<s>
A	O
passive	B-General_Concept
attack	I-General_Concept
on	O
a	O
cryptosystem	B-General_Concept
is	O
one	O
in	O
which	O
the	O
cryptanalyst	O
cannot	O
interact	O
with	O
any	O
of	O
the	O
parties	O
involved	O
,	O
attempting	O
to	O
break	O
the	O
system	O
solely	O
based	O
upon	O
observed	O
data	O
(	O
i.e.	O
</s>
<s>
The	O
main	O
types	O
of	O
passive	B-General_Concept
attacks	I-General_Concept
are	O
traffic	O
analysis	O
and	O
release	O
of	O
message	O
contents	O
.	O
</s>
<s>
A	O
passive	B-General_Concept
attack	I-General_Concept
monitors	O
the	O
contents	O
of	O
the	O
transmitted	O
data	O
.	O
</s>
<s>
Passive	B-General_Concept
attacks	I-General_Concept
are	O
very	O
difficult	O
to	O
detect	O
because	O
they	O
do	O
not	O
involve	O
any	O
alteration	O
of	O
the	O
data	O
.	O
</s>
