chapter 8: network security - plone sitesangio/so_currentaa/luc_so/security/... · 2014-05-05 ·...
TRANSCRIPT
8-2
Ne
two
rk S
ecu
rity
Chap
ter
8: N
etw
ork
Sec
uri
ty
Cha
pte
r go
als:
under
stan
dpri
nci
ple
sof net
work
sec
uri
ty:
cr
ypto
grap
hy a
nd
its
man
yuse
sbey
ond
“confiden
tial
ity”
au
then
tica
tion
m
essa
ge inte
grity
se
curi
tyin
pra
ctic
e:
fire
wal
lsan
din
trusi
on d
etec
tion s
yste
ms
se
curi
ty in a
pplic
atio
n,t
ransp
ort
,net
work
,lin
k la
yers
8-3
Ne
two
rk S
ecu
rity
Chap
ter
8 r
oad
map
8.1
Wha
tis n
etw
ork
secu
rity
?
8.2
Pri
nci
ple
sof cr
ypto
grap
hy
8.3
Mes
sage
inte
grity,
auth
entica
tion
8.4
Sec
uri
ng
e-m
ail
8.5
Secu
ring
TC
Pco
nnec
tions:
SSL
8.6
Net
work
lay
er s
ecuri
ty:I
Pse
c
8.7
Secu
ring
wir
eles
sLA
Ns
8.8
Oper
atio
nal
secu
rity
:fire
wal
lsan
dID
S
8-4
Ne
two
rk S
ecu
rity
What
is
net
work
sec
uri
ty?
confi
dent
ialit
y:only
sen
der
,inte
nded
rece
iver
should
“under
stan
d”
mes
sage
conte
nts
se
nder
encr
ypts
mes
sage
re
ceiv
er d
ecry
pts
mes
sage
auth
entic
atio
n:se
nder
,rec
eive
r w
ant
toco
nfirm
iden
tity
of
each
oth
er
mes
sage
inte
grity
:sen
der
,rec
eive
r w
ant
toen
sure
mes
sage
not
alte
red
(in t
ransi
t,or
afte
rwar
ds)
without
det
ection
acce
ss a
ndav
aila
bilit
y:se
rvic
esm
ust
be
acce
ssib
le a
nd
avai
lable
to
use
rs
8-5
Ne
two
rk S
ecu
rity
Frie
nds
and e
nem
ies:
Alic
e, B
ob,
Trudy
w
ell-kn
ow
n in n
etw
ork
sec
uri
ty w
orl
d
B
ob,A
lice
(love
rs!)
wan
t to
com
munic
ate
“sec
ure
ly”
Tr
udy
(intr
uder
)m
ay inte
rcep
t,del
ete,a
dd
mes
sage
s
se
cu
re
se
nd
er
sse
cu
re
rece
ive
r
ch
an
ne
ld
ata
, co
ntr
ol
me
ssa
ge
s
da
tad
ata
Alic
eB
ob
Tru
dy
8-6
Ne
two
rk S
ecu
rity
Who m
ight
Bob,A
lice
be?
…
wel
l,re
al-li
feB
obs
and
Alic
es!
W
eb b
row
ser/
serv
er for
elec
tronic
tran
sact
ions
(e.g
.,on-lin
e purc
has
es)
on-lin
e ban
king
clie
nt/
serv
er
DN
Sse
rver
s
route
rsex
chan
ging
routing
table
updat
es
oth
er e
xam
ple
s?
8-7
Ne
two
rk S
ecu
rity
Ther
e ar
e bad
guys
(an
d g
irls
) out
ther
e!
Q:W
hat
can a
“bad
guy”
do?
A:A
lot!
See
sec
tion 1
.6
ea
vesd
rop:
inte
rcep
tm
essa
ges
ac
tive
lyin
sert
mes
sage
sin
toco
nnec
tion
im
pers
onat
ion:
can fak
e (s
poof)
sourc
e ad
dre
ssin
pac
ket
(or
any
fiel
din
pac
ket)
hi
jack
ing:
“tak
e ove
r”ongo
ing
connec
tion b
yre
movi
ng
sender
or
rece
iver
,inse
rtin
ghim
self
in
pla
ce
de
nial
of s
ervi
ce:p
reve
nt
serv
ice
from
bei
ng
use
dby
oth
ers
(e.g
.,by
ove
rload
ing
reso
urc
es)
8-8
Ne
two
rk S
ecu
rity
Chap
ter
8 r
oad
map
8.1
What
isnet
work
sec
uri
ty?
8.2
Princ
iple
s of
cry
ptog
raph
y
8.3
Mes
sage
inte
grity,
auth
entica
tion
8.4
Sec
uri
ng
e-m
ail
8.5
Secu
ring
TC
Pco
nnec
tions:
SSL
8.6
Net
work
lay
er s
ecuri
ty:I
Pse
c
8.7
Secu
ring
wir
eles
sLA
Ns
8.8
Oper
atio
nal
secu
rity
:fire
wal
lsan
dID
S
8-9
Ne
two
rk S
ecu
rity
The
langu
age
of cr
ypto
grap
hy
mpla
inte
xt
mes
sage
KA(m
)ci
pher
text,
encr
ypte
dw
ith k
ey K
A
m =
KB(K
A(m
))
pla
inte
xt
pla
inte
xt
cip
hert
ext
KA
en
cry
ption
alg
ori
thm
de
cry
ptio
n
alg
ori
thm
Alic
e’s
en
cry
ption
ke
y
Bo
b’s
de
cry
ptio
n
ke
yK
B
8-1
0N
etw
ork
Se
cu
rity
Bre
akin
g an
encr
yption s
chem
e
ci
pher
-tex
t only
atta
ck:
Trudy
has
cipher
text
she
can a
nal
yze
tw
oap
pro
aches
:
bru
te forc
e:se
arch
th
rough
all
keys
st
atis
tica
lan
alys
is
kn
ow
n-p
lain
text
atta
ck:
Trudy
has
pla
inte
xt
corr
espondin
gto
cipher
text
e.g
.,in
monoal
phab
etic
cipher
,Tru
dy
det
erm
ines
pai
rings
for
a,l,i
,c,e
,b,o
,
ch
ose
n-p
lain
text
atta
ck:
Trudy
can g
et c
ipher
text
for
chose
n p
lain
text
8-1
1N
etw
ork
Se
cu
rity
Sym
met
ric
key
cryp
togr
aphy
sym
met
ric
key
cryp
to:B
ob a
nd
Alic
e sh
are
sam
e (s
ymm
etri
c)ke
y:K
e.g
.,ke
y is
know
ing
subst
itution p
atte
rn in m
ono
alphab
etic
su
bst
itution c
ipher
Q:h
ow
do
Bob a
nd
Alic
e ag
ree
on k
ey v
alue?
pla
inte
xt
cip
hert
ext
KS
en
cry
ption
alg
ori
thm
de
cry
ptio
n
alg
orith
m
S
KS
pla
inte
xt
me
ssa
ge
,m
K(m
)S
m=
KS(K
S(m
))
8-1
2N
etw
ork
Se
cu
rity
Sim
ple
encr
yption s
chem
e
subs
titut
ion
ciph
er:s
ubst
ituting
one
thin
gfo
r an
oth
er
monoal
phab
etic
cipher
:subst
itute
one
lett
er for
anoth
er
plaintext: abcdefghijklmnopqrstuvwxyz
ciphertext: mnbvcxzasdfghjklpoiuytrewq
Plaintext: bob. i love you. alice
ciphertext: nkn. s gktc wky. mgsbc
e.g
.: ncry
ptio
nke
y:m
appin
gfr
om
set
of 26 let
ters
tose
tof 26 let
ters
8-1
3N
etw
ork
Se
cu
rity
A m
ore
sophis
tica
ted e
ncr
yption a
ppro
ach
n s
ubst
itution c
ipher
s,M
1,M
2,…
,Mn
cy
clin
gpat
tern
:
e.g
.,n=
4:M
1,M
3,M
4,M
3,M
2;
M1,M
3,M
4,M
3,M
2;..
fo
r ea
ch n
ewpla
inte
xt
sym
bol,
use
subse
quen
tsu
bsi
tution p
atte
rn in c
yclic
pat
tern
dog:
dfr
om
M1,o
from
M3,g
from
M4
Enc
rypt
ion
key:
n s
ubst
itution c
ipher
s,an
dcy
clic
pat
tern
ke
y nee
dnot
be
just
n-b
it p
atte
rn
8-1
4N
etw
ork
Se
cu
rity
Sym
met
ric
key
cryp
to: D
ES
DES:
Dat
aEncr
yption S
tandar
d
US
encr
yption s
tandar
d[N
IST
1993]
56-b
it s
ymm
etri
c ke
y,64-b
it p
lain
text
input
blo
ck c
ipher
with c
ipher
blo
ck c
hai
nin
g
how
secu
re is
DES?
D
ES
Chal
lenge
:56-b
it-k
ey-e
ncr
ypte
dphra
se
dec
rypte
d(b
rute
forc
e)in
les
sth
an a
day
no
know
n g
ood
anal
ytic
att
ack
m
akin
gD
ES
more
sec
ure
:
3D
ES:
encr
ypt
3 t
imes
with 3
diff
eren
t ke
ys
8-1
5N
etw
ork
Se
cu
rity
Sym
met
ric
key
cryp
to: D
ES
initia
lper
muta
tion
16 iden
tica
l“r
ounds”
of
funct
ion a
pplic
atio
n,
each
usi
ng
diff
eren
t 48
bits
of ke
y
final
per
muta
tion
DES
oper
atio
n
8-1
6N
etw
ork
Se
cu
rity
AES:
Adva
nce
d E
ncr
yption S
tandar
d
sy
mm
etri
c-ke
yN
IST
sta
ndar
d,r
epla
cied
DES
(Nov
2001)
pro
cess
esdat
ain
128 b
itblo
cks
128,1
92,o
r 256 b
itke
ys
bru
te forc
e dec
ryption (
try
each
key
)ta
king
1 s
econ D
ES,
take
s149 t
rilli
on y
ears
for
AES
8-1
7N
etw
ork
Se
cu
rity
Public
Key
Cry
pto
grap
hy
sym
met
ric
key
cryp
to
requir
esse
nder
,rec
eive
rkn
ow
shar
edse
cret
key
Q
:how
toag
ree
on k
eyin
firs
tpla
ce (
par
ticu
larl
y if
nev
er “
met
”)?
publ
icke
y cr
ypto
ra
dic
ally
diff
eren
tap
pro
ach [
Diffi
e-H
ellm
an76,R
SA78]
se
nder
,rec
eive
r do
not
shar
e se
cret
key
pub
licen
cryp
tion k
ey
know
n t
oal
l
priva
tedec
ryption k
eykn
ow
n o
nly
to
rece
iver
8-1
8N
etw
ork
Se
cu
rity
Public
key
cry
pto
grap
hy
pla
inte
xt
me
ssa
ge
,m
cip
hert
ext
en
cry
ption
alg
ori
thm
de
cry
ptio
n
alg
orith
m
Bo
b’s
pu
blic
ke
y p
lain
text
me
ssa
ge
K(m
)B+
KB+
Bo
b’s
pri
va
te
ke
y
KB-
m=
K(K
(m))
B+
B-
8-1
9N
etw
ork
Se
cu
rity
Public
key
encr
yption a
lgori
thm
s
ne
ed
K(
)a
nd
K(
)su
ch
th
at
BB
..
giv
en
pu
blic
ke
y K
,it
sh
ou
ld b
e
imp
ossib
le t
o c
om
pute
priva
te
ke
y K
B
B
requir
emen
ts:
1 2 RSA
:Riv
est,
Sham
ir,A
del
son a
lgori
thm
+-
K(K
(m))
=m
BB-
+
+
-
8-2
0N
etw
ork
Se
cu
rity
Pre
requis
ite:
modula
r ar
ithm
etic
x m
od
n =
rem
ainder
of x w
hen
div
ide
byn
fa
cts:
[(a
mod
n)
+ (
b m
od
n)]
mod
n =
(a+
b)
mod
n
[(a
mod
n)
-(b
mod
n)]
mod
n =
(a-
b)
mod
n
[(a
mod
n)
* (b
mod
n)]
mod
n =
(a*
b)
mod
n
th
us
(am
od
n)d
mod
n =
adm
od
n
exam
ple
:x=
14,n
=10,d
=2:
(x m
od
n)d
mod
n =
42
mod
10 =
6x
d=
14
2=
196
xd
mod
10
=6
8-2
1N
etw
ork
Se
cu
rity
RSA
: get
ting
read
y
m
essa
ge:j
ust
abit p
atte
rn
bit p
atte
rn c
an b
e uniq
uel
y re
pre
sente
dby
an inte
ger
num
ber
th
us,
encr
ypting
am
essa
ge is
equiv
alen
t to
encr
ypting
anum
ber
.
exam
ple:
m
= 1
0010001 .T
his
mes
sage
is
uniq
uel
y re
pre
sente
dby
the
dec
imal
num
ber
145.
to
encr
ypt
m,w
e en
cryp
t th
e co
rres
pondin
gnu
mber
,w
hic
h g
ives
anew
num
ber
(th
e ci
pher
text)
.
8-2
2N
etw
ork
Se
cu
rity
RSA
: Cre
atin
g public
/pri
vate
key
pai
r
1.ch
oose
tw
ola
rge
pri
me
num
ber
sp,
q.(e
.g.,
1024 b
its
each
)
2.co
mpute
n=
pq,
z=
(p-1
)(q-
1)
3.ch
oose
e(w
ith
e<n)
that
has
no
com
mon fac
tors
with z
(e,z
are
“rel
ativ
ely
pri
me”
).
4.ch
oose
dsu
ch t
hat
ed-1
isex
actly
div
isib
le b
yz.
(in o
ther
word
s:ed
mod
z=
1 )
.
5.pu
blic
key
is(n
,e).
priv
ate
key
is(n
,d).
KB+
KB-
8-2
3N
etw
ork
Se
cu
rity
RSA
: encr
yption, d
ecry
ption
0.
give
n (
n,e)
and
(n,d
)as
com
pute
dab
ove
1.to
encr
ypt
mes
sage
m(<
n),c
om
pute
c=
mm
od
ne
2.to
dec
rypt
rece
ived
bit
pat
tern
,c,c
om
pute
m=
cm
od
nd
m
=
(m
mo
dn
)e
mo
dn
dm
agic
happ
ens!
c
8-2
4N
etw
ork
Se
cu
rity
RSA
exam
ple
:
Bo
bch
oo
se
s p
=5
,q
=7
.T
he
nn
=3
5,
z=
24
.
e=
5(s
oe
,z
rela
tive
ly p
rim
e).
d=
29
(so
ed
-1e
xa
ctly d
ivis
ible
by z
).
bit
pa
tte
rnm
me
c =
m
mo
dn
e
00
00
l00
01
22
48
32
17
en
cry
pt:
en
cry
ptin
g8
-bit
me
ssa
ge
s.
cm
= c
m
od
nd
17
48
19
68
57
21
06
75
09
15
09
14
11
82
52
23
07
16
97
12
cd
de
cry
pt:
8-2
5N
etw
ork
Se
cu
rity
Why
does
RSA
work
?
m
ust
show
that
cd
mod
n =
m
wher
e c
= m
em
od
n
fa
ct:f
or
any
x a
nd
y:x
ym
od
n =
x(y
mod
z)m
od
n
wher
e n=
pq a
nd z
=(p
-1)(
q-1
)
th
us,
cdm
od
n =
(m
em
od
n)d
mod
n
= m
edm
od
n
= m
(ed
mod
z)m
od
n
= m
1m
od
n
= m
8-2
6N
etw
ork
Se
cu
rity
RSA
: anoth
er im
port
ant
pro
per
ty
The
follo
win
gpro
per
tyw
illbe
very
use
fulla
ter:
K(K
(m))
=m
BB-
+K
(K(m
))B
B+-
=
use
public
key
firs
t,fo
llow
edby
pri
vate
key
use
pri
vate
key
firs
t,fo
llow
edby
public
key
resu
lt is t
he s
ame!
8-2
7N
etw
ork
Se
cu
rity
follo
ws
dir
ectly
from
modula
r ar
ithm
etic
:
(me
mod
n)d
mod
n =
med
mod
n
=m
de
mod
n
=(m
dm
od
n)e
mod
n
K(K
(m))
=m
BB-
+K
(K(m
))B
B+-
=W
hy?
8-2
8N
etw
ork
Se
cu
rity
Why
is
RSA
sec
ure
?
su
ppose
you k
now
Bob’s
public
key
(n,e
).H
ow
har
dis
itto
det
erm
ine
d?
es
sential
lynee
dto
find
fact
ors
of n w
ithout
know
ing
the
two
fact
ors
p a
nd
q
fa
ct:f
acto
ring
abig
num
ber
is
har
d
8-2
9N
etw
ork
Se
cu
rity
RSA
in p
ract
ice:
ses
sion k
eys
ex
ponen
tiat
ion in R
SAis
com
puta
tional
lyin
tensi
ve
D
ES
isat
leas
t100 t
imes
fast
er t
han
RSA
use
public
key
cryt
oto
esta
blis
h s
ecure
co
nnec
tion,t
hen
est
ablis
h s
econd
key
–
sym
met
ric
sess
ion k
ey– for
encr
ypting
dat
a
sess
ion
key,
KS
B
ob a
nd
Alic
e use
RSA
to
exch
ange
asy
mm
etri
c ke
y K
S
once
both
hav
e K
S,th
ey u
se s
ymm
etri
c ke
y cr
ypto
grap
hy
8-3
0N
etw
ork
Se
cu
rity
Chap
ter
8 r
oad
map
8.1
What
isnet
work
sec
uri
ty?
8.2
Pri
nci
ple
sof cr
ypto
grap
hy
8.3
Mes
sage
inte
grity,
auth
entic
atio
n
8.4
Sec
uri
ng
e-m
ail
8.5
Secu
ring
TC
Pco
nnec
tions:
SSL
8.6
Net
work
lay
er s
ecuri
ty:I
Pse
c
8.7
Secu
ring
wir
eles
sLA
Ns
8.8
Oper
atio
nal
secu
rity
:fire
wal
lsan
dID
S
8-3
1N
etw
ork
Se
cu
rity
Auth
entica
tion
Goa
l:B
ob w
ants
Alic
e to
“pro
ve”
her
iden
tity
tohim
Prot
ocol
ap1.0
:A
lice
says
“I a
m A
lice”
Fa
ilure
sce
na
rio
??
“Ia
m A
lice
”
8-3
2N
etw
ork
Se
cu
rity
ina
ne
two
rk,
Bo
bca
nn
ot“s
ee
”A
lice
,
so
Tru
dy s
imp
ly d
ecla
res
he
rse
lfto
be
Alic
e“I
am
Alic
e”
Auth
entica
tion
Goa
l:B
ob w
ants
Alic
e to
“pro
ve”
her
iden
tity
tohim
Prot
ocol
ap1.0
:A
lice
says
“I a
m A
lice”
8-3
3N
etw
ork
Se
cu
rity
Auth
entica
tion: a
noth
er t
ry
Pro
toco
la
p2
.0:
Alic
esa
ys “
Ia
m A
lice
”in
an
IPp
acke
t
co
nta
inin
gh
er
so
urc
eIP
ad
dre
ss
Fa
ilure
sce
na
rio
??
“Ia
mA
lice
”A
lice
’s
IP a
dd
ress
8-3
4N
etw
ork
Se
cu
rity
Tru
dy c
an
cre
ate
ap
acke
t“s
po
ofin
g”
Alic
e’s
ad
dre
ss
“Ia
mA
lice
”A
lice
’s
IP a
dd
ress
Auth
entica
tion: a
noth
er t
ry
Pro
toco
la
p2
.0:
Alic
esa
ys “
Ia
m A
lice
”in
an
IPp
acke
t
co
nta
inin
gh
er
so
urc
eIP
ad
dre
ss
8-3
5N
etw
ork
Se
cu
rity
Prot
ocol
ap3.0
:A
lice
says
“I a
m A
lice”
and
sends
her
secr
etpas
sword
to“p
rove
”it.
Fa
ilure
sce
na
rio
??
“I’m
Alic
e”
Alic
e’s
IPa
dd
r
Alic
e’s
pa
ssw
ord
OK
Alic
e’s
IPa
dd
r
Auth
entica
tion: a
noth
er t
ry
8-3
6N
etw
ork
Se
cu
rity
pla
yb
ack a
tta
ck:
Tru
dy
reco
rds A
lice
’s p
acke
t
an
dla
ter
pla
ys it
ba
ck t
oB
ob
“I’m
Alic
e”
Alic
e’s
IPa
dd
r
Alic
e’s
pa
ssw
ord
OK
Alic
e’s
IPa
dd
r
“I’m
Alic
e”
Alic
e’s
IPa
dd
r
Alic
e’s
pa
ssw
ord
Prot
ocol
ap3.0
:A
lice
says
“I a
m A
lice”
and
sends
her
secr
etpas
sword
to“p
rove
”it.
Auth
entica
tion: a
noth
er t
ry
8-3
7N
etw
ork
Se
cu
rity
Auth
entica
tion: y
et a
noth
er t
ry
Prot
ocol
ap3.1
:A
lice
says
“I a
m A
lice”
and
sends
her
encr
ypte
dse
cret
pas
sword
to“p
rove
”it.
Fa
ilure
sce
na
rio
??
“I’m
Alic
e”
Alic
e’s
IPa
dd
r
en
cry
pte
d
pa
ssw
ord
OK
Alic
e’s
IPa
dd
r
8-3
8N
etw
ork
Se
cu
rity
reco
rd
an
d
pla
yb
ack
still
wo
rks!
“I’m
Alic
e”
Alic
e’s
IPa
dd
r
en
cry
pte
d
pa
ssw
ord
OK
Alic
e’s
IPa
dd
r
“I’m
Alic
e”
Alic
e’s
IPa
dd
r
en
cry
pte
d
pa
ssw
ord
Auth
entica
tion: y
et a
noth
er t
ry
Prot
ocol
ap3.1
:A
lice
says
“I a
m A
lice”
and
sends
her
encr
ypte
dse
cret
pas
sword
to“p
rove
”it.
8-3
9N
etw
ork
Se
cu
rity
Goa
l:av
oid
pla
ybac
k at
tack
Fa
ilure
s,
dra
wb
acks?
nonc
e:num
ber
(R
)use
donly
onc
e-in
-a-li
fetim
e
ap4.0
:to
pro
ve A
lice
“liv
e”,B
ob s
ends
Alic
e no
nce,
R.
Alic
e
must
ret
urn
R,e
ncr
ypte
dw
ith s
har
edse
cret
key
“Ia
m A
lice
”
R
K
(R)
A-B
Alic
eis
live
,a
nd
on
ly A
lice
kn
ow
s
ke
yto
en
cry
pt
no
nce
,so
itm
ust
be
Alic
e!
Auth
entica
tion: y
et a
noth
er t
ry
8-4
0N
etw
ork
Se
cu
rity
Auth
entica
tion: a
p5.0
ap4.0
req
uir
essh
ared
sym
met
ric
key
ca
n w
e au
then
tica
te u
sing
public
key
tech
niq
ues
?
ap5.0
:use
nonce
,public
key
cryp
togr
aphy
“Ia
m A
lice
”
RB
ob
co
mp
ute
s
K
(R)
A-
“se
nd
me
yo
ur
pu
blic
ke
y” K A+
(K
(R))
= R
A-K
A+
an
dkn
ow
s o
nly
Alic
e
co
uld
ha
ve
the
priva
te
ke
y,th
at
en
cry
pte
dR
su
ch
tha
t
(K(R
))=
RA-
KA+
8-4
1N
etw
ork
Se
cu
rity
ap5.0
: sec
uri
ty h
ole
man
(or
wom
an)
inth
e m
iddl
e at
tack
:Tru
dy
pose
sas
Alic
e (t
oB
ob)
and
asB
ob (
toA
lice)
I a
m A
lice
I a
m A
lice
R
TK
(
R)
-
Se
nd
me
yo
ur
pu
blic
ke
y TK
+
AK
(
R)
-
Se
nd
me
yo
ur
pu
blic
ke
y
AK
+
TK
(
m)
+
Tm
= K
(K
(
m))
+ T
-T
rud
y g
ets
se
nd
s m
to
Alic
e
en
cry
pte
d w
ith
Alic
e’s
pu
blic
ke
y
AK
(m
)+
Am
= K
(K
(
m))
+ A
-
R
8-4
2N
etw
ork
Se
cu
rity
diffi
cult
todet
ect:
B
ob r
ecei
ves
ever
ythin
gth
at A
lice
sends,
and
vice
ver
sa.
(e.g
.,so
Bob,
Alic
e ca
n m
eet
one
wee
k la
ter
and
reca
llco
nver
sation!)
pro
ble
m is
that
Tru
dy
rece
ives
allm
essa
ges
asw
ell!
ap5.0
: sec
uri
ty h
ole
man
(or
wom
an)
inth
e m
iddl
e at
tack
:Tru
dy
pose
sas
Alic
e (t
oB
ob)
and
asB
ob (
toA
lice)
8-4
3N
etw
ork
Se
cu
rity
Chap
ter
8 r
oad
map
8.1
What
isnet
work
sec
uri
ty?
8.2
Pri
nci
ple
sof cr
ypto
grap
hy
8.3
Mes
sage
inte
grity
,auth
entica
tion
8.4
Sec
uri
ng
e-m
ail
8.5
Secu
ring
TC
Pco
nnec
tions:
SSL
8.6
Net
work
lay
er s
ecuri
ty:I
Pse
c
8.7
Secu
ring
wir
eles
sLA
Ns
8.8
Oper
atio
nal
secu
rity
:fire
wal
lsan
dID
S
8-4
4N
etw
ork
Se
cu
rity
Dig
ital
sig
nat
ure
s
cryp
togr
aphic
tech
niq
ue
anal
ogo
us
tohan
d-w
ritt
en
sign
ature
s:
sender
(Bob)
dig
ital
ly s
igns
docu
men
t, e
stab
lishin
g he
is d
ocu
men
t ow
ner
/cre
ator.
ve
rifia
ble,
non
forg
eabl
e:re
cipie
nt
(Alic
e) c
an p
rove
to
som
eone
that
Bob,
and
no
one
else
(incl
udin
g A
lice)
,m
ust
hav
e si
gned
docu
men
t
8-4
5N
etw
ork
Se
cu
rity
sim
ple
dig
ital
sign
ature
for
mes
sage
m:
B
ob s
igns
m b
y en
cryp
ting
with h
ispri
vate
key
KB,
crea
ting
“sig
ned
”m
essa
ge,K
B(m
)-
-
De
ar
Alic
e
Oh
,ho
wI
ha
ve
mis
se
d
yo
u.
Ith
ink o
fyo
ua
llth
e
tim
e!
…(b
lah
bla
h b
lah
)
Bo
b
Bo
b’s
me
ssa
ge
,m
Pu
blic
key
en
cry
ption
alg
orith
m
Bo
b’s
priva
te
ke
y
KB-
Bo
b’s
me
ssa
ge
,
m, sig
ne
d
(en
cry
pte
d)
with
his
pri
va
te k
ey
m,K
B-(m
)
Dig
ital
sig
nat
ure
s
8-4
6N
etw
ork
Se
cu
rity
-
Alic
e th
us
veri
fies
that
:
Bob s
igned
m
no
one
else
sig
ned
m
Bob s
igned
m a
nd
not
m‘
non-r
epudia
tion:
A
lice
can t
ake
m,a
nd
sign
ature
KB(m
)to
court
and
pro
ve t
hat
Bob s
igned
m
-
Dig
ital
sig
nat
ure
s
suppose
Alic
e re
ceiv
esm
sgm
,with s
ignat
ure
:m,K
B(m
)
A
lice
veri
fies
m s
igned
by
Bob b
y ap
ply
ing
Bob’s
public
key
KB
toK
B(m
)th
en c
hec
ksK
B(K
B(m
))
= m
.
If K
B(K
B(m
))
= m
,whoev
er s
igned
m m
ust
hav
e use
dB
ob’s
pri
vate
key
.
-
--
+
++
8-4
7N
etw
ork
Se
cu
rity
Mes
sage
dig
ests
com
puta
tional
ly e
xpen
sive
to
public
-key
-encr
ypt
long
mes
sage
s
goal
:fixe
d-len
gth,e
asy-
to-
com
pute
dig
ital
“finge
rpri
nt”
ap
ply
has
h funct
ion H
to
m,
get
fixe
dsi
ze m
essa
gedig
est,
H(m
).
Has
h funct
ion p
roper
ties
:
m
any-
to-1
pro
duce
sfixe
d-s
ize
msg
dig
est
(finge
rpri
nt)
gi
ven m
essa
ge d
iges
t x,
com
puta
tional
ly infe
asib
le t
ofind
m s
uch
that
x =
H(m
)
larg
e
me
ssa
ge
m
H:
Ha
sh
Fu
nctio
n
H(m
)
8-4
8N
etw
ork
Se
cu
rity
Inte
rnet
chec
ksum
: poor
cryp
to h
ash funct
ion
Inte
rnet
chec
ksum
has
som
e pro
per
ties
of has
h funct
ion:
pro
duce
sfixe
dle
ngt
h d
iges
t (1
6-b
it s
um
)of m
essa
ge
ism
any-
to-o
ne
But
give
n m
essa
ge w
ith g
iven
has
h v
alue,i
t is
easy
to
find
anoth
er
mes
sage
with s
ame
has
h v
alue:
IO
U1
00
.9
9B
OB
49
4F
55
31
30
30
2E
39
39
42
D2
42
me
ssa
ge
AS
CII
form
at
B2
C1
D2
AC
IO
U9
00
.1
9B
OB
49
4F
55
39
30
30
2E
31
39
42
D2
42
me
ssa
ge
AS
CII
form
at
B2
C1
D2
AC
diffe
ren
tm
essag
es
bu
tid
en
tica
lch
ecksu
ms!
8-4
9N
etw
ork
Se
cu
rity
larg
em
essa
ge
mH
(m)
Bo
b’s
pri
va
te
ke
y
KB-
+
Bob s
ends
dig
ital
lysi
gned
mes
sage
:A
lice
veri
fies
sign
ature
,inte
grity
of dig
ital
ly s
igned
mes
sage
:
KB(H
(m))
-
en
cry
pte
d
msg
dig
est
KB(H
(m))
-
en
cry
pte
d
msg
dig
est
larg
em
essa
ge
m
H(m
)H
(m)
Bo
b’s
pu
blic
ke
y
KB+
eq
ua
l
?
Dig
ital
sig
nat
ure
= s
igned
mes
sage
dig
est
8-5
0N
etw
ork
Se
cu
rity
Has
h funct
ion a
lgori
thm
s
M
D5 h
ash funct
ion w
idel
yuse
d(R
FC1321)
co
mpute
s128-b
it m
essa
ge d
iges
t in
4-s
tep p
roce
ss.
ar
bitra
ry 1
28-b
it s
trin
gx,a
ppea
rsdiffi
cult t
oco
nst
ruct
m
sgm
whose
MD
5 h
ash is
equal
tox
SH
A-1
is
also
use
d
US
stan
dar
d[N
IST,
FIPS
PU
B180-1
]
160-b
it m
essa
ge d
iges
t
8-5
1N
etw
ork
Se
cu
rity
Rec
all:
ap5.0
sec
uri
ty h
ole
man
(or
wom
an)
inth
e m
iddl
e at
tack
:Tru
dy
pose
sas
Alic
e (t
oB
ob)
and
asB
ob (
toA
lice)
I a
m A
lice
I a
m A
lice
R
TK
(
R)
-
Se
nd
me
yo
ur
pu
blic
ke
y TK
+
AK
(
R)
-
Se
nd
me
yo
ur
pu
blic
ke
y
AK
+
TK
(
m)
+
Tm
= K
(K
(
m))
+ T
-T
rud
y g
ets
se
nd
s m
to
Alic
e
en
cry
pte
d w
ith
Alic
e’s
pu
blic
ke
y
AK
(m
)+
Am
= K
(K
(
m))
+ A
-
R
8-5
2N
etw
ork
Se
cu
rity
Public
-key
cer
tifica
tion
m
otiva
tion:T
rudy
pla
yspiz
zapra
nk
on B
ob
Tr
udy
crea
tes
e-m
ailord
er:
Dea
r Pi
zza
Stor
e,Pl
ease
del
iver
to
me
four
pep
per
oni
piz
zas.
Tha
nk y
ou,B
ob
Tr
udy
sign
sord
er w
ith h
er p
riva
te k
ey
Tr
udy
sends
ord
er t
oPiz
zaSt
ore
Tr
udy
sends
toPiz
zaSt
ore
her
public
key
,but
says
it’s
Bob’s
public
key
Piz
zaSt
ore
ver
ifies
sign
ature
;then
del
iver
sfo
ur
pep
per
onipiz
zas
toB
ob
B
ob d
oes
n’t
eve
n lik
e pep
per
oni
8-5
3N
etw
ork
Se
cu
rity
Cer
tifica
tion a
uth
ori
ties
ce
rtifi
catio
nau
thor
ity (
CA):
bin
ds
public
key
to
par
ticu
lar
entity
,E.
E (
per
son,r
oute
r)re
gist
ers
its
public
key
with C
A.
E p
rovi
des
“pro
of of id
entity
”to
CA
.
C
Acr
eate
s ce
rtifi
cate
bin
din
gE t
oits
public
key.
ce
rtifi
cate
conta
inin
gE’s
public
key
dig
ital
lysi
gned
by
CA
– C
Asa
ys“t
his
is
E’s
public
key”
Bo
b’s
pu
blic
ke
y
KB+
Bo
b’s
ide
ntify
ing
info
rma
tio
n
CA
pri
va
te
ke
y K
CA-
KB+
ce
rtific
ate
for
Bo
b’s
pu
blic
ke
y,
sig
ne
db
y C
A
8-5
4N
etw
ork
Se
cu
rity
w
hen
Alic
e w
ants
Bob’s
public
key
:
ge
tsB
ob’s
cert
ifica
te (
Bob o
r el
sew
her
e).
ap
ply
CA
’spublic
key
to
Bob’s
cert
ifica
te,g
et B
ob’s
public
key
Bo
b’s
pu
blic
ke
y
KB+
CA
pu
blic
ke
y
KC
A+
KB+
Cer
tifica
tion a
uth
ori
ties