<s>
Security	B-Protocol
Support	I-Protocol
Provider	I-Protocol
Interface	I-Protocol
(	O
SSPI	B-Protocol
)	O
is	O
a	O
component	O
of	O
Windows	B-Library
API	I-Library
that	O
performs	O
security-related	O
operations	O
such	O
as	O
authentication	O
.	O
</s>
<s>
SSPI	B-Protocol
functions	O
as	O
a	O
common	O
interface	O
to	O
several	O
Security	B-Protocol
Support	I-Protocol
Providers	I-Protocol
(	O
SSPs	O
)	O
:	O
A	O
Security	B-Protocol
Support	I-Protocol
Provider	I-Protocol
is	O
a	O
dynamic-link	O
library	O
(	O
DLL	O
)	O
that	O
makes	O
one	O
or	O
more	O
security	O
packages	O
available	O
to	O
apps	O
.	O
</s>
<s>
NTLMSSP	O
(	O
msv1_0.dll	O
)	O
–	O
Introduced	O
in	O
Windows	B-Device
NT	I-Device
3.51	I-Device
.	O
</s>
<s>
Provides	O
NTLM	O
challenge/response	O
authentication	O
for	O
Windows	B-General_Concept
domains	I-General_Concept
prior	O
to	O
Windows	B-Application
2000	I-Application
and	O
for	O
systems	O
that	O
are	O
not	O
part	O
of	O
a	O
domain	O
.	O
</s>
<s>
Kerberos	B-Protocol
(	O
kerberos.dll	O
)	O
–	O
Introduced	O
in	O
Windows	B-Application
2000	I-Application
and	O
updated	O
in	O
Windows	B-Application
Vista	I-Application
to	O
support	O
AES	B-Algorithm
.	O
</s>
<s>
Performs	O
authentication	O
for	O
Windows	B-General_Concept
domains	I-General_Concept
in	O
Windows	B-Application
2000	I-Application
and	O
later	O
.	O
</s>
<s>
NegotiateSSP	B-Protocol
(	O
secur32.dll	O
)	O
–	O
Introduced	O
in	O
Windows	B-Application
2000	I-Application
.	O
</s>
<s>
Prior	O
to	O
Windows	B-Device
7	I-Device
,	O
it	O
tries	O
Kerberos	B-Protocol
before	O
falling	O
back	O
to	O
NTLM	O
.	O
</s>
<s>
On	O
Windows	B-Device
7	I-Device
and	O
later	O
,	O
NEGOExts	O
is	O
introduced	O
,	O
which	O
negotiates	O
the	O
use	O
of	O
installed	O
custom	O
SSPs	O
which	O
are	O
supported	O
on	O
the	O
client	O
and	O
server	O
for	O
authentication	O
.	O
</s>
<s>
Secure	O
Channel	O
(	O
schannel.dll	O
)	O
–	O
Introduced	O
in	O
Windows	B-Application
2000	I-Application
and	O
updated	O
in	O
Windows	B-Application
Vista	I-Application
to	O
support	O
stronger	O
AES	B-Algorithm
encryption	I-Algorithm
and	O
ECC	O
This	O
provider	O
uses	O
SSL/TLS	B-Protocol
records	O
to	O
encrypt	O
data	O
payloads	O
.	O
</s>
<s>
TLS/SSL	B-Protocol
–	O
Public	B-Application
key	I-Application
cryptography	I-Application
SSP	O
that	O
provides	O
encryption	O
and	O
secure	O
communication	O
for	O
authenticating	O
clients	O
and	O
servers	O
over	O
the	O
internet	O
.	O
</s>
<s>
Updated	O
in	O
Windows	B-Device
7	I-Device
to	O
support	O
TLS	O
1.2	O
.	O
</s>
<s>
Digest	B-Protocol
SSP	I-Protocol
(	O
wdigest.dll	O
)	O
–	O
Introduced	O
in	O
Windows	B-Application
XP	I-Application
.	O
</s>
<s>
Provides	O
challenge/response	O
based	O
HTTP	O
and	O
SASL	O
authentication	O
between	O
Windows	O
and	O
non-Windows	O
systems	O
where	O
Kerberos	B-Protocol
is	O
not	O
available	O
.	O
</s>
<s>
CredSSP	O
(	O
credssp.dll	O
)	O
–	O
Introduced	O
in	O
Windows	B-Application
Vista	I-Application
and	O
available	O
on	O
Windows	B-Application
XP	I-Application
SP3	O
.	O
</s>
<s>
Provides	O
single	O
sign-on	O
and	O
Network	B-General_Concept
Level	I-General_Concept
Authentication	I-General_Concept
for	O
Remote	B-Protocol
Desktop	I-Protocol
Services	I-Protocol
.	O
</s>
<s>
Distributed	O
Password	O
Authentication	O
(	O
DPA	O
,	O
msapsspc.dll	O
)	O
–	O
Introduced	O
in	O
Windows	B-Application
2000	I-Application
.	O
</s>
<s>
Public	B-Application
Key	I-Application
Cryptography	I-Application
User-to-User	O
(	O
PKU2U	O
,	O
pku2u.dll	O
)	O
–	O
Introduced	O
in	O
Windows	B-Device
7	I-Device
.	O
</s>
<s>
SSPI	B-Protocol
is	O
a	O
proprietary	O
variant	O
of	O
Generic	O
Security	O
Services	O
Application	O
Program	O
Interface	O
(	O
GSSAPI	O
)	O
with	O
extensions	O
and	O
very	O
Windows-specific	O
data	O
types	O
.	O
</s>
<s>
It	O
shipped	O
with	O
Windows	B-Device
NT	I-Device
3.51	I-Device
and	O
Windows	B-Application
95	I-Application
with	O
the	O
NTLMSSP	O
.	O
</s>
<s>
For	O
Windows	B-Application
2000	I-Application
,	O
an	O
implementation	O
of	O
Kerberos	B-Protocol
5	I-Protocol
was	O
added	O
,	O
using	O
token	O
formats	O
conforming	O
to	O
the	O
official	O
protocol	O
standard	O
RFC	O
1964	O
(	O
The	O
Kerberos	B-Protocol
5	I-Protocol
GSSAPI	O
mechanism	O
)	O
and	O
providing	O
wire-level	O
interoperability	O
with	O
Kerberos	B-Protocol
5	I-Protocol
implementations	O
from	O
other	O
vendors	O
.	O
</s>
<s>
The	O
tokens	O
generated	O
and	O
accepted	O
by	O
the	O
SSPI	B-Protocol
are	O
mostly	O
compatible	O
with	O
the	O
GSS-API	O
so	O
an	O
SSPI	B-Protocol
client	O
on	O
Windows	O
may	O
be	O
able	O
to	O
authenticate	O
with	O
a	O
GSS-API	O
server	O
on	O
Unix	O
depending	O
on	O
the	O
specific	O
circumstances	O
.	O
</s>
<s>
One	O
significant	O
shortcoming	O
of	O
SSPI	B-Protocol
is	O
its	O
lack	O
of	O
channel	O
bindings	O
,	O
which	O
makes	O
some	O
GSSAPI	O
interoperability	O
impossible	O
.	O
</s>
<s>
Another	O
fundamental	O
difference	O
between	O
the	O
IETF-defined	O
GSSAPI	O
and	O
Microsoft	O
's	O
SSPI	B-Protocol
is	O
the	O
concept	O
of	O
"	O
impersonation	O
"	O
.	O
</s>
<s>
The	O
obvious	O
negative	O
security	O
implications	O
of	O
the	O
impersonation	O
concept	O
are	O
prevented	O
in	O
Windows	B-Application
Vista	I-Application
by	O
restricting	O
impersonation	O
to	O
selected	O
service	O
accounts	O
.	O
</s>
<s>
While	O
this	O
means	O
an	O
unprivileged	O
process	O
cannot	O
elevate	O
its	O
privileges	O
,	O
it	O
also	O
means	O
that	O
to	O
take	O
advantage	O
of	O
impersonation	O
the	O
process	O
must	O
run	O
in	O
the	O
context	O
of	O
the	B-Application
root	I-Application
user	I-Application
account	I-Application
.	O
</s>
