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52 8 A p p e n d ı× E ı C a s e S tu d ie s

= A tta c k s a g a in s t th e r o u tin g s e r v ic e (E o p , ta m p e r in g , s p o o fin g )

= A tta c k s a g a in s t th e return d a ta flo w (ta m p e r in g , s p o o fin g )

3 T h e "

c u s to m e r e ffe c tiv e te lc o "

c a n s e e th e O T T

4 S y s te m s d e s ig n e cl to im p r o v e te x t m e s s a g e p r o c e s s in g c a n s e e t h e O

P o s s ib le R e d e s ig n s

In fo r m a tio n clis c lo s u r e th r e a ts c a n b e a d d r e s s e d b y a d d in g c r y p to g r a p h ic fu n c tio n s Sim p lifie d v e r s io n s o f w a y s to d o th a t in c lu d e th e fo llo w in g

= S e n d a n o n c e , e n c r y p te d to a k e y h e ld o n a s m a r 中 h o n e , th e n s e n d th e

d e c r y p te d n o n c e to th e a u th e n tic a tio n s e r v e r (m e s s a g e 1 = e p h o n e (n o n c e . ), m e s s a g e 2 - n o n c e

. ) T h e n th e s e r v e r c h e c k s w h e th e r th e n o n c e

n is th e o n e

th a t it e n c r y p te d fo r th e p h o n e , a p p r o v in g th e tr a n s a c tio n if it is

= S e n d a n o n c e to th e s m a r 中 h o n e , a n d th e n s e n d a s ig n e d v e r s io n o f th e n o n c e to th e s e r v e r [m e s s a g e 1 = n o n c e

p h . . E l m e s s a g e 2 = s ig n k e y (p h o n e )

(n o n c e p h . . .

) ] T h e s e r v e r v a lid a te s th a t th e s ig n a tu r e o n th e n o n c e p h . . .

Is fr o m th e e x p e c te d p h o n e

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s k e y , a n d is a g o o d s ig n a tu r e o n th e e x p e c te d n o n c e If b o th th o s e c h e c k s p a s s , th e n th e s e r v e r a p p r o v e s th e tr a n s a c tio n

= S e n d a n o n c e to th e s m a r tp h o n e T h e s m a r tp h o n e h a s h e s th e n o n c e w ith a s e c r e t v a lu e it h o ld s

, a n d s e n d s b a c k th e h a s h

F o r e a c h o f th e s e , it

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s im p o r ta n t to m a n a g e th e k e y s a p p r o p r ia te ly, a n d it '

s

p r o b a b ly u s e ħrl to in c lu d e tim e s ta m p s , m e s s a g e a d d r e s s in g , a n d o th e r e le m e n ts to m a k e th e s y s te m fu lly s e c u r e In c lu d in g th o s e in th is d is c u s s io n m a k e s it h a r d to s e e h o w c r y p to g r a p h ic b u ild in g b lo c k s c o u ld b e a p p lie d

T h e k e y in a ll d e s ig n c h a n g e s is u n d e r s ta n d in g th e d iffe r e n c e s in tr o d u c e d b y th e c h a n g e s , a n d h o w th o s e c h a n g e s in te r a c t w ith th e s o ftw a r e r e q u ir e m e n ts a s a w h o le

R e d e s ig n s th a t fo c u s o n u s in g th e p h o n e a s a p r o c e s s o r p r e c lu d e th e u s e o f a n o ld fa s h io n e d te le p h o n e , o r e v e n a m o b ile p h o n e (o f th e k in d w h e r e th e e n d u s e r c a n

' t e a s ily in s ta ll s o ftw a r e ) B e c a u s e s u c h p h o n e s s till e x is t

, it m a yb e th a t th e th r e a ts ju s t e n u m e r a te d a r e c o n s id e r e d a c c e p ta b le r is k , o r e v e n a n

im p r o v e m e n t o v e r tr a d itio n a ı p a s s w o r d s

S a m p le fo r Y o u to M o d e ı

Y o u c a n u s e th e m o d e ls p r e s e n te d a b o v e a s tr a in in g m o d e ls w ith a n s w e r k e y s(T h a t is , u s e th e s o ftw a r e m o d e l in F ig u r e E 1 a n d th e o p e r a tio n a l m o d e l in F ig u r eE 2 a n d fin d th r e a ts a g a in s t th e m y o u r s e lf Y o u c a n tr e a t th e e x a m p le th r e a ts

r A p p e n d ı× E ı C a s e S t u d ıe s 5 2 9

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a t th e fo llo w in g

= F ile o r k e y n a m e s

= F ile s iz e o r r e g is tr y d a ta

= L a s t u p d a te d tim e a n d d a te

= D a ta c h e c k s u m (M D 5 a n d /o r S H A I h a s h )

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T h e H o s t C o m p o n e n t

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re q u e s ts V a lid r e q u e s ts in c lu d e g e ttin g in fo r m a tio n a b o u t h o s t c o m p o n e n t v e r

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T h e A d m in C o n s o ıe

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