu cu khng gian lu tr trn server.

Trong , ba yu t u l cn c ch nhiu hn c [7]. Tuy nhin, i vi CSDL

ng (dynamic outsourced database) th cng cn thit phi xem xt n yu t th t

khi thc hin cp nht d liu. Yu t th 5 hu nh khng qu quan trng do cc

thit b dung lng ln ngy cng r.

M hnh ch k in t c chn ph bin hin nay l RSA vi chiu di ca ch k

l 1024 bit (theo nh gi th RSA 1024 c th an ton trong vi thp k ti). Tuy

nhin trong trng hp s lng dng d liu tr v ln th dn n vic lng ph v

mt bandwidth cng nh thi gian tnh ton ti server chng thc d liu. Mt gii

php c p dng l s dng m hnh Condensed-RSA. Condensed-RSA l mt m

hnh ch k in t bao gp. Gi s c tp t message {m1,,mt} vi tp ch k tng

ng {1,, t), ch k Condensed-RSA c tnh bi: 1,t = i i (mod n) , i = 1..t

Khi vic kim chng ch k 1,t tng ng vi vic kim chng t cha k i ring l. Mt li im khc l kch thc ca Condensed-RSA bng vi kch thc

ca mt RSA chuNn. N h vy, thay v tr v ton b cc ch k ca tng dng ring

l, server ch cn tnh ton ch k Condensed-RSA v tr v cho client c th thc

hin vic chng thc d liu.

Maithili v G.Tsudik [10, 21] a ra mt hng tip cn mi m bo tnh an ton v

hiu qu cho cc cu truy vn c s m khng i hi thm bt k mt cu trc d

liu phc tp no. Hng tip cn ny gi l Digital Signature Aggregation and

Chaining (DSAC). t c tnh ng, [10, 21] s dng li cch tip cn cp



trong [7]. Do , phn tip theo ca ti liu ch trnh by bin php t c tnh

y .

Tnh y Tnh y t c bng cch xy dng mt mi lin kt bo mt gia cc ch k

ca tng record, gi l signature-chain. Chui lin kt ny t c bng cch thay

i cch tnh ch k ca tng record nh sau:

Sign(r) = h(h(r)||h(IPR1(r))|| h(IPRl(r)))SK

Trong , h() l hm bm m ha (nh SHA), IPRi l record lin k trc dc theo

chiu i, l l s chiu c th thc hin truy vn, SK l kha ring ca data owner.

Cc record lin k trc ca mi record c xc nh bng cch sp xp quan h R

theo cc chiu c th truy vn, nh hnh sau:

Hnh 2.3. Sp xp quan h R theo cc chiu truy vn.

Cc record lin k trc ca R5 ln lc l R6, R2, R7. Khi , ch k ca R5 c

tnh nh sau: Sign(R5) = h(h(R5)||h(R6)||h(R2)||h(R7))SK.

Cch thc chng minh tnh y , v mt nguyn tc, l tng t nh phng php

dng trong AuthDS. N gha l, chng minh mt kt qu tr v ca mt cu truy vn,

server tr v chui ch k hai record bin ca kt qu cng vi cc chui ch k ca

hai record cn bin kt qu. T c th chng minh c kt qu tr v l y .

2.3 Hng tip cn s dng cu trc d liu c bit Mt hng tip cn khc nhm tha mn cc yu cu ca Query Assurance l s dng

cc cu trc d liu c bit lu tr cc thng tin gip cho vic m bo tnh ng

cng nh tnh y .

tng ca hng tip cn ny c th hin nh sau [14]:



Hnh 2.4. M hnh chng minh truy vn.

Ch k tng hp (Summary-signature) c tnh ton quy t di ln theo phng

php bm trn ton b cy ch mc (B-tree) i vi ton b cc record trong mt

relation. Gi tr ny c k bng sk0. Cc truy vn ca user c publisher thc thi

tr v kt qu cng vi mt cu trc d liu khc gi l verification-object, c dng

chng minh l kt qu tr v l ng v y .

Hng tip cn ny c mt s c tnh nh sau [14]:

- User ch cn tin cy vo kha pk0 ca owner. Owner ch tnh ton li ch k

tng hp khi thc hin cc cp nht, thay i trn CSDL. V vy kha ring sk0

hon ton c th c bo v offline, iu ny trnh c s tn cng t mng.

N goi ra, cn c th s dng phn cng hin thc kha ny.

- User khng cn thit phi tin cy cc DO. V vy, khi c s c vi mt

publisher no , th hu qu ch l mt i dch v cung cp bi publisher ny.

- Kch thc ca verification-object l tuyn tnh vi kt qu tr v ca cu truy

vn v tng quan logarit vi kch thc ca CSDL.

- Verification-object m bo rng kt qu tr li l chnh xc v y .

- Chi ph tnh ton ch k tng hp, verification-object (VO) v kim tra VO l

chp nhn c.

Mt cu trc in hnh ca hng tip cn ny l Merkle Hash Tree (MHT) [11]. Cy

MHT c xy dng da trn tp gi tr x1, x2,, xn c sp th t ca mt thuc

tnh trong mt quan h. Mi l ca cy c mi lin kt vi mt gi tr xi s cha gi tr



h(xi), trong , h() l hm bm mt chiu, chng hn nh MD5, SHA-1. Cc node

trong ca cy s cha gi tr bm ca hp tt c cc gi tr ca cc node con ca n.

Gi s v c hai node con l v1 v v2, th gi tr ca v l h(v1||v2). Cui cng, gi tr ti

node root s c xc thc bi ch k in t.

Tnh ng (correctness) chng minh tnh ng ca kt qu truy vn, server tr v VO cha co-path ca

node tr v. co-path ca mt node l tp cc node khc t c th tnh ton c

gi tr ca node root. Do ni dung ca root c k, nn so snh vi kt qu tnh

c, server c th chng minh c cu tr li ca mnh l ng. cy MHT di

y, khi kt qu truy vn node 5, server s tr v thm node h1 v h34. T hai node ny

ta c th d dng tnh c root nh hnh v sau.

h1 h2 h3 h43 5 6 9

h34 = h(h3||h4)h12 = h(h1||h2)

root = h(h12||h34)

Hnh 2.5. Binary Merkle Hash Tree.

Trong kt qu tr v {5}, server tr km thm {h1, h34, sign(root)}. Nh vy, client c th tnh c h12 = h(h1||h{5}); root = h(h12||h34). So snh root vi ch k ca root, client c m bo kt qu tr v l ng.

Tnh y

Trc tin ta xt trng hp server tr li cu truy vn l khng c mt reocrd no

trong CSDL tha iu kin truy vn. Khi , server phi chng minh c iu ny,

gi l cc empty proofs. iu ny c th thc hin bng cch tr v co-path ca hai

node k nhau sao cho khong tr cn truy vn nm trong khong gi tr ca cc node

ny.

Tnh y ca cu tr li t c bng cch gi km theo cc empty proofs cho cc

node l ln cn hai node bin nm trong kt qu tr v ca cu truy vn.



Mt gii hn ln ca AuthDS l i hi phi bo tr mt cu trc d liu phc tp bn

cnh d liu thc s. Cu trc ny cn phi c tnh ton y trc khi a ln

server. Mi thay i cp nht d liu i hi phi tn chi ph khng nh cp nht

li cc s liu trong cu trc [8, 10, 21]. Bn cnh , c th m bo tnh ng

cng nh y ca cy truy vn theo khong (range-query) i hi phi xy dng

mt cu trc cho tng thuc tnh, theo tng trt t sp xp (sort-order) [10, 21].

2.4 Hng tip cn Challenge Response. Radu Sion [8] a ra mt giao thc m bo tnh ng v tnh y ca cc

cu truy vn dng bt k da trn vic m rng giao thc ringer trong tnh ton phn

b (distributed computation).

Giao thc ringer trong tnh ton phn b c a ra trnh gian ln trong vic tnh

ton cc bi ton con. Giao thc ringer c nhiu bin th nh basic ringer, bogus

ringer v hybrid ringer (magic ringer). Xt bi ton sau: tm ra chui text ban u t

chui text m ha bng gii thut DES. Cc trm lm vic (working station) s pht

sinh ra cc chui bng phng php t hp, sau p dng gii thut DES trn chui

ny, nu kt qu trng khp vi chui m ha th chui pht sinh chnh l chui text

ban u cn tm. tng ca basic ringer trong [13] c th c tm tt nh sau:

- supervisor chn ra mt gi tr ngu nhin xi trong min tr Di m trm lm

vic i tnh ton trn n, sau tnh yi = DES(xi). Sau , supervisor gi cho

trm i gi tr yi v y. Trong , y l chui m ha cn gii m.

- Trm i nhn c min tr Di v thc hin tnh ton, nu vic tnh ton l

hon chnh (complete) th chc chn trm i s tm ra c gi tr ca xi hay x (y

= DES(x)) . Khi tr kt qu v cho supervisor, l xi (c th c c x). Khi

supervisor c th bit c thc s trm i thc hin y cng vic.

hin thc, [8] a ra mt cch t chc d liu nh sau. Gi s S l d liu

outsource. S c phn thnh nhiu on Si, mi Si s c xc nh bi mt hm

bm dng m bo d liu l chnh xc, khng b thay i. Gi tr ny gi l



identity-hash, c s dng chng thc cc cu truy vn identity query, l

nhng cu truy vn tr v ton b d liu trong Si.

Qu trnh thc thi cc cu truy vn nh sau:

- Trong tp cc query Q {Q1, Q2, Q3, .. Qa} cn thc thi, querier s chn vo cu

query Qx ti mt v tr bt k, querier bit trc kt qu tr v ca Qx. ng

thi, querier tnh ton mt challenge token bng {H(||(Qx)), }. Trong , H() l hm m ha mt chiu bt kh o (non-invertible one-way hashing

function); : l mt gi tr duy nht theo thi gian (timestamp) m bo challenge token l duy nht; (Qx) : l kt qu tr v c bit trc bi querier.

- N him v ca server l thc thi cc cu query v xc nh c gi tr x bng

cch p dng hm H() cho cc kt qu. V gi km x v cng vi kt qu ca

cc truy vn.

N u ch s dng mt challenge token th c th dn n trng hp server sau khi

tm c challenge token ri th ngng thc hin cc cu truy vn khc (hoc thc

hin khng y ). [8] cng trnh by mt s phng php khc phc vn .

u tin l c th s dng nhiu challenge token thay v mt. Tuy nhin v mt hnh

thc th cch thc ny thc ra vn khng th gii quyt c vn cn bn. N gha

l, vn c trng hp server sau khi nhn din c y cc challenge token th

ngng thc hin cc query cn li. ng thi vic pht sinh nhiu challenge token

tht s l mt gnh nng tnh ton cho cc thin-client (querier) nh cc thit b di

ng (mobile client). Mt gii php khc c ra l s dng cc fake token. Fake

token l mt challenge token gi, ngha l querier pht sinh ra ngu nhin ra mt

challenge token m khng cn quan tm n kt qu tr v t server. Trong tp cc

challenge token c gi n server s bao gm r challenge token thc s v f token

gi. Hai tham s r, f l c th thay i theo tng tp truy vn. V vy, server khng th

no c th xc nh c ton b s challenge token c gi n. Do , bt buc



server phi thc hin y cc cu query c th tm ra c cc challenge token

tht s.

N hng phng php trn ch tp trung cho gii quyt cc cu truy vn c d liu

(select query) ch cha gii quyt vn cho cc cu truy vn cp nht/thm mi d

liu (update/insert query). Vic cp nht d liu thc hin bng cch c ton b

on d liu c cha dng cn update (hay s cha hng insert). Sau thc hin cp

nht d liu, tnh ton li identity hash ri cp nht tr li server. Tuy nhin, vic

x l tnh hung cp nht d liu vn ch l bc khi u [8].

2.5 Hng tip cn da vo c th ca bi ton D dng nhn ra rng, c th xy dng c mt giao thc m bo cc yu cu

ca Query Assurance trong trng hp tng qut l mt cng vic cc k kh khn.

Do vy, mt hng tip cn mi gii quyt bi ton ny mt cch tng i hon

chnh l i vo gii quyt n trong tng trng hp d liu, truy vn c th..

Radu Sion, Bogdan Carbunar [12] trnh by mt giao thc dng truy vn cc d

liu m ha da trn t kha c th m bo cc yu cu privacy cng nh query

assurance.

Cc ti liu c lu thnh nhng vng ring l (file), mi ti liu s c mt s lng

t kha (keyword) nht nh. S cc t kha cho mi ti liu c lit k trc khi

c a ln server. Bi ton t ra l c th thc hin truy vn ti liu da v mt

hay nhiu t kha cho trc.

Mi ti liu c gn vi mt con s nh danh di ngu nhin, duy nht, khng lin

quan n ni dung ca ti liu . Do s lng t kha c xc nh trc, ng

vi mi t kha ny, xy dng mt tp cc nh danh ca ti liu c cha t kha, gi

l KDS (keyword document sets). Cc KDS c th c t ti chnh cc querier. Hay

c th c t server. Lc ny, cc KDS cn c m ha v c chng thc.

Mi KDS c th c m ha bi mt kha khc nhau. Kha ny c th c tnh

nh sau: Keyi = H(key || ki), trong : H() l hm bm mt chiu; key : l kha dng

chung; ki l t kha tng ng vi KDSi. trnh trng hp server c th loi b



mt entry trong KDS, mi KDS cn c b sung thm mt gi tr dng kim tra,

gi tr ny c tnh ton nh sau: Hcheck = H(d4||H(d3||H(d2||H(d1||0)))), vi gi thit

KDS = {d4, d3, d2, d1}.

Mt phng thc lu tr cc KDS l di dng ma trn, ct l cc nh danh ca

tt c ti liu, dng l tt c cc t kha, mi cell trong ma trn s nhn gi tr 0 hay 1

ty vo ti liu c cha t kha hay khng. Ma trn ny, gi l ma trn C, s qua

mt php bin i tr thnh C nh sau:

Ci,j = last_bit(F(ki , Rj , Cij))

trong : F l hm bitwise pseudo-random function, Rj l mt s ngu nhin pht sinh

bi hm sinh s ngu nhin G vi mt random seed R c nh.

Cu truy vn query = {k1, k2,, kq} c thc hin bng cch gi yu cu n server

ly v cc hng tng ng vi cc t kha. Querier ln lt pht sinh li cc gi tr

Rj , v thc hin tnh li ma trn Cij nh sau: nu last_bit(F(ki , Rj ,0)) = Cij th Cij = 0,

ngc li Cij = 1. Sau khi tnh li c ma trn C, querier hon ton c th xc nh

chnh xc c danh sch cc nh danh ti liu cn tm. T cc nh danh, querier c

th yu cu server tr v ng cc ti liu yu cu.

Do querier bit c chnh xc danh sch cc nh danh ti liu cn ly, nn, mt

cch hon ton t nhin, c th kim tra c tnh y ca kt qu tr v. m

bo tnh privacy, c th s dng cc PIR-like protocol.

2.6 Bo m truy vn cho d liu dng cy Mt hng tip cn tip theo da trn k thut ca Lin v Candan [2] trong vic m

bo tnh ring t . [16] m rng phng php ny cho php m bo ba yu cu ca

query assurance, vi ni dung c bn nh sau.

- m bo tnh ng, mi record u c ch k cho ring n (RSA). Trong

trng hp cn so snh tnh ng ca nhiu record, c th s dng m hnh

Condensed RSA.



- Tnh c m bo mt cch t nhin, do querier yu cu mt s lng

nht nh node. Khi , cn c vo s lng node yu cu v s lng node do

server tr v, hon ton c th tha mn c yu cu ny. N goi ra, m

bo y chnh l nhng node yu cu, trong d liu ca m ha ca mi node,

ta lu tr nh danh (nodeID) ca chnh node . Do tp cc nh danh node

yu cu l bit c, so snh vi cc nh danh ca cc node do server tr v

c th chng minh c y thc s l cc node mong mun.

- Tnh mi c tha mn bng cch bng cch b sung vo mt s thng tin

nh sau:

o Mi node cha thm mt gi tr thi gian (timestamp) cho bit thi gian cp nht ca node ny.

o Node cha lu ton b gi tr thi gian (timestamp) ca cc node con.

o Gi tr timestamp ca node gc l ph bin cho tt c cc querier.

N h vy, khi qu trnh duyt i t node gc xung cc node con, vi gi tr

timestamp bit trc, querier hon ton c th chng thc ni dung ca

node gc l mi. Cn c gi tr timestamp ca cc node con c lu tr ti

node gc, querier cng xc nh c tnh mi ca cc node con ny. V c

nh vy, lan truyn ti node l c th chng minh tnh mi ca node ny.

Nhn xt

Phng php tip cn ca [16] va m bo c tnh ring t (user privacy v data

privacy) do tn dng phng thc redundancy data access v node swapping ca Lin

v Candan [2, 4], v c th m bo c query assurance. Tuy nhin hng tip cn

ny ch ph hp cho cc cu trc d liu dng cy tm kim (search tree) nh B-Tree,

B+Tree, R-Tree,, cc cu trc ny c dng ph bin s dng lm ch mc

(index) cho cc d liu khc.



2.7 Nhn xt N goi tr trng hp ng dng cho bi ton c th c trnh by mc 2.5, cc

phng php khc, v mt bn cht, u p dng ch k in t hay ng dng tnh

cht khng th o trong khong thi gian tuyn tnh ca cc hm bm (secure hash)

chng minh tnh ng cng nh tnh y ca kt qu truy vn.

Hng tip cn ca Maithili, G.Tsudik [10, 21] v Prem Devanbu [14] cho php

chng minh c chnh xc kt qu tr v l ng v y . Tuy nhin, hin ti, cc

giao thc ny vn ch c th gii quyt cho cc cu truy vn ch c n gin khng

c cc hm bao gp (nh SUM, AVERAGE,). Mt khuyt im ca phng php

ny l ph thuc vo dng thc ca cu truy vn. i hi phi phn tch cu truy vn

thnh tng phn ring l c nhng tc v thch hp.

Hng tip cn ca Radu [8] c th p dng cho tt c cc loi truy vn, k c vic s

dng cc hm gp m [10, 14, 21] cha gii quyt c. u im chnh ca phng

php ny khng cn phn tch c php ca cc cu truy vn. T , c th trin khai

d dng hn. Tuy nhin, hng tip cn ny vn cn mt s iu cn xem xt nh

sau.

- Ch p dng cho tp cc cu truy vn, cha gii quyt cho trng hp thc thi

tng cu truy vn ring l, vn c s dng kh nhiu trong thc t. gii

quyt vn ny c th s dng cc hng nh sau: (1) s dng cc fake-

query km theo bin cu truy vn n thnh tp cc cu truy vn. Tuy

nhin, cch ny c th lm qu ti server, gim hiu nng ca ton h thng do

phi thc hin cc fake-query qu nhiu so vi cc truy vn thc s. (2) cc

cu query ring l c tp trung li ti mt trust-server v gi n server di

dng tp cc cu truy vn theo ng tinh thn ca gii php. Phng thc ny

hu nh khng kh thi do thi gian tr ca cu query trong thi gian ch i l

khng th chp nhn c. (3) l kt hp ca (1) v (2).

- Cha chng minh trit kt qu tr v l y . Xc sut server khng

thc thi hoc thc thi khng hon chnh i vi cu query cui cng l 33%



[8]. y l mt xc sut kh cao. iu ny phn no lm gim bt tnh tin cy

ca gii php.

Cc hng tip cn trn u c thc hin cho cc d liu dng quan h (relational

database). Do , c th p dng c trong CSDL XML cn phi c mt s thay

i nht nh.



Chng 3

D LIU XML

XML l mt dng d liu bn cu trc (semistructured data), dng cy (tree-

structured). n v lu tr thng tin ca XML l cc node v attribute. Cc node v

attribute phn bit thng qua tn v tm vc ca chng (chiu su ca cy, node cha).

D liu XML l dng vn bn c c. V vy, trc khi tin hnh outsource, ta cn

phi xc nh c cu trc lu tr ph hp vi cu trc d liu ca XML. iu ny

c bit quan trng, n nh hng rt ln n cc phng php s c p dng trong

x l truy vn v m bo truy vn.

3.1 M hnh lu tr Tng t nh RDB truyn thng, mi ti liu XML u c c trng bi mt lc

(schema) nh ngha mi quan h cha con gia cc node, s lng thuc tnh ca

ca mi node. V d nhin, lc ny c dng cy, gi l schema tree.

Mi node trong ti liu XML (xml element) tng ng vi mt t-node trong cy lun

l, mi thuc tnh ca xml element s tng ng vi a-node trong cy lun l. Hnh 6

v d v cy d liu lun l v cy cu trc rt ra t mt ti liu XML.

T cy cu trc, c th d dng chuyn i ti liu XML sang cc dng lu tr khc.

Ti liu ny trnh by hai phng php thng dng lu tr ti liu XML: dng

bng (table-based) v dng node (node-based).



Root

Customer Customer

Order Order

Code, 01 Amount, 5000 Code, 02 Amount, 10000

Name, Bob Name, Alice

t-node t-node

t-node

t-nodet-node a-node a-node

a-nodea-nodea-nodea-node

(A)

(B)

Root

Customer

Order

Cy cu trc ca ti liu XML

Cy d liu lun l

Name

Code Amount

a-node

t-node

Hnh 3.6. Cu trc cy lun l ca mt ti liu XML.

Trong cy d liu lun l v cy cu trc, mi node hnh ch nht gc trn i din cho mt node (element) trong ti liu XML. Cc node hnh ch vung gc i din cho mt thuc tnh (attribute) trong mt element ca ti liu XML.

3.1.1 Dng bng: Table-based T cy cu trc ca ti liu, c th chuyn i sang dng lc quan h theo cc

bc sau.

- Gn nhn (labeling) cc t-node cu trc sao cho mi node c mt gi tr nhn

duy nht.

- Mi t-node cu trc c chuyn thnh mt bng tng ng c tn l tn ca t-

node kt hp vi gi tr nhn. Cc a-node con ca t-node ny c chuyn

thnh cc ct ca bng. Mi bng b sung thm ct nodeid l nh danh ca

node trong bng d liu. N u t-node c cha, th b sung thm ct pnodeid tham

chiu n bng pht sinh t t-node cha.

T cy cu trc hnh 3.6.b, ta thc hin gn nhn cho cc node:



Hnh 3.7. Cy cu trc sau khi c gn nhn.

Sau , chuyn sang lc quan h nh sau.

Root_01(nodeid)

Customer_02(nodeid, name, pnodeid)

Order_03(nodeid, code, amount, pnodeid)

N goi ra, mi table cn c b sung thm mt s ct nh timestamp, sign, cc gi

tr ny c dng gip vic chng minh kt qu truy vn tr v sau ny.

u im Ti liu XML sau khi c chuyn i sang dng lc quan h t c

th p dng cc kt qu trc dng trong lc quan h. Ta c th p

dng bin php DSAC [10, 21] hay EMB Tree [15] c th m bo querry

assurance trong vic truy vn.

Khuyt im V pha ngi dng, CSDL c outsourced l ti liu XML, v vy cu truy

vn c thc hin thng thng l mt dng query trn ti liu XML (XPath,

XQuery,). Do , cn phi c mt bc chuyn i t ngn ng truy vn

ny sang ngn ng SQL bnh thng.

Mt vn cn c quan tm l: bn cht schema ca CSDL c th c thay

i ng bt c lc no. Mc khc, vic thay i schema ca ti liu XML l



kh linh ng. Tuy nhin iu ny dn vic thay i cu trc bng RDB tng

ng. iu ny c tc ng khng tt n d liu c lu tr (vic thm ct

d liu v mt bng c th dn n vic tnh ton li ton b cc ch k in

t, nu s dng phng php DSAC). M ha li ton b d liu. iu ny l

khng th trong trng hp d liu c outsourced.

Tuy cn tn ti mt s khuyt im, nhng trong trng CSDL XML khng thay i

v schema th vn c th p dng phng php ny c th tn dng c cc kt

qu c nghin cu tt trn CSDL quan h. Trong ti liu ny, chng ti cp

n mt hng tip cn khc da trn phng php lu tr d liu th hai: node-

based.

3.1.2 Dng node: Node-based Mt hng tip cn khc trong vic lu tr CSDL XML l lu cc t-node v a-node

ca cy d liu lun l.

Tng t nh phng php trn, u tin, cc node cu trc (bao gm c t-node v a-

node) u phi c gn nhn. Phng php gn nhn tng t nh trn (ch khc l

vic gn nhn bao gm c a-node). Khi , vic lu xung CSDL quan h s tn ti

hai bng d liu lu t-node v a-node c ni dung nh sau:

t-node(nodeid, xtype, datatype, nameid, pnodeid, lmaid, value) a-node(nodeid, xtype, datatype, nameid, pnodeid, sibid, value)

Trong 2:

- NodeID : l nh danh ca node.

- XType : dng phn bit cc loi i tng.

- Datatype : dng xc loi d liu

2 N goi cc thnh phn nh trn, ty theo cc gii thut chng thc khc nhau m cn b sung thm mt s cc thng tin khc vo t-node v a-node.



- NameID : nh danh ca tn ca node (t-node v a-node) . Tn ca mt node

c phn bit da vo ng cnh m tn xut hin. Mi tn s c nh

danh bi mt ch s duy nht trong ton CSDL.

- PNodeID: nh danh ca t-node cha ca t-node hin ti. Ch : i vi a-node,

pnodeid l nh danh ca t-node cha ca t-node cha ca a-node hin ti.

- LMAid: nh danh ca a-node tri nht.

- SibID: nh danh ca a-node anh em bn phi.

Vi dng thc lu tr nh vy, vic thay i schema (b sung/b bt mt thuc tnh)

ch n thun nh mt tc v insert/delete n gin, v ch nh hng n node hin

ti. Do , khng i hi thm bt k mt chi ph no khc m vn m bo c cc

yu cu bo mt t ra.

1. u im

Phn nh ng bn cht dng cy ca ti liu XML. Do , khc phc c

khuyt im ca phng php table-based, vic thay i cu trc ca ti liu

XML khng nh hng nhiu n ni dung lu tr hin ti. V ch nh hng

n node cn cp nht.

S dng c mt s kt qu nghin cu trc [2, 16] trong vic bo m

cc vn ca query assurance.

2. Khuyt im

Do tt c cc t-node, a-node c lu thnh nhng record ring l nn s

lng record c th tr nn rt ln so vi table-based. iu ny lm tng tnh

phc tp ca database.

N goi ra, cc bin php ch mc (indexing) trn RDB p dng khng my hiu

qu i vi d liu dng cy nh XML. Trong khi, cc phng php ch mc

chuyn cho XML vn cn trong giai on pht trin.



3.1.3 Nhn xt Trong hai phng php lu tr cp nh trn, phng php table-based chuyn

i ti liu XML sang dng table ca RDB truyn thng. T c th p dng li

c cc bin php bo m query assurance [10, 11, 14, 15, 21]. N hng phng

php ny c mt khuyt im kh ln l: khi cu trc ca ti liu XML thay i bng

cch b sung mi mt node mi hon ton (hay mt attribute mi) th cu trc ca

cc bng d liu s b thay i theo. iu ny i hi mt khi lng tnh ton kh

ln bm bo cc cu trc c dng trong m bo truy vn (bao gm vic k li

cc record, m ha d liu, xy dng li cc chui ch k hoc cc cu trc index

phc tp khc,)

Trong phm vi ca ti liu ny, chng ti s p dng phng php lu tr node-

based, ng thi ngh mt cu trc ch mc (indexing structure) chuyn dng cho

ti liu XML. T , nhng km mt s thng tin chng minh tnh ng, tnh y

v tnh mi.

3.2 Ch mc cho ti liu XML Ch mc l mt khi nim ht sc quan trng trong CSDL. N gip tng tc ng k

hiu sut truy vn d liu so vi phng php tm kim tun t c in, trong trng

hp l tng, tm kim s dng ch mc nhanh hn tm kim tun t l N/log2N ln.

i vi CSDL quan h (relational databases), ch mc c p dng ht sc c hiu

qu v ph bin trong hu ht cc RDBMS. Cc cu trc ch mc thng dng l :

bng bm (hash table), bitmap v cc cu trc ch mc dng cy.

i vi CSDL bn cu trc dng cy nh CSDL XML, hin ti c nhiu nguyn cu

trong vic xy dng ch mc ph hp[17, 18]. Trong phm vi ca mnh, ti liu ny

khng i chi tit vo cc phng php ch mc cho ti liu XML v cng khng c

nh so snh chng, m ch a ra mt cu trc ch mc cho ti liu XML, m qua

c th nhng vo mt s thng tin nhm phc v cho mc tiu m bo query

assurance.



Trong cc phng php ch mc, phng php ch mc dng cy c s dng kh

ph bin. Trong in hnh l B+Tree c p dng rt thnh cng trong vic to

ch mc trn cc RDBMS hin ti. Vi c tnh ca mnh, B+Tree c th to ch mc

cho mt s lng ln cc record m phc tp khng cao (nu cy B+Tree c

fanout l 100, chiu cao l 4 th c th qun l c 100x100x100 = 1.000.000

record).



Chng 4

M BO TRUY VN

4.1 Phng php m bo truy vn (Query assurance) nhm mc tiu chng minh vi ngi dng kt

qu truy vn tr t server l: ng, , mi. Tnh ng c th thc hin kh d dng

thng qua ch k in t. Chng minh tnh ca kt qu truy vn thng da vo

tnh cht ca tng loi query.

Xt hai loi truy vn: truy vn theo vng (khong gi tr tha mn) v truy vn theo

im (bng mt gi tr c th). Truy vn im thc cht l dng suy bin ca truy vn

vng vi hai cn tin n bng nhau. N h vy ch cn xem xt i vi truy vn vng.

Xt mt truy vn theo vng i vi cn l LB v UB. Kt qu tr v l cc record

tha mn.

S = { R | R LB, R UB }

N u cc record R c m bo l sp xp tng dn (hoc gim dn), chng minh

kt qu tr v l y , server ch cn tr v hai record nm hai bin :

S = S {RL | RL = max(Ri), Ri < LB, i} {RU | RU = min(Rj), Rj > UB, j} N u server c th chng minh c gia RL v RU ch c cc record tr v l c th

chng minh c kt qu l hon ton y .

N h vy, cc record cn c sp xp theo th t v th t ny c th chng minh

c. Mt cch n gin t c iu ny l sau khi sp xp R theo th t, ta tnh

gi tr bm nh sau:

S = h(h(R0) | h(R1) | h(R2) |.| h(RN))SK

Trong : h l hm bm bo mt (security hash) nh SHA1, MD5.



Sau thc hin k ln gi tr bm va tnh c bng gii thut m ha bt i xng

(nh RSA). Trong kt qu tr v, server tr v km theo cc h(Ri) cn li v gi tr S.

Client hon ton c th tnh li bm ca cc record theo quy tc trn v thc hin

kim chng vi S bng kha cng cng ca gii thut k.

4.2 Nested B+ Tree N h trnh by phn trn, phng php p dng chng minh tnh y cn

bn da trn dy th t cc record v ch k ln dy th t ny. iu ny c th t

c bng mt cu trc ch mc ph hp vi cch thc lu tr d liu c trnh

by mc 3.1 ca ti liu ny.

Xt mt ti liu XML, cc node c nh v bi path, tc ng i t node gc n

node hin ti. Cc truy vn trn XML thng thng c xc nh path. N h vy, ch

mc XML, ngoi gi tr ca node, cn phi cha thm thng tin v path ca node.

Quay li phng php lu tr c cp phn trn, gi tr nameid l duy nht

i vi mi node cu trc, do c th c s dng tng ng vi path. N h vy,

mi node cn c ch mc trn b hai thuc tnh (nameid, value).

Tuy nhin, ngoi vic truy vn theo gi tr, vi bn cht cha/con ca d liu dng cy

XML th yu cu truy vn cc node con khi bit c node cha l thng xuyn.

chng minh completeness cho cc truy vn ny, cn b sung thm ch mc ca b

ba gi tr (nameid, pnodeid, value) cc record c sp xp theo node cha.

Ta c th xy dng hai cy ch mc ring l cho hai b gi tr trn. Tuy nhin, iu

ny c th dn n mt s vn phc tp trong vic cp nht d liu, chng minh

truy vn v lng ph ni lu tr (do c trng thuc tnh u l nameid).



... ...

NameTree

ParentTree ValueTree

(nam

eid)

(pno

deid,

value

)

(value

)

Hnh 4.8. Cu trc NB+Tree.

S kt hp ca ba loi cy NameTree, ParentTree v ValueTree cho php sp th t ton b cc attribute v cc element ca ti liu XML theo hai th t: (nameid, value) v (nameid, pnodeid, value), m bo cho vic truy vn nhanh chng cng nh kh nng m bo truy vn trn ti liu XML.

m bo c yu cu trn, c th s dng kt hp cc cu trc cy nh sau. Xy

dng mt cy B+-Tree vi kha so snh l nameid, gi l NameTree. Ti node l ca

NameTree cha gc ca hai cy B+Tree theo kha ln lt l (pnodeid, value) v

(value). Hai cy ny c tn l: ParentTree v ValueTree. Tp hp ba loi cy ny to

thnh mt cu trc d liu, gi l Nested B+Tree, cho php lp ch mc cho ti liu

XML trn hai b gi tr (nameid, pnodeid, value) v (nameid, value).

N goi ra, vic phn b ca d liu cng nh hng mt phn kh ln n cu trc

cy. N u d liu b tp trung vo mt vng nht nh c th lm qu trnh tch node

din ra thng xuyn, lm cho hiu sut s dng ca cy B+ khng cao. hn ch

iu ny, cy B+ a vo thao tc ti phn b (redistribute) d liu cc node gc.

Trong cy N B+, ngoi c tnh trn, cc kha (key) cng c thc hin ti phn b

trc khi thc hin vic tch node hay hp nht (merge) node.

Mt hng tip cn khc, l s dng mt cu trc ch mc a chiu (multi-dimension

index) to ch mc cho ti liu XML da trn b bn thuc tnh (nameid, prefixid,

pnodeid, value) nh h cy R (R-Tree, R+Tree, R* Tree, X-Tree,). Tuy nhin, cc



cu trc ch mc ny khng m bo c th t tng dn ca cc record (hoc ch

m bo cho mt thuc tnh) v vy khng ph hp cho vic chng minh

completeness trong truy vn.

Nested Merkle B+ Tree

N M+Tree c th chng minh kt qu truy vn, cn nhng km mt s thng tin

tng t nh cy Merkle Hash Tree (MHT) vo cy N B+Tree nh sau: gi H(node) l

bm ca mt node bt k thuc N B+Tree, khi h(node) c tnh nh sau:

- Node l node l ca ValueTree, ParentTree: H(node) = h(A(node))

- Node l node l ca NameTree: H(node)=h(H(R(ParentTree))||H(R(PrefixTree)))

- Node l node ni : H(node)= h(I H(Childi(node))) , i = 1..s con ca node. - Node l gc ca NameTree: H(node)= h(||I H(Childi(node))) , i = 1..s con ca

node.

Trong : h l hm bm bo mt tha tnh khng ng v khng th o trong thi

gian tuyn tnh (collusion-free and non-invertable) nh SHA1, MD5. A(node) l t-

node hoc a-node lin kt vi node l ny. R(tree) l node gc ca tree. Childi (node)

l node con th i ca node. l mt gi tr duy nht theo thi gian (timestamp), gi tr no c cung cp ti tt c cc client khi c s thay i. Sau , thc hin k ln ni

dung ca R(PrefixTree) bng gii thut ch k s.

N h vy, vi vic p dng tng ca MHT ln N B+Tree, ta c N MB+Tree

(Nested Merkle B+ Tree), va dng lm ch mc trong truy vn va c dng

chng minh truy vn trn ton d liu XML.

Phn tip theo ca ti liu trnh by cch thc vn dng N MB+Tree trong vic thc

hin truy vn cng nh chng minh kt qu tr v.

4.3 Tc v chn Php chn (Selection) l cu truy vn c x dng thng xuyn nht. i vi RDB,

l pht biu SELECT trong SQL. Trong XML, c nhiu ngn ng c dng truy



vn nh XPath, XQuery. Ti liu ny minh ha cho mt vi dng cu truy vn XPath

thng dng.

Xt mt ti liu XML c cu trc nh sau:

Hnh 4.9. Cy cu trc ca mt ti liu XML

Cc ch s nh k bn cc node l nameid ca node . Ti liu s kho st qua mt

s dng truy vn thng gp.

4.3.1 Dng truy vn lin quan mt node, iu kin n L dng truy vn n gin nht, v d /Customer/Order/Item[@name=TV]: tm tt

c cc hng mc c tn l TV. Theo quy tc gn tn, ta c nh danh tn ca thuc

tnh name ca node Item l 12. N h vy, tr li cu truy vn ny, thc hin tm trn

N MB+Tree vi kha tm kim (nameid=13, value=TV). Kt qu tr v cc a-node

Name_13 ca Item_8. T cc a-node, c th d dng xc nh c cc t-node Item_8

tng ng. Sau , ta c th ly c cc a-node khc (nh price_14, qty_15).

Tnh ng v Tnh y

N goi cc a-node Name tha iu kin, server tr v thm hai a-node bin ca tp kt

qu, v cc bm ca cc node ln cn tnh bm ca node cha, ng thi tr

thm gi tr bm ca cc node anh em ca node cha. Cc kt qu ny gip cho client

c th tnh ngc li c gi tr bm ca nt gc.



Ti nt gc, t gi tr bm tnh c kt hp vi temp thi gian lu tr, client c th

kim tra vi ch k ca nt gc. Do c tnh mt chiu, bt-kh-o ca cc hm bm

c p dng nn c th chng minh tnh ng (correctness).

Do cc record c sp xp theo th t tng dn theo b thuc tnh (nameid, value),

kt hp vi hai record bin km theo, c th chng minh c tnh y

(completeness) ca d liu.

Tnh mi

Do trong bm ca node gc c cha ng gi tr temp thi gian (timestamp). N u data owner ph bin gi tr ny cho tt c cc client. T client c th xc nh c tnh mi ca d liu.

N h vy, ch sau mt thao tc kim tra, client c th kim tra y c ba vn t

ra ca query assurance chi thng qua cc php bm vi chi ph thp hn rt nhiu vi

cc php ton s nguyn ln ca cc ch k s.

Chng minh khng c record tha mn (empty proof)

Mt phng din khc cn c quan tm l chng minh kt qu tr v l trng,

ngha l khng c record no tha iu kin tm kim. chng minh, server tr v

hai record nm k nhau trong dy th t c gi tr ln v nh hn gi tr cn truy vn.

4.3.2 Dng lin quan nhiu node, iu kin n L dng truy vn tng i phc tp hn lin quan n nhiu node. iu ny tng

ng vi php join query ca RDB.

Xt cu truy vn : /Customer[@name=Marry]/Order/Item : tr v tt c cc hng

mc do khch hng c tn l Mary mua. Tng t nh trn, xy dng mt VO

chng minh cho truy vn (nameid=4, prefixid=1, value=Marry). Tuy nhin, VO

ny ch cn cha cc a-node Name_4 v cc t-node Customer_1 tng ng. Cc a-

node Name_4 c dng chng minh t_node Customer_1 y .



ng vi mi t-node Customer_1 xy dng mt VO m bo query assurance ca

truy vn (nameid=3, prefixid=1, pnodeid=)

ly ra kt qu cho t-node Order_3.

Tng t, ta c th m bo cho kt qu truy vn cho cc node Item tr v.

Tng t cho cu truy vn /Customer[@name=Marry]/Order/Item[@name=

TV] : ly cc hng mc c tn l TV do khch hng tn Marry mua. Phng

php x l kt hp gia cu truy vn trn v x l ca trng hp u tin.

4.3.3 Cc dng khc Hai v d trn l cch thc vn dng cy N MB+ trong vic thc hin truy vn v

chng minh kt qu truy vn. x l cc cu truy vn khc phc tp hn, ta c th

phn tch chng thnh nhng cu truy vn n v t xy dng mt k hoch thc

thi (execution plan) vi cc bc thc hin n. V d, ta c execution plan cho cc

cu truy vn trn nh sau.

/Customer/Order/Item[@name=TV] STEP#1 IndexMethod : Vtree, nameID=13 Condition : equal to [TV] Result level : not included Retrieval : node only StepValue : PNODEID [For each matched items, perform] STEP#2 IndexMethod : DirectIDAccess, id=ParentStepValue Result level : 1 Retrieval : node and all its attributes /Customer[@name=Marry]/Order/Item STEP#1 IndexMethod : Vtree, nameID=4 Condition : equal to [Marry] Result level : not included Retrieval : node only StepValue : PNODEID [For each matched items, perform] STEP#2 IndexMethod : DirectIDAccess, value=ParentStepValue Result level : not included Retrieval : node only StepValue : ID [For each matched items, perform] STEP#3 IndexMethod : Ptree, nameID=3, pid=ParentStepValue Result level : not included Retrieval : node only StepValue : ID [For each matched items, perform] STEP#4 IndexMethod : Ptree, nameID=8, pid=ParentStepValue Result level : 1 Retrieval : node and all its attributes



4.3.4 Hp nht cc VO Trong vic thc thi mt cu truy vn, hu ht cc trng hp, server cn tr v cho

client nhiu hn mt VO. V d, trong trng hp cu truy vn mc 4.2.2, s lng

VO server cn tr v phc thuc vo s lng record Customer tha iu kin

@name=Marry. iu ny c th dn n s qu ti pha Client trong vic kim

tra cc VO.

hn ch trng hp trn, server cn phi thc hin hp nht cc VO ny tr thnh

mt VO duy nht v gi tr VO ny v cho client. N h vy, client ch cn thc hin

kim tra mt ln duy nht c th xc nh query assurance cho ton b d liu

nhn c.

Vic hp nht cc VO c th thc hin c d dng. Mi VO ban u c xc nh

bi mt on cc record lin tc nhau cng vi (ti a) hai record bin. Vi nhiu

VO, ta s c nhiu on. V vy, thay v pht sinh co-path cho tng on, ta c th

thc hin pht sinh co-path cho ton b cc on.

4.4 Cc tc v cp nht d liu Cc tc v cp nht khi d liu c outsourced i hi thm mt s chi ph nht

nh. Trong trng hp mt bn sao ca CSDL c lu tr data owner, s lng

cc ln cp nht xy ra khng thng xuyn (thi gian gia hai ln cp nht l ln)

v s lng cp nht l nhiu, data owner c th thc hin cp nht d liu cc b.

Sau thc hin outsourced li d liu.

y, ti liu trnh by mt phng thc cp nht d liu trc tip c dng

trong trng hp data owner khng lu tr li bn sao ca d liu outsourced hoc

chi ph cho mi ln outsource l kh ln.

4.4.1 Tc v thm mi (insertion) Data owner gi cc d liu cn thm mi (cc xml element, attrbiute) n server.

Server thc hin thm cc record mi vo CSDL, cp nht li cu trc index. Tnh

ton v cp nht cc gi tr bm ca cc node l c lin quan v lan truyn ln n

node gc ca cy N MB+. Server gi tr v cho data owner gi tr bm mi ca node



gc. Data owner pht sinh mt gi tr timestamp mi, kt hp vi gi tr bm nhn

c. Sau thc hin k ln cc gi tr ny. Data owner gi li cho server gi tr

timestamp mi cng vi ch k mi. Server cp nht gi tr timestamp v ch k va

nhn c vo CSDL.

Giao thc cp nht nhiu giai on nh trn c minh ha nh hnh sau.

Hnh 4.10. Cc bc thc hin insert

4.4.2 Tc v xa v cp nht (deletion/updation) Tc v xa/cp nht d liu cng c thc hin thng qua cc bc tng t nh tc

v thm mi. Data owner gi yu cu n server. Server thc hin vic cp nht

xung CSDL ng thi tnh ton li cc gi tr bm ca cc node trong cy N MB+.

Gi tr bm mi ca node gc c tr v cho data owner thc hin k. Ch k

cng gi tr timestamp mi c gi tr v cho server cp nht vo CSDL.



Chng 5

PHN TCH

Chng ti trnh by gii php lu tr v s dng cy ch mc N MB+ chng

minh truy vn i vi d liu XML c outsourced. Trong phn ny, chng ti

cp n cc kha cnh bo mt cng nh chi ph ca gii php.

Tt c d liu, k c cc node ca cy ch mc, trc khi lu tr u c m ha

bng gii thut m ha i xng (nh Rijndael) nhm m bo tnh bo mt ca d

liu cng nh hiu sut khi thc hin truy vn. N h vy, phng php ny tha mn

c yu cu data confidentiality.

Gii php trn khng cp n tnh ring t. Tuy nhin, do c tnh ca d liu dng

cy, nn hon ton c th p dng cc kt qu ca Lin v Candan [2] c th t

c tnh ring t.

i vi query assurance, ti liu trnh by phng thc gii quyt i vi cc cu

truy vn vng v im ca mt iu kin n. i vi cu truy vn vng vi nhiu

iu kin kt hp, ta c th gii quyt tng t nh cch thc x l cc tc v tp hp

(set operations) bao gm php ton giao v hi nh trnh by trong [10, 14, 21]

- Php Hi : c thc hin n gin nh hai cu truy vn ring bit. Cc VO pht

sinh t hai cu truy vn s c hp nht nh trnh by.

- Php Giao : mt gii php n gin, vi cc tp kt qu t hai cy truy vn con

theo tng iu kin, server chn mt tp kt qu nh hn, ng vi mi kt qu

thuc tp ny khng tha mn tp kia, server tr v mt empty proof. Tt c cc

VO sau cng s c hp nht thc hin kim tra mt ln pha client.

Mt iu cn quan tm trong query assurance l chng minh cho php join. Trong d

liu dng cy nh XML, php join c p dng ch yu cho quan h t node cha



xung node con. y l mi quan h ph bin trong CSDL XML. Cy N MB+ s

dng PTree chng minh truy vn cho php join ny vi chi ph thp nht trong vic

xy dng VO cng nh chi ph kim tra ti pha client.

Gii php ny khng p dng trc tip cho cc cu truy vn c s dng cc hm tnh

ton bao gp (aggregated function). Cho ti thi im hin ti, theo hiu bit ca

chng ti, ch c gii php ca Radu Sion. [8] gii quyt cho trng hp ny, tuy

nhin gii php cng tn ti mt s hn ch nh trnh by trn. i vi cc cu

truy vn ny, ta c th chng minh cc cu truy vn ny tng t nh cu truy vn

vng, vi iu kin l iu kin lc ca cu truy vn ban u. Kt qu ca hm bao

gp c th c tnh ton ti server v c client kim tra li ngu nhin sau khi

chng thc c query assurance cho cc record tha mn iu kin. Hoc hon ton

c tnh ton ti client.

Tip theo, ti liu tin hnh phn tch v mt chi ph ca gii php. Do hin ti, cha

c mt nghin cu trong lnh vc v query assurance cho CSDL XML, nn cc phn

tch chi ph c nh gi da trn chi ph ti a v ti thiu theo tnh ton l thuyt.

ng thi, y, chng ti ch cp n cc chi ph pht sinh nhm m bo query

assurance.

Trc tin, ti liu trnh by mt s k hiu quy c c s dng bao gm:

n Tng s phn t (s element v s attribute).

s Tng s phn t tr v ca mt truy vn.

f Tham s fanout ca cy N MB+.

h Chiu cao ca cy.

L S node l ca cy.

N Tng s node ca cy.

|sign| Kch thc gi tr bm (20 byte cho SHA-1)



Chi ph lu tr ti server (storage cost): chi ph pht sinh cho vic lu tr ti server

l chi ph dng lu cy N MB+. Cy N MB+ l kt hp bi mt cy NameTree v

cc cy ValueTree, ParentTree cc l ca cy NameTree. Kch thc ca cy

NameTree ph thuc vo s lng node trong cy cu trc (shema tree) ca ti liu

XML. S lng node ny thng l rt nh so vi s lng node ca cy d liu

(data tree) XML, ng thi t bin ng trong thi gian sng ca d liu. Do , chi

ph lu tr ch yu l chi ph lu cc cy ParentTree v ValueTree.

Do s lng ValueTree v ParentTree bin i ty theo s phn t ca schema tree,

v chiu cao ca cc cy l bin i ph thuc v s phn t d liu tng ng vi

mi phn t cu trc. N h vy, tin cho vic nh gi, ta gi s schema tree ca ti

liu XML ch c duy nht mt phn t, v do ch c mt cy ValueTree v mt cy

ParentTree.

D dng nhn ra rng, tng s phn t d liu cc l ca cy ValueTree v

ParentTree l ging nhau. Gi s rng cc phn t d liu l phn bit nhau qua

(nameid, value), ngha l, mi slot ca mt node l bt k ch cha lin kt n mt

phn t d liu duy nht. Khi ta c:

=

=fnL

fnL VTreeVTree 2, maxmin (5.1)

Ta c s node l cn thit ti thiu trong trng hp tt c cc node l u y v s

node l ti a trong trng hp tt cc cc node l ch cha s phn t. T s Lmin v Lmax, c th xc nh c s node ti thiu v ti a ca cy nh sau.

1log minmin += VTreefVTree Lh (5.2)

1log max2

max +

= VTreefVTree Lh (5.3)



111

11 1minmin

min +

=

f

fLNh

VTree (5.4)

121

211

maxmax

max

+

=

f

fLN

h

VTree (5.5)

Cc cng thc (5.2),(5.3),(5.4),(5.5) c th c chng minh nh sau. Gi s, cy B+

c L node l, khi ta c:

S node ti thiu ti

su S node ti a ti su

h Lmin Lmax h-1 Lmin/f 2Lmax/f h-2 Lmin/f2 22Lmax/f2

h-(h-1) Lmin/fh-1 = 1 2h-1Lmax/fh-1 = 1

1log minmin += VTreefVTree Lh 1log max2

max +

= VTreefVTree Lh

N min = Lmin + Lmin/f + Lmin/f2 + + 1 =

f

fLh

11

11 1min

min

+ 1

N max = Lmax + 2Lmax/f + 22Lmax/f2 + + 1 =

f

fL

h

21

211

max

max

+ 1



N h vy, chi ph lu tr pht sinh c th tnh nh sau:

+=++=+=++=

VTreeNTreePTreeVTreeNTreestorage

VTreeNTreePTreeVTreeNTreestorage

NNNNNC

NNNNNC

maxmaxmaxmax

minminminmin

2

2 (5.6)

Thc t, tn ti kh nhiu phn t c kha so snh trng nhau, tc l c b gi tr

(nameid, value) i vi ValueTree hoc (nameid, pnodeid, value) i vi ParentTree

ging nhau. N hng phn t ny chim cng mt slot trong node l ca cy ch mc.

Do , tng s slot s dng trong cc node l lun nh hn tng s phn t cn ch

mc.

N u gi n, n ln lt l s cc phn t phn bit qua (nameid, value) v (nameid,

pnodeid, value), d dng nhn ra rng: n < n < n. N h vy, tnh c chi ph

lu tr, cn xc nh gi tr n v n. Sau thay vo cng thc (5.4), (5.5) xc

nh chi ph cho ValueTree v ParentTree.

Kch thc VO: trong phn tch ny, chng ti ch quan tm n phn d liu phi

thm vo VO c th chng minh truy vn, do , khi nim kch thc VO l kch

thc thng tin thm vo. N goi kt qu truy vn, server tr v hai gi tr kha bin

(value cho ValueTree v pnodeid, value cho ParentTree) cng bm ca record tng

ng ca hai kha trn. Cng vi kch thc ca co-path dng tnh ton bm ca

node gc. N h trnh by phn trn, mt cu truy vn XPath c th c phn tch

thnh nhiu on truy vn vng, v vy c nhiu VO cho cc vng ny. Kch thc

VO tr v l tng kch thc ca cc VO con.

Xt kch thc VO cho mt truy vn, ta c:

S node su S phn t b sung vo

co-path

h

+=f

sLh2 CVOh = f.Lh - s + 2

h-1 Lh-1 = Lh/f CVOh-1 = f.Lh-1 Lh



h-i Lh-i = Lh-i+1/f CVOh-i = f.Lh-i Lh-i+1 Kch thc VO: CVO =|sign| CVOi , i = 1,hNMBTree (5.7)

Chi ph CPU: chi ph CPU (CPU time) l tng thi gian x l k t lc server nhn

c yu cu truy vn cho n khi kt qu truy vn c gii m hon tt pha client

sau khi loi b thi gian cho vic truyn nhn d liu trn ng truyn.

C th chia cc giai on x l mt cu truy vn thnh cc giai on sau:

serv

er s

ide

clie

nt s

ide

Hnh 5.11. Cc bc thc thi query.

- Parse : phn tch cc thnh phn ca cu truy vn, loi b cc k t i din nu

cn thit. C th t mt cu truy vn ban u s c phn tch thnh nhiu cu

truy vn con.

- Plan : xy dng chin lc thc thi cc cu truy vn va phn tch.

- Fetch data : thc hin truy vn trn cy ch mc, c cc record tha mn iu

kin t CSDL.



- Build VO : b sung cc thng tin cn thit xy dng cc VO phc v cho vic

chng minh truy vn, bao gm c thi gian to ra cc co-path cho kt qu truy

vn.

- Verify VO : kim tra kt qu truy vn da vo thng tin VO nhn c.

- Generate XML : phc hi li d liu dng XML. Do d liu XML ban u lu

xung CSDL chuyn thnh cc t-node v a-node, nn kt qu tr v phi c

phc hi sang dng XML ban u.

Hin ti, do gii hn v thi gian, chng trnh nh gi khng thc hin hai bc

u l Parse v Plan. Cc cu truy vn c dng thc thi c cung cp di

dng execution plan. Do , cng vic cn li ch bt u t bc fetch data.



Chng 6

THC NGHIM

nh gi thc nghim, chng ti hin thc gii php trn nn tng .N ET

Framework 2.0, th vin m ha s dng Rijndael v SHA1 cung cp bi .N ET 2.0.

S dng MS SQL Server 2005 Express Edition lu tr CSDL.

Chng trnh th nghim trn h thng PC P4 2.8GHz, 512MB. Ti liu XML mu l

Modial [19] vi 69,846 hng mc (gm 22,423 element 47,423 attribute). Lc

ca ti liu ny c trnh by phn ph lc. H s fanout ca cy N MB+ l 10.

Cc tiu ch c o c bao gm:

- Chi ph lu tr (tng s node ca cy N MB+ theo thc t, so snh vi s node tnh

trn l thuyt trnh by mc 5).

- Kch thc VO (s lng cc hng mc tr km v chng minh truy vn).

- Thi gian thc thi truy vn bao gm cc giai on: fetch data, build VO, verify

VO, generate XML v thi gian tng cng k t lc cu truy vn bt u c thc

thi cho n khi d liu XML kt qu c gii m hon tt. Cc thi gian ny

c so snh trn tng quan s lng record tr v trn tng s record ca

CSDL thy c tnh tng quan ca thi gian thc thi vi cc thng s khc

(yu cu l tng quan tuyn tnh vi kt qu tr v v tng quan logarit vi kch

thc CSDL).

N goi ra, thi gian ny cn c so snh vi thi gian thc thi cu truy vn trong

iu kin khng bo mt o c chi ph pht sinh cho vic bo mt ca gii

php.



Cc s liu o c da trn cu truy vn /mondial/country/city[population > 500000].

K hoch thc thi cho cu truy vn ny c trnh by phn ph lc.

Chi ph lu tr

y, chng ti b qua chi ph lu tr cho d liu XML m ch tp trung vo phn

chi ph pht sinh cn thit lu tr cu trc cy ch mc. Chi ph ny c nh gi

thng qua s lng node cn thit ca cy thc hin ch mc cho s lng cc

phn t cn thit.

nh gi chi ph da trn chi ph tnh ton t cng thc (5.4) v (5.5) cho kch thc

ti thiu v ti a. T kch thc ca CSDL (database size) (s lng phn t), xc

nh c s phn t phn bit nhau qua b thuc tnh (nameid, value) v (nameid,

pnodeid, value) xc nh s lng slot cn lu tr ti cc node l ca cy chi mc

theo (5.4), (5.5). Kt qu trnh by bng di y.

Database Size 10K 20K 30K 40K 50K 60K 70K

Valu

e Tr

ee

Distinct items 5,415 10,743 16,128 20,907 22,279 22,499 24,913Min Leaves 542 1,075 1,613 2,091 2,228 2,250 2,492Min Height 4 5 5 5 5 5 5Min Nodes 603 1,196 1,794 2,325 2,477 2,501 2,770Max Leaves 1,083 2,149 3,226 4,182 4,456 4,500 4,983Max Height 5 6 6 6 6 6 6Max Nodes 679 1,345 2,018 2,615 2,786 2,814 3,116

Pare

nt T

ree

Distinct items 9,126 18,108 27,181 36,376 43,612 50,379 57,497Min Leaves 913 1,811 2,719 3,638 4,362 5,038 5,750Min Height 4 5 5 5 5 5 5Min Nodes 1,015 2,014 3,022 4,043 4,848 5,599 6,390Max Leaves 1,826 3,622 5,437 7,276 8,723 10,076 11,500Max Height 6 6 6 7 7 7 7Max Nodes 1,143 2,265 3,400 4,549 5,454 6,299 7,189

Bng 6.2. Kch thc cy ValueTree, ParentTree min, max

Bng 6.3. Chi ph lu tr

Data size 10K 20K 30K 40K 50K 60K 70K Min nodes 1,618 3,210 4,816 6,368 7,325 8,100 9,160Ma