Certificates for Mobile Code Security
Hock Kim Tan
Department of Electronics and Computer
Science
University of Southampton
Southampton SO17 1BJ, UK
Luc Moreau
Department of Electronics and Computer
Science
University of Southampton
Southampton SO17 1BJ, UK
Keywords
!"#
%$& '(
ABSTRACT
)*,+-$.+ /0210$-3 *4
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1.
INTRODUCTION
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# ++7#1N$:*,',1P# S1+#$
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Wp+" H1A$0*N^ R$0
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SAC 2002, Madrid, Spain
@2002 ACM 1-58113-445-2/02/03 ...
u5.00
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sP4Q/Q 0# " /'=# &*#1/= "1S3 <2 N&*" P*" #<=M7B1<=+7#18 112/#?JxZE2K +P$H&*5&*" L"1M "17#E8
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C1 *$:3<2 A$,%
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)*3 #4]$P*%&*FM' 81#1] 4& "12K /0N7/1+##13"1+7"13$Z E4N K J$& 4 G$:H L# ,2<2&* H [GJ\/ OU$& 4
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$3*R1O$ ^ /SS1+# #.PSS
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r??NF" & <=J# $4 YG%&*% /$& '(7?G@A,*3*#'9*#'a*H&*K F# J7H E2"1#1RP*" ZG+7& H ,4#1/*&1 +" M*" Hk !"# *" H P14#1N "1J3 K #1^',*^*N E2/$, [G\/U&? /3 B /*2
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] 9 ++= &*a$:8 E2"1B*5 E & S&*FHS*" G# N70& #1J/[G\/U <2 M*S++& ./$Z !"# ?
Uaf2 a{H' E+ >*#'Tk^4> 521O K 8$& '(5S $:GB & ^" ?xZE & S*^1 7#1^ I5 "15SJ^4& * 4S<=P5&*5 N$& '(OH44!"#1.?Sf2 ^K *03 2<=<=#1J3 SJ$& '(M*" 2<=<=P 8 E2"1#1<= 8$G*R" Z EO& K J&*F?G)*S+7 & ,$Q*P< ,0%* $& '(]& #1];f2 aq?_f2 ;iB1 K #1N'(J2<=<2/ !"# ,0',*3 "13f2 nL"1',*N ,3 R "1R P1J$$:'(7?
2.
TRUST IN A CODE SECURITY
FRAME-WORK
U M+<20+" +7 Rgh#zjm'/++7#13*PS$4, L +7& Z+7QR*1<=+$7 0$& '(/$:
M21N?N@AN I53 kJ*M'
" ++7S$:R+#4/B 3J
%$& '(
!"#$%&'($%*)+,&-&. $%/0$1324$5&6/ ?^Wt %+7C$,*&*K FR1<=+7#1^$r M*" #<=N7^$:"1571 !"R /P/ +7 L+7 S ?GUe,L(=%*" L $:RO$& 4 R*" S 112L*R21MK NP+*<=M',7#1J/+7& S /JK " M$&*F?Z)*<=$4QJ 0+" G EK 2<2H# 7P#1% , M" $:0*S +++ J" O$Q&*F ++%*" ,2<2#?
789%):);=<,9>,#?9,#2);&*@ A$%/BDC $132:$5&6/ ?GWL* H+7& G1 & 3N* 1+#$Q M&*FL*L<= *# 13#1 ',*R,#?,E E + E0$:# #1R211 /B 3+7 $:3 J
X
S& 4#18%3 Q21Y *" R*/7N & ^ & D ++# ?FE C J',*C 8+#1 !"#1B & B8C 4#1 + $:O'L13 ++N$:# 3R #13+7H$ H21L "1N4& ,*" H L # R H$: ',*0 N Q,N M4#1/+ $:_'1R*" #<= ,/21/$:# #1.?
2.1
Using execution tracing to establish trust
UA & rG & 3<= 3gh{#jmLghqjm,g{{#j0B*<FG*" NDI3MOIQPRM&*& +7 ?G)&*F&*3 H21 $:# 3 "1M +#1/$: ,1#1MS+<= # $:,3 + >$S*8 321
X
r??;3 +K
;; B3 ',* 8*O d. %$S*83 +
P(2#',30+#1 & L/*L3 + , "1N',*&*', <=" R# 1RL*H+Z$" 1< & HL* 3 + Y, "18 J+7"18R+# #18 *%1+##?CsP#'<= *1]&*]3 + ] K #o* NR+<2BO1 RM "1^"1 & (=J+K <=%# JD*3+" B*4N+ $:O?DUD d. # *R4P21QS<= O+4M* .38L4#1 , . "133 E3 # 0 P"1 & (=NM+<= +7R%# &*o?
)&*F/*" J1 R& +7 Z&*D R EA& K . #'_*M1<=+,$ N/+ E%4P21r? SB #',5 *4R+ $: E A M "15* &*&(2/*L$*L Eo207H+7P 1$*J1d. P<=P$G4L*" S# 87M4& *#1 O*" P*4S+ $: **8& M3 *3 # SK <=J " S$G*R
X
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X
^ 11 E^& YL*" R#157N ++#1^^*" R+" K M*4R+ $:OQBN',*^*N" H< $:L*S/$Q4,8 J21/%$& '(7?
@;*A= &1J8*G'3',0+#B ED& ^ /N21J8&*FM5*M$& '(O*" S' / 70N1<=+ "1'/1 7S*#'9P$Q*PK " 12& '," &(2,$Z E%& N# 7/<= PO ++= &*o?)* N* M1 B&*" S #< &*a $:'0 &1a6g{j/ "1>4& 5 ++& Jg~#jmP E2K A& 5*#'<= Nd. R*3+7& N 1< & 3$ 7M ,R1 & +7 /$ N+" H$.*L H*" L " % E#1% ,++7#13J%+7!"S+7" 0*/# S',**P$: ,'N&*" /g{{#jm?
2.2
Execution tracing
UM ER& L*4G+ $: EP N G K / & J$ B TS E5*" S& S+ *S,$Z21S*" 0' / E#1%*S/ P 'Q P o*S E2 " o< 0*" ,' S# 13*/ #?P@;*O*MJ P#F4L3<=. *" *5$ *Q& , "1M$"* TG #1 4& 0 0#1J *P*40+ $:O?)*0" & Km+"1 %+K <21P<21H*" L+7!"04& $7 E
X
P',* +7"1S&YQ'0 &*<=#1JN*0*4+ $: +B& o?9)*& 8N*C$:'0 &1#1] * ',*^*N " N /%*J E2/*4R+ $: *O5 T% & ?6)*8 'w*4%+ $:}', 4S*& P * ,',*%*S ';& /, # 0',*
EJ*S/ #?
UP+7^ B$*N #* M#', M3
X
$ **S+7 H*" *PS '0 ,0 3 E2K #1"YH#F4,*/+ /& R$Z*R TP E
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+ $:tM',*&*3*SS ,& #1?H)*S #', #F4H$p*+ $:p*L*" *%$o*,& S "1
$0* TR #1 J#Q7*B#1B5*J!4
*4%+ $:O?6Ue$P*8*" *3+7"1]',*>*& <=#1^$ *N!4M*4M+ $: "1^*N #1 4& H$*J #1/ Eo*H Q#', Z(2#',*" *P!4,*4L+ $:T"1 (% M L E$Q* #?0)*L+P,+7# #1.*/ 4P*4P+ $: *" L*M S& #1?LUe$ SR+7S 31 +" R$:"1A1*N<= !"# D$0*J& 3+<21#1^B +" 0*4H+ $:O*3 S3 *4H*" H731 K #1.?
)* 0*" #<=7J G$"*G ++= &*o?G)*3 12& '," &(2M N*Nk% "1^2J7 /$0RO7J & #1. "1*S$r L*" ,*R1 8+P, #1OO +%*" , O 0*" 07%3 + #1.? * +K "1,*L1 J$o& /*, ENH$ JKm*# 1#1% ?
3.
COMPONENTS OF THE MOBILE CODE
SECURITY FRAMEWORK
UO*P o7'J1 7R*R< LP5P21 C$& '(70"1^* !"# *" ',L7 #1D8$r & O*& ]$L*%$& '(A',*] [G\/U&?)*L[G\/UZHM*04',1 1+#1N *21 $:,1+#/+,(= N +& +*M&*FGM &*<=
#
X
+" C *# 7Y/] 814#K #1a2<2#?`U& 9$R*5$& '(>',* O[G\/U,'15*2S+$^M " G+& 5$:M # Km'1OR P ++# O" ?
3.1
Agent templates
W,10 "1 Mg{#j.*" #<=,4#1N*LL$ 01
+" 3C+$]*5+$M4 ] A
$:0+7!"S ++# ?HWL% ,1<=+7 # *2 O$ 4& "1 &1;& *T,+& %$M* +" L "1J/J+S+" 0+7R NNK + JJ #?MW`+7M$:* R1<=+P$HK % R+ /'1A2<=<=N !"*4& "1 &1 +& HM!*P+7!"P#F$Z M S ++# o"&*8 0+# o Ke S" P1 K 7#15Cgljm?RU8&*^ ^4& 7*R+ M#18 7M4& #1',*8*R 8+" &
X
&*5 L* 1O$G*R #.,& #<= & "*R+21 L7 +&*" #1AN"F#1A $ # YR "1AN1B*A7%1 K +##1%#1 ?
3.2
Entities in the framework
UO,$& '(7*S$:#',%,# O7R1 !"#1 "1 M1 7#1%7#'/?
3.2.1
Certificate authority (CA)
)*AVWv;2<23+7"1%A*^VWv9 [G\/U&',*3 , "1N+7?HUe',.L* O !"# 0J*S* L,%*P$& '( "1"1 & (=P* L (= %3 " , <2?
3.2.2
Agent owner platform
)*N /#', /+ $:P*M" + $:$ ',*&*A %N R/ ^ &*#18$vO % K
* L, " <= J#1 R21P+21 S*&1 +" R*" JG L'(2S0 G$ + *" 0# 7P4& #1% ,N*S ,#', ,+ $:%Y ',* N "1*O& +7#1O*R#', S+ $:5 P3 #?ZU% N# *P 0#', 0+ $:0 4K #15O73 %+& <=$0*N*23 7= k# " 1+# ,$Z*/ #?
3.2.3
Host platform
)* $: 3^*O E>2<2N*" *O H+7 & ,H& H '0 N$p#', + K $:O?Ox &*A*4M+ $: ',7# +" 3$0*48 *" D C N "1B',73# +" 3$L+<21*34K %L$:P $:R & 87 'OJ+/ EK S ?GWLJ G#', G+ $:`# N S70 L*4G+ K $: $:J* J M &*#15$ 1d. J M#', + $:$Z*,0#F#1.?
3.2.4
Verification server
)*J<= !"# ^ <= // 4#1O*&18+" O*" /"1 K & (=0*/<= !"# O$G E%& L#13%*4 + $:MD7*" $,$0*% M#', N+ $:O?OUeR$: K S P "1O<=ZVW 3# +" 8 !"# /*4H+ $:G*" "1# ,*0# +" N$ S+"
*4M+ $: B E+7!" R+
?
3.2.5
Capability certificates
)* % !"# M*" N *1A$P O*4 + $:t',*O,# +" %$Z E
X
r?? E K M MKe3 3 YG+7!"/ 0+ R+#1^^*M1!" ?)*3+3 B1d. 7 'D O# +" B !"# % "1A 3 !"# 3 *" S*J+J(= 83 5+SS+ #1^5*J# K +" !"# M J+ /1!" #',*&*81!" */+7!"R4& #1OM L+ S*" L# 87 E#1A $:CB*3*4N+ $:b #1.?A)*% K !"# % 8#1]',*>*O+< O(= C$S*+7 <= <= !"# B <= R "15# ^7J<= !"#15%*J+J(= $S* <= #',*&*>314#1C+" & >a ^3
!"#
X
#13*RVWSYHN 4#1%+" ?
WL**O J<= !"# O <= L,# +" R$Q& N*S E K M$7 M Q+ 1!" Q <='L+7& ++7
Ue0 #',,<= !"# %M7P3 &*#1JR, #< K ?
d. R /+
X
R+7!"#1^8* + G1!" &Y7+7Z1d. QkQ "1/<=$ + EOO*M+& O$*P$: " K ?P)*J L$M "1P3<= $O* E>',P+7"1>>B*O$r 'r? +7 & %$M*5<= !"# ; <= # a*2 3 (=J1/8',*&*B S+7P* 8 J', /<= $JJ*0" H$7H # %+7 *,+7 <=S <= ?
UeL+7 0+7!"M # 5$ & ?W6<= K !"# <= ',o*" #<=LJ PP+7$QK N',* R= 7$& '(N*L<=H$r
#1A$,* J]F4A'0 N# R5= A 3!"" Z& B*^$/' #? +7 & K S# B = B /',*&*^ /* 5 M', J(%%*,+7 <=/<= !"# O <= ?
3.2.6
Execution certificates
UD 11A8# +" A !"# G ED !"# /#1%J1$%*S,$G&*O J< 1 O+ "1 ,++" #1N "1J#1MN S<= !"# <= / *4R+ $:v+7^4$:+ ^$H*J< 1 +?Ax &*C ED !"# %& N 8*" *D$,* S21J "1O4& o N4& +o*R1O$G*M<= K !"# 5 <= ,*" P E #13*/& "*/1$Z* *4+ $: *" N"1 (B*% EC$L*% N R' R*NM$,< 1 O*" R& ?8x &* E> !"# 8#1]',*]*O+< (= C$S* <= !"# D <= N "1AM< 1 #1AA* 33 M */# +" !"# ?
3.2.7
Capability certificate revocation list
)*P4PP " PN*/4& "1 &1O !"# /<=# 4
X
V QY$:"18^ 3[G\/U&7 "18P#1O32< 1 M+<2K 5#18# +" 5 !"# S8*M4& J$ 5K < 1N EN& L7R1 #1NN S<= !"# <= #? x &*^88*S4/S#1O8 3<= !"# ^ <= "1N',7"1,*,1N$o*, <= 0 "1N*,*4+ K $:O7*R$r R1 #188*R& N "18 4& +o?SWL L# O&*/N+7 ,*,4P+,N& J '6+ $:O?
3.3
Changes in the execution tracing protocol
)*S+3 31d. P7 '%*P" o E3& K + "18*M'0 ^RR+##18^*P$& '( *" *8 %#', %+ $:}3B %+7 $:<= $^*& %#1CC*4%+ $:?9UK 4# 1C 8 'Z*+K%I3H PM LI3H3K%I3H8"1 & (=R* <2OO7*" $$Z*M P#', #?7S #1OO*S $R*& 5<= !"# o,*8<= !"# ; <= 3',S !"# P%*4S+ $:L%"1# R*S# +" 5$ E^ N] 5< 1D3 #?D)* !K # L P*14#1%'0 &1J#', ,+ $:0',* / 0*" ',*J& PM*S*4,+ $:? )*M 0',*O11R*/" L$Z*S$:3 N*, !"# ',* * HHH $:LGR& 0S* +7 <=*4G+ $:ZR*G<=M & ?Z)* H', 7H 0 H2J7 .$<= !"# R <= 14#1S**K Q*H44O# +" $<= $L*G& Z$"<= /L ENO o*S*4L+ $:,*S44O?
4.
OPERATION OF THE FRAMEWORK
U* o2'P1 7L*L+7 & 0$o*,$& '( ',*A $: N(EQ?^h5$:#',5*J& H$L P L,& 0***S '(7?
4.1
Before migrating to a new host platform
J L',Q#1= M5 N+" O & K D',*D*N"1#1^& *4J+ $:b+J5K & C* 5$ *O*4O+ $:X
O#', + $:%Y&?tx &*6 ',/*" #<=^ D48$R+ 51K
X X
Host Platform
Host Platform
Host Platform
Verification server
Mobile
agent
a) Identifiers
c)
d)
b) Capability
certificates
f) Execution
certificate
g)
e) Execution trace
'"89-&0 !);=
+7#1O$O?S)*o 3',*8*RJ& R21M+7K
5$G*J #7S#18%*J P#', /+ $:
+<=P& +7 % /* /*4/+ $:?M)*J1!" #1^5*3*4+ $: *" J*3 "1N& S
X
EQ?,hR =Y&?
)**4+ $:b<2^*1!" J*C&*&(2M ,',* * +7, N# +" !"# H*" K & 5MR Z$*M1!" P+7!"#1.?/)*N R* #1M" &(MS*,, #',*/# N*N3 (=* 1C5& %N
X
EQ?>h%7Y&?AWLJ 5 $: D&*&(7 *M S3 5 115P*R# +" 8 !"# <=# ;4%D & ;',* * ]$/*8# +" !"# M<=#1A*" #<=37D2< 1 #1.?5Ue$0*% J 4!"#1a= &1C*5 $: a$J%"1#1;14" K o0', P * ,*4L+ $:T* L12" # +#1N/*, E214" 3% /+#1 !"#1J & ?
4.2
Migration to and execution on the new
host platform
R 18L3 1*/R P& ,<= , J"1#1A14"
X
EQ?Ch1"Y&Z',* 3 ECNK "1 3 E& P++" #1J*,*40+ K $:O?G)*G& 0G#1RP*0 <= !"# <=
X
EQ?0hPY&',*M# 3< 1 P0 &1?GUe$.*H& L<= K !"S++7 o 5 E^ !"# JS++" #15 "18K #1%" &(3N*/*4L+ $:
X
EQ?Ph/$&Y&?0W6+$Z* !"# 0G4#1M# Z**4G+ $:- "1R*K " R1+" &*#1B ',*B*J /*J E2 + $:
X
EQ?hY&?G)* EM !"# 0Z R
L +& L$.*,L M*, E2+ $:O?
4.3
Periodical checking of traces
WL**5 E8& R M#1 3+7!"M<= K !"# ^ <= S$v 3*4S+ $:v<= J B S E#1NN*" H+ $:O*0& H#1N7,&*&(=#1 7*L?G)*P1# MHR33*P4& *#1347 K '^*J*4R+ $: "18*N<= !"# B <= R /' S*J+/"1 4& "1%^+" /$H*J*4R+ $: *" ,<2 8$Q*40 *+o"$G1 #1.2',oK & . /# 0L
X
**% +++ L &Y N& 4#1B8*3+7= D*" N*M7%& #1 **5 O"1 #1<2 o?0U*,'0 */<= *# 1 O# &*O<= !"# 8 <= L2<=<=#1%O&*&(2J<= E& /# O7P#1#1.?
4.4
Necessity of execution certificate at
receiv-ing host platform
)*/+8$Z*/ E8 !"# RL+%$: *^ 'v*4O+ $: ] +8 "1; E8*^ #?ZUe$&*M , !"# HQ$:*,',*J ,+#1 K !"#13S#" MJ# %$r RL3 0& NK +7 5N #1A "1B*3% NJ1# &1#1A$ *R '_+ $:wP*" G44P& #1?,)*P+<21P +7& Q +7 Q$ $:" &1,**4Q+ $:9$_K *" Q3 S*" #<=#'A7+7 M1 1PN+7R2<= %$T*S+<2,+ $:O?
4.5
Safeguarding against malicious
verifica-tion servers
)C $:" &19 = 4O*8+7;$J D3 <= !K # 6 <=
X
r??t D<= !"# 9 <= %*" O" 3 H*P*40+ $:t3 11M2< 1R* # +" ] !"# %<=# >4 YN J'L N^+<21 $: 8#1"1
X
5*M<=S$*R$r N$ 3<= !"# K D <= R*" J O*4M+ $: 1+7"1R7Y&G O*4M+ K $: # ]#F4# +" C !"# N$:* %NK + /$w<= & Q1d. L<= !"# 5 <= ?UeP# * J^ " %7 'A*%<= !"# D <= M',*
3 !"# R5+7J3#F4P$v
L*" P M 7L& S#?LVH+P$G E !"# 0 & #1% 0*P*40+ $:t$T1d. 0<= K !"# D <= R# A <=3 R<21A*+O $ *N+73" B',* 3 3 R<= !"# A <=
+N3 *S*4L+ $:O?
4.6
Advantages achieved over original
tech-nique
)*J21!"# 5$G*M" G E8& 3+ ^*$:b*" 37Bk#1]C*$& '(C"1 <= & +7& L 1< &
h?,xZEO& 3# 8#'_7R+7 $:#1O <= K !"# <= ,O M*40+ $:T/ MS >*" 3+ $:}+ E?9U]*OK " P+rP E>& A'0 >+7B *L #', THP $ H*,L *" 1NNK + #1C ON$LJ & ?BUC 11o& 5 #'a+M$:# &**4H+ $: "1N +K " H <28 #1^^ %+R R#', # RS*J# N',*^*J" H+r?3)*M #', *R1 O$G3 ,& +7 N L5 ,P K
{?,)o& LR #170 & #13 H*,*4+ K $:O3 " S$G o& N<21/L1= #1 R*L<= !"# <= #?G)*0$:3 3',.7PK # + #1NJ*H$:-$.# +" "1J EN K !"# R "18',7JJ #7O %3 $Q*L,$Z R& S& * 0*" MN$Q*S & /$?
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5.
RELATED WORK
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$:L/ "y= Bgh#jQ21,
!"# 8 8 DI" E^3 %] E+%*^+<2 #1]',*> ^ #?>W% !"# 3 J#1%',*^ N&*" T*" P+7 ,*R4& $G J+7 %/&1 0N+<21/ R$& '(3*" 0# 7J& #1^O S*J^+7 B$0"1<21" ++K # ?asP9ghh jPCC++73<= & ,&*" M$: 1R+3 % Ke#13[G\/UQ$Tf[G\/Uf
f2Ugi#jo "1 M?i|l^ !"# O4& "1 &1?])*"1%*%$P4 1= >&*" J&*] N&*" Km#1.**1] "1 "1" L1= o?aVH !"# 3 +##1DD* ++= &*% 3 ^# NA 112N*!43 +7 %$/K R ,*G*4,?GU% & r7 M !"# / 1+" &*#1 J',*%*P/ L "13,< " #1% *M<2*4/+ $:O1 R*J *k# *P< S44wS*" S*157N &1#1 J*/ #?
'(JG*0!4R 112*0,$o !"# ',* 8[G\/USO& &(2*3 " <= +7 J$L3 N K *O218?a)*33 &*<=#1]+3 D** *85$R# +" a !"# %*" ^#1]> +7 L*43+ $: A B8 B"1# O*
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6.
CONCLUSION
UA*J+" +7 #G'%*" #<=%1#1C 8A$& '(B$: R ,*" L E2"10*/ E& &*F ^3 (=%3 +++ $:3 O# O2<2?C)* (= ^^B*/$& '(^/*<= !"# A <= R*" "1 & (=R*3 ED& B <2AC7*" $L$L* 3#', 3+ $: "1C# +" > "1] E
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> ^3 " A AVWSYR^*< K H*4H+ $:HN*,44O?V +" !"# +21#1M/<= $J*0 $:
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*+" G$& '(8*" R'*" #<=P44J1 7#1.?3U +" #Z 3+& # +& 5$ E5& *" o o,7G# k#1/M S3 #4QH Q44O?Q)* & L7 '*R1d. ,L*P$& '( #1M^73$:3 k#1C5*" N+7!"D++7 # ^7R1!"#15 "183 & #1.7$H+7?SU2<=4= #1ZS7# #1NZ',*J= &1ZP*0* Z+7Z$. K &*F*" 0# 7P+##1%4 %',* EO& % "1%*R3 L',*&*O* # 87RK & #1aB*$& '(7?_)*51 & #1>$:3 %$S* # +" A "1B EB !"# M#1SO7 E #1 LH*#'A* /*Q74$:M& #1R,* K !"# M3 " P <2P$ N4& "1 &15[G\/U&? 4S S# 4#.*R+# P$H "1O+# !K # 03*P3 01 7#1%* P#1HM7P2<=4= #1 ^# M1 & QO1 R/<2 8$:R " ++K # o?
7.
ACKNOWLEDGMENTS
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8.
REFERENCES
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