Suppose an intermediate node for onion routing were malicious, exposing the source and destination of communications it forwarded. Clearly the disclosure would damage the confidentiality onion routing was designed to achieve. If the malicious node were one of the two in the middle, what would be exposed. If it were one of three, what would be lost. Explain your answer in terms of the malicious

Question

node in each of the first, second, and third positions. How many nonmalicious nodes are necessary to preserve privacy?

What will be an ideal response?

Answer 1

In
order
to
preserve
anonymity,
a
nonmalicious
intermediate
node
is
needed
on
each
side
of
the
malicious
intermediate
node
(e.g.,
if
A
communicates
with
B
along
the
path
A-­?>X-­?>Y-­?>Z-­?>B,
X
and
Z
must
not
be
malicious).
If
a
malicious
node
is
on
the
end
of
the
intermediate
chain
(either
X
or
Z,
in
the
previous
example),
then
the
anonymity
of
either
the
sender
or
recipient
of
the
communication
is
compromised.
Consequently,
if
a
single
intermediate
node
in
a
two-­?node
system
is
malicious,
either
the
sender's
or
recipient's
anonymity
is
lost.