<s>
Password	B-Protocol
Authentication	I-Protocol
Protocol	I-Protocol
(	O
PAP	B-Protocol
)	O
is	O
a	O
password-based	O
authentication	B-Protocol
protocol	I-Protocol
used	O
by	O
Point-to-Point	B-Protocol
Protocol	I-Protocol
(	O
PPP	O
)	O
to	O
validate	O
users	O
.	O
</s>
<s>
PAP	B-Protocol
is	O
specified	O
in	O
.	O
</s>
<s>
Almost	O
all	O
network	B-Protocol
operating	I-Protocol
systems	I-Protocol
support	O
PPP	O
with	O
PAP	B-Protocol
,	O
as	O
do	O
most	O
network	O
access	O
servers	O
.	O
</s>
<s>
PAP	B-Protocol
is	O
also	O
used	O
in	O
PPPoE	B-Protocol
,	O
for	O
authenticating	O
DSL	O
users	O
.	O
</s>
<s>
As	O
the	O
Point-to-Point	B-Protocol
Protocol	I-Protocol
(	O
PPP	O
)	O
sends	O
data	O
unencrypted	O
and	O
"	O
in	O
the	O
clear	O
"	O
,	O
PAP	B-Protocol
is	O
vulnerable	O
to	O
any	O
attacker	O
who	O
can	O
observe	O
the	O
PPP	O
session	O
.	O
</s>
<s>
Some	O
additional	O
security	O
can	O
be	O
gained	O
on	O
the	O
PPP	O
link	O
by	O
using	O
CHAP	B-Protocol
or	O
EAP	B-Protocol
.	O
</s>
<s>
When	O
PAP	B-Protocol
is	O
used	O
in	O
PPP	O
,	O
it	O
is	O
considered	O
a	O
weak	O
authentication	O
scheme	O
.	O
</s>
<s>
Weak	O
schemes	O
are	O
simpler	O
and	O
have	O
lighter	O
computational	O
overhead	O
than	O
more	O
complex	O
schemes	O
such	O
as	O
Transport	B-Protocol
Layer	I-Protocol
Security	I-Protocol
(	O
TLS	O
)	O
,	O
but	O
they	O
are	O
much	O
more	O
vulnerable	O
to	O
attack	O
.	O
</s>
<s>
Where	O
the	O
transport	O
layer	O
is	O
not	O
physically	O
secure	O
a	O
system	O
such	O
as	O
Transport	B-Protocol
Layer	I-Protocol
Security	I-Protocol
(	O
TLS	O
)	O
or	O
Internet	B-Protocol
Protocol	I-Protocol
Security	I-Protocol
(	O
IPsec	B-Protocol
)	O
is	O
used	O
instead	O
.	O
</s>
<s>
PAP	B-Protocol
is	O
also	O
used	O
to	O
describe	O
password	O
authentication	O
in	O
other	O
protocols	O
such	O
as	O
RADIUS	B-Protocol
and	O
Diameter	B-Protocol
.	O
</s>
<s>
However	O
,	O
those	O
protocols	O
provide	O
for	O
transport	O
or	O
network	O
layer	O
security	O
,	O
and	O
therefore	O
that	O
usage	O
of	O
PAP	B-Protocol
does	O
not	O
have	O
the	O
security	O
issues	O
seen	O
when	O
PAP	B-Protocol
is	O
used	O
with	O
PPP	O
.	O
</s>
<s>
As	O
a	O
result	O
,	O
while	O
PAP	B-Protocol
passwords	O
are	O
less	O
secure	O
when	O
sent	O
over	O
a	O
PPP	O
link	O
,	O
they	O
allow	O
for	O
more	O
secure	O
storage	O
"	O
at	O
rest	O
"	O
than	O
with	O
other	O
methods	O
such	O
as	O
CHAP	B-Protocol
.	O
</s>
<s>
PAP	B-Protocol
authentication	O
is	O
only	O
done	O
at	O
the	O
time	O
of	O
the	O
initial	O
link	O
establishment	O
,	O
and	O
verifies	O
the	O
identity	O
of	O
the	O
client	O
using	O
a	O
two-way	B-Protocol
handshake	I-Protocol
.	O
</s>
<s>
PAP	B-Protocol
packet	O
embedded	O
in	O
a	O
PPP	O
frame	O
.	O
</s>
