<s>
MS-CHAP	B-Algorithm
is	O
the	O
Microsoft	O
version	O
of	O
the	O
Challenge-Handshake	B-Protocol
Authentication	I-Protocol
Protocol	I-Protocol
,	O
CHAP	O
.	O
</s>
<s>
The	O
protocol	O
exists	O
in	O
two	O
versions	O
,	O
MS-CHAPv1	B-Algorithm
(	O
defined	O
in	O
RFC	O
2433	O
)	O
and	O
MS-CHAPv2	B-Algorithm
(	O
defined	O
in	O
RFC	O
2759	O
)	O
.	O
</s>
<s>
MS-CHAPv2	B-Algorithm
was	O
introduced	O
with	O
pptp3-fix	O
that	O
was	O
included	O
in	O
Windows	B-Device
NT	I-Device
4.0	I-Device
SP4	O
and	O
was	O
added	O
to	O
Windows	B-Device
98	I-Device
in	O
the	O
"	O
Windows	B-Device
98	I-Device
Dial-Up	O
Networking	O
Security	O
Upgrade	O
Release	O
"	O
and	O
Windows	B-Application
95	I-Application
in	O
the	O
"	O
Dial	O
Up	O
Networking	O
1.3	O
Performance	O
&	O
Security	O
Update	O
for	O
MS	B-Application
Windows	I-Application
95	I-Application
"	O
upgrade	O
.	O
</s>
<s>
Windows	B-Application
Vista	I-Application
dropped	O
support	O
for	O
MS-CHAPv1	B-Algorithm
.	O
</s>
<s>
MS-CHAP	B-Algorithm
is	O
used	O
as	O
one	O
authentication	O
option	O
in	O
Microsoft	O
's	O
implementation	O
of	O
the	O
PPTP	B-Protocol
protocol	O
for	O
virtual	B-Application
private	I-Application
networks	I-Application
.	O
</s>
<s>
It	O
is	O
also	O
used	O
as	O
an	O
authentication	O
option	O
with	O
RADIUS	B-Protocol
servers	I-Protocol
which	O
are	O
used	O
with	O
IEEE	O
802.1X	O
(	O
e.g.	O
,	O
WiFi	O
security	O
using	O
the	O
WPA-Enterprise	O
protocol	O
)	O
.	O
</s>
<s>
Compared	O
with	O
CHAP	O
,	O
MS-CHAP	B-Algorithm
:	O
</s>
<s>
MS-CHAPv2	B-Algorithm
provides	O
mutual	O
authentication	O
between	O
peers	O
by	O
piggybacking	O
a	O
peer	O
challenge	O
on	O
the	O
Response	O
packet	O
and	O
an	O
authenticator	O
response	O
on	O
the	O
Success	O
packet	O
.	O
</s>
<s>
MS-CHAP	B-Algorithm
requires	O
each	O
peer	O
to	O
either	O
know	O
the	O
plaintext	O
password	O
,	O
or	O
an	O
MD4	O
hash	O
of	O
the	O
password	O
.	O
</s>
<s>
Several	O
weaknesses	O
have	O
been	O
identified	O
in	O
MS-CHAP	B-Algorithm
and	O
MS-CHAPv2	B-Algorithm
.	O
</s>
<s>
The	O
DES	B-Algorithm
encryption	O
used	O
in	O
NTLMv1	O
and	O
MS-CHAPv2	B-Algorithm
to	O
encrypt	O
the	O
NTLM	O
password	O
hash	O
make	O
custom	O
hardware	O
attacks	O
utilizing	O
the	O
method	O
of	O
brute	O
force	O
feasible	O
.	O
</s>
<s>
More	O
recently	O
,	O
MS-CHAP	B-Algorithm
has	O
been	O
completely	O
broken	O
.	O
</s>
